[clang][Frontend] Add missing error handling

[LemonBoy]

Summary

Some early errors during the ASTUnit creation were not transferred to the FailedParseDiagnostic so when the code in LoadFromCommandLine swaps its content with the content of StoredDiagnostics they cannot be retrieved by the user in any way.

[LemonBoy]

Fix a C&P error in the attached test case.

[LemonBoy]

Ping?

[LemonBoy]

Ping?

[LemonBoy]

Ping?

[LemonBoy]

Ping?

[andrewrk]

ping?

[LemonBoy]

Ping with some more reviewers, hoping to land this in time for LLVM 99.

[dblaikie]

Perhaps this'd be more robust with ScopeExit? ( https://llvm.org/doxygen/ScopeExit_8h_source.html )

[LemonBoy]

Perhaps this'd be more robust with ScopeExit?

Not really, OnError is not executed when/if the function succeeds.

[dblaikie]

In D78658#2327615, @LemonBoy wrote:

Perhaps this'd be more robust with ScopeExit?

Not really, OnError is not executed when/if the function succeeds.

Ah, sorry - ScopeExit has a 'release()' function intended to disengage it/disable the execution of the payload.

The use would often look something like:

auto x = make_scope_exit(...);
if (failed())
  return fail;
if (failed())
  return fail;
x.release();
return success;

[LemonBoy]

Use ScopeExit instead of a bare lambda.

[dblaikie]

clang/lib/Frontend/ASTUnit.cpp

1156–1160

You can remove these braces now - since it's a superfluous change here now there's no need to add an extra function call.

1216–1220

Skip the braces here, since it's a single-line scope.

[dblaikie]

Looks good to me - thanks!

[LemonBoy]

Looks good to me - thanks!

Great! Can you please commit this for me as I have no commit access?