[clang][AST] Handle implicit first argument in CallExpr::getBeginLoc()

[HighCommander4]

Fixes #135522

[llvmbot]

@llvm/pr-subscribers-clang

Author: Nathan Ridge (HighCommander4)

Changes

Fixes #135522

---

Full diff: https://github.com/llvm/llvm-project/pull/135757.diff

2 Files Affected:

• (modified) clang/lib/AST/Expr.cpp (+5-2)
• (modified) clang/test/SemaCXX/cxx2b-deducing-this.cpp (+7)

diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index 5fab2c73f214b..59c0e47c7c195 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -1652,8 +1652,11 @@ SourceLocation CallExpr::getBeginLoc() const {
   if (!isTypeDependent()) {
     if (const auto *Method =
             dyn_cast_if_present<const CXXMethodDecl>(getCalleeDecl());
-        Method && Method->isExplicitObjectMemberFunction())
-      return getArg(0)->getBeginLoc();
+        Method && Method->isExplicitObjectMemberFunction()) {
+      if (auto FirstArgLoc = getArg(0)->getBeginLoc(); FirstArgLoc.isValid()) {
+        return FirstArgLoc;
+      }
+    }
   }
 
   SourceLocation begin = getCallee()->getBeginLoc();
diff --git a/clang/test/SemaCXX/cxx2b-deducing-this.cpp b/clang/test/SemaCXX/cxx2b-deducing-this.cpp
index 6f17ce7275456..7e392213710a4 100644
--- a/clang/test/SemaCXX/cxx2b-deducing-this.cpp
+++ b/clang/test/SemaCXX/cxx2b-deducing-this.cpp
@@ -1134,3 +1134,10 @@ struct S {
 static_assert((S{} << 11) == a);
 // expected-error@-1 {{use of undeclared identifier 'a'}}
 }
+
+namespace GH135522 {
+struct S {
+  auto f(this auto) -> S;
+  bool g() { return f(); } // expected-error {{no viable conversion from returned value of type 'S' to function return type 'bool'}}
+};
+}

[HighCommander4]

Note, I took the approach of falling through if FirstArgLoc is invalid for any reason; presumably we never want to return an invalid location when we might fall through to a valid one in getCallee()->getBeginLoc().

We could alternatively make the check more specific, to e.g. !getArg(0)->isImplicitCXXThis().

[cor3ntin]

Can you add a changelog entry?
Otherwise LGTM

[HighCommander4]

Added changelog entry.

Should we backport this to 20.x?

[zyn0217]

Yes, would be great to see it get backported

[HighCommander4]

Yes, would be great to see it get backported

Filed backport issue: #135922