[clang] [clang]Avoid diagnose invalid consteval call for invalid function decl (PR #68646)

[Erich Keane via cfe-commits]

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@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -verify -std=c++20 -fsyntax-only %s
+
+// expected-note at +2{{candidate constructor (the implicit move constructor) not viable: no known conversion from 'int' to 'S &&' for 1st argument}}
+// expected-note at +1{{candidate constructor (the implicit copy constructor) not viable: no known conversion from 'int' to 'const S &' for 1st argument}}
+struct S {
+    int e;
+};
+
+template<class T>
+consteval int get_format() {
+	return nullptr; // expected-error{{cannot initialize return object of type 'int' with an rvalue of type 'std::nullptr_t'}}
+}
+
+template<class T>
+constexpr S f(T) noexcept {
+	return get_format<T>(); // expected-error{{no viable conversion from returned value of type 'int' to function return type 'S'}}
+}
+
+// expected-note at +1{{in instantiation of function template specialization 'f<int>' requested here}}
+constexpr S x = f(0); // expected-error{{constexpr variable 'x' must be initialized by a constant expression}}
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erichkeane wrote:

Need newline at end of file.

https://github.com/llvm/llvm-project/pull/68646