[Clang] Diagnose invalid function types in dependent contexts

clang/docs/ReleaseNotes.rst

@@ -655,6 +655,7 @@ Bug Fixes to C++ Support
 - Fixed an assertion when trying to constant-fold various builtins when the argument
   referred to a reference to an incomplete type. (#GH129397)
 - Fixed a crash when a cast involved a parenthesized aggregate initialization in dependent context. (#GH72880)
+- Fixed a crash when forming an invalid function type in a dependent context. (#GH138657) (#GH115725) (#GH68852)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaExpr.cpp

@@ -6541,6 +6541,15 @@ ExprResult Sema::ActOnCallExpr(Scope *Scope, Expr *Fn, SourceLocation LParenLoc,
   return Call;
 }
 
+// Any type that could be used to form a callable expression
+static bool MayBeFunctionType(const ASTContext &Context, QualType T) {
+  return T == Context.BoundMemberTy || T == Context.UnknownAnyTy ||
+         T == Context.BuiltinFnTy || T == Context.OverloadTy ||
+         T->isFunctionType() || T->isFunctionReferenceType() ||
+         T->isMemberFunctionPointerType() || T->isFunctionPointerType() ||
+         T->isBlockPointerType() || T->isRecordType();
+}
+
 ExprResult Sema::BuildCallExpr(Scope *Scope, Expr *Fn, SourceLocation LParenLoc,
                                MultiExprArg ArgExprs, SourceLocation RParenLoc,
                                Expr *ExecConfig, bool IsExecConfig,
@@ -6594,6 +6603,15 @@ ExprResult Sema::BuildCallExpr(Scope *Scope, Expr *Fn, SourceLocation LParenLoc,
             *this, dyn_cast<UnresolvedMemberExpr>(Fn->IgnoreParens()),
             Fn->getBeginLoc());
 
+        // If the type of the function itself is not dependent
+        // check that it is a reasonable as a function, as type deduction
+        // later assume the CallExpr has a sensible TYPE.
+        if (!Fn->getType()->isDependentType() &&
+            !MayBeFunctionType(Context, Fn->getType()))
+          return ExprError(
+              Diag(LParenLoc, diag::err_typecheck_call_not_function)
+              << Fn->getType() << Fn->getSourceRange());
+
         return CallExpr::Create(Context, Fn, ArgExprs, Context.DependentTy,
                                 VK_PRValue, RParenLoc, CurFPFeatureOverrides());
       }

clang/test/SemaTemplate/fun-template-def.cpp

@@ -1,6 +1,7 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c++98 %s
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 %s
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++20 %s
 
 // Tests that dependent expressions are always allowed, whereas non-dependent
 // are checked as usual.
@@ -32,7 +33,7 @@ T f1(T t1, U u1, int i1, T** tpp)
   i1 = t1[u1];
   i1 *= t1;
 
-  i1(u1, t1); // error
+  i1(u1, t1); // expected-error {{called object type 'int' is not a function or function pointer}}
   u1(i1, t1);
 
   U u2 = (T)i1;
@@ -60,3 +61,51 @@ void f3() {
   f2<int*>(0);
   f2<int>(0); // expected-error {{no matching function for call to 'f2'}}
 }
+
+#if __cplusplus >= 202002L
+namespace GH138657 {
+template <auto V> // #gh138657-template-head
+class meta {};
+template<int N>
+class meta<N()> {}; // expected-error {{called object type 'int' is not a function or function point}}
+
+template<int N[1]>
+class meta<N()> {}; // expected-error {{called object type 'int *' is not a function or function point}}
+
+template<char* N>
+class meta<N()> {}; // expected-error {{called object type 'char *' is not a function or function point}}
+
+struct S {};
+template<S>
+class meta<S()> {}; // expected-error {{template argument for non-type template parameter is treated as function type 'S ()'}}
+                    // expected-note@#gh138657-template-head {{template parameter is declared here}}
+
+}
+
+namespace GH115725 {
+template<auto ...> struct X {};
+template<typename T, typename ...Ts> struct A {
+  template<Ts ...Ns, T *...Ps>
+  A(X<0(Ps)...>, Ts (*...qs)[Ns]);
+  // expected-error@-1{{called object type 'int' is not a function or function pointer}}
+
+};
+}
+
+namespace GH68852 {
+template <auto v>
+struct constexpr_value {
+  template <class... Ts>
+  constexpr constexpr_value<v(Ts::value...)> call(Ts...) {
+    //expected-error@-1 {{called object type 'int' is not a function or function pointer}}
+    return {};
+  }
+};
+
+template <auto v> constexpr static inline auto c_ = constexpr_value<v>{};
+// expected-note@-1 {{in instantiation of template}}
+auto k = c_<1>; // expected-note {{in instantiation of variable}}
+
+}
+
+#endif