[clang] [Clang] suggest headers on undeclared errors (#120388) (PR #140247)

[Vlad Serebrennikov via cfe-commits]

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@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+void f(void) {
+  int_val2 = 0; // expected-error{{use of undeclared identifier}}
+  sin(0); // expected-error{{use of undeclared identifier 'sin'}} \
+          // expected-note{{perhaps `#include <cmath>` is needed?}}
+
+  std::cout << "Hello world\n"; // expected-error{{use of undeclared identifier 'std'}} \
+                                // expected-note{{perhaps `#include <iostream>` is needed?}}
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Endilll wrote:

This note sounds like `<iostream>` provides `std`, which doesn't feel right.

https://github.com/llvm/llvm-project/pull/140247