[clangd] Include the correct header for typeid()

[nridge]

Summary

Fixes https://github.com/clangd/clangd/issues/1449

[kadircet]

thanks for catching this!

clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp

1531

nit: i'd actually drop the test, as this is too much of a detail to test against.

[nridge]

Remove test

clang-tools-extra/clangd/IncludeFixer.cpp

case diag::ext_implicit_function_decl_c99:
     }
     break;
 
   // Cases where clang explicitly knows which header to include.
   // (There's no fix provided for boring formatting reasons).
   case diag::err_implied_std_initializer_list_not_found:
     return only(insertHeader("<initializer_list>"));
   case diag::err_need_header_before_typeid:
-    return only(insertHeader("<typeid>"));
+    return only(insertHeader("<typeinfo>"));
   case diag::err_need_header_before_placement_new:
   case diag::err_implicit_coroutine_std_nothrow_type_not_found:
     return only(insertHeader("<new>"));
   case diag::err_omp_implied_type_not_found:
   case diag::err_omp_interop_type_not_found:
     return only(insertHeader("<omp.h>"));
   case diag::err_implied_coroutine_type_not_found:
     return only(insertHeader("<coroutine>"));

clang-tools-extra/clangd/unittests/DiagnosticsTests.cpp

TEST(IncludeFixerTest, CImplicitFunctionDecl) {
   TU.ExtraArgs = {"-std=c89", "-Wall"};
   EXPECT_THAT(*TU.build().getDiagnostics(),
               ElementsAre(AllOf(
                   Diag(Test.range(), "implicit declaration of function 'foo'"),
                   withFix(Fix(Range{}, "#include \"foo.h\"\n",
                               "Include \"foo.h\" for symbol foo")))));
 }
 
+TEST(IncludeFixerTest, Typeid) {
+  Annotations Test(R"cpp(
+    $insert[[]]void func() {
+      [[typeid]](int); // error-ok
+    }
+  )cpp");
+  auto TU = TestTU::withCode(Test.code());
+  auto Index = buildIndexWithSymbol({});
+  TU.ExternalIndex = Index.get();
+  EXPECT_THAT(
+      *TU.build().getDiagnostics(),
+      ElementsAre(AllOf(
+          Diag(Test.range(), "you need to include <typeinfo> before using "
+                             "the 'typeid' operator"),
+          withFix(Fix(Test.range("insert"), "#include <typeinfo>\n",
+                      "Include <typeinfo>")))));
+}
+
 TEST(DiagsInHeaders, DiagInsideHeader) {
   Annotations Main(R"cpp(
     #include [["a.h"]]
     void foo() {})cpp");
   Annotations Header("[[no_type_spec]]; // error-ok");
   TestTU TU = TestTU::withCode(Main.code());
   TU.AdditionalFiles = {{"a.h", std::string(Header.code())}};
   EXPECT_THAT(*TU.build().getDiagnostics(),