VsCode: spurious "x is never used" if Rust-analyzer > Check On Save > All Targets, is selected in rust-analyzer options

[DanielJoyce]

VSCode:

Version: 1.54.3
Commit: 2b9aebd5354a3629c3aba0a5f5df49f43d6689f8
Date: 2021-03-15T10:55:24.277Z
Electron: 11.3.0
Chrome: 87.0.4280.141
Node.js: 12.18.3
V8: 8.7.220.31-electron.0
OS: Linux x64 5.8.0-7642-generic

Rust Analyzer Version: 0.2.565

Rust Version: 1.51

If I disable Rust-analyzer > Check On Save > All Targets, the spurious warnings go away.

Cargo check also does not show any matching warnings.

It seems that when merging results between targets, especially when checking the test target and the default target, rust analyzer gets confused or doesn't do it properly?

[DanielJoyce]

This has caused me to remove what I thought was dead code, then having cargo build fail because I deleted code that was in use. 😛

[lnicola]

Do you have a code sample?

[DanielJoyce]

If I disable the feature, then rust-analyzer stops checking tests.

[DanielJoyce]

I can attach logs if someone wants, then I check it off, here is the config shown in the output of rust analyzer

INFO [4/22/2021, 11:22:16 AM]: Extension version: 0.2.565
INFO [4/22/2021, 11:22:16 AM]: Using configuration {
  cargoRunner: null,
  runnableEnv: null,
  inlayHints: {
    enable: true,
    chainingHints: true,
    maxLength: 25,
    parameterHints: false,
    typeHints: false
  },
  updates: { channel: 'stable', askBeforeDownload: true },
  server: { path: null, extraEnv: null },
  trace: { server: 'off', extension: false },
  debug: {
    engine: 'auto',
    sourceFileMap: {
      '/rustc/<id>': '${env:USERPROFILE}/.rustup/toolchains/<toolchain-id>/lib/rustlib/src/rust'
    },
    openDebugPane: false,
    engineSettings: {}
  },
  assist: {
    importMergeBehavior: 'last',
    importPrefix: 'plain',
    importGroup: true
  },
  callInfo: { full: true },
  cargo: {
    autoreload: true,
    allFeatures: true,
    features: [],
    runBuildScripts: true,
    useRustcWrapperForBuildScripts: true,
    noDefaultFeatures: false,
    target: null,
    noSysroot: false,
    loadOutDirsFromCheck: true
  },
  checkOnSave: {
    enable: true,
    allFeatures: null,
    allTargets: true,
    command: 'check',
    noDefaultFeatures: null,
    target: null,
    extraArgs: [],
    features: null,
    overrideCommand: null
  },
  completion: {
    addCallArgumentSnippets: true,
    addCallParenthesis: true,
    postfix: { enable: true },
    autoimport: { enable: true }
  },
  diagnostics: {
    enable: true,
    enableExperimental: true,
    disabled: [],
    warningsAsHint: [],
    warningsAsInfo: []
  },
  files: { watcher: 'client', excludeDirs: [] },
  hoverActions: {
    debug: true,
    enable: true,
    gotoTypeDef: true,
    implementations: true,
    run: true,
    linksInHover: true
  },
  lens: {
    debug: true,
    enable: true,
    implementations: true,
    run: true,
    methodReferences: false,
    references: false
  },
  linkedProjects: [],
  lruCapacity: null,
  notifications: { cargoTomlNotFound: true },
  procMacro: { enable: true, server: null },
  runnables: { overrideCargo: null, cargoExtraArgs: [] },
  rustcSource: null,
  rustfmt: { extraArgs: [], overrideCommand: null }
}

When I turn it off:

INFO [4/22/2021, 11:24:43 AM]: Extension version: 0.2.565
INFO [4/22/2021, 11:24:43 AM]: Using configuration {
  cargoRunner: null,
  runnableEnv: null,
  inlayHints: {
    enable: true,
    chainingHints: true,
    maxLength: 25,
    parameterHints: false,
    typeHints: false
  },
  updates: { channel: 'stable', askBeforeDownload: true },
  server: { path: null, extraEnv: null },
  trace: { server: 'off', extension: false },
  debug: {
    engine: 'auto',
    sourceFileMap: {
      '/rustc/<id>': '${env:USERPROFILE}/.rustup/toolchains/<toolchain-id>/lib/rustlib/src/rust'
    },
    openDebugPane: false,
    engineSettings: {}
  },
  assist: {
    importMergeBehavior: 'last',
    importPrefix: 'plain',
    importGroup: true
  },
  callInfo: { full: true },
  cargo: {
    autoreload: true,
    allFeatures: true,
    features: [],
    runBuildScripts: true,
    useRustcWrapperForBuildScripts: true,
    noDefaultFeatures: false,
    target: null,
    noSysroot: false,
    loadOutDirsFromCheck: true
  },
  checkOnSave: {
    enable: true,
    allFeatures: null,
    allTargets: false,
    command: 'check',
    noDefaultFeatures: null,
    target: null,
    extraArgs: [],
    features: null,
    overrideCommand: null
  },
  completion: {
    addCallArgumentSnippets: true,
    addCallParenthesis: true,
    postfix: { enable: true },
    autoimport: { enable: true }
  },
  diagnostics: {
    enable: true,
    enableExperimental: true,
    disabled: [],
    warningsAsHint: [],
    warningsAsInfo: []
  },
  files: { watcher: 'client', excludeDirs: [] },
  hoverActions: {
    debug: true,
    enable: true,
    gotoTypeDef: true,
    implementations: true,
    run: true,
    linksInHover: true
  },
  lens: {
    debug: true,
    enable: true,
    implementations: true,
    run: true,
    methodReferences: false,
    references: false
  },
  linkedProjects: [],
  lruCapacity: null,
  notifications: { cargoTomlNotFound: true },
  procMacro: { enable: true, server: null },
  runnables: { overrideCargo: null, cargoExtraArgs: [] },
  rustcSource: null,
  rustfmt: { extraArgs: [], overrideCommand: null }
}

[DanielJoyce]

Okay, I've tracked this down to the use of mockall_double::double macro, which is an attribute macro used to rewrite imports for testing.

When run in release, it uses one impl, in test it uses another.

It basically emits in test mode:

#[cfg(test)]
pub use crat::some_module::MockClient as Client

and in debug/release:

#[cfg(not(test))]
pub use crate::some_module::Client

So rust analyzer is facing two mutually exclusive module imports on test vs debug/release

I don't know if this is 'fixable', I admit it's a bit weird. But I suspect this might come up with rust_analyzer facing any mutually exclusive of cfg based features as well.

[DanielJoyce]

I'll see what the behavior is with explicit cfg values.

[DanielJoyce]

Manually expanded:

    #[cfg(test)] // These two lines are bright and highlighted, telling me this is the config rust-analyzer is using
    pub use super::some_crate::MockClient as Client; // Rust analyzer complains here, says it can't find it
    #[cfg(not(test))] // Greyed out/pale in vsCode
    pub use super::some_crate::HbaseQueryClient;

Cargo check is still happy, but rust_analyzer now says it can't find MockClient, though MockClient should be created from Client via the mock_all macro.

If I get some time, I will see if I can gin up a simple POC. I believe the fundamental issue might be support of #[cfg(not(test))] ?

[lnicola]

Note that we don't support attribute proc macros, nor crate splitting for your case (#7459).

[DanielJoyce]

I think I have a fix for mockall_double.

EDIT: Nope. Pebkac, but I just learned something...

[flodiebold]

Do you not get the warning with cargo check --all-targets?

[DanielJoyce]

I get the warning with --all-targets, I do not get it with it turned off.

EDIT: I mean with --all-targets enabled for rust-analyzer. Cargo checks them correctly, Rust-analyzer produces more warnings.

[flodiebold]

Then this is a cargo bug, if at all. (This might very well be expected behavior though.)

[DanielJoyce]

@lnicola So #8486 refernced in #7459 won't fix it?

[flodiebold]

No.

[DanielJoyce]

Sorry, I mean, cargo check --all-targets works correctly. rust-analyzer with check-all-targets reports more unused variables (spurious warnings) than cargo does with the same flag.

[flodiebold]

@DanielJoyce Can you provide an example project that shows this behavior?

[flodiebold]

To be clear, rust-analyzer currently doesn't emit "unused variable" warnings from its own analysis, so these warnings can only come from cargo check. So the only question here is what's the difference between how RA is calling cargo check, vs. how you are calling it on the command line. You might try cargo check --all-targets --all-features.

[lnicola]

Not enough info to reproduce this, closing.