[analyzer] analyzer starts leaking when typing a switch expression

[incendial]

When I type the following code, analyzer memory usage just skyrockets. Restarting the process via VS Code does not kill the existing one.

Been able to repro this 2 times in a row.

Here is a video on produced errors.

Screen.Recording.2023-05-11.at.17.06.20.mov

Let me know what else I need to provide for this to be fixed.

#### General info

- Dart 3.0.0-417.4.beta (beta) (Tue May 2 10:26:14 2023 +0000) on "macos_x64"
- on macos / Version 12.6 (Build 21G115)
- locale is en-GB

#### Project info

- sdk constraint: '>=3.0.0-417.1.beta <4.0.0'
- dependencies: ansicolor, collection, crypto, file, glob, html, meta, path, pub_semver, recase, source_span, xml, yaml
- dev_dependencies: lints, mocktail, test
- elided dependencies: 4

#### Process info

|  Memory |   CPU | Elapsed time | Command line                                                                           |
| ------: | ----: | -----------: | -------------------------------------------------------------------------------------- |
| 6996 MB | 67.8% |        07:31 | dart language-server --protocol=lsp --client-id=VS-Code --client-version=3.65.20230510 |

[incendial]

And it just keeps growing...

[bwilkerson]

@scheglov

[scheglov]

It would be nice if you provided snippets of code with your issues.
It is somewhat inconvenient try to retype code from video :-P

[scheglov]

I cannot reproduce it with a simple example.

  solo_test_X() async {
    await assertErrorsInCode(r'''
void f(Object? x) {
  final innerIf = switch (x) {
    Block(statements: [IfStatement inner]) => inner,
  };
}

class Block {
  List<Statement> get statements => [];
}

class Statement {}

class IfStatement extends Statement {}
''', [
      error(WarningCode.UNUSED_LOCAL_VARIABLE, 28, 7),
      error(CompileTimeErrorCode.NON_EXHAUSTIVE_SWITCH_EXPRESSION, 38, 6),
    ]);

    final node = findNode.singleSwitchExpression;
    assertResolvedNodeText(node, r'''
''');
  }

From the fact that it uses CPU, it seems that it might got into an infinite cycle somewhere.

Locally, I always run DAS with Observatory enabled.
To do so, I set dart.server.vm.options in my IntelliJ to --no_dds --observe:8181 --serve-observatory --disable-service-auth-codes, and then use cpu profile (table) on (main) isolate to see if there is anything interesting.

[incendial]

Sure, will do!

It happened on typing (at least that how it looked). So I'm not sure that tests can spot it.

[scheglov]

I tried to type something similar in the IDE, outside tests, but cannot get it into "sticky errors" when it cycles :-(

void f(IfStatement node) {
  final innerIf = switch (node.thenStatement) {
    Block(statements: [IfStatement inner]) => inner,
    _ => null,
  };
  print(innerIf);
}

[incendial]

Interesting, now I also cant repro it in one go. I understood that when "dart.fix" added final:

final innerIf = switch (node.thenStatement) {
  Block(statements: [final IfStatement inner]) => inner,
};

will try again, maybe it has something to do with the order in which code is added.

[incendial]

Yep, got it again. Trying to extract steps.

[incendial]

Screen.Recording.2023-05-11.at.23.14.46.mov

Screen.Recording.2023-05-11.at.23.16.31.mov

From my edit history exactly before the initial report.

Affects dcm as well.

[incendial]

As you can see on the second video analyzer is already slowed down, but it was not recorded instantly, probably after 2-3 GB leaked.

[incendial]

There is only one other issue present in the file (maybe it's related somehow).

  bool _isCollapsibleIf(IfStatement node) =>
      node.elseStatement == null && node.expression.;

[incendial]

After the process is killed manually, this code does not trigger the leak (not typing this code, but its presence).

 final innerIf = switch (node.thenStatement) {
        Block(statements: [final IfStatement inner]) =>inner,
      };

[incendial]

[incendial]

Let me know if you need anything else.

[scheglov]

It might be not obvious, but I cannot reproduce it.
From the provided info I see that there is a problem, but I have no idea why and where.

[incendial]

I'll try to extract the exact step, I think I'm close.

[incendial]

final innerIf = switch (node.thenStatement) {
        Block(statements: [if])
      };

can you try this one? restarting analyzer here leads to immediate leak.

[incendial]

Note: I got if by typo in final. Or I wanted to write IfStatement 🤔

[scheglov]

It seems to did it! y IDE does not update semantic highlighting, and the DAS process eats CPU.
Thank you!

[scheglov]

It looks to be cycling in the parser.

[incendial]

You're welcome! This one was very tricky.
Actually, I was assuming it is something related to the parser.

[scheglov]

I cleaned it up to

void f(Object? x) {
  switch (x) {
    case [if]
  };
}

This code cycles the unit test code above.

[scheglov]

@stereotype441 could you take a look?

[incendial]

It even does not matter whether it's case [] or ObjectPattern with []? Interesting. So it might be something old?

[stereotype441]

I'm able to reproduce this and I'm investigating.

[stereotype441]

Thanks @incendial and @scheglov for tracking down such a small repro! It made it a lot easier to debug the problem.

I've landed a fix in the main development branch, and I've requested approval too cherry-pick it into the 3.0.1 stable release (#52376).

[incendial]

Thanks! Considering the fix was in _fe_analyzer_shared, do you have a release date for the new version?

[stereotype441]

The code that gets run under the hood when you're interacting with your editor is the code that's included in the Dart SDK, even if that code comes ultimately from the _fe_analyzer_shared or analyzer package instead of directly from the analysis server. So it actually doesn't matter when we release _fe_analyzer_shared--you'll get the fix when you install a version of the SDK that includes it.

So far there's no published version of the SDK that includes the fix. Hopefully it will show up in the dev channel later today (dev channel builds have been happening about once every four hours recently). After that it will hopefully show up in the 3.0.1 stable hotfix (assuming my cherry-pick request gets approved). I'm currently checking whether there's a target date for 3.0.1 that I can share publicly.

[incendial]

I work on a tool that uses analyzer and _fe_analyzer_shared directly and I'm asking to be able to pick the changes as well. The only way I can do that is when there is a new published version available in pub.

So it matters to me 🙂.

[stereotype441]

Ah, ok. In that case I'll defer to @scheglov, who usually does the releases of analyzer and _fe_analyzer_shared.

[scheglov]

I'm not ready to publish yet, would like to wait a few days after a3956e4

https://dart-review.googlesource.com/c/sdk/+/303012 for now, not that it is much useful for you, but it record that this issue is fixed :-)