Better source location for -Wignored-qualifiers on trailing return types

We collect the source location of a trailing return type in the parser,
improving the location for regular functions and providing a location
for lambdas, where previously there was none.

Fixes PR47732.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D90129

7 files changed, 32 insertions, 9 deletions

diff --git a/clang/include/clang/Sema/DeclSpec.h b/clang/include/clang/Sema/DeclSpec.h
index 93a9126..33b57db 100644
--- a/clang/include/clang/Sema/DeclSpec.h
+++ b/clang/include/clang/Sema/DeclSpec.h
@@ -1363,6 +1363,10 @@ struct DeclaratorChunk {
     /// type specified.
     UnionParsedType TrailingReturnType;
 
+    /// If HasTrailingReturnType is true, this is the location of the trailing
+    /// return type.
+    unsigned TrailingReturnTypeLoc;
+
     /// Reset the parameter list to having zero parameters.
     ///
     /// This is used in various places for error recovery.
@@ -1499,6 +1503,11 @@ struct DeclaratorChunk {
 
     /// Get the trailing-return-type for this function declarator.
     ParsedType getTrailingReturnType() const { return TrailingReturnType; }
+
+    /// Get the trailing-return-type location for this function declarator.
+    SourceLocation getTrailingReturnTypeLoc() const {
+      return SourceLocation::getFromRawEncoding(TrailingReturnTypeLoc);
+    }
   };
 
   struct BlockPointerTypeInfo {
@@ -1633,6 +1642,8 @@ struct DeclaratorChunk {
                                      Declarator &TheDeclarator,
                                      TypeResult TrailingReturnType =
                                                     TypeResult(),
+                                     SourceLocation TrailingReturnTypeLoc =
+                                                    SourceLocation(),
                                      DeclSpec *MethodQualifiers = nullptr);
 
   /// Return a DeclaratorChunk for a block.
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 01a1657..281cd6d 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -6429,6 +6429,7 @@ void Parser::ParseFunctionDeclarator(Declarator &D,
   CachedTokens *ExceptionSpecTokens = nullptr;
   ParsedAttributesWithRange FnAttrs(AttrFactory);
   TypeResult TrailingReturnType;
+  SourceLocation TrailingReturnTypeLoc;
 
   /* LocalEndLoc is the end location for the local FunctionTypeLoc.
      EndLoc is the end location for the function declarator.
@@ -6539,6 +6540,7 @@ void Parser::ParseFunctionDeclarator(Declarator &D,
         SourceRange Range;
         TrailingReturnType =
             ParseTrailingReturnType(Range, D.mayBeFollowedByCXXDirectInit());
+        TrailingReturnTypeLoc = Range.getBegin();
         EndLoc = Range.getEnd();
       }
     } else if (standardAttributesAllowed()) {
@@ -6571,7 +6573,8 @@ void Parser::ParseFunctionDeclarator(Declarator &D,
                     DynamicExceptionRanges.data(), DynamicExceptions.size(),
                     NoexceptExpr.isUsable() ? NoexceptExpr.get() : nullptr,
                     ExceptionSpecTokens, DeclsInPrototype, StartLoc,
-                    LocalEndLoc, D, TrailingReturnType, &DS),
+                    LocalEndLoc, D, TrailingReturnType, TrailingReturnTypeLoc,
+                    &DS),
                 std::move(FnAttrs), EndLoc);
 }
 
diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
index a903896..6e9eced 100644
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -3898,6 +3898,7 @@ void Parser::ParseTrailingRequiresClause(Declarator &D) {
       auto &FunctionChunk = D.getFunctionTypeInfo();
       FunctionChunk.HasTrailingReturnType = TrailingReturnType.isUsable();
       FunctionChunk.TrailingReturnType = TrailingReturnType.get();
+      FunctionChunk.TrailingReturnTypeLoc = Range.getBegin().getRawEncoding();
     } else
       SkipUntil({tok::equal, tok::l_brace, tok::arrow, tok::kw_try, tok::comma},
                 StopAtSemi | StopBeforeMatch);
diff --git a/clang/lib/Parse/ParseExprCXX.cpp b/clang/lib/Parse/ParseExprCXX.cpp
index b225bb7..8181d2a 100644
--- a/clang/lib/Parse/ParseExprCXX.cpp
+++ b/clang/lib/Parse/ParseExprCXX.cpp
@@ -1293,6 +1293,7 @@ ExprResult Parser::ParseLambdaExpressionAfterIntroducer(
   }
 
   TypeResult TrailingReturnType;
+  SourceLocation TrailingReturnTypeLoc;
   if (Tok.is(tok::l_paren)) {
     ParseScope PrototypeScope(this,
                               Scope::FunctionPrototypeScope |
@@ -1379,6 +1380,7 @@ ExprResult Parser::ParseLambdaExpressionAfterIntroducer(
       SourceRange Range;
       TrailingReturnType =
           ParseTrailingReturnType(Range, /*MayBeFollowedByDirectInit*/ false);
+      TrailingReturnTypeLoc = Range.getBegin();
       if (Range.getEnd().isValid())
         DeclEndLoc = Range.getEnd();
     }
@@ -1395,7 +1397,7 @@ ExprResult Parser::ParseLambdaExpressionAfterIntroducer(
                       NoexceptExpr.isUsable() ? NoexceptExpr.get() : nullptr,
                       /*ExceptionSpecTokens*/ nullptr,
                       /*DeclsInPrototype=*/None, LParenLoc, FunLocalRangeEnd, D,
-                      TrailingReturnType, &DS),
+                      TrailingReturnType, TrailingReturnTypeLoc, &DS),
                   std::move(Attr), DeclEndLoc);
 
     // Parse requires-clause[opt].
diff --git a/clang/lib/Sema/DeclSpec.cpp b/clang/lib/Sema/DeclSpec.cpp
index dc37474..b139855 100644
--- a/clang/lib/Sema/DeclSpec.cpp
+++ b/clang/lib/Sema/DeclSpec.cpp
@@ -181,6 +181,8 @@ DeclaratorChunk DeclaratorChunk::getFunction(bool hasProto,
                                              SourceLocation LocalRangeEnd,
                                              Declarator &TheDeclarator,
                                              TypeResult TrailingReturnType,
+                                             SourceLocation
+                                                 TrailingReturnTypeLoc,
                                              DeclSpec *MethodQualifiers) {
   assert(!(MethodQualifiers && MethodQualifiers->getTypeQualifiers() & DeclSpec::TQ_atomic) &&
          "function cannot have _Atomic qualifier");
@@ -210,6 +212,7 @@ DeclaratorChunk DeclaratorChunk::getFunction(bool hasProto,
   I.Fun.HasTrailingReturnType   = TrailingReturnType.isUsable() ||
                                   TrailingReturnType.isInvalid();
   I.Fun.TrailingReturnType      = TrailingReturnType.get();
+  I.Fun.TrailingReturnTypeLoc   = TrailingReturnTypeLoc.getRawEncoding();
   I.Fun.MethodQualifiers        = nullptr;
   I.Fun.QualAttrFactory         = nullptr;
 
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index 1ba1869..21aa208 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -3084,12 +3084,12 @@ void Sema::diagnoseIgnoredQualifiers(unsigned DiagID, unsigned Quals,
 static void diagnoseRedundantReturnTypeQualifiers(Sema &S, QualType RetTy,
                                                   Declarator &D,
                                                   unsigned FunctionChunkIndex) {
-  if (D.getTypeObject(FunctionChunkIndex).Fun.hasTrailingReturnType()) {
-    // FIXME: TypeSourceInfo doesn't preserve location information for
-    // qualifiers.
+  const DeclaratorChunk::FunctionTypeInfo &FTI =
+      D.getTypeObject(FunctionChunkIndex).Fun;
+  if (FTI.hasTrailingReturnType()) {
     S.diagnoseIgnoredQualifiers(diag::warn_qual_return_type,
                                 RetTy.getLocalCVRQualifiers(),
-                                D.getIdentifierLoc());
+                                FTI.getTrailingReturnTypeLoc());
     return;
   }
 
diff --git a/clang/test/SemaCXX/return.cpp b/clang/test/SemaCXX/return.cpp
index 1550d00..ef45e61 100644
--- a/clang/test/SemaCXX/return.cpp
+++ b/clang/test/SemaCXX/return.cpp
@@ -61,9 +61,12 @@ _Atomic // expected-warning {{'_Atomic' type qualifier on return type has no eff
     int
     atomic();
 
-auto
-    trailing_return_type() -> // expected-warning {{'const' type qualifier on return type has no effect}}
-    const int;
+auto trailing_return_type() ->
+    const int; // expected-warning {{'const' type qualifier on return type has no effect}}
+
+auto trailing_return_type_lambda = [](const int &x) ->
+    const int // expected-warning {{'const' type qualifier on return type has no effect}}
+    { return x; };
 
 const int ret_array()[4]; // expected-error {{cannot return array}}
 }