[clang] [clang][AST] Handle dependent representation of call to function with explicit object parameter in CallExpr::getBeginLoc() (PR #126868)

[Nathan Ridge via cfe-commits]

https://github.com/HighCommander4 updated https://github.com/llvm/llvm-project/pull/126868

>From dc03bb6854545dabb9023d6c66e7593d692f8a82 Mon Sep 17 00:00:00 2001
From: Nathan Ridge <zeratul976 at hotmail.com>
Date: Wed, 12 Feb 2025 02:37:49 -0500
Subject: [PATCH] [clang][AST] Handle dependent representation of call to
 function with explicit object parameter in CallExpr::getBeginLoc()

This fixes a crash where CallExpr::getBeginLoc() tries to access the
first argument of a CallExpr representing a call to a function with
an explicit object parameter, assuming that a first argument exists
because it's the object argument.

This is the case for non-dependent calls, but for dependent calls
the object argument is part of the callee (the semantic analysis
that separates it out has not been performed yet) and so there may
not be a first argument.

Fixes https://github.com/llvm/llvm-project/issues/126720
---
 clang/lib/AST/Expr.cpp                        | 21 ++++++++++++++-----
 .../test/AST/ast-dump-cxx2b-deducing-this.cpp | 13 ++++++++++++
 2 files changed, 29 insertions(+), 5 deletions(-)

diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index c22aa66ba2cfb..6978fd837cbd0 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/clang/lib/AST/Expr.cpp
@@ -1645,11 +1645,22 @@ SourceLocation CallExpr::getBeginLoc() const {
   if (const auto *OCE = dyn_cast<CXXOperatorCallExpr>(this))
     return OCE->getBeginLoc();
 
-  if (const auto *Method =
-          dyn_cast_if_present<const CXXMethodDecl>(getCalleeDecl());
-      Method && Method->isExplicitObjectMemberFunction()) {
-    assert(getNumArgs() > 0 && getArg(0));
-    return getArg(0)->getBeginLoc();
+  // A non-dependent call to a member function with an explicit object parameter
+  // is modelled with the object expression being the first argument, e.g. in
+  // `o.f(x)`, the callee will be just `f`, and `o` will be the first argument.
+  // Since the first argument is written before the callee, the expression's
+  // begin location should come from the first argument.
+  // This does not apply to dependent calls, which are modelled with `o.f`
+  // being the callee.
+  if (!isTypeDependent()) {
+    if (const auto *Method =
+            dyn_cast_if_present<const CXXMethodDecl>(getCalleeDecl());
+        Method && Method->isExplicitObjectMemberFunction()) {
+      bool HasFirstArg = getNumArgs() > 0 && getArg(0);
+      assert(HasFirstArg);
+      if (HasFirstArg)
+        return getArg(0)->getBeginLoc();
+    }
   }
 
   SourceLocation begin = getCallee()->getBeginLoc();
diff --git a/clang/test/AST/ast-dump-cxx2b-deducing-this.cpp b/clang/test/AST/ast-dump-cxx2b-deducing-this.cpp
index 854d12b4cdba6..abe9d6a5b5bc6 100644
--- a/clang/test/AST/ast-dump-cxx2b-deducing-this.cpp
+++ b/clang/test/AST/ast-dump-cxx2b-deducing-this.cpp
@@ -13,3 +13,16 @@ void main() {
   // CHECK-NEXT: | `-DeclRefExpr 0x{{[^ ]*}} <col:13> 'int (S &)' lvalue CXXMethod 0x{{[^ ]*}} 'f' 'int (S &)'
 }
 }
+
+namespace GH1269720 {
+template <typename T>
+struct S {
+  void f(this S&);
+  void g(S s) {
+    s.f();
+  }
+  // CHECK: CallExpr 0x{{[^ ]*}} <line:22:5, col:9> '<dependent type>'
+  // CHECK-NEXT: `-MemberExpr 0x{{[^ ]*}} <col:5, col:7> '<bound member function type>' .f
+  // CHECK-NEXT:   `-DeclRefExpr 0x{{[^ ]*}} <col:5> 'S<T>' lvalue ParmVar 0x{{[^ ]*}} 's' 'S<T>'
+};
+}