failed inference on complex nested, generic closures

[elindsey]

This is a somewhat complex case. On this line: https://github.com/TimelyDataflow/timely-dataflow/blob/master/timely/examples/wordcount.rs#L32

rust-analyzer fails to infer the types for input/output (showing "unknown"), and thus fails to infer most of the types in the rest of that closure as well. RLS handles this case correctly.

That example has nested closures and a multitude of generics in that call; I've tried coming up with a more minimal repro but have so far failed. Enabling server-side logging didn't turn up any errors, so I'm not entirely sure where to go from here.

Does that pattern look like something that's a currently known failure? If not, do you have any tips on other logging or methods of looking into rust-analyzer's processing to try to determine what exactly is tripping it up?

[flodiebold]

I think we're hitting the (arbitrary, maybe too small) goal size limit here. We should probably increase it when other Chalk performance problems (i.e. primarily #6432) have been solved.

(To debug this, I mostly ran RA_LOG=hir_ty::traits=info CHALK_DEBUG=debug CHALK_PRINT=yes rust-analyzer analysis-stats -o main_xxx ., having renamed the main function to main_xxx to be able to analyse that single one, and having commented out everything later in the function to reduce the log size a bit.)

[umanwizard]

@flodiebold I am a colleague of @elindsey and also involved with a project that heavily uses timely-dataflow. This issue is a big pain point for me, so I'm willing to tolerate rust-analyzer being slow or using a lot of memory if it solves the issue.

I'll try compiling r-a from source myself and bumping up that 30 number; do you have any suggestions on what to set it to? (If not, I can just try something huge and report my findings)

[flodiebold]

You'll be able to set it by env variable once #6597 is merged. I'd suggest just doubling it and seeing whether that helps.

[umanwizard]

Is there an easy way to set env vars for rust-analyzer in vscode? (Other than setting serverPath to a wrapper script that sets the environment and then invokes the binary)

[flodiebold]

@umanwizard You could just set the env variable in the environment for VSCode.

[lnicola]

There's also rust-analyzer.server.extraEnv.

[umanwizard]

@lnicola I don't think that existed when I posted that message :) anyway, thanks.