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`

I open this PR to receive some feedback, mainly related to performance. We have lots of `Lock`s, `with_lock` and similar functions (also lots of cloning), so the filtering performance is not the best.

In an older iteration, instead of doing this in the parsing phase, we developed a visitor with the same function but without so many locks, would reverting to that change help? I'm not sure tbh.

Cargo.lock

@@ -4342,6 +4342,7 @@ 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

@@ -210,7 +210,7 @@ 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_lint/src/builtin.rs

@@ -73,6 +73,7 @@ use rustc_trait_selection::traits::{self, misc::type_allowed_to_implement_copy};
 
 use crate::nonstandard_style::{method_context, MethodLateContext};
 
+use std::default::Default;
 use std::fmt::Write;
 
 // hardwired lints from rustc_lint_defs
@@ -462,6 +463,7 @@ declare_lint! {
     report_in_external_macro
 }
 
+#[derive(Default)]
 pub struct MissingDoc;
 
 impl_lint_pass!(MissingDoc => [MISSING_DOCS]);
@@ -903,8 +905,8 @@ 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

@@ -316,6 +316,9 @@ 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/late.rs

@@ -325,6 +325,9 @@ impl LintPass for RuntimeCombinedLateLintPass<'_, '_> {
     fn name(&self) -> &'static str {
         panic!()
     }
+    fn get_lints(&self) -> crate::LintVec {
+        panic!()
+    }
 }
 
 macro_rules! impl_late_lint_pass {
@@ -360,13 +363,41 @@ 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_to_emit, lints_allowed) = &**tcx.lints_that_can_emit(());
+        // let lints_to_emit = &lints_that_can_emit.0;
+        // let lints_allowed = &lints_that_can_emit.1;
+
+        // Now, we'll filtered passes in a way that discards any lint that won't trigger.
+        // If any lint is a given pass is detected to be emitted, we will keep that pass.
+        // Otherwise, we don't
+        let mut filtered_passes: Vec<Box<dyn LateLintPass<'tcx>>> = passes
+            .into_iter()
+            .filter(|pass| {
+                let pass = LintPass::get_lints(pass);
+                pass.iter().any(|&lint| {
+                    let lint_name = &lint.name.to_lowercase()
+                        // Doing some calculations here to account for those separators
+                        [lint.name.find("::").unwrap_or(lint.name.len() - 2) + 2..]
+                        .to_string();
+                    lints_to_emit.contains(&lint_name)
+                        || (!lints_allowed.contains(&lint_name)
+                            && lint.default_level != crate::Level::Allow)
+                })
+            })
+            .collect();
+
+        filtered_passes.push(Box::new(builtin_lints));
+
+        let pass = RuntimeCombinedLateLintPass { passes: &mut filtered_passes[..] };
         late_lint_mod_inner(tcx, module_def_id, context, pass);
     }
 }

compiler/rustc_lint/src/levels.rs

@@ -15,7 +15,10 @@ use crate::{
 };
 use rustc_ast as ast;
 use rustc_ast_pretty::pprust;
-use rustc_data_structures::fx::FxIndexMap;
+use rustc_data_structures::{
+    fx::FxIndexMap,
+    sync::{join, Lock, Lrc},
+};
 use rustc_errors::{Diag, DiagMessage, LintDiagnostic, MultiSpan};
 use rustc_feature::{Features, GateIssue};
 use rustc_hir as hir;
@@ -151,6 +154,19 @@ fn lint_expectations(tcx: TyCtxt<'_>, (): ()) -> Vec<(LintExpectationId, LintExp
     builder.provider.expectations
 }
 
+/// Walk the whole crate collecting nodes where lint levels change
+/// (e.g. `#[allow]` attributes), and joins that list with the warn-by-default
+/// (and not allowed in the crate) and CLI lints. The returned value is a tuple
+/// of 1. The lints that will emit (or at least, should run), and 2.
+/// The lints that are allowed at the crate level and will not emit.
+pub fn lints_that_can_emit(tcx: TyCtxt<'_>, (): ()) -> Lrc<(Vec<String>, Vec<String>)> {
+    let mut visitor = LintLevelMinimum::new(tcx);
+    visitor.process_opts();
+    visitor.lint_level_minimums();
+
+    Lrc::new((visitor.lints_to_emit.into_inner(), visitor.lints_allowed.into_inner()))
+}
+
 #[instrument(level = "trace", skip(tcx), ret)]
 fn shallow_lint_levels_on(tcx: TyCtxt<'_>, owner: hir::OwnerId) -> ShallowLintLevelMap {
     let store = unerased_lint_store(tcx.sess);
@@ -253,7 +269,7 @@ impl LintLevelsProvider for LintLevelQueryMap<'_> {
     }
 }
 
-struct QueryMapExpectationsWrapper<'tcx> {
+pub(crate) struct QueryMapExpectationsWrapper<'tcx> {
     tcx: TyCtxt<'tcx>,
     /// HirId of the currently investigated element.
     cur: HirId,
@@ -450,6 +466,60 @@ impl<'tcx> Visitor<'tcx> for LintLevelsBuilder<'_, QueryMapExpectationsWrapper<'
     }
 }
 
+/// Visitor with the only function of visiting every item-like in a crate and
+/// computing the highest level that every lint gets put to.
+///
+/// E.g., if a crate has a global #![allow(lint)] attribute, but a single item
+/// uses #[warn(lint)], this visitor will set that lint level as `Warn`
+struct LintLevelMinimum<'tcx> {
+    tcx: TyCtxt<'tcx>,
+    /// The actual list of detected lints.
+    lints_to_emit: Lock<Vec<String>>,
+    lints_allowed: Lock<Vec<String>>,
+}
+
+impl<'tcx> LintLevelMinimum<'tcx> {
+    pub fn new(tcx: TyCtxt<'tcx>) -> Self {
+        Self {
+            tcx,
+            // That magic number is the current number of lints + some more for possible future lints
+            lints_to_emit: Lock::new(Vec::with_capacity(230)),
+            lints_allowed: Lock::new(Vec::with_capacity(100)),
+        }
+    }
+
+    fn process_opts(&mut self) {
+        for (lint, level) in &self.tcx.sess.opts.lint_opts {
+            if *level == Level::Allow {
+                self.lints_allowed.with_lock(|lints_allowed| lints_allowed.push(lint.to_string()));
+            } else {
+                self.lints_to_emit.with_lock(|lints_to_emit| lints_to_emit.push(lint.to_string()));
+            }
+        }
+    }
+
+    fn lint_level_minimums(&mut self) {
+        join(
+            || {
+                self.tcx.sess.psess.lints_that_can_emit.with_lock(|vec| {
+                    for lint_symbol in vec {
+                        self.lints_to_emit
+                            .with_lock(|lints_to_emit| lints_to_emit.push(lint_symbol.to_string()));
+                    }
+                });
+            },
+            || {
+                self.tcx.sess.psess.lints_allowed.with_lock(|vec| {
+                    for lint_symbol in vec {
+                        self.lints_allowed
+                            .with_lock(|lints_allowed| lints_allowed.push(lint_symbol.to_string()));
+                    }
+                });
+            },
+        );
+    }
+}
+
 pub struct LintLevelsBuilder<'s, P> {
     sess: &'s Session,
     features: &'s Features,
@@ -1133,7 +1203,8 @@ impl<'s, P: LintLevelsProvider> LintLevelsBuilder<'s, P> {
 }
 
 pub(crate) fn provide(providers: &mut Providers) {
-    *providers = Providers { shallow_lint_levels_on, lint_expectations, ..*providers };
+    *providers =
+        Providers { shallow_lint_levels_on, lint_expectations, lints_that_can_emit, ..*providers };
 }
 
 pub fn parse_lint_and_tool_name(lint_name: &str) -> (Option<Symbol>, &str) {

compiler/rustc_lint/src/lib.rs

@@ -30,6 +30,7 @@
 #![feature(rustdoc_internals)]
 #![feature(array_windows)]
 #![feature(box_patterns)]
+#![feature(box_into_inner)]
 #![feature(control_flow_enum)]
 #![feature(extract_if)]
 #![feature(if_let_guard)]
@@ -156,15 +157,15 @@ early_lint_methods!(
     [
         pub BuiltinCombinedEarlyLintPass,
         [
-            UnusedParens: UnusedParens::new(),
+            UnusedParens: UnusedParens::default(),
             UnusedBraces: UnusedBraces,
             UnusedImportBraces: UnusedImportBraces,
             UnsafeCode: UnsafeCode,
             SpecialModuleName: SpecialModuleName,
             AnonymousParameters: AnonymousParameters,
             EllipsisInclusiveRangePatterns: EllipsisInclusiveRangePatterns::default(),
             NonCamelCaseTypes: NonCamelCaseTypes,
-            DeprecatedAttr: DeprecatedAttr::new(),
+            DeprecatedAttr: DeprecatedAttr::default(),
             WhileTrue: WhileTrue,
             NonAsciiIdents: NonAsciiIdents,
             HiddenUnicodeCodepoints: HiddenUnicodeCodepoints,
@@ -545,23 +546,23 @@ fn register_builtins(store: &mut LintStore) {
 }
 
 fn register_internals(store: &mut LintStore) {
-    store.register_lints(&LintPassImpl::get_lints());
+    store.register_lints(&LintPassImpl::default().get_lints());
     store.register_early_pass(|| Box::new(LintPassImpl));
-    store.register_lints(&DefaultHashTypes::get_lints());
+    store.register_lints(&DefaultHashTypes::default().get_lints());
     store.register_late_mod_pass(|_| Box::new(DefaultHashTypes));
-    store.register_lints(&QueryStability::get_lints());
+    store.register_lints(&QueryStability::default().get_lints());
     store.register_late_mod_pass(|_| Box::new(QueryStability));
-    store.register_lints(&ExistingDocKeyword::get_lints());
+    store.register_lints(&ExistingDocKeyword::default().get_lints());
     store.register_late_mod_pass(|_| Box::new(ExistingDocKeyword));
-    store.register_lints(&TyTyKind::get_lints());
+    store.register_lints(&TyTyKind::default().get_lints());
     store.register_late_mod_pass(|_| Box::new(TyTyKind));
-    store.register_lints(&Diagnostics::get_lints());
+    store.register_lints(&Diagnostics::default().get_lints());
     store.register_late_mod_pass(|_| Box::new(Diagnostics));
-    store.register_lints(&BadOptAccess::get_lints());
+    store.register_lints(&BadOptAccess::default().get_lints());
     store.register_late_mod_pass(|_| Box::new(BadOptAccess));
-    store.register_lints(&PassByValue::get_lints());
+    store.register_lints(&PassByValue::default().get_lints());
     store.register_late_mod_pass(|_| Box::new(PassByValue));
-    store.register_lints(&SpanUseEqCtxt::get_lints());
+    store.register_lints(&SpanUseEqCtxt::default().get_lints());
     store.register_late_mod_pass(|_| Box::new(SpanUseEqCtxt));
     // FIXME(davidtwco): deliberately do not include `UNTRANSLATABLE_DIAGNOSTIC` and
     // `DIAGNOSTIC_OUTSIDE_OF_IMPL` here because `-Wrustc::internal` is provided to every crate and

compiler/rustc_lint/src/passes.rs

@@ -108,7 +108,7 @@ macro_rules! declare_combined_late_lint_pass {
 
             $v fn get_lints() -> $crate::LintVec {
                 let mut lints = Vec::new();
-                $(lints.extend_from_slice(&$pass::get_lints());)*
+                $(lints.extend_from_slice(&$pass::default().get_lints());)*
                 lints
             }
         }
@@ -122,6 +122,9 @@ macro_rules! declare_combined_late_lint_pass {
             fn name(&self) -> &'static str {
                 panic!()
             }
+            fn get_lints(&self) -> LintVec {
+                panic!()
+            }
         }
     )
 }
@@ -218,7 +221,7 @@ macro_rules! declare_combined_early_lint_pass {
 
             $v fn get_lints() -> $crate::LintVec {
                 let mut lints = Vec::new();
-                $(lints.extend_from_slice(&$pass::get_lints());)*
+                $(lints.extend_from_slice(&$pass::default().get_lints());)*
                 lints
             }
         }
@@ -232,6 +235,9 @@ macro_rules! declare_combined_early_lint_pass {
             fn name(&self) -> &'static str {
                 panic!()
             }
+            fn get_lints(&self) -> LintVec {
+                panic!()
+            }
         }
     )
 }

compiler/rustc_lint/src/types.rs

@@ -170,7 +170,7 @@ declare_lint! {
     "detects ambiguous wide pointer comparisons"
 }
 
-#[derive(Copy, Clone)]
+#[derive(Copy, Clone, Default)]
 pub struct TypeLimits {
     /// Id of the last visited negated expression
     negated_expr_id: Option<hir::HirId>,

compiler/rustc_lint/src/unused.rs

@@ -1018,8 +1018,8 @@ pub struct UnusedParens {
     parens_in_cast_in_lt: Vec<ast::NodeId>,
 }
 
-impl UnusedParens {
-    pub fn new() -> Self {
+impl Default for UnusedParens {
+    fn default() -> Self {
         Self { with_self_ty_parens: false, parens_in_cast_in_lt: Vec::new() }
     }
 }

compiler/rustc_lint_defs/src/lib.rs

@@ -870,6 +870,7 @@ pub type LintVec = Vec<&'static Lint>;
 
 pub trait LintPass {
     fn name(&self) -> &'static str;
+    fn get_lints(&self) -> LintVec;
 }
 
 /// Implements `LintPass for $ty` with the given list of `Lint` statics.
@@ -878,9 +879,7 @@ macro_rules! impl_lint_pass {
     ($ty:ty => [$($lint:expr),* $(,)?]) => {
         impl $crate::LintPass for $ty {
             fn name(&self) -> &'static str { stringify!($ty) }
-        }
-        impl $ty {
-            pub fn get_lints() -> $crate::LintVec { vec![$($lint),*] }
+            fn get_lints(&self) -> $crate::LintVec { vec![$($lint),*] }
         }
     };
 }
@@ -890,7 +889,18 @@ macro_rules! impl_lint_pass {
 #[macro_export]
 macro_rules! declare_lint_pass {
     ($(#[$m:meta])* $name:ident => [$($lint:expr),* $(,)?]) => {
-        $(#[$m])* #[derive(Copy, Clone)] pub struct $name;
+        $(#[$m])* #[derive(Copy, Clone, Default)] pub struct $name;
         $crate::impl_lint_pass!($name => [$($lint),*]);
     };
 }
+
+#[allow(rustc::lint_pass_impl_without_macro)]
+impl<P: LintPass + ?Sized> LintPass for Box<P> {
+    fn name(&self) -> &'static str {
+        (**self).name()
+    }
+
+    fn get_lints(&self) -> LintVec {
+        (**self).get_lints()
+    }
+}

compiler/rustc_middle/Cargo.toml

@@ -27,6 +27,7 @@ rustc_graphviz = { path = "../rustc_graphviz" }
 rustc_hir = { path = "../rustc_hir" }
 rustc_hir_pretty = { path = "../rustc_hir_pretty" }
 rustc_index = { path = "../rustc_index" }
+rustc_lint_defs = { path = "../rustc_lint_defs" }
 rustc_macros = { path = "../rustc_macros" }
 rustc_query_system = { path = "../rustc_query_system" }
 rustc_serialize = { path = "../rustc_serialize" }

compiler/rustc_middle/src/lint.rs

@@ -117,7 +117,7 @@ impl ShallowLintLevelMap {
     /// This lint level is not usable for diagnostics, it needs to be corrected by
     /// `reveal_actual_level` beforehand.
     #[instrument(level = "trace", skip(self, tcx), ret)]
-    fn probe_for_lint_level(
+    pub fn probe_for_lint_level(
         &self,
         tcx: TyCtxt<'_>,
         id: LintId,