[clang] [LifetimeSafety] Correctly place lifetimebound attr in corner cases (PR #181699)

[Gábor Horváth via cfe-commits]

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@@ -2952,10 +2958,24 @@ class LifetimeSafetySemaHelperImpl : public LifetimeSafetySemaHelper {
     unsigned DiagID = (Scope == SuggestionScope::CrossTU)
                           ? diag::warn_lifetime_safety_cross_tu_this_suggestion
                           : diag::warn_lifetime_safety_intra_tu_this_suggestion;
-    SourceLocation InsertionPoint;
-    InsertionPoint = Lexer::getLocForEndOfToken(
-        MD->getTypeSourceInfo()->getTypeLoc().getEndLoc(), 0,
-        S.getSourceManager(), S.getLangOpts());
+    const auto MDL = MD->getTypeSourceInfo()->getTypeLoc();
+    SourceLocation InsertionPoint = Lexer::getLocForEndOfToken(
+        MDL.getEndLoc(), 0, S.getSourceManager(), S.getLangOpts());
+    if (const auto *FPT = MD->getType()->getAs<FunctionProtoType>();
+        FPT && FPT->hasTrailingReturn()) {
+      // For trailing return types, 'getEndLoc()' includes the return type
+      // after '->', placing the attribute in an invalid position.
+      // Instead use 'getLocalRangeEnd()' which gives the '->' location
+      // for trailing returns, so find the last token before it.
+      const auto FTL = MDL.getAs<FunctionTypeLoc>();
+      assert(FTL);
+      InsertionPoint = Lexer::getLocForEndOfToken(
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Xazax-hun wrote:

Yup, moving these utils over to clang would make a lot of sense to me. Your proposal of adding a new header next to `Rewriter.h` sounds good to me. 

https://github.com/llvm/llvm-project/pull/181699