Update last modified date directly in touch

[greglittlefield-wf]

This mitigates race conditions in which concurrent Pub processes "touch"
pubspec.lock at the same time and leave it with a trailing NUL character.

---

Long-winded background info

We've been seeing intermittent failures in our automated builds for some time now, which looked like this:

Error on line 1177, column 1 of pubspec.lock: Unexpected character.

^

However, we had a hard time tracking them down. Eventually, we determined that the unexpected character in that message was actually a NUL character.

"What was modifying pubspec.lock and adding a NUL character?" We weren't in our scripts, and there shouldn't be any reason for Pub to modify it since in all cases we've seen this issue, the pubspec.lock is checked in and didn't change after pub get.

However, looking at Pub's source, it looks like its touch utility operates by writing a NUL character to the end of the file and then writing to it again with the original contents.

We were running multiple Pub commands in parallel, which would explain this issue: two Pub processes could be performing touch at the same time,
resulting in a NUL character being preserved in the output.

pub run also always touches pubspec.lock when there are path dependencies, which we had in all the repos we encountered this issue in, which explains why we were seeing it so often.

To reproduce locally: with the following files...

• pubspec.yaml

  name: foo
  dependencies:
    path_dep:
      path: ./path_dep

• foo.dart

  main() {}

• path_dep/pubspec.yaml

  name: path_dep

... run the following command in several of terminals at once;
eventually you'll get "Unexpected character" errors.

while true; do pub run ./foo.dart; done

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[greglittlefield-wf]

I signed it! (My company, Workiva, signed it!)

I know in the past, our CLA hasn't been picked up by googlebot. I see that the CLA instructions have changed, so perhaps I need to get in touch with our Point of Contact. I don't know who that is, though ☹️.

[natebosch]

cc @mit-mit

[mit-mit]

What do you see if you go to https://cla.developers.google.com/clas ?

Did the git commit use an @workiva.com email address?

[greglittlefield-wf]

I see this:

Yes, the commit uses [email protected].

[mit-mit]

Got it, let me do some debugging on my end

[greglittlefield-wf]

Thanks!!

[mit-mit]

Can you verify that you are a member of [email protected]? That's the group that the class is tied to.

[greglittlefield-wf]

Hm, not that I can tell. Let me ask around...

[greglittlefield-wf]

Hey @mit-mit, I just got added to that group!

[googlebot]

CLAs look good, thanks!

[mit-mit]

@jonasfj & @natebosch can you take a look at this PR?

[robbecker-wf]

🎉 Any idea which Dart SDK version this will be released in?

[kevmoo]

Need to merge it into the SDK first. Then it'll be "the next one".

Updated dart-lang/sdk#36026 to make the request for @sigurdm