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

[HighCommander4]

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

Fixes #116335

[llvmbot]

@llvm/pr-subscribers-clang

Author: Nathan Ridge (HighCommander4)

Changes

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

Fixes #116335

---

Full diff: https://github.com/llvm/llvm-project/pull/117841.diff

3 Files Affected:

• (modified) clang/lib/AST/Expr.cpp (+7)
• (modified) clang/lib/Sema/SemaOverload.cpp (+1-1)
• (modified) clang/test/AST/ast-dump-cxx2b-deducing-this.cpp (+2-2)

diff --git a/clang/lib/AST/Expr.cpp b/clang/lib/AST/Expr.cpp
index a4fb4d5a1f2ec4..8b10a2609c2ab0 100644
--- a/clang/lib/AST/Expr.cpp
+++ b/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();
diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 4c9e37bd286dee..e4bf9aa521224b 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/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();
 
diff --git a/clang/test/AST/ast-dump-cxx2b-deducing-this.cpp b/clang/test/AST/ast-dump-cxx2b-deducing-this.cpp
index 04cff07376885a..1b385e0fc33319 100644
--- a/clang/test/AST/ast-dump-cxx2b-deducing-this.cpp
+++ b/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 &)'
 }
 }

[zwuis]

Suggested change

	dyn_cast_or_null<const CXXMethodDecl>(getCalleeDecl());
	dyn_cast_if_present<const CXXMethodDecl>(getCalleeDecl());

[zyn0217]

I think this also needs a selection tree test to demonstrate the original case works with the current approach.

Besides, If we can't highlight the loci differences (compared to the behavior before the last PR) using simple -ast-dump flags, then perhaps we should reconsider the necessity of clang/test/AST/ast-dump-cxx2b-deducing-this.cpp - removing it might be a good option.

That said, I was still thinking if there's any possibility for us to find a better AST model for such use cases, rather than relying on special-casing it in CallExpr::getBeginLoc

[HighCommander4]

That said, I was still thinking if there's any possibility for us to find a better AST model for such use cases, rather than relying on special-casing it in CallExpr::getBeginLoc

A more general implementation of CallExpr::getBeginLoc that occurs to me is: return the earlier of the callee's begin loc and the first argument's (if present) begin loc.

[tbaederr]

Suggested change

	if (const CXXMethodDecl *Method =
	if (const auto *Method =