[Parse] Remove TimeTraceScope for "ParseTemplate"

[MaskRay]

Summary

Fix https://github.com/llvm/llvm-project/issues/56554

#include "1.h"
#include "2.h"
int foo();

Suppose that 1.h ends with a template function. When parsing the function,
the ParseFunctionDefinition call after the TimeTraceScope object
may consume a r_brace token and lex the end of file (1.h), resulting
in an ExitFile event in SemaPPCallbacks::FileChanged. This event will call llvm::timeTraceProfilerEnd();,
which incorrectly ends "ParseTemplate" instead of "Source" (1.h).
Once 2.h has been fully parsed, the destructor of 1.h's TimeTraceScope object
will end "Source" (1.h).

This behavior erroneously extends the end of "Source" (1.h), which makes
"Source" (2.h) appear to be nested inside "Source" (1.h). This bug is difficult
to fix correctly in an elegant way, and we have two options: either end
"ParseTemplate" when ending "Source" (1.h), or delay the ExitFile event.

However, both approaches require complex code. For now, we can remove the
"ParseTemplate" TimeTraceScope. This can be re-added if properly repaired.

[anton-afanasyev]

Ok, let's remove it for now.

[MaggieYi]

Thanks @MaskRay, the fix is fine for me.

clang/lib/Parse/ParseTemplate.cpp

Decl *Parser::ParseSingleDeclarationAfterTemplate(
   if (!DeclaratorInfo.hasName()) {
     // If so, skip until the semi-colon or a }.
     SkipUntil(tok::r_brace, StopAtSemi | StopBeforeMatch);
     if (Tok.is(tok::semi))
       ConsumeToken();
     return nullptr;
   }
 
-  llvm::TimeTraceScope TimeScope("ParseTemplate", [&]() {
-    return std::string(DeclaratorInfo.getIdentifier() != nullptr
-                           ? DeclaratorInfo.getIdentifier()->getName()
-                           : "<unknown>");
-  });
-
   LateParsedAttrList LateParsedAttrs(true);
   if (DeclaratorInfo.isFunctionDeclarator()) {
     if (Tok.is(tok::kw_requires)) {
       CXXScopeSpec &ScopeSpec = DeclaratorInfo.getCXXScopeSpec();
       DeclaratorScopeObj DeclScopeObj(*this, ScopeSpec);
       if (ScopeSpec.isValid() &&
           Actions.ShouldEnterDeclaratorScope(getCurScope(), ScopeSpec))
         DeclScopeObj.EnterDeclaratorScope();