Auto merge of rust-lang#132666 - dingxiangfei2009:skip-if-let-rescope-lint, r=compiler-errors

Skip `if-let-rescope` lint unless requested by migration

Tracked by rust-lang#124085
Related to rust-lang#131984 (comment)

Given that `if-let-rescope` is a lint to be enabled globally by an edition migration, there is no point in extracting the precise lint level on the HIR expression. This mitigates the performance regression discovered by the earlier perf-run.

cc `@Kobzol` `@rylev` `@traviscross` I propose a `rust-timer` run to measure how much performance that we can recover from the mitigation. 🙇

Author: bors

compiler/rustc_lint/src/if_let_rescope.rs

@@ -9,7 +9,7 @@ use rustc_errors::{
 use rustc_hir::{self as hir, HirIdSet};
 use rustc_macros::LintDiagnostic;
 use rustc_middle::ty::TyCtxt;
-use rustc_session::lint::{FutureIncompatibilityReason, Level};
+use rustc_session::lint::{FutureIncompatibilityReason, LintId};
 use rustc_session::{declare_lint, impl_lint_pass};
 use rustc_span::Span;
 use rustc_span::edition::Edition;
@@ -245,12 +245,12 @@ impl_lint_pass!(
 
 impl<'tcx> LateLintPass<'tcx> for IfLetRescope {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'tcx>) {
-        if expr.span.edition().at_least_rust_2024() {
-            return;
-        }
-        if let (Level::Allow, _) = cx.tcx.lint_level_at_node(IF_LET_RESCOPE, expr.hir_id) {
+        if expr.span.edition().at_least_rust_2024()
+            || cx.tcx.lints_that_dont_need_to_run(()).contains(&LintId::of(IF_LET_RESCOPE))
+        {
             return;
         }
+
         if let hir::ExprKind::Loop(block, _label, hir::LoopSource::While, _span) = expr.kind
             && let Some(value) = block.expr
             && let hir::ExprKind::If(cond, _conseq, _alt) = value.kind
@@ -290,7 +290,6 @@ struct IfLetRescopeLint {
     rewrite: Option<IfLetRescopeRewrite>,
 }
 
-// #[derive(Subdiagnostic)]
 struct IfLetRescopeRewrite {
     match_heads: Vec<SingleArmMatchBegin>,
     consequent_heads: Vec<ConsequentRewrite>,