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Rollup merge of #97739 - a2aaron:let_underscore, r=estebank

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Uplift the `let_underscore` lints from clippy into rustc.

This PR resolves #97241.

This PR adds three lints from clippy--`let_underscore_drop`, `let_underscore_lock`, and `let_underscore_must_use`, which are meant to capture likely-incorrect uses of `let _ = ...` bindings (in particular, doing this on a type with a non-trivial `Drop` causes the `Drop` to occur immediately, instead of at the end of the scope. For a type like `MutexGuard`, this effectively releases the lock immediately, which is almost certainly the wrong behavior)

In porting the lints from clippy I had to copy over a bunch of utility functions from `clippy_util` that these lints also relied upon. Is that the right approach?

Note that I've set the `must_use` and `drop` lints to Allow by default and set `lock` to Deny by default (this matches the same settings that clippy has). In talking with `@estebank` he informed me to do a Crater run (I am not sure what type of Crater run to request here--I think it's just "check only"?)

On the linked issue, there's some discussion about using `must_use` and `Drop` together as a heuristic for when to warn--I did not implement this yet.

r? `@estebank`
This commit is contained in:
Guillaume Gomez 2022-09-02 11:34:45 +02:00 • committed by GitHub
commit 07f43a1ca1
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5
compiler/rustc_lint/src/lib.rs
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@ -55,6 +55,7 @@ mod expect;
pub mod hidden_unicode_codepoints;
mod internal;
mod late;
mod let_underscore;
mod levels;
mod methods;
mod non_ascii_idents;
@ -86,6 +87,7 @@ use builtin::*;
use enum_intrinsics_non_enums::EnumIntrinsicsNonEnums;
use hidden_unicode_codepoints::*;
use internal::*;
use let_underscore::*;
use methods::*;
use non_ascii_idents::*;
use non_fmt_panic::NonPanicFmt;
@ -189,6 +191,7 @@ macro_rules! late_lint_mod_passes {
VariantSizeDifferences: VariantSizeDifferences,
BoxPointers: BoxPointers,
PathStatements: PathStatements,
LetUnderscore: LetUnderscore,
// Depends on referenced function signatures in expressions
UnusedResults: UnusedResults,
NonUpperCaseGlobals: NonUpperCaseGlobals,
@ -315,6 +318,8 @@ fn register_builtins(store: &mut LintStore, no_interleave_lints: bool) {
REDUNDANT_SEMICOLONS
);
add_lint_group!("let_underscore", LET_UNDERSCORE_DROP, LET_UNDERSCORE_LOCK);
add_lint_group!(
"rust_2018_idioms",
BARE_TRAIT_OBJECTS,