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

Add information about group a lint belongs to

# Description

Fixes: rust-lang#65464

## Changes Made
- Extended the default lint settings message to include the lint group they belong to
- Modified the proposed fix message wording from "part of" to "implied by" for better accuracy
  - Old message: `` `#[warn(unused_variables)]` (part of `#[warn(unused)]`) on by default ``
  - New message: `` `#[warn(unused_variables)]` (implied by `#[warn(unused)]`) on by default ``

## Rationale
1. The new wording ("implied by") better reflects the actual relationship between lint groups and their members
2. It maintains consistency with messages shown when manually setting lint levels
3. The change helps users understand the hierarchy of lint settings

## Implementation Notes
- Only affects messages for default lint levels (not shown when levels are overridden)
- External lints remain unchanged (potential discussion point for future changes)

## Examples

### Case 1: Unchanged behavior when lint level is overridden
```rust
#[deny(unused)]
fn main() {
    let x = 5;
}
```
Result:
```
note: the lint level is defined here
 --> src/main.rs:1:8
  |
1 | #[deny(unused)]
  |        ^^^^^^
  = note: `#[deny(unused_variables)]` implied by `#[deny(unused)]`
```

### Case 2: Changed behavior for default lint levels
```rust
fn main() {
    let x = 5;
}
```
New output:
```
= note: `#[warn(unused_variables)]` (part of `#[warn(unused)]`) on by default
```
Previous output:
```
= note: `#[warn(unused_variables)]` on by default
```

## Discussion Points
- Should we extend this change to external lints as well?
- Is "part of" the most accurate terminology?
- Doesn't this additional info bloat the message? Perhaps a clippy lint suggesting overriding a whole group instead of a few lints manually would be better

Author: Zalathar

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