[clang] [clang][Interp] Pass callee decl to null_callee diagnostics (PR #104426)

[Timm Baeder via cfe-commits]

https://github.com/tbaederr created https://github.com/llvm/llvm-project/pull/104426

The callee is null, not the full call expression.

>From 1d4f1403b65f9b1b5c5655e73217beee50b104eb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Timm=20B=C3=A4der?= <tbaeder at redhat.com>
Date: Thu, 15 Aug 2024 12:06:57 +0200
Subject: [PATCH] [clang][Interp] Pass callee decl to null_callee diagnostics

The callee is null, not the full call expression.
---
 clang/lib/AST/Interp/Interp.h       |  4 ++--
 clang/test/AST/Interp/functions.cpp | 11 +++++++++++
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/clang/lib/AST/Interp/Interp.h b/clang/lib/AST/Interp/Interp.h
index 3eab0cfd871385..7dbda9ae65fe78 100644
--- a/clang/lib/AST/Interp/Interp.h
+++ b/clang/lib/AST/Interp/Interp.h
@@ -2702,9 +2702,9 @@ inline bool CallPtr(InterpState &S, CodePtr OpPC, uint32_t ArgSize,
 
   const Function *F = FuncPtr.getFunction();
   if (!F) {
-    const Expr *E = S.Current->getExpr(OpPC);
+    const CallExpr *E = cast<CallExpr>(S.Current->getExpr(OpPC));
     S.FFDiag(E, diag::note_constexpr_null_callee)
-        << const_cast<Expr *>(E) << E->getSourceRange();
+        << const_cast<Expr *>(E->getCallee()) << E->getSourceRange();
     return false;
   }
 
diff --git a/clang/test/AST/Interp/functions.cpp b/clang/test/AST/Interp/functions.cpp
index f190262ad3ebee..b00f59a8d8d433 100644
--- a/clang/test/AST/Interp/functions.cpp
+++ b/clang/test/AST/Interp/functions.cpp
@@ -221,6 +221,17 @@ namespace Comparison {
   static_assert(pg == &g, "");
 }
 
+  constexpr int Double(int n) { return 2 * n; }
+  constexpr int Triple(int n) { return 3 * n; }
+  constexpr int Twice(int (*F)(int), int n) { return F(F(n)); }
+  constexpr int Quadruple(int n) { return Twice(Double, n); }
+  constexpr auto Select(int n) -> int (*)(int) {
+    return n == 2 ? &Double : n == 3 ? &Triple : n == 4 ? &Quadruple : 0;
+  }
+  constexpr int Apply(int (*F)(int), int n) { return F(n); } // both-note {{'F' evaluates to a null function pointer}}
+
+  constexpr int Invalid = Apply(Select(0), 0); // both-error {{must be initialized by a constant expression}} \
+                                               // both-note {{in call to 'Apply(nullptr, 0)'}}
 }
 
 struct F {