[clang] Compute accurate begin location for CallExpr with explicit object parameter

The explicit object parameter is written before the callee expression,
so the begin location should come from the explicit object parameter.

Fixes #116335

Author: HighCommander4

clang/lib/AST/Expr.cpp

@@ -1639,6 +1639,13 @@ SourceLocation CallExpr::getBeginLoc() const {
   if (const auto *OCE = dyn_cast<CXXOperatorCallExpr>(this))
     return OCE->getBeginLoc();
 
+  if (const CXXMethodDecl *Method =
+          dyn_cast_or_null<const CXXMethodDecl>(getCalleeDecl());
+      Method && Method->isExplicitObjectMemberFunction()) {
+    assert(getNumArgs() > 0 && getArg(0));
+    return getArg(0)->getBeginLoc();
+  }
+
   SourceLocation begin = getCallee()->getBeginLoc();
   if (begin.isInvalid() && getNumArgs() > 0 && getArg(0))
     begin = getArg(0)->getBeginLoc();

clang/lib/Sema/SemaOverload.cpp

@@ -15565,7 +15565,7 @@ ExprResult Sema::BuildCallToMemberFunction(Scope *S, Expr *MemExprE,
     // Build the actual expression node.
     ExprResult FnExpr =
         CreateFunctionRefExpr(*this, Method, FoundDecl, MemExpr,
-                              HadMultipleCandidates, MemExpr->getBeginLoc());
+                              HadMultipleCandidates, MemExpr->getExprLoc());
     if (FnExpr.isInvalid())
       return ExprError();
 

clang/test/AST/ast-dump-cxx2b-deducing-this.cpp

@@ -9,7 +9,7 @@ int main() {
   S s;
   int x = s.f();
   // CHECK: CallExpr 0x{{[^ ]*}} <col:11, col:15> 'int
-  // CHECK-NEXT: |-ImplicitCastExpr 0x{{[^ ]*}} <col:11> 'int (*)(S &)' <FunctionToPointerDecay>
-  // CHECK-NEXT: | `-DeclRefExpr 0x{{[^ ]*}} <col:11> 'int (S &)' lvalue CXXMethod 0x{{[^ ]*}} 'f' 'int (S &)'
+  // CHECK-NEXT: |-ImplicitCastExpr 0x{{[^ ]*}} <col:13> 'int (*)(S &)' <FunctionToPointerDecay>
+  // CHECK-NEXT: | `-DeclRefExpr 0x{{[^ ]*}} <col:13> 'int (S &)' lvalue CXXMethod 0x{{[^ ]*}} 'f' 'int (S &)'
 }
 }