detects redundant imports that can be eliminated.
for #117772 :
In order to facilitate review and modification, split the checking code and
removing redundant imports code into two PR.
reading both stdout & stderr is a common gotcha, you need to drain them
concurrently to avoid deadlocks. Not sure why I didn't do the right
thing from the start. Seems like I assumed the stderr is short? That's
not the case when cargo spams `compiling xyz` messages
These were the warnings previously:
```
warning: could not parse code block as Rust code
--> crates/stdx/src/lib.rs:137:9
|
137 | /// ∀ x in slice[..idx]: pred(x)
| _________^
138 | | /// && ∀ x in slice[idx..]: !pred(x)
| |____^
|
= note: error from rustc: unknown start of token: \u{2200}
warning: 1 warning emitted
warning: unresolved link to `package`
--> crates/base_db/src/input.rs:181:15
|
181 | /// it's [package].name, can be different for other project types or even
| ^^^^^^^ no item named `package` in scope
|
= note: `#[warn(broken_intra_doc_links)]` on by default
= help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
warning: unresolved link to `package`
--> crates/base_db/src/input.rs:181:15
|
181 | /// it's [package].name, can be different for other project types or even
| ^^^^^^^ no item named `package` in scope
|
= help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
warning: 2 warnings emitted
warning: unresolved link to `package`
--> crates/base_db/src/input.rs:181:15
|
181 | /// it's [package].name, can be different for other project types or even
| ^^^^^^^ no item named `package` in scope
|
= note: `#[warn(broken_intra_doc_links)]` on by default
= help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
warning: unresolved link to `package`
--> crates/base_db/src/input.rs:181:15
|
181 | /// it's [package].name, can be different for other project types or even
| ^^^^^^^ no item named `package` in scope
|
= help: to escape `[` and `]` characters, add '\' before them like `\[` or `\]`
warning: 2 warnings emitted
```
This does *not* fix the following warning, because it is actually rust
code and rustdoc is being over eager:
```
warning: Rust code block is empty
--> crates/parser/src/grammar.rs:16:5
|
16 | //! ```
| _____^
17 | | //! // test function_with_zero_parameters
18 | | //! // fn foo() {}
19 | | //! ```
| |_______^
|
help: mark blocks that do not contain Rust code as text
|
16 | //! ```text
| ^^^^^^^
```
https://github.com/rust-lang/rust/pull/79816 should make this
configurable so the warning can be `allow`ed.
