[Tooling/Inclusion] Handle std::get symbol.

Currently, we handle it as a symbol without a header. In general, for
the include-cleaner case, the std::get comes with the type header, it is
safe to ignore it.

Differential Revision: https://reviews.llvm.org/D144484

Author: hokein

clang-tools-extra/clangd/index/CanonicalIncludes.cpp

@@ -717,7 +717,8 @@ llvm::StringRef CanonicalIncludes::mapSymbol(llvm::StringRef Scope,
   if (Scope == "std::" && Name == "move")
     return "<utility>";
   if (auto StdSym = tooling::stdlib::Symbol::named(Scope, Name, Lang))
-    return StdSym->header().name();
+    if (auto Header = StdSym->header())
+      return Header->name();
   return "";
 }
 

clang/include/clang/Tooling/Inclusions/StandardLibrary.h

@@ -81,7 +81,7 @@ class Symbol {
   llvm::StringRef name() const;
   llvm::StringRef qualifiedName() const;
   // The preferred header for this symbol (e.g. the suggested insertion).
-  Header header() const;
+  std::optional<Header> header() const;
   // Some symbols may be provided by multiple headers.
   llvm::SmallVector<Header> headers() const;
 

clang/lib/Tooling/Inclusions/Stdlib/StandardLibrary.cpp

@@ -14,6 +14,7 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Casting.h"
+#include <optional>
 
 namespace clang {
 namespace tooling {
@@ -120,7 +121,8 @@ static int initialize(Lang Language) {
     }
     Mapping->SymbolNames[SymIndex] = {
         QName.data(), NSLen, static_cast<unsigned int>(QName.size() - NSLen)};
-    Mapping->SymbolHeaderIDs[SymIndex].push_back(AddHeader(HeaderName));
+    if (!HeaderName.empty())
+       Mapping->SymbolHeaderIDs[SymIndex].push_back(AddHeader(HeaderName));
 
     NSSymbolMap &NSSymbols = AddNS(QName.take_front(NSLen));
     NSSymbols.try_emplace(QName.drop_front(NSLen), SymIndex);
@@ -205,8 +207,11 @@ std::optional<Symbol> Symbol::named(llvm::StringRef Scope, llvm::StringRef Name,
   }
   return std::nullopt;
 }
-Header Symbol::header() const {
-  return Header(getMappingPerLang(Language)->SymbolHeaderIDs[ID][0], Language);
+std::optional<Header> Symbol::header() const {
+  const auto& Headers = getMappingPerLang(Language)->SymbolHeaderIDs[ID];
+  if (Headers.empty())
+    return std::nullopt;
+  return Header(Headers.front(), Language);
 }
 llvm::SmallVector<Header> Symbol::headers() const {
   llvm::SmallVector<Header> Results;

clang/lib/Tooling/Inclusions/Stdlib/StdSpecialSymbolMap.inc

@@ -218,3 +218,8 @@ SYMBOL(ssize, std::, <string_view>)
 SYMBOL(ssize, std::, <unordered_map>)
 SYMBOL(ssize, std::, <unordered_set>)
 SYMBOL(ssize, std::, <vector>)
+
+// std::get has a few variants for different types (tuple, array, pair etc)
+// which is tricky to disambiguate without type information.
+// Don't set any header for it, as it comes with the type header.
+SYMBOL(get, std::, /*no headers*/)

clang/unittests/Tooling/StandardLibraryTest.cpp

@@ -58,6 +58,9 @@ TEST(StdlibTest, All) {
   EXPECT_EQ(Vector->header(), *VectorH);
   EXPECT_THAT(Vector->headers(), ElementsAre(*VectorH));
 
+  EXPECT_TRUE(stdlib::Symbol::named("std::", "get"));
+  EXPECT_FALSE(stdlib::Symbol::named("std::", "get")->header());
+
   EXPECT_THAT(stdlib::Symbol::named("std::", "basic_iostream")->headers(),
               ElementsAre(stdlib::Header::named("<istream>"),
                           stdlib::Header::named("<iostream>"),