Auto merge of #50724 - zackmdavis:applicability_rush, r=Manishearth

add suggestion applicabilities to librustc and libsyntax

A down payment on #50723. Interested in feedback on whether my `MaybeIncorrect` vs. `MachineApplicable` judgement calls are well-calibrated (and that we have a consensus on what this means).

r? @Manishearth
cc @killercup @estebank

src/librustc/infer/error_reporting/mod.rs

@@ -70,7 +70,7 @@ use ty::{self, Region, Ty, TyCtxt, TypeFoldable, TypeVariants};
 use ty::error::TypeError;
 use syntax::ast::DUMMY_NODE_ID;
 use syntax_pos::{Pos, Span};
-use errors::{DiagnosticBuilder, DiagnosticStyledString};
+use errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString};
 
 use rustc_data_structures::indexed_vec::Idx;
 
@@ -1097,7 +1097,10 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             if let Some((sp, has_lifetimes)) = type_param_span {
                 let tail = if has_lifetimes { " + " } else { "" };
                 let suggestion = format!("{}: {}{}", bound_kind, sub, tail);
-                err.span_suggestion_short(sp, consider, suggestion);
+                err.span_suggestion_short_with_applicability(
+                    sp, consider, suggestion,
+                    Applicability::MaybeIncorrect // Issue #41966
+                );
             } else {
                 err.help(consider);
             }

src/librustc/lint/levels.rs

@@ -10,7 +10,7 @@
 
 use std::cmp;
 
-use errors::DiagnosticBuilder;
+use errors::{Applicability, DiagnosticBuilder};
 use hir::HirId;
 use ich::StableHashingContext;
 use lint::builtin;
@@ -265,10 +265,11 @@ impl<'a> LintLevelsBuilder<'a> {
                                     store.check_lint_name(&name_lower) {
                                 db.emit();
                             } else {
-                                db.span_suggestion(
+                                db.span_suggestion_with_applicability(
                                     li.span,
                                     "lowercase the lint name",
-                                    name_lower
+                                    name_lower,
+                                    Applicability::MachineApplicable
                                 ).emit();
                             }
                         } else {

src/librustc/middle/liveness.rs

@@ -109,6 +109,7 @@ use self::VarKind::*;
 use hir::def::*;
 use ty::{self, TyCtxt};
 use lint;
+use errors::Applicability;
 use util::nodemap::{NodeMap, NodeSet};
 
 use std::collections::VecDeque;
@@ -1535,11 +1536,15 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
                     let mut err = self.ir.tcx
                         .struct_span_lint_node(lint::builtin::UNUSED_VARIABLES, id, sp, &msg);
                     if self.ir.variable_is_shorthand(var) {
-                        err.span_suggestion(sp, "try ignoring the field",
-                                            format!("{}: _", name));
+                        err.span_suggestion_with_applicability(sp, "try ignoring the field",
+                                                               format!("{}: _", name),
+                                                               Applicability::MachineApplicable);
                     } else {
-                        err.span_suggestion_short(sp, &suggest_underscore_msg,
-                                                  format!("_{}", name));
+                        err.span_suggestion_short_with_applicability(
+                            sp, &suggest_underscore_msg,
+                            format!("_{}", name),
+                            Applicability::MachineApplicable,
+                        );
                     }
                     err.emit()
                 }

src/librustc/traits/error_reporting.rs

@@ -27,7 +27,7 @@ use super::{
     Overflow,
 };
 
-use errors::DiagnosticBuilder;
+use errors::{Applicability, DiagnosticBuilder};
 use hir;
 use hir::def_id::DefId;
 use infer::{self, InferCtxt};
@@ -852,9 +852,12 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                 if let Some(ref expr) = local.init {
                     if let hir::ExprIndex(_, _) = expr.node {
                         if let Ok(snippet) = self.tcx.sess.codemap().span_to_snippet(expr.span) {
-                            err.span_suggestion(expr.span,
-                                                "consider borrowing here",
-                                                format!("&{}", snippet));
+                            err.span_suggestion_with_applicability(
+                                expr.span,
+                                "consider borrowing here",
+                                format!("&{}", snippet),
+                                Applicability::MachineApplicable
+                            );
                         }
                     }
                 }
@@ -897,7 +900,9 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                         let format_str = format!("consider removing {} leading `&`-references",
                                                  remove_refs);
 
-                        err.span_suggestion_short(sp, &format_str, String::from(""));
+                        err.span_suggestion_short_with_applicability(
+                            sp, &format_str, String::from(""), Applicability::MachineApplicable
+                        );
                         break;
                     }
                 } else {
@@ -1042,10 +1047,11 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                     let sugg = fields.iter()
                         .map(|(name, _)| name.to_owned())
                         .collect::<Vec<String>>().join(", ");
-                    err.span_suggestion(found_span,
-                                        "change the closure to take multiple arguments instead of \
-                                         a single tuple",
-                                        format!("|{}|", sugg));
+                    err.span_suggestion_with_applicability(found_span,
+                                                           "change the closure to take multiple \
+                                                            arguments instead of a single tuple",
+                                                           format!("|{}|", sugg),
+                                                           Applicability::MachineApplicable);
                 }
             }
             if let &[ArgKind::Tuple(_, ref fields)] = &expected_args[..] {
@@ -1073,10 +1079,13 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                             "".to_owned()
                         },
                     );
-                    err.span_suggestion(found_span,
-                                        "change the closure to accept a tuple instead of \
-                                         individual arguments",
-                                        sugg);
+                    err.span_suggestion_with_applicability(
+                        found_span,
+                        "change the closure to accept a tuple instead of \
+                         individual arguments",
+                        sugg,
+                        Applicability::MachineApplicable
+                    );
                 }
             }
         }

src/librustc_errors/diagnostic.rs

@@ -330,6 +330,23 @@ impl Diagnostic {
         self
     }
 
+    pub fn span_suggestion_short_with_applicability(
+        &mut self, sp: Span, msg: &str, suggestion: String, applicability: Applicability
+    ) -> &mut Self {
+        self.suggestions.push(CodeSuggestion {
+            substitutions: vec![Substitution {
+                parts: vec![SubstitutionPart {
+                    snippet: suggestion,
+                    span: sp,
+                }],
+            }],
+            msg: msg.to_owned(),
+            show_code_when_inline: false,
+            applicability: applicability,
+        });
+        self
+    }
+
     pub fn set_span<S: Into<MultiSpan>>(&mut self, sp: S) -> &mut Self {
         self.span = sp.into();
         self

src/librustc_errors/diagnostic_builder.rs

@@ -205,6 +205,12 @@ impl<'a> DiagnosticBuilder<'a> {
                                                  suggestions: Vec<String>,
                                                  applicability: Applicability)
                                                  -> &mut Self);
+    forward!(pub fn span_suggestion_short_with_applicability(&mut self,
+                                                             sp: Span,
+                                                             msg: &str,
+                                                             suggestion: String,
+                                                             applicability: Applicability)
+                                                             -> &mut Self);
     forward!(pub fn set_span<S: Into<MultiSpan>>(&mut self, sp: S) -> &mut Self);
     forward!(pub fn code(&mut self, s: DiagnosticId) -> &mut Self);
 

src/libsyntax/attr.rs

@@ -20,7 +20,7 @@ use ast::{MetaItem, MetaItemKind, NestedMetaItem, NestedMetaItemKind};
 use ast::{Lit, LitKind, Expr, ExprKind, Item, Local, Stmt, StmtKind};
 use codemap::{BytePos, Spanned, respan, dummy_spanned};
 use syntax_pos::Span;
-use errors::Handler;
+use errors::{Applicability, Handler};
 use feature_gate::{Features, GatedCfg};
 use parse::lexer::comments::{doc_comment_style, strip_doc_comment_decoration};
 use parse::parser::Parser;
@@ -1067,14 +1067,20 @@ pub fn find_repr_attrs(diagnostic: &Handler, attr: &Attribute) -> Vec<ReprAttr>
                                     "incorrect `repr(align)` attribute format");
                                 match value.node {
                                     ast::LitKind::Int(int, ast::LitIntType::Unsuffixed) => {
-                                        err.span_suggestion(item.span,
-                                                            "use parentheses instead",
-                                                            format!("align({})", int));
+                                        err.span_suggestion_with_applicability(
+                                            item.span,
+                                            "use parentheses instead",
+                                            format!("align({})", int),
+                                            Applicability::MachineApplicable
+                                        );
                                     }
                                     ast::LitKind::Str(s, _) => {
-                                        err.span_suggestion(item.span,
-                                                            "use parentheses instead",
-                                                            format!("align({})", s));
+                                        err.span_suggestion_with_applicability(
+                                            item.span,
+                                            "use parentheses instead",
+                                            format!("align({})", s),
+                                            Applicability::MachineApplicable
+                                        );
                                     }
                                     _ => {}
                                 }

src/libsyntax/ext/expand.rs

@@ -13,7 +13,7 @@ use ast::{MacStmtStyle, StmtKind, ItemKind};
 use attr::{self, HasAttrs};
 use codemap::{ExpnInfo, NameAndSpan, MacroBang, MacroAttribute, dummy_spanned, respan};
 use config::{is_test_or_bench, StripUnconfigured};
-use errors::FatalError;
+use errors::{Applicability, FatalError};
 use ext::base::*;
 use ext::derive::{add_derived_markers, collect_derives};
 use ext::hygiene::{self, Mark, SyntaxContext};
@@ -331,7 +331,11 @@ impl<'a, 'b> MacroExpander<'a, 'b> {
                             let trait_list = traits.iter()
                                 .map(|t| format!("{}", t)).collect::<Vec<_>>();
                             let suggestion = format!("#[derive({})]", trait_list.join(", "));
-                            err.span_suggestion(span, "try an outer attribute", suggestion);
+                            err.span_suggestion_with_applicability(
+                                span, "try an outer attribute", suggestion,
+                                // We don't 𝑘𝑛𝑜𝑤 that the following item is an ADT
+                                Applicability::MaybeIncorrect
+                            );
                         }
                         err.emit();
                     }

src/libsyntax/parse/lexer/mod.rs

@@ -11,7 +11,7 @@
 use ast::{self, Ident};
 use syntax_pos::{self, BytePos, CharPos, Pos, Span, NO_EXPANSION};
 use codemap::{CodeMap, FilePathMapping};
-use errors::{FatalError, DiagnosticBuilder};
+use errors::{Applicability, FatalError, DiagnosticBuilder};
 use parse::{token, ParseSess};
 use str::char_at;
 use symbol::{Symbol, keywords};
@@ -1379,11 +1379,12 @@ impl<'a> StringReader<'a> {
                             self.sess.span_diagnostic
                                 .struct_span_err(span,
                                                  "character literal may only contain one codepoint")
-                                .span_suggestion(span,
-                                                 "if you meant to write a `str` literal, \
-                                                  use double quotes",
-                                                 format!("\"{}\"", &self.src[start..end]))
-                                .emit();
+                                .span_suggestion_with_applicability(
+                                    span,
+                                    "if you meant to write a `str` literal, use double quotes",
+                                    format!("\"{}\"", &self.src[start..end]),
+                                    Applicability::MachineApplicable
+                                ).emit();
                             return Ok(token::Literal(token::Str_(Symbol::intern("??")), None))
                         }
                         if self.ch_is('\n') || self.is_eof() || self.ch_is('/') {