rust-lang/rust: "failed to switch build data" messages

[lf-]

Steps I did to reproduce:

Open compiler/rustc_hir/src/hir.rs with this suggested config from the dev guide:

{
    "rust-analyzer.checkOnSave.overrideCommand": [
        "./x.py",
        "check",
        "--json-output"
    ],
    "rust-analyzer.rustfmt.overrideCommand": [
      "./build/x86_64-unknown-linux-gnu/stage0/bin/rustfmt"
    ],
    "rust-analyzer.cargo.runBuildScripts": false,
    "rust-analyzer.procMacro.enable": true
}

and it did this and showed a sad popup in the corner:

[ERROR rust_analyzer::reload] failed to switch build data: cargo check failed:
error: could not compile `crc32fast`

To learn more, run the command again with --verbose.
error: build failed

Why would it do such a thing? This error looks similar to what cargo check in r-l/r would fail like.... pokes through r-a code, patches in a debug log (it would be nice if we could spit this out automatically, but my patch here requires rust-lang/rust#44434):

[DEBUG project_model::build_data] run cargo in Some("/home/jade/dev/rust") with ["check", "--quiet", "--workspace", "--message-format=json", "--manifest-path", "/home/jade/dev/rust/Cargo.toml", "--all-targets"]

So from what I can understand, project_model::build_data is calling cargo check with its own generated command, which it should not do in r-l/r and probably some other places, in spite of there being a configured checkOnSave.overrideCommand. I'm not sure how this should be handled, but I'm filing it to document it as an issue with r-l/r.

cc #8915

[flodiebold]

Setting procMacro.enable to true (contrary to the dev guide) overrides the runBuildScripts setting (as the documentation for the setting mentions), so cargo check will be run.

[lf-]

Oh, shoot. I mixed that up while looking for the proc macro issues :/ oops.