From 607c2984939dab5395ded1dcf41ede12de261d66 Mon Sep 17 00:00:00 2001
From: Holly Borla <hborla@apple.com>
Date: Thu, 6 Feb 2020 12:16:28 -0800
Subject: [PATCH 01/13] [Diagnostics] Refactor diagnoseAmbigutiyWithFixes to
 use the differences between solutions in order to figure out the source of
 ambiguity.

---
 lib/Sema/ConstraintSystem.cpp              | 167 +++++++++------------
 lib/Sema/ConstraintSystem.h                |  14 +-
 test/Constraints/closures.swift            |   2 +-
 test/Constraints/one_way_constraints.swift |   2 +-
 4 files changed, 85 insertions(+), 100 deletions(-)

diff --git a/lib/Sema/ConstraintSystem.cpp b/lib/Sema/ConstraintSystem.cpp
index 531f51cdb9916..99dd5898f6266 100644
--- a/lib/Sema/ConstraintSystem.cpp
+++ b/lib/Sema/ConstraintSystem.cpp
@@ -2749,13 +2749,66 @@ bool ConstraintSystem::diagnoseAmbiguityWithFixes(
       return false;
   }
 
-  // Problems related to fixes forming ambiguous solution set
-  // could only be diagnosed (at the moment), if all of the fixes
-  // have the same callee locator, which means they fix different
-  // overloads of the same declaration.
-  ConstraintLocator *commonCalleeLocator = nullptr;
+  // Collect aggregated fixes from all solutions
+  llvm::SmallMapVector<std::pair<ConstraintLocator *, FixKind>,
+      llvm::SmallVector<ConstraintFix *, 4>, 4> aggregatedFixes;
+  for (const auto &solution: solutions) {
+    for (auto fixesPerLocator: solution.getAggregatedFixes()) {
+      for (auto kindAndFixes: fixesPerLocator.second) {
+        aggregatedFixes[{fixesPerLocator.first, kindAndFixes.first}]
+            .push_back(kindAndFixes.second.front());
+      }
+    }
+  }
+
+  // If there are no overload differences, diagnose the common fixes.
+  SolutionDiff solutionDiff(solutions);
+  if (solutionDiff.overloads.size() == 0) {
+    bool diagnosed = false;
+    ConstraintSystem::SolverScope scope(*this);
+    applySolution(solutions.front());
+    for (auto fixes: aggregatedFixes) {
+      // A common fix must appear in all solutions
+      if (fixes.second.size() < solutions.size()) continue;
+      diagnosed |= fixes.second.front()->diagnose();
+    }
+    return diagnosed;
+  }
+
+  // If there is an overload difference, let's see if there's a common callee
+  // locator for all of the fixes.
+  auto ambiguousOverload = llvm::find_if(solutionDiff.overloads,
+      [&](const auto &overloadDiff) {
+        return llvm::all_of(aggregatedFixes, [&](const auto &aggregatedFix) {
+          auto *locator = aggregatedFix.first.first;
+          auto *anchor = locator->getAnchor();
+          // Assignment failures are all about the source expression, because
+          // they treat destination as a contextual type.
+          if (auto *assignExpr = dyn_cast<AssignExpr>(anchor))
+            anchor = assignExpr->getSrc();
+
+          if (auto *callExpr = dyn_cast<CallExpr>(anchor)) {
+            if (!isa<TypeExpr>(callExpr->getDirectCallee()))
+              anchor = callExpr->getDirectCallee();
+          } else if (auto *applyExpr = dyn_cast<ApplyExpr>(anchor)) {
+            anchor = applyExpr->getFn();
+          }
+
+          return overloadDiff.locator->getAnchor() == anchor;
+        });
+      });
+
+  if (ambiguousOverload == solutionDiff.overloads.end())
+    return false;
+
+  ConstraintLocator* commonCalleeLocator = ambiguousOverload->locator;
   SmallPtrSet<ValueDecl *, 4> distinctChoices;
   SmallVector<const Solution *, 4> viableSolutions;
+  assert(ambiguousOverload->choices.size() == solutions.size());
+  for (unsigned i = 0; i < solutions.size(); ++i) {
+    if (distinctChoices.insert(ambiguousOverload->choices[i].getDecl()).second)
+      viableSolutions.push_back(&solutions[i]);
+  }
 
   enum class AmbiguityKind {
     /// There is exactly one fix associated with each candidate.
@@ -2771,103 +2824,23 @@ bool ConstraintSystem::diagnoseAmbiguityWithFixes(
   };
   auto ambiguityKind = AmbiguityKind::CloseMatch;
 
-  bool diagnosable = llvm::all_of(solutions, [&](const Solution &solution) {
-    ArrayRef<ConstraintFix *> fixes = solution.Fixes;
-
-    if (fixes.empty())
+  // FIXME: Can this be re-written in a cleaner way?
+  for (const auto &solution: solutions) {
+    if (solution.Fixes.empty())
       return false;
 
-    if (fixes.size() > 1) {
-      // Attempt to disambiguite in cases where the argument matches
-      // involves tuple mismatches. e.g.
-      // func t<T, U>(_: (T, U), _: (U, T)) {}
-      // func useTuples(_ x: Int, y: Float) {
-      //     t((x, y), (x, y))
-      // }
-      // So fixes are ambiguous in all solutions.
-      if ((ambiguityKind == AmbiguityKind::CloseMatch ||
-           ambiguityKind == AmbiguityKind::ArgumentMismatch) &&
-          llvm::all_of(fixes, [](const ConstraintFix *fix) -> bool {
-            return fix->getKind() == FixKind::AllowTupleTypeMismatch;
-          })) {
-        ambiguityKind = AmbiguityKind::ArgumentMismatch;
-      } else {
-        ambiguityKind =
-            (ambiguityKind == AmbiguityKind::CloseMatch ||
-             ambiguityKind == AmbiguityKind::ArgumentMismatch ||
-             ambiguityKind == AmbiguityKind::ParameterList) &&
-                    llvm::all_of(
-                        fixes,
-                        [](const ConstraintFix *fix) -> bool {
-                          auto *locator = fix->getLocator();
-                          return locator
-                              ->findLast<LocatorPathElt::ApplyArgument>()
-                              .hasValue();
-                        })
-                ? AmbiguityKind::ParameterList
-                : AmbiguityKind::General;
-      }
+    if (solution.Fixes.size() > 1) {
+      ambiguityKind = (ambiguityKind == AmbiguityKind::CloseMatch ||
+                       ambiguityKind == AmbiguityKind::ParameterList) &&
+          llvm::all_of(solution.Fixes, [](const ConstraintFix *fix) -> bool {
+            auto *locator = fix->getLocator();
+            return locator->findLast<LocatorPathElt::ApplyArgument>().hasValue();
+          }) ? AmbiguityKind::ParameterList
+             : AmbiguityKind::General;
     }
-
-    if (fixes.size() == 1) {
-      // Attempt to disambiguite in cases where all the solutions
-      // produces the same fixes for different generic arguments e.g.
-      //   func f<T>(_: T, _: T) {}
-      //   f(Int(1), Float(1))
-      //
-      ambiguityKind =
-          ((ambiguityKind == AmbiguityKind::CloseMatch ||
-            ambiguityKind == AmbiguityKind::ArgumentMismatch) &&
-           fixes.front()->getKind() == FixKind::AllowArgumentTypeMismatch)
-              ? AmbiguityKind::ArgumentMismatch
-              : AmbiguityKind::CloseMatch;
-    }
-
-    for (const auto *fix : fixes) {
-      auto *locator = fix->getLocator();
-      // Assignment failures are all about the source expression,
-      // because they treat destination as a contextual type.
-      if (auto *anchor = locator->getAnchor()) {
-        if (auto *assignExpr = dyn_cast<AssignExpr>(anchor))
-          locator = getConstraintLocator(assignExpr->getSrc());
-      }
-
-      auto *calleeLocator = solution.getCalleeLocator(locator);
-      if (!commonCalleeLocator)
-        commonCalleeLocator = calleeLocator;
-      else if (commonCalleeLocator != calleeLocator)
-        return false;
-    }
-
-    auto overload = solution.getOverloadChoiceIfAvailable(commonCalleeLocator);
-    if (!overload)
-      return false;
-
-    auto *decl = overload->choice.getDeclOrNull();
-    if (!decl)
-      return false;
-
-    // If this declaration is distinct, let's record this solution
-    // as viable, otherwise we'd produce the same diagnostic multiple
-    // times, which means that actual problem is elsewhere.
-    if (distinctChoices.insert(decl).second)
-      viableSolutions.push_back(&solution);
-    return true;
-  });
-
-  if (ambiguityKind == AmbiguityKind::ArgumentMismatch &&
-      viableSolutions.size() == 1) {
-    // Let's apply the solution so the contextual generic types
-    // are available in the system for diagnostics.
-    applySolution(*viableSolutions[0]);
-    solutions.front().Fixes.front()->diagnose(/*asNote*/ false);
-    return true;
   }
 
-  if (!diagnosable || viableSolutions.size() < 2)
-    return false;
-
-  auto *decl = *distinctChoices.begin();
+  auto *decl = ambiguousOverload->choices.front().getDecl();
   assert(solverState);
 
   bool diagnosed = true;
diff --git a/lib/Sema/ConstraintSystem.h b/lib/Sema/ConstraintSystem.h
index aa8e3ca3febd0..d4f4055c759f1 100644
--- a/lib/Sema/ConstraintSystem.h
+++ b/lib/Sema/ConstraintSystem.h
@@ -837,9 +837,21 @@ class Solution {
   llvm::DenseMap<std::pair<CanType, CanType>, ConversionRestrictionKind>
     ConstraintRestrictions;
 
+  using ConstraintFixVector = llvm::SmallVector<ConstraintFix *, 4>;
   /// The list of fixes that need to be applied to the initial expression
   /// to make the solution work.
-  llvm::SmallVector<ConstraintFix *, 4> Fixes;
+  ConstraintFixVector Fixes;
+
+  using AggregatedFixesMap = llvm::SmallMapVector<ConstraintLocator *,
+      llvm::SmallMapVector<FixKind, ConstraintFixVector, 4>, 4>;
+
+  AggregatedFixesMap getAggregatedFixes() const {
+    AggregatedFixesMap aggregatedFixes;
+    for (auto *fix: Fixes) {
+      aggregatedFixes[fix->getLocator()][fix->getKind()].push_back(fix);
+    }
+    return aggregatedFixes;
+  }
 
   /// The set of disjunction choices used to arrive at this solution,
   /// which informs constraint application.
diff --git a/test/Constraints/closures.swift b/test/Constraints/closures.swift
index 42299524f07ed..876b5a1b76260 100644
--- a/test/Constraints/closures.swift
+++ b/test/Constraints/closures.swift
@@ -371,7 +371,7 @@ func someGeneric19997471<T>(_ x: T) {
 func rdar21078316() {
   var foo : [String : String]?
   var bar : [(String, String)]?
-  bar = foo.map { ($0, $1) }  // expected-error {{contextual closure type '(Dictionary<String, String>) throws -> (Dictionary<String, String>, _)' expects 1 argument, but 2 were used in closure body}}
+  bar = foo.map { ($0, $1) }  // expected-error {{contextual closure type '([String : String]) throws -> [(String, String)]' expects 1 argument, but 2 were used in closure body}}
 }
 
 
diff --git a/test/Constraints/one_way_constraints.swift b/test/Constraints/one_way_constraints.swift
index d830367d35d78..4546880149afe 100644
--- a/test/Constraints/one_way_constraints.swift
+++ b/test/Constraints/one_way_constraints.swift
@@ -10,7 +10,7 @@ func testTernaryOneWay(b: Bool) {
   let _: Float = b ? 3.14159 : 17
 
   // Errors due to one-way inference.
-  let _: Float = b ? Builtin.one_way(3.14159) // expected-error{{result values in '? :' expression have mismatching types 'Double' and 'Int'}}
+  let _: Float = b ? Builtin.one_way(3.14159) // expected-error{{cannot convert value of type 'Double' to specified type 'Float'}}
                    : 17
   let _: Float = b ? 3.14159 // expected-error {{cannot convert value of type 'Int' to specified type 'Float'}}
                    : Builtin.one_way(17)

From 54706ba79b84fbdf9c753e8ca08a62cb229d7ec6 Mon Sep 17 00:00:00 2001
From: Holly Borla <hborla@apple.com>
Date: Thu, 6 Feb 2020 16:50:30 -0800
Subject: [PATCH 02/13] [Diagnostics] Simplify diagnoseAmbiguityWithFixes by
 removing AmbiguityKind.

---
 lib/Sema/ConstraintSystem.cpp          | 192 ++++++++-----------------
 test/Constraints/diagnostics.swift     |   2 +-
 test/decl/subscript/subscripting.swift |   4 +-
 3 files changed, 64 insertions(+), 134 deletions(-)

diff --git a/lib/Sema/ConstraintSystem.cpp b/lib/Sema/ConstraintSystem.cpp
index 99dd5898f6266..ab019e79e3722 100644
--- a/lib/Sema/ConstraintSystem.cpp
+++ b/lib/Sema/ConstraintSystem.cpp
@@ -2801,45 +2801,7 @@ bool ConstraintSystem::diagnoseAmbiguityWithFixes(
   if (ambiguousOverload == solutionDiff.overloads.end())
     return false;
 
-  ConstraintLocator* commonCalleeLocator = ambiguousOverload->locator;
-  SmallPtrSet<ValueDecl *, 4> distinctChoices;
-  SmallVector<const Solution *, 4> viableSolutions;
-  assert(ambiguousOverload->choices.size() == solutions.size());
-  for (unsigned i = 0; i < solutions.size(); ++i) {
-    if (distinctChoices.insert(ambiguousOverload->choices[i].getDecl()).second)
-      viableSolutions.push_back(&solutions[i]);
-  }
-
-  enum class AmbiguityKind {
-    /// There is exactly one fix associated with each candidate.
-    CloseMatch,
-    /// Solution is ambiguous because all candidates had partially matching
-    /// parameter lists.
-    ParameterList,
-    /// General ambiguity failure.
-    General,
-    /// Argument mismatch ambiguity where each solution has the same
-    /// argument mismatch fixes for the same call.
-    ArgumentMismatch
-  };
-  auto ambiguityKind = AmbiguityKind::CloseMatch;
-
-  // FIXME: Can this be re-written in a cleaner way?
-  for (const auto &solution: solutions) {
-    if (solution.Fixes.empty())
-      return false;
-
-    if (solution.Fixes.size() > 1) {
-      ambiguityKind = (ambiguityKind == AmbiguityKind::CloseMatch ||
-                       ambiguityKind == AmbiguityKind::ParameterList) &&
-          llvm::all_of(solution.Fixes, [](const ConstraintFix *fix) -> bool {
-            auto *locator = fix->getLocator();
-            return locator->findLast<LocatorPathElt::ApplyArgument>().hasValue();
-          }) ? AmbiguityKind::ParameterList
-             : AmbiguityKind::General;
-    }
-  }
-
+  auto *commonCalleeLocator = ambiguousOverload->locator;
   auto *decl = ambiguousOverload->choices.front().getDecl();
   assert(solverState);
 
@@ -2851,66 +2813,71 @@ bool ConstraintSystem::diagnoseAmbiguityWithFixes(
     auto &DE = getASTContext().Diags;
     auto name = decl->getFullName();
 
-    auto emitGeneralAmbiguityFailure = [&]() {
-      // Three choices here:
-      // 1. If this is a special name avoid printing it because
-      //    printing kind is sufficient;
-      // 2. If all of the labels match, print a full name;
-      // 3. If labels in different choices are different, it means
-      //    that we can only print a base name.
-      if (name.isSpecial()) {
-        DE.diagnose(commonAnchor->getLoc(),
-                    diag::no_overloads_match_exactly_in_call_special,
-                    decl->getDescriptiveKind());
-      } else if (name.isOperator()) {
-        auto operatorId = name.getBaseIdentifier();
-        diagnoseOperatorAmbiguity(*this, operatorId, solutions,
-                                  commonCalleeLocator);
-      } else if (llvm::all_of(distinctChoices,
-                              [&name](const ValueDecl *choice) {
-                                return choice->getFullName() == name;
-                              })) {
-        DE.diagnose(commonAnchor->getLoc(),
-                    diag::no_overloads_match_exactly_in_call,
-                    decl->getDescriptiveKind(), name);
-      } else {
-        DE.diagnose(commonAnchor->getLoc(),
-                    diag::no_overloads_match_exactly_in_call_no_labels,
-                    decl->getDescriptiveKind(), name.getBaseName());
-      }
-    };
+    if (name.isOperator()) {
+      diagnoseOperatorAmbiguity(*this, name.getBaseIdentifier(), solutions,
+                                commonCalleeLocator);
+      return true;
+    }
 
-    switch (ambiguityKind) {
-    case AmbiguityKind::ArgumentMismatch:
-    case AmbiguityKind::CloseMatch:
-      // Handled below
-      break;
-    case AmbiguityKind::ParameterList: {
-      emitGeneralAmbiguityFailure();
+    // Emit an error message for the ambiguity.
+    if (aggregatedFixes.size() == 1 &&
+        aggregatedFixes.front().first.first
+            ->getLastElementAs<LocatorPathElt::ContextualType>()) {
+      auto *anchor = aggregatedFixes.front().first.first->getAnchor();
+      auto baseName = name.getBaseName();
+      DE.diagnose(commonAnchor->getLoc(), diag::no_candidates_match_result_type,
+                  baseName.userFacingName(), getContextualType(anchor));
+    } else if (name.isSpecial()) {
+      // If this is a special name, avoid printing it because printing the
+      // decl kind is sufficient.
+      DE.diagnose(commonAnchor->getLoc(),
+                  diag::no_overloads_match_exactly_in_call_special,
+                  decl->getDescriptiveKind());
+    } else if (llvm::all_of(ambiguousOverload->choices,
+                            [&name](const OverloadChoice &choice) {
+                              return choice.getDecl()->getFullName() == name;
+                            })) {
+      // If the labels match in each overload, print a full name.
+      DE.diagnose(commonAnchor->getLoc(),
+                  diag::no_overloads_match_exactly_in_call,
+                  decl->getDescriptiveKind(), name);
+    } else {
+      // If the labels are different, we can only print a base name.
+      DE.diagnose(commonAnchor->getLoc(),
+                  diag::no_overloads_match_exactly_in_call_no_labels,
+                  decl->getDescriptiveKind(), name.getBaseName());
+    }
+
+    // Produce candidate notes
+    SmallPtrSet<ValueDecl *, 4> distinctChoices;
+    llvm::SmallSet<CanType, 4> candidateTypes;
+    for (const auto &solution: solutions) {
+      auto overload = solution.getOverloadChoice(commonCalleeLocator);
+      auto *decl = overload.choice.getDecl();
+      auto type = solution.simplifyType(overload.openedType);
+      // Skip if we've already produced a note for this overload
+      if (!distinctChoices.insert(decl).second)
+        continue;
 
-      for (const auto &viable: viableSolutions) {
-        auto overload = viable->getOverloadChoice(commonCalleeLocator);
-        auto *fn = overload.openedType->getAs<AnyFunctionType>();
+      if (solution.Fixes.size() == 1) {
+        // Create scope so each applied solution is rolled back.
+        ConstraintSystem::SolverScope scope(*this);
+        applySolution(solution);
+        // All of the solutions supposed to produce a "candidate" note.
+        diagnosed &= solution.Fixes.front()->diagnose(/*asNote*/ true);
+      } else if (llvm::all_of(solution.Fixes,
+                              [&](ConstraintFix *fix) {
+                                return fix->getLocator()
+                                  ->findLast<LocatorPathElt::ApplyArgument>().hasValue();
+                              })) {
+        // All fixes have to do with arguments, so let's show the parameter lists.
+        auto *fn = type->getAs<AnyFunctionType>();
         assert(fn);
-        DE.diagnose(overload.choice.getDecl()->getLoc(),
+        DE.diagnose(decl->getLoc(),
                     diag::candidate_partial_match,
                     fn->getParamListAsString(fn->getParams()));
-      }
-
-      return true;
-    }
-    case AmbiguityKind::General: {
-      emitGeneralAmbiguityFailure();
-
-      // Notes for operators are diagnosed through emitGeneralAmbiguityFailure
-      if (name.isOperator())
-        return true;
-
-      llvm::SmallSet<CanType, 4> candidateTypes;
-      for (const auto &viable: viableSolutions) {
-        auto overload = viable->getOverloadChoice(commonCalleeLocator);
-        auto *decl = overload.choice.getDecl();
-        auto type = viable->simplifyType(overload.openedType);
+      } else {
+        // Emit a general "found candidate" note
         if (decl->getLoc().isInvalid()) {
           if (candidateTypes.insert(type->getCanonicalType()).second)
             DE.diagnose(commonAnchor->getLoc(), diag::found_candidate_type, type);
@@ -2918,43 +2885,6 @@ bool ConstraintSystem::diagnoseAmbiguityWithFixes(
           DE.diagnose(decl->getLoc(), diag::found_candidate);
         }
       }
-
-      return true;
-    }
-    }
-
-    auto *fix = viableSolutions.front()->Fixes.front();
-    if (fix->getKind() == FixKind::UseSubscriptOperator) {
-      auto *UDE = cast<UnresolvedDotExpr>(commonAnchor);
-      DE.diagnose(commonAnchor->getLoc(),
-                  diag::could_not_find_subscript_member_did_you_mean,
-                  getType(UDE->getBase()));
-    } else if (fix->getKind() == FixKind::TreatRValueAsLValue) {
-      DE.diagnose(commonAnchor->getLoc(),
-                  diag::no_overloads_match_exactly_in_assignment,
-                  decl->getBaseName());
-    } else if (llvm::all_of(
-                   viableSolutions,
-                   [](const Solution *viable) {
-                     auto *locator = viable->Fixes.front()->getLocator();
-                     return locator
-                         ->isLastElement<LocatorPathElt::ContextualType>();
-                   })) {
-      auto anchor =
-          viableSolutions.front()->Fixes.front()->getLocator()->getAnchor();
-      auto baseName = name.getBaseName();
-      DE.diagnose(commonAnchor->getLoc(), diag::no_candidates_match_result_type,
-                  baseName.userFacingName(), getContextualType(anchor));
-    } else {
-      emitGeneralAmbiguityFailure();
-    }
-
-    for (const auto &viable : viableSolutions) {
-      // Create scope so each applied solution is rolled back.
-      ConstraintSystem::SolverScope scope(*this);
-      applySolution(*viable);
-      // All of the solutions supposed to produce a "candidate" note.
-      diagnosed &= viable->Fixes.front()->diagnose(/*asNote*/ true);
     }
 
     // If not all of the fixes produced a note, we can't diagnose this.
diff --git a/test/Constraints/diagnostics.swift b/test/Constraints/diagnostics.swift
index b9ffb4a484c80..9c6397c2cd276 100644
--- a/test/Constraints/diagnostics.swift
+++ b/test/Constraints/diagnostics.swift
@@ -1085,7 +1085,7 @@ func SR_6272_c() {
 struct SR_6272_D: ExpressibleByIntegerLiteral {
   typealias IntegerLiteralType = Int
   init(integerLiteral: Int) {}
-  static func +(lhs: SR_6272_D, rhs: Int) -> Float { return 42.0 } // expected-note 2 {{candidate expects value of type 'Int' for parameter #2}}
+  static func +(lhs: SR_6272_D, rhs: Int) -> Float { return 42.0 }
 }
 
 func SR_6272_d() {
diff --git a/test/decl/subscript/subscripting.swift b/test/decl/subscript/subscripting.swift
index c7b92dc292d9c..1065c0e69d31e 100644
--- a/test/decl/subscript/subscripting.swift
+++ b/test/decl/subscript/subscripting.swift
@@ -385,9 +385,9 @@ func testSubscript1(_ s1 : SubscriptTest1) {
   _ = s1.subscript(SuperClass())
   // expected-error@-1 {{no exact matches in call to subscript}}
   _ = s1.subscript("hello")
-  // expected-error@-1 {{value of type 'SubscriptTest1' has no property or method named 'subscript'; did you mean to use the subscript operator?}}
+  // expected-error@-1 {{no exact matches in call to subscript}}
   _ = s1.subscript("hello"
-  // expected-error@-1 {{value of type 'SubscriptTest1' has no property or method named 'subscript'; did you mean to use the subscript operator?}}
+  // expected-error@-1 {{no exact matches in call to subscript}}
   // expected-note@-2 {{to match this opening '('}}
 
   let _ = s1["hello"]

From 651c27b50baafad32a4dc8149759a8d01dba1cc0 Mon Sep 17 00:00:00 2001
From: Holly Borla <hborla@apple.com>
Date: Fri, 7 Feb 2020 16:25:46 -0800
Subject: [PATCH 03/13] [Diagnostics] Add CSFix::diagnoseForAmbiguity for
 diagnosing common fixes that appear in all solutions.

---
 lib/Sema/CSFix.cpp                       | 18 +++++++++++++++
 lib/Sema/CSFix.h                         | 20 ++++++++++++++++
 lib/Sema/ConstraintSystem.cpp            | 29 +++++++++++-------------
 test/Constraints/closures.swift          |  2 +-
 test/Misc/misc_diagnostics.swift         |  6 ++---
 test/Sema/diag_ambiguous_overloads.swift |  4 ++--
 test/type/protocol_composition.swift     |  4 +---
 7 files changed, 58 insertions(+), 25 deletions(-)

diff --git a/lib/Sema/CSFix.cpp b/lib/Sema/CSFix.cpp
index 19f553667c775..c127f3cb014dc 100644
--- a/lib/Sema/CSFix.cpp
+++ b/lib/Sema/CSFix.cpp
@@ -479,6 +479,24 @@ bool DefineMemberBasedOnUse::diagnose(bool asNote) const {
   return AlreadyDiagnosed || failure.diagnose(asNote);
 }
 
+bool
+DefineMemberBasedOnUse::diagnoseForAmbiguity(ArrayRef<Solution> solutions) const {
+  Type concreteBaseType;
+  for (const auto &solution: solutions) {
+    auto baseType = solution.simplifyType(BaseType);
+    if (!concreteBaseType)
+      concreteBaseType = baseType;
+
+    if (concreteBaseType->getCanonicalType() != baseType->getCanonicalType()) {
+      getConstraintSystem().getASTContext().Diags.diagnose(getAnchor()->getLoc(),
+          diag::unresolved_member_no_inference, Name);
+      return true;
+    }
+  }
+
+  return diagnose();
+}
+
 DefineMemberBasedOnUse *
 DefineMemberBasedOnUse::create(ConstraintSystem &cs, Type baseType,
                                DeclNameRef member, bool alreadyDiagnosed,
diff --git a/lib/Sema/CSFix.h b/lib/Sema/CSFix.h
index d4c453070228d..e2b6121ff0594 100644
--- a/lib/Sema/CSFix.h
+++ b/lib/Sema/CSFix.h
@@ -289,6 +289,8 @@ class ConstraintFix {
   /// Diagnose a failure associated with this fix.
   virtual bool diagnose(bool asNote = false) const = 0;
 
+  virtual bool diagnoseForAmbiguity(ArrayRef<Solution> solutions) const { return false; }
+
   void print(llvm::raw_ostream &Out) const;
 
   SWIFT_DEBUG_DUMP;
@@ -843,6 +845,8 @@ class DefineMemberBasedOnUse final : public ConstraintFix {
 
   bool diagnose(bool asNote = false) const override;
 
+  bool diagnoseForAmbiguity(ArrayRef<Solution> solutions) const override;
+
   static DefineMemberBasedOnUse *create(ConstraintSystem &cs, Type baseType,
                                         DeclNameRef member, bool alreadyDiagnosed,
                                         ConstraintLocator *locator);
@@ -1109,6 +1113,10 @@ class AddMissingArguments final
 
   bool diagnose(bool asNote = false) const override;
 
+  bool diagnoseForAmbiguity(ArrayRef<Solution> solutions) const override {
+    return diagnose();
+  }
+
   static AddMissingArguments *create(ConstraintSystem &cs,
                                      llvm::ArrayRef<Param> synthesizedArgs,
                                      ConstraintLocator *locator);
@@ -1149,6 +1157,10 @@ class RemoveExtraneousArguments final
 
   bool diagnose(bool asNote = false) const override;
 
+  bool diagnoseForAmbiguity(ArrayRef<Solution> solutions) const override {
+    return diagnose();
+  }
+
   /// FIXME(diagnostics): Once `resolveDeclRefExpr` is gone this
   /// logic would be obsolete.
   ///
@@ -1349,6 +1361,10 @@ class DefaultGenericArgument final : public ConstraintFix {
 
   bool diagnose(bool asNote = false) const override;
 
+  bool diagnoseForAmbiguity(ArrayRef<Solution> solutions) const override {
+    return diagnose();
+  }
+
   static DefaultGenericArgument *create(ConstraintSystem &cs,
                                         GenericTypeParamType *param,
                                         ConstraintLocator *locator);
@@ -1420,6 +1436,10 @@ class IgnoreContextualType : public ContextualMismatch {
 
   bool diagnose(bool asNote = false) const override;
 
+  bool diagnoseForAmbiguity(ArrayRef<Solution> solutions) const override {
+    return diagnose();
+  }
+
   static IgnoreContextualType *create(ConstraintSystem &cs, Type resultTy,
                                       Type specifiedTy,
                                       ConstraintLocator *locator);
diff --git a/lib/Sema/ConstraintSystem.cpp b/lib/Sema/ConstraintSystem.cpp
index ab019e79e3722..b3e2a81430f3b 100644
--- a/lib/Sema/ConstraintSystem.cpp
+++ b/lib/Sema/ConstraintSystem.cpp
@@ -2761,22 +2761,9 @@ bool ConstraintSystem::diagnoseAmbiguityWithFixes(
     }
   }
 
-  // If there are no overload differences, diagnose the common fixes.
-  SolutionDiff solutionDiff(solutions);
-  if (solutionDiff.overloads.size() == 0) {
-    bool diagnosed = false;
-    ConstraintSystem::SolverScope scope(*this);
-    applySolution(solutions.front());
-    for (auto fixes: aggregatedFixes) {
-      // A common fix must appear in all solutions
-      if (fixes.second.size() < solutions.size()) continue;
-      diagnosed |= fixes.second.front()->diagnose();
-    }
-    return diagnosed;
-  }
-
   // If there is an overload difference, let's see if there's a common callee
   // locator for all of the fixes.
+  SolutionDiff solutionDiff(solutions);
   auto ambiguousOverload = llvm::find_if(solutionDiff.overloads,
       [&](const auto &overloadDiff) {
         return llvm::all_of(aggregatedFixes, [&](const auto &aggregatedFix) {
@@ -2798,8 +2785,18 @@ bool ConstraintSystem::diagnoseAmbiguityWithFixes(
         });
       });
 
-  if (ambiguousOverload == solutionDiff.overloads.end())
-    return false;
+  // If we didn't find an ambiguous overload, diagnose the common fixes.
+  if (ambiguousOverload == solutionDiff.overloads.end()) {
+    bool diagnosed = false;
+    ConstraintSystem::SolverScope scope(*this);
+    applySolution(solutions.front());
+    for (auto fixes: aggregatedFixes) {
+      // A common fix must appear in all solutions
+      if (fixes.second.size() < solutions.size()) continue;
+      diagnosed |= fixes.second.front()->diagnoseForAmbiguity(solutions);
+    }
+    return diagnosed;
+  }
 
   auto *commonCalleeLocator = ambiguousOverload->locator;
   auto *decl = ambiguousOverload->choices.front().getDecl();
diff --git a/test/Constraints/closures.swift b/test/Constraints/closures.swift
index 876b5a1b76260..67d87f40203ca 100644
--- a/test/Constraints/closures.swift
+++ b/test/Constraints/closures.swift
@@ -186,7 +186,7 @@ func testMap() {
 }
 
 // <rdar://problem/22414757> "UnresolvedDot" "in wrong phase" assertion from verifier
-[].reduce { $0 + $1 }  // expected-error {{cannot invoke 'reduce' with an argument list of type '(_)'}}
+[].reduce { $0 + $1 }  // expected-error {{missing argument for parameter #1 in call}}
 
 
 
diff --git a/test/Misc/misc_diagnostics.swift b/test/Misc/misc_diagnostics.swift
index 4449414e68fa5..b26c78b0aa66a 100644
--- a/test/Misc/misc_diagnostics.swift
+++ b/test/Misc/misc_diagnostics.swift
@@ -47,12 +47,12 @@ takesInt(noParams(1)) // expected-error{{argument passed to call that takes no a
 takesInt(takesAndReturnsInt("")) // expected-error{{cannot convert value of type 'String' to expected argument type 'Int'}}
 
 // Test error recovery for type expressions.
-struct MyArray<Element> {}
+struct MyArray<Element> {} // expected-note {{'Element' declared as parameter to type 'MyArray'}}
 class A {
     var a: MyArray<Int>
     init() {
-        a = MyArray<Int // expected-error{{binary operator '<' cannot be applied to operands of type 'MyArray<_>.Type' and 'Int.Type'}}
-	// expected-note @-1 {{overloads for '<' exist with these partially matching parameter lists:}}
+        a = MyArray<Int // expected-error {{generic parameter 'Element' could not be inferred}}
+        // expected-note@-1 {{explicitly specify the generic arguments to fix this issue}}
     }
 }
 
diff --git a/test/Sema/diag_ambiguous_overloads.swift b/test/Sema/diag_ambiguous_overloads.swift
index 52891a8f34dfe..a1b941d0934b7 100644
--- a/test/Sema/diag_ambiguous_overloads.swift
+++ b/test/Sema/diag_ambiguous_overloads.swift
@@ -12,8 +12,8 @@ func fe(_: Int, _: Int) {}
 fe(E.baz) // expected-error {{type 'E' has no member 'baz'; did you mean 'bar'?}}
 fe(.baz) // expected-error {{reference to member 'baz' cannot be resolved without a contextual type}}
 
-// FIXME: maybe complain about .nope also?
-fe(.nope, .nyet) // expected-error {{reference to member 'nyet' cannot be resolved without a contextual type}}
+fe(.nope, .nyet) // expected-error {{type 'Int' has no member 'nope'}}
+// expected-error@-1 {{reference to member 'nyet' cannot be resolved without a contextual type}}
 
 func fg<T>(_ f: (T) -> T) -> Void {} // expected-note {{in call to function 'fg'}}
 fg({x in x}) // expected-error {{generic parameter 'T' could not be inferred}}
diff --git a/test/type/protocol_composition.swift b/test/type/protocol_composition.swift
index a75b0414b5aa5..b78a9af3a5fd0 100644
--- a/test/type/protocol_composition.swift
+++ b/test/type/protocol_composition.swift
@@ -173,9 +173,7 @@ takesP1AndP2([Swift.AnyObject & P1 & P2]())
 takesP1AndP2([AnyObject & protocol_composition.P1 & P2]())
 takesP1AndP2([AnyObject & P1 & protocol_composition.P2]())
 takesP1AndP2([DoesNotExist & P1 & P2]()) // expected-error {{use of unresolved identifier 'DoesNotExist'}}
-// TODO(diagnostics): The problem here is that `&` is interpreted as a binary operator, we need to re-think
-// how "missing member" fix is implemented because currently it finds N solutions with multiple fixes.
-takesP1AndP2([Swift.DoesNotExist & P1 & P2]()) // expected-error {{cannot invoke '' with no arguments}}
+takesP1AndP2([Swift.DoesNotExist & P1 & P2]()) // expected-error {{module 'Swift' has no member named 'DoesNotExist'}}
 
 typealias T08 = P1 & inout P2 // expected-error {{'inout' may only be used on parameters}}
 typealias T09 = P1 & __shared P2 // expected-error {{'__shared' may only be used on parameters}}

From 1a628f31077ca60f9f5a415b0ed7b8c3b4729212 Mon Sep 17 00:00:00 2001
From: Holly Borla <hborla@apple.com>
Date: Fri, 7 Feb 2020 16:36:56 -0800
Subject: [PATCH 04/13] [Diagnostics] Simplify logic in
 diagnoseAmbiguityWithFixes for emitting the ambiguity diagnostic by combining
 a few special errors into one.

---
 include/swift/AST/DiagnosticsSema.def | 10 ++--------
 lib/Sema/ConstraintSystem.cpp         | 20 +++-----------------
 test/Sema/diag_non_ephemeral.swift    |  2 +-
 test/decl/ext/protocol.swift          |  4 ++--
 4 files changed, 8 insertions(+), 28 deletions(-)

diff --git a/include/swift/AST/DiagnosticsSema.def b/include/swift/AST/DiagnosticsSema.def
index 610c9c897fd28..7c06b1fe1e8da 100644
--- a/include/swift/AST/DiagnosticsSema.def
+++ b/include/swift/AST/DiagnosticsSema.def
@@ -61,14 +61,8 @@ ERROR(ambiguous_member_overload_set,none,
 ERROR(ambiguous_reference_to_decl,none,
       "ambiguous reference to %0 %1", (DescriptiveDeclKind, DeclName))
 ERROR(no_overloads_match_exactly_in_call,none,
-      "no exact matches in call to %0 %1",
-      (DescriptiveDeclKind, DeclName))
-ERROR(no_overloads_match_exactly_in_call_no_labels,none,
-      "no exact matches in call to %0 %1",
-      (DescriptiveDeclKind, DeclBaseName))
-ERROR(no_overloads_match_exactly_in_call_special,none,
-      "no exact matches in call to %0",
-      (DescriptiveDeclKind))
+      "no exact matches in call to %0 %select{%2|}1",
+      (DescriptiveDeclKind, bool, DeclBaseName))
 ERROR(no_overloads_match_exactly_in_assignment,none,
       "no exact matches in assignment to %0",
       (DeclBaseName))
diff --git a/lib/Sema/ConstraintSystem.cpp b/lib/Sema/ConstraintSystem.cpp
index b3e2a81430f3b..b75d211a1178b 100644
--- a/lib/Sema/ConstraintSystem.cpp
+++ b/lib/Sema/ConstraintSystem.cpp
@@ -2824,25 +2824,11 @@ bool ConstraintSystem::diagnoseAmbiguityWithFixes(
       auto baseName = name.getBaseName();
       DE.diagnose(commonAnchor->getLoc(), diag::no_candidates_match_result_type,
                   baseName.userFacingName(), getContextualType(anchor));
-    } else if (name.isSpecial()) {
-      // If this is a special name, avoid printing it because printing the
-      // decl kind is sufficient.
-      DE.diagnose(commonAnchor->getLoc(),
-                  diag::no_overloads_match_exactly_in_call_special,
-                  decl->getDescriptiveKind());
-    } else if (llvm::all_of(ambiguousOverload->choices,
-                            [&name](const OverloadChoice &choice) {
-                              return choice.getDecl()->getFullName() == name;
-                            })) {
-      // If the labels match in each overload, print a full name.
-      DE.diagnose(commonAnchor->getLoc(),
-                  diag::no_overloads_match_exactly_in_call,
-                  decl->getDescriptiveKind(), name);
     } else {
-      // If the labels are different, we can only print a base name.
       DE.diagnose(commonAnchor->getLoc(),
-                  diag::no_overloads_match_exactly_in_call_no_labels,
-                  decl->getDescriptiveKind(), name.getBaseName());
+                  diag::no_overloads_match_exactly_in_call,
+                  decl->getDescriptiveKind(), name.isSpecial(),
+                  name.getBaseName());
     }
 
     // Produce candidate notes
diff --git a/test/Sema/diag_non_ephemeral.swift b/test/Sema/diag_non_ephemeral.swift
index 451d625989865..8868afa5ea051 100644
--- a/test/Sema/diag_non_ephemeral.swift
+++ b/test/Sema/diag_non_ephemeral.swift
@@ -489,7 +489,7 @@ func takesPointerOverload(x: Int = 0, @_nonEphemeral _ ptr: UnsafeMutablePointer
 
 func testAmbiguity() {
   var arr = [1, 2, 3]
-  takesPointerOverload(&arr) // expected-error {{no exact matches in call to global function 'takesPointerOverload(x:_:)'}}
+  takesPointerOverload(&arr) // expected-error {{no exact matches in call to global function 'takesPointerOverload'}}
 }
 
 func takesPointerOverload2(@_nonEphemeral _ ptr: UnsafePointer<Int>) {}
diff --git a/test/decl/ext/protocol.swift b/test/decl/ext/protocol.swift
index 70e6a1cd65abd..2628bbc8aab11 100644
--- a/test/decl/ext/protocol.swift
+++ b/test/decl/ext/protocol.swift
@@ -236,9 +236,9 @@ extension P4 where Self.AssocP4 == Bool {
 }
 
 func testP4(_ s4a: S4a, s4b: S4b, s4c: S4c, s4d: S4d) {
-  s4a.extP4a() // expected-error{{no exact matches in call to instance method 'extP4a()'}}
+  s4a.extP4a() // expected-error{{no exact matches in call to instance method 'extP4a'}}
   s4b.extP4a() // ok
-  s4c.extP4a() // expected-error{{no exact matches in call to instance method 'extP4a()'}}
+  s4c.extP4a() // expected-error{{no exact matches in call to instance method 'extP4a'}}
   s4c.extP4Int() // okay
   var b1 = s4d.extP4a() // okay, "Bool" version
   b1 = true // checks type above

From d1f6b3e2efc536b6cf2c5610c8113fe757989f02 Mon Sep 17 00:00:00 2001
From: Holly Borla <hborla@apple.com>
Date: Mon, 10 Feb 2020 12:12:37 -0800
Subject: [PATCH 05/13] [Diagnostics] When diagnosing an ambiguous overload,
 don't mention "call" if the expression is not a function application.

---
 include/swift/AST/DiagnosticsSema.def             | 7 ++-----
 lib/Sema/ConstraintSystem.cpp                     | 7 +++++++
 test/Constraints/diagnostics.swift                | 2 +-
 test/Constraints/patterns.swift                   | 2 +-
 test/NameBinding/import-resolution-overload.swift | 2 +-
 test/Parse/super.swift                            | 2 +-
 6 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/include/swift/AST/DiagnosticsSema.def b/include/swift/AST/DiagnosticsSema.def
index 7c06b1fe1e8da..7fbe23b1c17a7 100644
--- a/include/swift/AST/DiagnosticsSema.def
+++ b/include/swift/AST/DiagnosticsSema.def
@@ -61,11 +61,8 @@ ERROR(ambiguous_member_overload_set,none,
 ERROR(ambiguous_reference_to_decl,none,
       "ambiguous reference to %0 %1", (DescriptiveDeclKind, DeclName))
 ERROR(no_overloads_match_exactly_in_call,none,
-      "no exact matches in call to %0 %select{%2|}1",
-      (DescriptiveDeclKind, bool, DeclBaseName))
-ERROR(no_overloads_match_exactly_in_assignment,none,
-      "no exact matches in assignment to %0",
-      (DeclBaseName))
+      "no exact matches in %select{reference|call}0 to %1 %select{%3|}2",
+      (bool, DescriptiveDeclKind, bool, DeclBaseName))
 
 NOTE(candidate_partial_match,none,
      "candidate has partially matching parameter list %0",
diff --git a/lib/Sema/ConstraintSystem.cpp b/lib/Sema/ConstraintSystem.cpp
index b75d211a1178b..94518ff045190 100644
--- a/lib/Sema/ConstraintSystem.cpp
+++ b/lib/Sema/ConstraintSystem.cpp
@@ -2807,6 +2807,8 @@ bool ConstraintSystem::diagnoseAmbiguityWithFixes(
     DiagnosticTransaction transaction(getASTContext().Diags);
 
     auto *commonAnchor = commonCalleeLocator->getAnchor();
+    if (auto *callExpr = dyn_cast<CallExpr>(commonAnchor))
+      commonAnchor = callExpr->getDirectCallee();
     auto &DE = getASTContext().Diags;
     auto name = decl->getFullName();
 
@@ -2825,8 +2827,13 @@ bool ConstraintSystem::diagnoseAmbiguityWithFixes(
       DE.diagnose(commonAnchor->getLoc(), diag::no_candidates_match_result_type,
                   baseName.userFacingName(), getContextualType(anchor));
     } else {
+      bool isApplication = llvm::find_if(ArgumentInfos, [&](const auto argInfo) {
+        return argInfo.first->getAnchor() == commonAnchor;
+      }) != ArgumentInfos.end();
+
       DE.diagnose(commonAnchor->getLoc(),
                   diag::no_overloads_match_exactly_in_call,
+                  isApplication,
                   decl->getDescriptiveKind(), name.isSpecial(),
                   name.getBaseName());
     }
diff --git a/test/Constraints/diagnostics.swift b/test/Constraints/diagnostics.swift
index 9c6397c2cd276..6ba8223922fce 100644
--- a/test/Constraints/diagnostics.swift
+++ b/test/Constraints/diagnostics.swift
@@ -935,7 +935,7 @@ class CacheValue {
 
 func valueForKey<K>(_ key: K) -> CacheValue? {
   let cache = NSCache<K, CacheValue>()
-  return cache.object(forKey: key)?.value // expected-error {{no exact matches in call to instance method 'value'}}
+  return cache.object(forKey: key)?.value // expected-error {{no exact matches in reference to instance method 'value'}}
 }
 
 // SR-2242: poor diagnostic when argument label is omitted
diff --git a/test/Constraints/patterns.swift b/test/Constraints/patterns.swift
index ef03365f1ce4a..401fbf542f2d6 100644
--- a/test/Constraints/patterns.swift
+++ b/test/Constraints/patterns.swift
@@ -301,7 +301,7 @@ switch staticMembers {
   // TODO: repeated error message
   case .optProp: break // expected-error* {{not unwrapped}}
 
-  case .method: break // expected-error{{no exact matches in call to static method 'method'}}
+  case .method: break // expected-error{{no exact matches in reference to static method 'method'}}
   case .method(0): break
   case .method(_): break // expected-error{{'_' can only appear in a pattern}}
   case .method(let x): break // expected-error{{cannot appear in an expression}}
diff --git a/test/NameBinding/import-resolution-overload.swift b/test/NameBinding/import-resolution-overload.swift
index 9f5a89eb13247..ce9c493560811 100644
--- a/test/NameBinding/import-resolution-overload.swift
+++ b/test/NameBinding/import-resolution-overload.swift
@@ -46,7 +46,7 @@ scopedFunction = 42
 // FIXME: Should be an error -- a type name and a function cannot overload.
 var _ : Int = TypeNameWins(42)
 
-TypeNameWins = 42 // expected-error {{no exact matches in assignment to 'TypeNameWins'}}
+TypeNameWins = 42 // expected-error {{no exact matches in reference to global function 'TypeNameWins'}}
 var _ : TypeNameWins // no-warning
 
 // rdar://problem/21739333
diff --git a/test/Parse/super.swift b/test/Parse/super.swift
index c4317a4bf18b8..a7acb18b2ad76 100644
--- a/test/Parse/super.swift
+++ b/test/Parse/super.swift
@@ -39,7 +39,7 @@ class D : B {
     super.bar        // expected-error {{expression resolves to an unused function}}
     super.bar()
     // FIXME: should also say "'super.init' cannot be referenced outside of an initializer"
-    super.init // expected-error{{no exact matches in call to initializer}}
+    super.init // expected-error{{no exact matches in reference to initializer}}
     super.init() // expected-error{{'super.init' cannot be called outside of an initializer}}
     super.init(0) // expected-error{{'super.init' cannot be called outside of an initializer}} // expected-error {{missing argument label 'x:' in call}}
     super[0]        // expected-error {{expression resolves to an unused subscript}}

From ab59032ebbe36bf2cb72cc46412688f0315d2152 Mon Sep 17 00:00:00 2001
From: Holly Borla <hborla@apple.com>
Date: Mon, 10 Feb 2020 12:51:07 -0800
Subject: [PATCH 06/13] [CSDiag] Remove obsolete ambiguity code.

---
 include/swift/AST/DiagnosticsSema.def | 13 -------------
 lib/Sema/CSDiag.cpp                   | 11 -----------
 2 files changed, 24 deletions(-)

diff --git a/include/swift/AST/DiagnosticsSema.def b/include/swift/AST/DiagnosticsSema.def
index 7fbe23b1c17a7..87bcef6d6ce8a 100644
--- a/include/swift/AST/DiagnosticsSema.def
+++ b/include/swift/AST/DiagnosticsSema.def
@@ -68,9 +68,6 @@ NOTE(candidate_partial_match,none,
      "candidate has partially matching parameter list %0",
      (StringRef))
 
-ERROR(ambiguous_subscript,none,
-      "ambiguous subscript with base type %0 and index type %1",
-      (Type, Type))
 ERROR(could_not_find_value_subscript,none,
       "value of type %0 has no subscripts",
       (Type))
@@ -273,16 +270,6 @@ ERROR(no_candidates_match_result_type,none,
       "no '%0' candidates produce the expected contextual result type %1",
       (StringRef, Type))
 
-ERROR(candidates_no_match_result_type,none,
-      "'%0' produces %1, not the expected contextual result type %2",
-      (StringRef, Type, Type))
-
-
-
-ERROR(invalid_callee_result_type,none,
-      "cannot convert call result type %0 to expected type %1",
-      (Type, Type))
-
 
 ERROR(cannot_invoke_closure,none,
       "cannot invoke closure expression with an argument list of type '%0'",
diff --git a/lib/Sema/CSDiag.cpp b/lib/Sema/CSDiag.cpp
index b46e4dd281c65..bfd91aea71859 100644
--- a/lib/Sema/CSDiag.cpp
+++ b/lib/Sema/CSDiag.cpp
@@ -1247,17 +1247,6 @@ void FailureDiagnosis::diagnoseAmbiguity(Expr *E) {
     return;
   }
 
-  // Diagnose ".foo" expressions that lack context specifically.
-  if (auto UME =
-        dyn_cast<UnresolvedMemberExpr>(E->getSemanticsProvidingExpr())) {
-    if (!CS.getContextualType(E)) {
-      diagnose(E->getLoc(), diag::unresolved_member_no_inference,UME->getName())
-        .highlight(SourceRange(UME->getDotLoc(),
-                               UME->getNameLoc().getSourceRange().End));
-      return;
-    }
-  }
-
   // Attempt to re-type-check the entire expression, allowing ambiguity, but
   // ignoring a contextual type.
   if (expr == E) {

From 5437622d2da556b23ab459452d2d4bcfb0dd0d13 Mon Sep 17 00:00:00 2001
From: Pavel Yaskevich <pyaskevich@apple.com>
Date: Wed, 12 Feb 2020 17:23:07 -0800
Subject: [PATCH 07/13] [Diagnostics] Diagnose ambiguity with conflicting
 arguments to generic parameters

It's done by first retrieving all generic parameters from each solution,
filtering boundings into distrinct set and diagnosing any differences.

For example:

```swift
func foo<T>(_: T, _: T) {}
func bar(x: Int, y: Float) {
  foo(x, y)
}
```
---
 include/swift/AST/DiagnosticsSema.def         |   4 +
 lib/Sema/CSDiagnostics.cpp                    |  34 ----
 lib/Sema/CSFix.cpp                            |   6 +
 lib/Sema/CSFix.h                              |   6 +
 lib/Sema/ConstraintSystem.cpp                 | 154 +++++++++++++++++-
 lib/Sema/ConstraintSystem.h                   |   2 +
 test/Generics/deduction.swift                 |  10 +-
 .../suppress-argument-labels-in-types.swift   |   2 +-
 test/Sema/type_join.swift                     |   4 +-
 test/decl/func/default-values.swift           |   2 +-
 test/type/opaque.swift                        |   9 +-
 11 files changed, 187 insertions(+), 46 deletions(-)

diff --git a/include/swift/AST/DiagnosticsSema.def b/include/swift/AST/DiagnosticsSema.def
index 87bcef6d6ce8a..cb18f72f48422 100644
--- a/include/swift/AST/DiagnosticsSema.def
+++ b/include/swift/AST/DiagnosticsSema.def
@@ -385,6 +385,10 @@ ERROR(cannot_convert_argument_value_generic,none,
       "cannot convert value of type %0 (%1) to expected argument type %2 (%3)",
       (Type, StringRef, Type, StringRef))
 
+ERROR(conflicting_arguments_for_generic_parameter,none,
+      "conflicting arguments to generic parameter %0 (%1)",
+      (Type, StringRef))
+
 // @_nonEphemeral conversion diagnostics
 ERROR(cannot_pass_type_to_non_ephemeral,none,
       "cannot pass %0 to parameter; argument %1 must be a pointer that "
diff --git a/lib/Sema/CSDiagnostics.cpp b/lib/Sema/CSDiagnostics.cpp
index f853f146d9919..6471c45973e1b 100644
--- a/lib/Sema/CSDiagnostics.cpp
+++ b/lib/Sema/CSDiagnostics.cpp
@@ -5585,40 +5585,6 @@ bool ArgumentMismatchFailure::diagnoseArchetypeMismatch() const {
   if (!(paramDecl && argDecl))
     return false;
 
-  auto describeGenericType = [&](ValueDecl *genericParam,
-                                 bool includeName = false) -> std::string {
-    if (!genericParam)
-      return "";
-
-    Decl *parent = nullptr;
-    if (auto *AT = dyn_cast<AssociatedTypeDecl>(genericParam)) {
-      parent = AT->getProtocol();
-    } else {
-      auto *dc = genericParam->getDeclContext();
-      parent = dc->getInnermostDeclarationDeclContext();
-    }
-
-    if (!parent)
-      return "";
-
-    llvm::SmallString<64> result;
-    llvm::raw_svector_ostream OS(result);
-
-    OS << Decl::getDescriptiveKindName(genericParam->getDescriptiveKind());
-
-    if (includeName && genericParam->hasName())
-      OS << " '" << genericParam->getBaseName() << "'";
-
-    OS << " of ";
-    OS << Decl::getDescriptiveKindName(parent->getDescriptiveKind());
-    if (auto *decl = dyn_cast<ValueDecl>(parent)) {
-      if (decl->hasName())
-        OS << " '" << decl->getFullName() << "'";
-    }
-
-    return OS.str();
-  };
-
   emitDiagnostic(
       getAnchor()->getLoc(), diag::cannot_convert_argument_value_generic, argTy,
       describeGenericType(argDecl), paramTy, describeGenericType(paramDecl));
diff --git a/lib/Sema/CSFix.cpp b/lib/Sema/CSFix.cpp
index c127f3cb014dc..67bbe57cbfdad 100644
--- a/lib/Sema/CSFix.cpp
+++ b/lib/Sema/CSFix.cpp
@@ -1106,6 +1106,12 @@ UseValueTypeOfRawRepresentative::attempt(ConstraintSystem &cs, Type argType,
   return nullptr;
 }
 
+unsigned AllowArgumentMismatch::getParamIdx() const {
+  const auto *locator = getLocator();
+  auto elt = locator->castLastElementTo<LocatorPathElt::ApplyArgToParam>();
+  return elt.getParamIdx();
+}
+
 bool AllowArgumentMismatch::diagnose(bool asNote) const {
   auto &cs = getConstraintSystem();
   ArgumentMismatchFailure failure(cs, getFromType(), getToType(),
diff --git a/lib/Sema/CSFix.h b/lib/Sema/CSFix.h
index e2b6121ff0594..15d0378ef98b2 100644
--- a/lib/Sema/CSFix.h
+++ b/lib/Sema/CSFix.h
@@ -1499,11 +1499,17 @@ class AllowArgumentMismatch : public ContextualMismatch {
     return "allow argument to parameter type conversion mismatch";
   }
 
+  unsigned getParamIdx() const;
+
   bool diagnose(bool asNote = false) const override;
 
   static AllowArgumentMismatch *create(ConstraintSystem &cs, Type argType,
                                        Type paramType,
                                        ConstraintLocator *locator);
+
+  static bool classof(const ConstraintFix *fix) {
+    return fix->getKind() == FixKind::AllowArgumentTypeMismatch;
+  }
 };
 
 class ExpandArrayIntoVarargs final : public AllowArgumentMismatch {
diff --git a/lib/Sema/ConstraintSystem.cpp b/lib/Sema/ConstraintSystem.cpp
index 94518ff045190..e42e6cc1deaca 100644
--- a/lib/Sema/ConstraintSystem.cpp
+++ b/lib/Sema/ConstraintSystem.cpp
@@ -2729,6 +2729,154 @@ static void diagnoseOperatorAmbiguity(ConstraintSystem &cs,
               llvm::join(parameters, ", "));
 }
 
+std::string swift::describeGenericType(ValueDecl *GP, bool includeName) {
+  if (!GP)
+    return "";
+
+  Decl *parent = nullptr;
+  if (auto *AT = dyn_cast<AssociatedTypeDecl>(GP)) {
+    parent = AT->getProtocol();
+  } else {
+    auto *dc = GP->getDeclContext();
+    parent = dc->getInnermostDeclarationDeclContext();
+  }
+
+  if (!parent)
+    return "";
+
+  llvm::SmallString<64> result;
+  llvm::raw_svector_ostream OS(result);
+
+  OS << Decl::getDescriptiveKindName(GP->getDescriptiveKind());
+
+  if (includeName && GP->hasName())
+    OS << " '" << GP->getBaseName() << "'";
+
+  OS << " of ";
+  OS << Decl::getDescriptiveKindName(parent->getDescriptiveKind());
+  if (auto *decl = dyn_cast<ValueDecl>(parent)) {
+    if (decl->hasName())
+      OS << " '" << decl->getFullName() << "'";
+  }
+
+  return OS.str();
+}
+
+/// Special handling of conflicts associated with generic arguments.
+///
+/// func foo<T>(_: T, _: T) {}
+/// func bar(x: Int, y: Float) {
+///   foo(x, y)
+/// }
+///
+/// It's done by first retrieving all generic parameters from each solution,
+/// filtering boundings into distrinct set and diagnosing any differences.
+static bool diagnoseConflictingArguments(ConstraintSystem &cs,
+                                         const SolutionDiff &diff,
+                                         ArrayRef<Solution> solutions) {
+  if (!diff.overloads.empty())
+    return false;
+
+  if (!llvm::all_of(solutions, [](const Solution &solution) -> bool {
+        return llvm::all_of(
+            solution.Fixes, [](const ConstraintFix *fix) -> bool {
+              return fix->getKind() == FixKind::AllowArgumentTypeMismatch ||
+                     fix->getKind() == FixKind::AllowFunctionTypeMismatch ||
+                     fix->getKind() == FixKind::AllowTupleTypeMismatch;
+            });
+      }))
+    return false;
+
+  auto &DE = cs.getASTContext().Diags;
+
+  llvm::SmallDenseMap<TypeVariableType *, SmallVector<Type, 4>> conflicts;
+
+  for (const auto &binding : solutions[0].typeBindings) {
+    auto *typeVar = binding.first;
+
+    if (!typeVar->getImpl().getGenericParameter())
+      continue;
+
+    llvm::SmallSetVector<Type, 4> arguments;
+    arguments.insert(binding.second);
+
+    if (!llvm::all_of(solutions.slice(1), [&](const Solution &solution) {
+          auto binding = solution.typeBindings.find(typeVar);
+          if (binding == solution.typeBindings.end())
+            return false;
+
+          if (auto *opaque =
+                  binding->second->getAs<OpaqueTypeArchetypeType>()) {
+            auto *decl = opaque->getDecl();
+            arguments.remove_if([&](Type argType) -> bool {
+              if (auto *otherOpaque =
+                      argType->getAs<OpaqueTypeArchetypeType>()) {
+                return decl == otherOpaque->getDecl();
+              }
+              return false;
+            });
+          }
+
+          arguments.insert(binding->second);
+          return true;
+        }))
+      continue;
+
+    if (arguments.size() > 1) {
+      conflicts[typeVar].append(arguments.begin(), arguments.end());
+    }
+  }
+
+  auto getGenericTypeDecl = [&](ArchetypeType *archetype) -> ValueDecl * {
+    auto type = archetype->getInterfaceType();
+
+    if (auto *GTPT = type->getAs<GenericTypeParamType>())
+      return GTPT->getDecl();
+
+    if (auto *DMT = type->getAs<DependentMemberType>())
+      return DMT->getAssocType();
+
+    return nullptr;
+  };
+
+  bool diagnosed = false;
+  for (auto &conflict : conflicts) {
+    auto *typeVar = conflict.first;
+    auto *locator = typeVar->getImpl().getLocator();
+    auto conflictingArguments = conflict.second;
+
+    llvm::SmallString<64> arguments;
+    llvm::raw_svector_ostream OS(arguments);
+
+    interleave(
+        conflictingArguments,
+        [&](Type argType) {
+          OS << "'" << argType << "'";
+
+          if (auto *opaque = argType->getAs<OpaqueTypeArchetypeType>()) {
+            auto *decl = opaque->getDecl()->getNamingDecl();
+            OS << " (result type of '" << decl->getBaseName().userFacingName()
+               << "')";
+            return;
+          }
+
+          if (auto archetype = argType->getAs<ArchetypeType>()) {
+            if (auto *GTD = getGenericTypeDecl(archetype))
+              OS << " (" << describeGenericType(GTD) << ")";
+          }
+        },
+        [&OS] { OS << " vs. "; });
+
+    auto *anchor = locator->getAnchor();
+    DE.diagnose(anchor->getLoc(),
+                diag::conflicting_arguments_for_generic_parameter,
+                typeVar->getImpl().getGenericParameter(), OS.str());
+    diagnosed = true;
+  }
+
+  return diagnosed;
+}
+
 bool ConstraintSystem::diagnoseAmbiguityWithFixes(
     SmallVectorImpl<Solution> &solutions) {
   if (solutions.empty())
@@ -2749,6 +2897,11 @@ bool ConstraintSystem::diagnoseAmbiguityWithFixes(
       return false;
   }
 
+  SolutionDiff solutionDiff(solutions);
+
+  if (diagnoseConflictingArguments(*this, solutionDiff, solutions))
+    return true;
+
   // Collect aggregated fixes from all solutions
   llvm::SmallMapVector<std::pair<ConstraintLocator *, FixKind>,
       llvm::SmallVector<ConstraintFix *, 4>, 4> aggregatedFixes;
@@ -2763,7 +2916,6 @@ bool ConstraintSystem::diagnoseAmbiguityWithFixes(
 
   // If there is an overload difference, let's see if there's a common callee
   // locator for all of the fixes.
-  SolutionDiff solutionDiff(solutions);
   auto ambiguousOverload = llvm::find_if(solutionDiff.overloads,
       [&](const auto &overloadDiff) {
         return llvm::all_of(aggregatedFixes, [&](const auto &aggregatedFix) {
diff --git a/lib/Sema/ConstraintSystem.h b/lib/Sema/ConstraintSystem.h
index d4f4055c759f1..f08c1a6afcae3 100644
--- a/lib/Sema/ConstraintSystem.h
+++ b/lib/Sema/ConstraintSystem.h
@@ -5115,6 +5115,8 @@ bool exprNeedsParensOutsideFollowingOperator(
 /// Determine whether this is a SIMD operator.
 bool isSIMDOperator(ValueDecl *value);
 
+std::string describeGenericType(ValueDecl *GP, bool includeName = false);
+
 /// Apply the given function builder transform within a specific solution
 /// to produce the rewritten body.
 ///
diff --git a/test/Generics/deduction.swift b/test/Generics/deduction.swift
index 9ce7ff1f3419a..2a5ad2cfe60f7 100644
--- a/test/Generics/deduction.swift
+++ b/test/Generics/deduction.swift
@@ -28,7 +28,6 @@ func useIdentity(_ x: Int, y: Float, i32: Int32) {
   xx = identity2(yy) // expected-error{{no exact matches in call to global function 'identity2'}}
 }
 
-// FIXME: Crummy diagnostic!
 func twoIdentical<T>(_ x: T, _ y: T) -> T {}
 
 func useTwoIdentical(_ xi: Int, yi: Float) {
@@ -40,7 +39,7 @@ func useTwoIdentical(_ xi: Int, yi: Float) {
   y = twoIdentical(1.0, y)
   y = twoIdentical(y, 1.0)
   
-  twoIdentical(x, y) // expected-error{{cannot convert value of type 'Float' to expected argument type 'Int'}}
+  twoIdentical(x, y) // expected-error{{conflicting arguments to generic parameter 'T' ('Int' vs. 'Float')}}
 }
 
 func mySwap<T>(_ x: inout T,
@@ -67,8 +66,9 @@ func takeTuples<T, U>(_: (T, U), _: (U, T)) {
 func useTuples(_ x: Int, y: Float, z: (Float, Int)) {
   takeTuples((x, y), (y, x))
 
-  takeTuples((x, y), (x, y)) // expected-error{{cannot convert value of type '(Int, Float)' to expected argument type '(Float, Int)'}}
-
+  takeTuples((x, y), (x, y))
+  // expected-error@-1 {{conflicting arguments to generic parameter 'U' ('Float' vs. 'Int')}}
+  // expected-error@-2 {{conflicting arguments to generic parameter 'T' ('Int' vs. 'Float')}}
   // FIXME: Use 'z', which requires us to fix our tuple-conversion
   // representation.
 }
@@ -315,7 +315,7 @@ struct A {}
 func foo() {
     for i in min(1,2) { // expected-error{{for-in loop requires 'Int' to conform to 'Sequence'}}
     }
-    let j = min(Int(3), Float(2.5)) // expected-error{{cannot convert value of type 'Float' to expected argument type 'Int'}}
+    let j = min(Int(3), Float(2.5)) // expected-error{{conflicting arguments to generic parameter 'T' ('Int' vs. 'Float')}}
     let k = min(A(), A()) // expected-error{{global function 'min' requires that 'A' conform to 'Comparable'}}
     let oi : Int? = 5
     let l = min(3, oi) // expected-error{{global function 'min' requires that 'Int?' conform to 'Comparable'}}
diff --git a/test/Sema/suppress-argument-labels-in-types.swift b/test/Sema/suppress-argument-labels-in-types.swift
index adff0d0d7a1d9..7945ea146fe89 100644
--- a/test/Sema/suppress-argument-labels-in-types.swift
+++ b/test/Sema/suppress-argument-labels-in-types.swift
@@ -203,7 +203,7 @@ class C0 {
 }
 
 // Check diagnostics changes.
-let _ = min(Int(3), Float(2.5)) // expected-error{{cannot convert value of type 'Float' to expected argument type 'Int'}}
+let _ = min(Int(3), Float(2.5)) // expected-error{{conflicting arguments to generic parameter 'T' ('Int' vs. 'Float')}}
 
 // SR-11429
 func testIntermediateCoercions() {
diff --git a/test/Sema/type_join.swift b/test/Sema/type_join.swift
index ad6d2b78cdc27..29509a43e8838 100644
--- a/test/Sema/type_join.swift
+++ b/test/Sema/type_join.swift
@@ -98,9 +98,9 @@ func joinFunctions(
   //        Any to be inferred for the generic type. That's pretty
   //        arbitrary.
   _ = commonSupertype(escaping, x)
-  // expected-error@-1 {{cannot convert value of type 'Int' to expected argument type '() -> ()'}}
+  // expected-error@-1 {{conflicting arguments to generic parameter 'T' ('() -> ()' vs. 'Int')}}
   _ = commonSupertype(x, escaping)
-  // expected-error@-1 {{cannot convert value of type '() -> ()' to expected argument type 'Int'}}
+  // expected-error@-1 {{conflicting arguments to generic parameter 'T' ('Int' vs. '() -> ()')}}
 
   let a: Any = 1
   _ = commonSupertype(nonescaping, a)
diff --git a/test/decl/func/default-values.swift b/test/decl/func/default-values.swift
index 7a90c2587d9f3..a389c6691203b 100644
--- a/test/decl/func/default-values.swift
+++ b/test/decl/func/default-values.swift
@@ -92,7 +92,7 @@ defaultArgTuplesNotMaterializable(identity(5))
 
 // <rdar://problem/22333090> QoI: Propagate contextual information in a call to operands
 defaultArgTuplesNotMaterializable(identity((5, y: 10)))
-// expected-error@-1 {{cannot convert value of type '(Int, y: Int)' to expected argument type 'Int'}}
+// expected-error@-1 {{conflicting arguments to generic parameter 'T' ('(Int, y: Int)' vs. 'Int')}}
 
 
 // rdar://problem/21799331
diff --git a/test/type/opaque.swift b/test/type/opaque.swift
index 9d0b7bdb95e6b..9471164136377 100644
--- a/test/type/opaque.swift
+++ b/test/type/opaque.swift
@@ -270,10 +270,15 @@ func associatedTypeIdentity() {
 
   sameType(cr, c.r_out())
   sameType(dr, d.r_out())
-  sameType(cr, dr) // expected-error {{cannot convert value of type '(some opaque.R).S' (associated type of protocol 'R') to expected argument type '(some opaque.R).S' (associated type of protocol 'R')}}
+  sameType(cr, dr) // expected-error {{conflicting arguments to generic parameter 'T' ('(some R).S' (associated type of protocol 'R') vs. '(some R).S' (associated type of protocol 'R'))}}
   sameType(gary(candace()).r_out(), gary(candace()).r_out())
   sameType(gary(doug()).r_out(), gary(doug()).r_out())
-  sameType(gary(doug()).r_out(), gary(candace()).r_out()) // expected-error {{cannot convert value of type 'some R' (result of 'candace()') to expected argument type 'some R' (result of 'doug()')}}
+  // TODO(diagnostics): This is not great but we the problem comes from the way solver discovers and attempts bindings, if we could detect that
+  // `(some R).S` from first reference to `gary()` in incosistent with the second one based on the parent type of `S` it would be much easier to diagnose.
+  sameType(gary(doug()).r_out(), gary(candace()).r_out())
+  // expected-error@-1:3  {{conflicting arguments to generic parameter 'T' ('(some R).S' (associated type of protocol 'R') vs. '(some R).S' (associated type of protocol 'R'))}}
+  // expected-error@-2:12 {{conflicting arguments to generic parameter 'T' ('some R' (result type of 'doug') vs. 'some R' (result type of 'candace'))}}
+  // expected-error@-3:34 {{conflicting arguments to generic parameter 'T' ('some R' (result type of 'doug') vs. 'some R' (result type of 'candace'))}}
 }
 
 func redeclaration() -> some P { return 0 } // expected-note 2{{previously declared}}

From af65c0e2f360be7d99ec44d51470fc609250b6b9 Mon Sep 17 00:00:00 2001
From: Pavel Yaskevich <pyaskevich@apple.com>
Date: Wed, 12 Feb 2020 17:42:11 -0800
Subject: [PATCH 08/13] [Diagnostics] Prioritize contextual type mismatch other
 ambiguities

---
 lib/Sema/ConstraintSystem.cpp | 26 ++++++++++----------------
 1 file changed, 10 insertions(+), 16 deletions(-)

diff --git a/lib/Sema/ConstraintSystem.cpp b/lib/Sema/ConstraintSystem.cpp
index e42e6cc1deaca..91cbef6682624 100644
--- a/lib/Sema/ConstraintSystem.cpp
+++ b/lib/Sema/ConstraintSystem.cpp
@@ -2904,14 +2904,11 @@ bool ConstraintSystem::diagnoseAmbiguityWithFixes(
 
   // Collect aggregated fixes from all solutions
   llvm::SmallMapVector<std::pair<ConstraintLocator *, FixKind>,
-      llvm::SmallVector<ConstraintFix *, 4>, 4> aggregatedFixes;
-  for (const auto &solution: solutions) {
-    for (auto fixesPerLocator: solution.getAggregatedFixes()) {
-      for (auto kindAndFixes: fixesPerLocator.second) {
-        aggregatedFixes[{fixesPerLocator.first, kindAndFixes.first}]
-            .push_back(kindAndFixes.second.front());
-      }
-    }
+                       llvm::TinyPtrVector<ConstraintFix *>, 4>
+      aggregatedFixes;
+  for (const auto &solution : solutions) {
+    for (auto *fix : solution.Fixes)
+      aggregatedFixes[{fix->getLocator(), fix->getKind()}].push_back(fix);
   }
 
   // If there is an overload difference, let's see if there's a common callee
@@ -2964,20 +2961,17 @@ bool ConstraintSystem::diagnoseAmbiguityWithFixes(
     auto &DE = getASTContext().Diags;
     auto name = decl->getFullName();
 
-    if (name.isOperator()) {
-      diagnoseOperatorAmbiguity(*this, name.getBaseIdentifier(), solutions,
-                                commonCalleeLocator);
-      return true;
-    }
-
     // Emit an error message for the ambiguity.
     if (aggregatedFixes.size() == 1 &&
-        aggregatedFixes.front().first.first
-            ->getLastElementAs<LocatorPathElt::ContextualType>()) {
+        aggregatedFixes.front().first.first->isForContextualType()) {
       auto *anchor = aggregatedFixes.front().first.first->getAnchor();
       auto baseName = name.getBaseName();
       DE.diagnose(commonAnchor->getLoc(), diag::no_candidates_match_result_type,
                   baseName.userFacingName(), getContextualType(anchor));
+    } else if (name.isOperator()) {
+      diagnoseOperatorAmbiguity(*this, name.getBaseIdentifier(), solutions,
+                                commonCalleeLocator);
+      return true;
     } else {
       bool isApplication = llvm::find_if(ArgumentInfos, [&](const auto argInfo) {
         return argInfo.first->getAnchor() == commonAnchor;

From 4d5c676ca9e897765f3382e0c66fb663d60f2ae4 Mon Sep 17 00:00:00 2001
From: Pavel Yaskevich <pyaskevich@apple.com>
Date: Wed, 12 Feb 2020 18:01:27 -0800
Subject: [PATCH 09/13] [ConstraintSystem] NFC: Remove obsolete code related to
 fixes from Solution

---
 lib/Sema/ConstraintSystem.h | 14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)

diff --git a/lib/Sema/ConstraintSystem.h b/lib/Sema/ConstraintSystem.h
index f08c1a6afcae3..218d9e5d9e7d7 100644
--- a/lib/Sema/ConstraintSystem.h
+++ b/lib/Sema/ConstraintSystem.h
@@ -837,21 +837,9 @@ class Solution {
   llvm::DenseMap<std::pair<CanType, CanType>, ConversionRestrictionKind>
     ConstraintRestrictions;
 
-  using ConstraintFixVector = llvm::SmallVector<ConstraintFix *, 4>;
   /// The list of fixes that need to be applied to the initial expression
   /// to make the solution work.
-  ConstraintFixVector Fixes;
-
-  using AggregatedFixesMap = llvm::SmallMapVector<ConstraintLocator *,
-      llvm::SmallMapVector<FixKind, ConstraintFixVector, 4>, 4>;
-
-  AggregatedFixesMap getAggregatedFixes() const {
-    AggregatedFixesMap aggregatedFixes;
-    for (auto *fix: Fixes) {
-      aggregatedFixes[fix->getLocator()][fix->getKind()].push_back(fix);
-    }
-    return aggregatedFixes;
-  }
+  llvm::SmallVector<ConstraintFix *, 4> Fixes;
 
   /// The set of disjunction choices used to arrive at this solution,
   /// which informs constraint application.

From 3f10bfa74e4a946d6bb6650141d667e994e377a4 Mon Sep 17 00:00:00 2001
From: Pavel Yaskevich <pyaskevich@apple.com>
Date: Wed, 12 Feb 2020 18:17:04 -0800
Subject: [PATCH 10/13] [Diagnostics] NFC: Rename
 `diagnoseConflictingArguments` into `diagnoseConflictingGenericArguments`

---
 lib/Sema/ConstraintSystem.cpp | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lib/Sema/ConstraintSystem.cpp b/lib/Sema/ConstraintSystem.cpp
index 91cbef6682624..54b60ba298d5b 100644
--- a/lib/Sema/ConstraintSystem.cpp
+++ b/lib/Sema/ConstraintSystem.cpp
@@ -2771,9 +2771,9 @@ std::string swift::describeGenericType(ValueDecl *GP, bool includeName) {
 ///
 /// It's done by first retrieving all generic parameters from each solution,
 /// filtering boundings into distrinct set and diagnosing any differences.
-static bool diagnoseConflictingArguments(ConstraintSystem &cs,
-                                         const SolutionDiff &diff,
-                                         ArrayRef<Solution> solutions) {
+static bool diagnoseConflictingGenericArguments(ConstraintSystem &cs,
+                                                const SolutionDiff &diff,
+                                                ArrayRef<Solution> solutions) {
   if (!diff.overloads.empty())
     return false;
 
@@ -2899,7 +2899,7 @@ bool ConstraintSystem::diagnoseAmbiguityWithFixes(
 
   SolutionDiff solutionDiff(solutions);
 
-  if (diagnoseConflictingArguments(*this, solutionDiff, solutions))
+  if (diagnoseConflictingGenericArguments(*this, solutionDiff, solutions))
     return true;
 
   // Collect aggregated fixes from all solutions

From 60a210b6575d41470a454099940edc5f8b03a72f Mon Sep 17 00:00:00 2001
From: Pavel Yaskevich <pyaskevich@apple.com>
Date: Thu, 13 Feb 2020 00:44:13 -0800
Subject: [PATCH 11/13] [ConstraintSystem] NFC: Fix a couple of typos in
 comments

---
 lib/Sema/ConstraintSystem.cpp | 2 +-
 test/type/opaque.swift        | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/Sema/ConstraintSystem.cpp b/lib/Sema/ConstraintSystem.cpp
index 54b60ba298d5b..d0f29a3420c75 100644
--- a/lib/Sema/ConstraintSystem.cpp
+++ b/lib/Sema/ConstraintSystem.cpp
@@ -2770,7 +2770,7 @@ std::string swift::describeGenericType(ValueDecl *GP, bool includeName) {
 /// }
 ///
 /// It's done by first retrieving all generic parameters from each solution,
-/// filtering boundings into distrinct set and diagnosing any differences.
+/// filtering bindings into a distinct set and diagnosing any differences.
 static bool diagnoseConflictingGenericArguments(ConstraintSystem &cs,
                                                 const SolutionDiff &diff,
                                                 ArrayRef<Solution> solutions) {
diff --git a/test/type/opaque.swift b/test/type/opaque.swift
index 9471164136377..276933e611580 100644
--- a/test/type/opaque.swift
+++ b/test/type/opaque.swift
@@ -273,7 +273,7 @@ func associatedTypeIdentity() {
   sameType(cr, dr) // expected-error {{conflicting arguments to generic parameter 'T' ('(some R).S' (associated type of protocol 'R') vs. '(some R).S' (associated type of protocol 'R'))}}
   sameType(gary(candace()).r_out(), gary(candace()).r_out())
   sameType(gary(doug()).r_out(), gary(doug()).r_out())
-  // TODO(diagnostics): This is not great but we the problem comes from the way solver discovers and attempts bindings, if we could detect that
+  // TODO(diagnostics): This is not great but the problem comes from the way solver discovers and attempts bindings, if we could detect that
   // `(some R).S` from first reference to `gary()` in incosistent with the second one based on the parent type of `S` it would be much easier to diagnose.
   sameType(gary(doug()).r_out(), gary(candace()).r_out())
   // expected-error@-1:3  {{conflicting arguments to generic parameter 'T' ('(some R).S' (associated type of protocol 'R') vs. '(some R).S' (associated type of protocol 'R'))}}

From b872bdfca1be8a86735c2ab13226097d5072c972 Mon Sep 17 00:00:00 2001
From: Pavel Yaskevich <pyaskevich@apple.com>
Date: Thu, 13 Feb 2020 00:45:44 -0800
Subject: [PATCH 12/13] [Diagnostics] Replace `llvm::find_if` with
 `llvm::any_of` in `diagnoseAmbiguityWithFixes`

---
 lib/Sema/ConstraintSystem.cpp | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/lib/Sema/ConstraintSystem.cpp b/lib/Sema/ConstraintSystem.cpp
index d0f29a3420c75..ef17b29af6efc 100644
--- a/lib/Sema/ConstraintSystem.cpp
+++ b/lib/Sema/ConstraintSystem.cpp
@@ -2973,9 +2973,10 @@ bool ConstraintSystem::diagnoseAmbiguityWithFixes(
                                 commonCalleeLocator);
       return true;
     } else {
-      bool isApplication = llvm::find_if(ArgumentInfos, [&](const auto argInfo) {
-        return argInfo.first->getAnchor() == commonAnchor;
-      }) != ArgumentInfos.end();
+      bool isApplication =
+          llvm::any_of(ArgumentInfos, [&](const auto &argInfo) {
+            return argInfo.first->getAnchor() == commonAnchor;
+          });
 
       DE.diagnose(commonAnchor->getLoc(),
                   diag::no_overloads_match_exactly_in_call,

From 172c2003ea5bbafa5ccd267bcbd83ea72f4f20d8 Mon Sep 17 00:00:00 2001
From: Pavel Yaskevich <pyaskevich@apple.com>
Date: Thu, 13 Feb 2020 00:54:51 -0800
Subject: [PATCH 13/13] [Diagnostics] NFC: Add a comment about special handling
 of opaque result types

---
 lib/Sema/ConstraintSystem.cpp | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lib/Sema/ConstraintSystem.cpp b/lib/Sema/ConstraintSystem.cpp
index ef17b29af6efc..37b52e68c627b 100644
--- a/lib/Sema/ConstraintSystem.cpp
+++ b/lib/Sema/ConstraintSystem.cpp
@@ -2805,6 +2805,9 @@ static bool diagnoseConflictingGenericArguments(ConstraintSystem &cs,
           if (binding == solution.typeBindings.end())
             return false;
 
+          // Contextual opaque result type is uniquely identified by
+          // declaration it's associated with, so we have to compare
+          // declarations instead of using pointer equality on such types.
           if (auto *opaque =
                   binding->second->getAs<OpaqueTypeArchetypeType>()) {
             auto *decl = opaque->getDecl();