Auto merge of #125116 - blyxyas:ignore-allowed-lints-final, r=cjgillot

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

Before this change, 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 ``@eval_always` = true` marker to label it as loadbearing. A loadbearing lint will never be filtered (it will always run)

Fixes #106983

clippy_lints/src/cognitive_complexity.rs

@@ -31,6 +31,7 @@ declare_clippy_lint! {
     pub COGNITIVE_COMPLEXITY,
     nursery,
     "functions that should be split up into multiple functions"
+    @eval_always = true
 }
 
 pub struct CognitiveComplexity {

clippy_lints/src/ctfe.rs

@@ -0,0 +1,40 @@
+use rustc_hir::def_id::LocalDefId;
+use rustc_hir::intravisit::FnKind;
+use rustc_hir::{Body, FnDecl};
+use rustc_lint::Level::Deny;
+use rustc_lint::{LateContext, LateLintPass, Lint};
+use rustc_session::declare_lint_pass;
+use rustc_span::Span;
+
+/// Ensures that Constant-time Function Evaluation is being done (specifically, MIR lint passes).
+/// As Clippy deactivates codegen, this lint ensures that CTFE (used in hard errors) is still ran.
+pub static CLIPPY_CTFE: &Lint = &Lint {
+    name: &"clippy::CLIPPY_CTFE",
+    default_level: Deny,
+    desc: "Ensure CTFE is being made",
+    edition_lint_opts: None,
+    report_in_external_macro: true,
+    future_incompatible: None,
+    is_externally_loaded: true,
+    crate_level_only: false,
+    eval_always: true,
+    ..Lint::default_fields_for_macro()
+};
+
+// No static CLIPPY_CTFE_INFO because we want this lint to be invisible
+
+declare_lint_pass! { ClippyCtfe => [CLIPPY_CTFE] }
+
+impl<'tcx> LateLintPass<'tcx> for ClippyCtfe {
+    fn check_fn(
+        &mut self,
+        cx: &LateContext<'_>,
+        _: FnKind<'tcx>,
+        _: &'tcx FnDecl<'tcx>,
+        _: &'tcx Body<'tcx>,
+        _: Span,
+        defid: LocalDefId,
+    ) {
+        cx.tcx.ensure().mir_drops_elaborated_and_const_checked(defid); // Lint
+    }
+}

clippy_lints/src/declare_clippy_lint.rs

@@ -9,6 +9,7 @@ macro_rules! declare_clippy_lint {
         $desc:literal,
         $version_expr:expr,
         $version_lit:literal
+        $(, $eval_always: literal)?
     ) => {
         rustc_session::declare_tool_lint! {
             $(#[doc = $lit])*
@@ -17,6 +18,7 @@ macro_rules! declare_clippy_lint {
             $category,
             $desc,
             report_in_external_macro:true
+            $(, @eval_always = $eval_always)?
         }
 
         pub(crate) static ${concat($lint_name, _INFO)}: &'static crate::LintInfo = &crate::LintInfo {
@@ -33,11 +35,12 @@ macro_rules! declare_clippy_lint {
         pub $lint_name:ident,
         restriction,
         $desc:literal
+        $(@eval_always = $eval_always: literal)?
     ) => {
         declare_clippy_lint! {@
             $(#[doc = $lit])*
             pub $lint_name, Allow, crate::LintCategory::Restriction, $desc,
-            Some($version), $version
+            Some($version), $version $(, $eval_always)?
         }
     };
     (
@@ -46,12 +49,12 @@ macro_rules! declare_clippy_lint {
         pub $lint_name:ident,
         style,
         $desc:literal
+        $(@eval_always = $eval_always: literal)?
     ) => {
         declare_clippy_lint! {@
             $(#[doc = $lit])*
             pub $lint_name, Warn, crate::LintCategory::Style, $desc,
-            Some($version), $version
-
+            Some($version), $version $(, $eval_always)?
         }
     };
     (
@@ -60,11 +63,12 @@ macro_rules! declare_clippy_lint {
         pub $lint_name:ident,
         correctness,
         $desc:literal
+        $(@eval_always = $eval_always: literal)?
     ) => {
         declare_clippy_lint! {@
             $(#[doc = $lit])*
             pub $lint_name, Deny, crate::LintCategory::Correctness, $desc,
-            Some($version), $version
+            Some($version), $version $(, $eval_always)?
 
         }
     };
@@ -74,11 +78,12 @@ macro_rules! declare_clippy_lint {
         pub $lint_name:ident,
         perf,
         $desc:literal
+        $(@eval_always = $eval_always: literal)?
     ) => {
         declare_clippy_lint! {@
             $(#[doc = $lit])*
             pub $lint_name, Warn, crate::LintCategory::Perf, $desc,
-            Some($version), $version
+            Some($version), $version $(, $eval_always)?
         }
     };
     (
@@ -87,11 +92,12 @@ macro_rules! declare_clippy_lint {
         pub $lint_name:ident,
         complexity,
         $desc:literal
+        $(@eval_always = $eval_always: literal)?
     ) => {
         declare_clippy_lint! {@
             $(#[doc = $lit])*
             pub $lint_name, Warn, crate::LintCategory::Complexity, $desc,
-            Some($version), $version
+            Some($version), $version $(, $eval_always)?
         }
     };
     (
@@ -100,11 +106,12 @@ macro_rules! declare_clippy_lint {
         pub $lint_name:ident,
         suspicious,
         $desc:literal
+        $(@eval_always = $eval_always: literal)?
     ) => {
         declare_clippy_lint! {@
             $(#[doc = $lit])*
             pub $lint_name, Warn, crate::LintCategory::Suspicious, $desc,
-            Some($version), $version
+            Some($version), $version $(, $eval_always)?
         }
     };
     (
@@ -113,11 +120,12 @@ macro_rules! declare_clippy_lint {
         pub $lint_name:ident,
         nursery,
         $desc:literal
+        $(@eval_always = $eval_always: literal)?
     ) => {
         declare_clippy_lint! {@
             $(#[doc = $lit])*
             pub $lint_name, Allow, crate::LintCategory::Nursery, $desc,
-            Some($version), $version
+            Some($version), $version $(, $eval_always)?
         }
     };
     (
@@ -126,11 +134,12 @@ macro_rules! declare_clippy_lint {
         pub $lint_name:ident,
         pedantic,
         $desc:literal
+        $(@eval_always = $eval_always: literal)?
     ) => {
         declare_clippy_lint! {@
             $(#[doc = $lit])*
             pub $lint_name, Allow, crate::LintCategory::Pedantic, $desc,
-            Some($version), $version
+            Some($version), $version $(, $eval_always)?
         }
     };
     (
@@ -139,11 +148,12 @@ macro_rules! declare_clippy_lint {
         pub $lint_name:ident,
         cargo,
         $desc:literal
+        $(@eval_always = $eval_always: literal)?
     ) => {
         declare_clippy_lint! {@
             $(#[doc = $lit])*
             pub $lint_name, Allow, crate::LintCategory::Cargo, $desc,
-            Some($version), $version
+            Some($version), $version $(, $eval_always)?
         }
     };
 

clippy_lints/src/lib.rs

@@ -65,6 +65,7 @@ extern crate clippy_utils;
 #[cfg_attr(feature = "internal", allow(clippy::missing_clippy_version_attribute))]
 mod utils;
 
+pub mod ctfe; // Very important lint, do not remove (rust#125116)
 pub mod declared_lints;
 pub mod deprecated_lints;
 
@@ -605,6 +606,8 @@ pub fn register_lints(store: &mut rustc_lint::LintStore, conf: &'static Conf) {
         });
     }
 
+    store.register_late_pass(|_| Box::new(ctfe::ClippyCtfe));
+
     store.register_late_pass(move |_| Box::new(operators::arithmetic_side_effects::ArithmeticSideEffects::new(conf)));
     store.register_late_pass(|_| Box::new(utils::dump_hir::DumpHir));
     store.register_late_pass(|_| Box::new(utils::author::Author));

tests/ui-internal/author.rs

@@ -1,3 +1,5 @@
+#![warn(clippy::author)]
+
 fn main() {
     #[clippy::author]
     let x: char = 0x45 as char;

tests/ui/no_lints.rs

@@ -0,0 +1,3 @@
+#![deny(clippy::all)]
+
+fn main() {}