Rollup merge of rust-lang#140794 - karolzwolak:allow-unused-doc-65464, r=davidtwco

mention lint group in default level lint note

### Summary

This PR updates lint diagnostics so that default-level notes now mention the lint group they belong to, if any.
Fixes: rust-lang#65464.

### Example

```rust
fn main() {
    let x = 5;
}
```

Before:

```
= note: `#[warn(unused_variables)]` on by default
```

After:

```
= note: `#[warn(unused_variables)]` (part of `#[warn(unused)]`) on by default
```

### Unchanged Cases

Messages remain the same when the lint level is explicitly set, e.g.:

* Attribute on the lint `#[warn(unused_variables)]`:

  ```
  note: the lint level is defined here
  LL | #[warn(unused_variables)]
     |        ^^^^^^^^^^^^^^^^
  ```
* Attribute on the group `#[warn(unused)]:`:

  ```
  = note: `#[warn(unused_variables)]` implied by `#[warn(unused)]`
  ```
* CLI option `-W unused`:

  ```
  = note: `-W unused-variables` implied by `-W unused`
  = help: to override `-W unused` add `#[allow(unused_variables)]`
  ```
* CLI option `-W unused-variables`:

  ```
  = note: requested on the command line with `-W unused-variables`
  ```

Author: jhpratt

compiler/rustc_lint/src/context.rs

@@ -24,7 +24,7 @@ use rustc_middle::ty::layout::{LayoutError, LayoutOfHelpers, TyAndLayout};
 use rustc_middle::ty::print::{PrintError, PrintTraitRefExt as _, Printer, with_no_trimmed_paths};
 use rustc_middle::ty::{self, GenericArg, RegisteredTools, Ty, TyCtxt, TypingEnv, TypingMode};
 use rustc_session::lint::{FutureIncompatibleInfo, Lint, LintBuffer, LintExpectationId, LintId};
-use rustc_session::{LintStoreMarker, Session};
+use rustc_session::{DynLintStore, Session};
 use rustc_span::edit_distance::find_best_match_for_names;
 use rustc_span::{Ident, Span, Symbol, sym};
 use tracing::debug;
@@ -62,7 +62,13 @@ pub struct LintStore {
     lint_groups: FxIndexMap<&'static str, LintGroup>,
 }
 
-impl LintStoreMarker for LintStore {}
+impl DynLintStore for LintStore {
+    fn lint_groups_iter(&self) -> Box<dyn Iterator<Item = rustc_session::LintGroup> + '_> {
+        Box::new(self.get_lint_groups().map(|(name, lints, is_externally_loaded)| {
+            rustc_session::LintGroup { name, lints, is_externally_loaded }
+        }))
+    }
+}
 
 /// The target of the `by_name` map, which accounts for renaming/deprecation.
 #[derive(Debug)]

compiler/rustc_middle/src/lint.rs

@@ -211,11 +211,28 @@ impl LintExpectation {
 }
 
 fn explain_lint_level_source(
+    sess: &Session,
     lint: &'static Lint,
     level: Level,
     src: LintLevelSource,
     err: &mut Diag<'_, ()>,
 ) {
+    // Find the name of the lint group that contains the given lint.
+    // Assumes the lint only belongs to one group.
+    let lint_group_name = |lint| {
+        let lint_groups_iter = sess.lint_groups_iter();
+        let lint_id = LintId::of(lint);
+        lint_groups_iter
+            .filter(|lint_group| !lint_group.is_externally_loaded)
+            .find(|lint_group| {
+                lint_group
+                    .lints
+                    .iter()
+                    .find(|lint_group_lint| **lint_group_lint == lint_id)
+                    .is_some()
+            })
+            .map(|lint_group| lint_group.name)
+    };
     let name = lint.name_lower();
     if let Level::Allow = level {
         // Do not point at `#[allow(compat_lint)]` as the reason for a compatibility lint
@@ -224,7 +241,15 @@ fn explain_lint_level_source(
     }
     match src {
         LintLevelSource::Default => {
-            err.note_once(format!("`#[{}({})]` on by default", level.as_str(), name));
+            let level_str = level.as_str();
+            match lint_group_name(lint) {
+                Some(group_name) => {
+                    err.note_once(format!("`#[{level_str}({name})]` (part of `#[{level_str}({group_name})]`) on by default"));
+                }
+                None => {
+                    err.note_once(format!("`#[{level_str}({name})]` on by default"));
+                }
+            }
         }
         LintLevelSource::CommandLine(lint_flag_val, orig_level) => {
             let flag = orig_level.to_cmd_flag();
@@ -427,7 +452,7 @@ pub fn lint_level(
             decorate(&mut err);
         }
 
-        explain_lint_level_source(lint, level, src, &mut err);
+        explain_lint_level_source(sess, lint, level, src, &mut err);
         err.emit()
     }
     lint_level_impl(sess, lint, level, span, Box::new(decorate))

compiler/rustc_session/src/session.rs

@@ -44,6 +44,7 @@ use crate::config::{
     SwitchWithOptPath,
 };
 use crate::filesearch::FileSearch;
+use crate::lint::LintId;
 use crate::parse::{ParseSess, add_feature_diagnostics};
 use crate::search_paths::SearchPath;
 use crate::{errors, filesearch, lint};
@@ -139,7 +140,10 @@ pub struct CompilerIO {
     pub temps_dir: Option<PathBuf>,
 }
 
-pub trait LintStoreMarker: Any + DynSync + DynSend {}
+pub trait DynLintStore: Any + DynSync + DynSend {
+    /// Provides a way to access lint groups without depending on `rustc_lint`
+    fn lint_groups_iter(&self) -> Box<dyn Iterator<Item = LintGroup> + '_>;
+}
 
 /// Represents the data associated with a compilation
 /// session for a single crate.
@@ -164,7 +168,7 @@ pub struct Session {
     pub code_stats: CodeStats,
 
     /// This only ever stores a `LintStore` but we don't want a dependency on that type here.
-    pub lint_store: Option<Arc<dyn LintStoreMarker>>,
+    pub lint_store: Option<Arc<dyn DynLintStore>>,
 
     /// Cap lint level specified by a driver specifically.
     pub driver_lint_caps: FxHashMap<lint::LintId, lint::Level>,
@@ -240,6 +244,12 @@ impl CodegenUnits {
     }
 }
 
+pub struct LintGroup {
+    pub name: &'static str,
+    pub lints: Vec<LintId>,
+    pub is_externally_loaded: bool,
+}
+
 impl Session {
     pub fn miri_unleashed_feature(&self, span: Span, feature_gate: Option<Symbol>) {
         self.miri_unleashed_features.lock().push((span, feature_gate));
@@ -596,6 +606,13 @@ impl Session {
             (&*self.target.staticlib_prefix, &*self.target.staticlib_suffix)
         }
     }
+
+    pub fn lint_groups_iter(&self) -> Box<dyn Iterator<Item = LintGroup> + '_> {
+        match self.lint_store {
+            Some(ref lint_store) => lint_store.lint_groups_iter(),
+            None => Box::new(std::iter::empty()),
+        }
+    }
 }
 
 // JUSTIFICATION: defn of the suggested wrapper fns

src/tools/clippy/tests/ui/checked_unwrap/simple_conditionals.stderr

@@ -330,7 +330,7 @@ LL |         if X.is_some() {
    |
    = note: for more information, see <https://doc.rust-lang.org/edition-guide/rust-2024/static-mut-references.html>
    = note: shared references to mutable statics are dangerous; it's undefined behavior if the static is mutated or if a mutable reference is created for it while the shared reference lives
-   = note: `#[deny(static_mut_refs)]` on by default
+   = note: `#[deny(static_mut_refs)]` (part of `#[deny(rust_2024_compatibility)]`) on by default
 
 error: aborting due to 36 previous errors
 

tests/ui/abi/unsupported.aarch64.stderr

@@ -165,7 +165,7 @@ LL | fn cdecl_ptr(f: extern "cdecl" fn()) {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #137018 <https://github.com/rust-lang/rust/issues/137018>
    = help: use `extern "C"` instead
-   = note: `#[warn(unsupported_calling_conventions)]` on by default
+   = note: `#[warn(unsupported_calling_conventions)]` (part of `#[warn(future_incompatible)]`) on by default
 
 warning: "cdecl" is not a supported ABI for the current target
   --> $DIR/unsupported.rs:104:1

tests/ui/abi/unsupported.arm.stderr

@@ -147,7 +147,7 @@ LL | fn cdecl_ptr(f: extern "cdecl" fn()) {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #137018 <https://github.com/rust-lang/rust/issues/137018>
    = help: use `extern "C"` instead
-   = note: `#[warn(unsupported_calling_conventions)]` on by default
+   = note: `#[warn(unsupported_calling_conventions)]` (part of `#[warn(future_incompatible)]`) on by default
 
 warning: "cdecl" is not a supported ABI for the current target
   --> $DIR/unsupported.rs:104:1

tests/ui/abi/unsupported.riscv32.stderr

@@ -159,7 +159,7 @@ LL | fn cdecl_ptr(f: extern "cdecl" fn()) {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #137018 <https://github.com/rust-lang/rust/issues/137018>
    = help: use `extern "C"` instead
-   = note: `#[warn(unsupported_calling_conventions)]` on by default
+   = note: `#[warn(unsupported_calling_conventions)]` (part of `#[warn(future_incompatible)]`) on by default
 
 warning: "cdecl" is not a supported ABI for the current target
   --> $DIR/unsupported.rs:104:1

tests/ui/abi/unsupported.riscv64.stderr

@@ -159,7 +159,7 @@ LL | fn cdecl_ptr(f: extern "cdecl" fn()) {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #137018 <https://github.com/rust-lang/rust/issues/137018>
    = help: use `extern "C"` instead
-   = note: `#[warn(unsupported_calling_conventions)]` on by default
+   = note: `#[warn(unsupported_calling_conventions)]` (part of `#[warn(future_incompatible)]`) on by default
 
 warning: "cdecl" is not a supported ABI for the current target
   --> $DIR/unsupported.rs:104:1

tests/ui/abi/unsupported.x64.stderr

@@ -141,7 +141,7 @@ LL | fn cdecl_ptr(f: extern "cdecl" fn()) {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #137018 <https://github.com/rust-lang/rust/issues/137018>
    = help: use `extern "C"` instead
-   = note: `#[warn(unsupported_calling_conventions)]` on by default
+   = note: `#[warn(unsupported_calling_conventions)]` (part of `#[warn(future_incompatible)]`) on by default
 
 warning: "cdecl" is not a supported ABI for the current target
   --> $DIR/unsupported.rs:104:1

tests/ui/abi/unsupported.x64_win.stderr

@@ -109,7 +109,7 @@ LL | fn stdcall_ptr(f: extern "stdcall" fn()) {
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: for more information, see issue #137018 <https://github.com/rust-lang/rust/issues/137018>
    = help: if you need `extern "stdcall"` on win32 and `extern "C"` everywhere else, use `extern "system"`
-   = note: `#[warn(unsupported_calling_conventions)]` on by default
+   = note: `#[warn(unsupported_calling_conventions)]` (part of `#[warn(future_incompatible)]`) on by default
 
 warning: "stdcall" is not a supported ABI for the current target
   --> $DIR/unsupported.rs:87:1