cargo check --all-targets can generate duplicate messages.

[mooman219]

When running cargo check --all-targets, messages are sometimes duplicated in the output.

Version: cargo 1.27.0-nightly (9e53ac6 2018-05-07)

Example erroneous code in a simple new binary project:

fn main() {}

fn bar(foo: i32 bar: f32) -> f32 {
    return (foo as f32) + bar;
}

Corresponding output:

~/Downloads/test/vscode-test $ cargo check --all-targets
    Checking vscode-test v0.1.0 (file:///C:/Users/Mooma/Downloads/test/vscode-test)
error: expected one of `!`, `(`, `+`, `,`, `::`, or `<`, found `bar`
 --> src\main.rs:3:17
  |
3 | fn bar(foo: i32 bar: f32) -> f32 {
  |                 ^^^ expected one of `!`, `(`, `+`, `,`, `::`, or `<` here

error: expected one of `!`, `(`, `+`, `,`, `::`, or `<`, found `bar`
 --> src\main.rs:3:17
  |
3 | fn bar(foo: i32 bar: f32) -> f32 {
  |                 ^^^ expected one of `!`, `(`, `+`, `,`, `::`, or `<` here

error: aborting due to previous error

error: aborting due to previous error

error: Could not compile `vscode-test`.
warning: build failed, waiting for other jobs to finish...
error: Could not compile `vscode-test`.

To learn more, run the command again with --verbose.

[ehuss]

The duplicates are due to the same file (main.rs in this case) being used for different targets (binary and unit test). You can use the various target flags (--bin, --lib, --test, etc.) to limit which targets are checked. It depends on your use case. I have my editor set up to automatically check as a test (cargo check --bin vscode-test --profile=test in this case) to ensure that any tests get checked (a few lints will be disabled, such as missing_docs when checking as a test, but those are rare).

[alexcrichton]

What's actually happening here is that the library is being compiled twice (once with --test and once for doc tests later on), and this is a dupe of #1534, #851, and #1198. This is intended behavior though, and you can use various flags like --test, --lib, or -j to not run rustc in parallel, so I'm going to close this.