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Add documentation for unused-externs(-silent)

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Jeremy Fitzhardinge 2023-11-17 20:15:45 -08:00
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commit 8880b702fe
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src/doc/rustc/src/json.md
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@ -262,6 +262,36 @@ information, even if the diagnostics have been suppressed (such as with an
}
```
## Unused Dependency Notifications
The options `--json=unused-externs` and `--json=unused-externs-silent` in
conjunction with the `unused-crate-dependencies` lint will emit JSON structures
reporting any crate dependencies (specified with `--extern`) which never had any
symbols referenced. These are intended to be consumed by the build system which
can then emit diagnostics telling the user to remove the unused dependencies
from `Cargo.toml` (or whatever build-system file defines dependencies).
The JSON structure is:
```json
{
"lint_level": "deny", /* Level of the warning */
"unused_names": [
"foo" /* Names of unused crates, as specified with --extern foo=libfoo.rlib */
],
}
```
The warn/deny/forbid lint level (as defined either on the command line or in the
source) dictates the `lint_level` in the JSON. With `unused-externs`, a
`deny` or `forbid` level diagnostic will also cause `rustc` to exit with a
failure exit code.
`unused-externs-silent` will report the diagnostic the same way, but will not
cause `rustc` to exit with failure - it's up to the consumer to flag failure
appropriately. (This is needed by Cargo which shares the same dependencies
across multiple build targets, so it should only report an unused dependency if
its not used by any of the targets.)
[option-emit]: command-line-arguments.md#option-emit
[option-error-format]: command-line-arguments.md#option-error-format
[option-json]: command-line-arguments.md#option-json