[clang] [clang][AST] Handle implicit first argument in CallExpr::getBeginLoc() (PR #135757)

[Nathan Ridge via cfe-commits]

https://github.com/HighCommander4 updated https://github.com/llvm/llvm-project/pull/135757

>From a1569727c432ba67a96de07c899b562fcf349d1e Mon Sep 17 00:00:00 2001
From: Nathan Ridge <zeratul976 at hotmail.com>
Date: Tue, 15 Apr 2025 03:40:37 -0400
Subject: [PATCH] [clang][AST] Handle implicit first argument in
 CallExpr::getBeginLoc()

---
 clang/docs/ReleaseNotes.rst                | 2 ++
 clang/lib/AST/Expr.cpp                     | 7 +++++--
 clang/test/SemaCXX/cxx2b-deducing-this.cpp | 7 +++++++
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 97de736c4bad3..060a99cfdcc7c 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -398,6 +398,8 @@ Bug Fixes in This Version
 
     #if 1 ? 1 : 999999999999999999999
     #endif
+- Fixed a clang 20 regression where diagnostics attached to some calls to member functions
+  using C++23 "deducing this" did not have a diagnostic location (#GH135522)
 
 Bug Fixes to Compiler Builtins
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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 at -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'}}
+};
+}