Auto merge of #125116 - blyxyas:ignore-allowed-lints-final, r=<try>

(Big performance change) Do not run lints that cannot emit

Before this lint, adding a lint was a difficult matter because it always had some overhead involved. This was because all lints would run, no matter their default level, or if the user had `#![allow]`ed them. This PR changes that. This change would improve both the Rust lint infrastructure and Clippy, but Clippy will see the most benefit, as it has about 900 registered lints (and growing!)

So yeah, with this little patch we filter all lints pre-linting, and remove any lint that is either:
- Manually `#![allow]`ed in the whole crate,
- Allowed in the command line, or
- Not manually enabled with `#[warn]` or similar, and its default level is `Allow`

As some lints **need** to run, this PR also adds **loadbearing lints**. On a lint declaration, you can use the `[loadbearing: true]` marker to label it as loadbearing. A loadbearing lint will never be filtered.

**Phase 1/2** Not all lints are being filtered, I'm still working on it, but this branch still gives us about a 2% improvement, so why not merge it already.

Fixes #106983

Cargo.lock

@@ -4033,6 +4033,7 @@ dependencies = [
  "rustc_hir",
  "rustc_hir_pretty",
  "rustc_index",
+ "rustc_lint_defs",
  "rustc_macros",
  "rustc_query_system",
  "rustc_serialize",

compiler/rustc_ast/src/attr/mod.rs

@@ -223,7 +223,7 @@ impl AttrItem {
         self.args.span().map_or(self.path.span, |args_span| self.path.span.to(args_span))
     }
 
-    fn meta_item_list(&self) -> Option<ThinVec<NestedMetaItem>> {
+    pub fn meta_item_list(&self) -> Option<ThinVec<NestedMetaItem>> {
         match &self.args {
             AttrArgs::Delimited(args) if args.delim == Delimiter::Parenthesis => {
                 MetaItemKind::list_from_tokens(args.tokens.clone())

compiler/rustc_interface/src/passes.rs

@@ -895,7 +895,7 @@ fn analysis(tcx: TyCtxt<'_>, (): ()) -> Result<()> {
                         tcx.ensure().check_mod_privacy(module);
                     });
                 });
-            }
+            } // { sess.time("mir_checking", || { tcx.hir().mir_for }) }
         );
 
         // This check has to be run after all lints are done processing. We don't

compiler/rustc_lint/src/builtin.rs

@@ -20,6 +20,7 @@
 //! If you define a new `LateLintPass`, you will also need to add it to the
 //! `late_lint_methods!` invocation in `lib.rs`.
 
+use std::default::Default;
 use std::fmt::Write;
 
 use ast::token::TokenKind;
@@ -73,6 +74,10 @@ use crate::{
     fluent_generated as fluent, EarlyContext, EarlyLintPass, LateContext, LateLintPass, Level,
     LintContext,
 };
+// use std::fmt::Write;
+
+// hardwired lints from rustc_lint_defs
+// pub use rustc_session::lint::builtin::*;
 
 declare_lint! {
     /// The `while_true` lint detects `while true { }`.
@@ -242,7 +247,8 @@ declare_lint! {
     /// behavior.
     UNSAFE_CODE,
     Allow,
-    "usage of `unsafe` code and other potentially unsound constructs"
+    "usage of `unsafe` code and other potentially unsound constructs",
+    [loadbearing: true]
 }
 
 declare_lint_pass!(UnsafeCode => [UNSAFE_CODE]);
@@ -390,6 +396,7 @@ declare_lint! {
     report_in_external_macro
 }
 
+#[derive(Default)]
 pub struct MissingDoc;
 
 impl_lint_pass!(MissingDoc => [MISSING_DOCS]);
@@ -830,8 +837,8 @@ pub struct DeprecatedAttr {
 
 impl_lint_pass!(DeprecatedAttr => []);
 
-impl DeprecatedAttr {
-    pub fn new() -> DeprecatedAttr {
+impl Default for DeprecatedAttr {
+    fn default() -> Self {
         DeprecatedAttr { depr_attrs: deprecated_attributes() }
     }
 }

compiler/rustc_lint/src/early.rs

@@ -312,6 +312,9 @@ impl LintPass for RuntimeCombinedEarlyLintPass<'_> {
     fn name(&self) -> &'static str {
         panic!()
     }
+    fn get_lints(&self) -> crate::LintVec {
+        panic!()
+    }
 }
 
 macro_rules! impl_early_lint_pass {

compiler/rustc_lint/src/internal.rs

@@ -421,7 +421,8 @@ declare_tool_lint! {
     pub rustc::UNTRANSLATABLE_DIAGNOSTIC,
     Deny,
     "prevent creation of diagnostics which cannot be translated",
-    report_in_external_macro: true
+    report_in_external_macro: true,
+    [loadbearing: true]
 }
 
 declare_tool_lint! {
@@ -434,7 +435,8 @@ declare_tool_lint! {
     pub rustc::DIAGNOSTIC_OUTSIDE_OF_IMPL,
     Deny,
     "prevent diagnostic creation outside of `Diagnostic`/`Subdiagnostic`/`LintDiagnostic` impls",
-    report_in_external_macro: true
+    report_in_external_macro: true,
+    [loadbearing: true]
 }
 
 declare_lint_pass!(Diagnostics => [UNTRANSLATABLE_DIAGNOSTIC, DIAGNOSTIC_OUTSIDE_OF_IMPL]);

compiler/rustc_lint/src/late.rs

@@ -24,13 +24,14 @@ use rustc_hir::def_id::{LocalDefId, LocalModDefId};
 use rustc_hir::{intravisit as hir_visit, HirId};
 use rustc_middle::hir::nested_filter;
 use rustc_middle::ty::{self, TyCtxt};
+use rustc_session::lint::builtin::HardwiredLints;
 use rustc_session::lint::LintPass;
 use rustc_session::Session;
 use rustc_span::Span;
 use tracing::debug;
 
 use crate::passes::LateLintPassObject;
-use crate::{LateContext, LateLintPass, LintStore};
+use crate::{LateContext, LateLintPass, LintId, LintStore};
 
 /// Extract the [`LintStore`] from [`Session`].
 ///
@@ -327,6 +328,9 @@ impl LintPass for RuntimeCombinedLateLintPass<'_, '_> {
     fn name(&self) -> &'static str {
         panic!()
     }
+    fn get_lints(&self) -> crate::LintVec {
+        panic!()
+    }
 }
 
 macro_rules! impl_late_lint_pass {
@@ -362,13 +366,33 @@ pub fn late_lint_mod<'tcx, T: LateLintPass<'tcx> + 'tcx>(
     // Note: `passes` is often empty. In that case, it's faster to run
     // `builtin_lints` directly rather than bundling it up into the
     // `RuntimeCombinedLateLintPass`.
-    let late_module_passes = &unerased_lint_store(tcx.sess).late_module_passes;
-    if late_module_passes.is_empty() {
+    let store = unerased_lint_store(tcx.sess);
+
+    if store.late_module_passes.is_empty() {
         late_lint_mod_inner(tcx, module_def_id, context, builtin_lints);
     } else {
-        let mut passes: Vec<_> = late_module_passes.iter().map(|mk_pass| (mk_pass)(tcx)).collect();
-        passes.push(Box::new(builtin_lints));
-        let pass = RuntimeCombinedLateLintPass { passes: &mut passes[..] };
+        let passes: Vec<_> =
+            store.late_module_passes.iter().map(|mk_pass| (mk_pass)(tcx)).collect();
+        // Filter unused lints
+        let lints_that_dont_need_to_run = tcx.lints_that_dont_need_to_run(());
+        let mut filtered_passes: Vec<Box<dyn LateLintPass<'tcx>>> = passes
+            .into_iter()
+            .filter(|pass| {
+                let lints = LintPass::get_lints(pass);
+                if lints.is_empty() {
+                    true
+                } else {
+                    lints
+                        .iter()
+                        .any(|lint| !lints_that_dont_need_to_run.contains(&LintId::of(lint)))
+                }
+            })
+            .collect();
+
+        filtered_passes.push(Box::new(builtin_lints));
+        filtered_passes.push(Box::new(HardwiredLints));
+
+        let pass = RuntimeCombinedLateLintPass { passes: &mut filtered_passes[..] };
         late_lint_mod_inner(tcx, module_def_id, context, pass);
     }
 }
@@ -399,7 +423,7 @@ fn late_lint_mod_inner<'tcx, T: LateLintPass<'tcx>>(
 
 fn late_lint_crate<'tcx>(tcx: TyCtxt<'tcx>) {
     // Note: `passes` is often empty.
-    let mut passes: Vec<_> =
+    let passes: Vec<_> =
         unerased_lint_store(tcx.sess).late_passes.iter().map(|mk_pass| (mk_pass)(tcx)).collect();
 
     if passes.is_empty() {
@@ -417,7 +441,30 @@ fn late_lint_crate<'tcx>(tcx: TyCtxt<'tcx>) {
         only_module: false,
     };
 
-    let pass = RuntimeCombinedLateLintPass { passes: &mut passes[..] };
+    let lints_that_dont_need_to_run = tcx.lints_that_dont_need_to_run(());
+
+    // dbg!(&lints_that_dont_need_to_run);
+    let mut filtered_passes: Vec<Box<dyn LateLintPass<'tcx>>> = passes
+        .into_iter()
+        .filter(|pass| {
+            let lints = LintPass::get_lints(pass);
+            !lints.iter().all(|lint| lints_that_dont_need_to_run.contains(&LintId::of(lint)))
+        })
+        .collect();
+
+    filtered_passes.push(Box::new(HardwiredLints));
+
+    // let mut filtered_passes: Vec<Box<dyn LateLintPass<'tcx>>> = passes
+    // .into_iter()
+    // .filter(|pass| {
+    //     let lints = LintPass::get_lints(pass);
+    //     lints.iter()
+    //         .any(|lint|
+    //             !lints_that_dont_need_to_run.contains(&LintId::of(lint)))
+    // }).collect();
+    //
+
+    let pass = RuntimeCombinedLateLintPass { passes: &mut filtered_passes[..] };
     late_lint_crate_inner(tcx, context, pass);
 }