Suppress unused_mut if unused_variables is reported

compiler/rustc_borrowck/src/consumers.rs

@@ -34,6 +34,6 @@ pub fn get_body_with_borrowck_facts<'tcx>(
     tcx.infer_ctxt().with_opaque_type_inference(DefiningAnchor::Bind(def.did)).enter(|infcx| {
         let input_body: &Body<'_> = &input_body.borrow();
         let promoted: &IndexVec<_, _> = &promoted.borrow();
-        *super::do_mir_borrowck(&infcx, input_body, promoted, true).1.unwrap()
+        *super::do_mir_borrowck(&infcx, input_body, promoted, &None, true).1.unwrap()
     })
 }

compiler/rustc_borrowck/src/lib.rs

@@ -17,7 +17,7 @@ extern crate rustc_middle;
 #[macro_use]
 extern crate tracing;
 
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexSet};
 use rustc_data_structures::graph::dominators::Dominators;
 use rustc_errors::{Diagnostic, DiagnosticBuilder, ErrorGuaranteed};
 use rustc_hir as hir;
@@ -129,16 +129,22 @@ fn mir_borrowck<'tcx>(
     def: ty::WithOptConstParam<LocalDefId>,
 ) -> &'tcx BorrowCheckResult<'tcx> {
     let (input_body, promoted) = tcx.mir_promoted(def);
-    debug!("run query mir_borrowck: {}", tcx.def_path_str(def.did.to_def_id()));
+
+    let def_id = def.did.to_def_id();
+    debug!("run query mir_borrowck: {}", tcx.def_path_str(def_id));
+
     let hir_owner = tcx.hir().local_def_id_to_hir_id(def.did).owner;
 
+    let is_fn = matches!(tcx.hir().body_owner_kind(def.did), hir::BodyOwnerKind::Fn);
+    let unused_variables_spans = if is_fn { tcx.check_liveness(def_id) } else { &None };
+
     let opt_closure_req = tcx
         .infer_ctxt()
         .with_opaque_type_inference(DefiningAnchor::Bind(hir_owner))
         .enter(|infcx| {
             let input_body: &Body<'_> = &input_body.borrow();
             let promoted: &IndexVec<_, _> = &promoted.borrow();
-            do_mir_borrowck(&infcx, input_body, promoted, false).0
+            do_mir_borrowck(&infcx, input_body, promoted, unused_variables_spans, false).0
         });
     debug!("mir_borrowck done");
 
@@ -155,6 +161,7 @@ fn do_mir_borrowck<'a, 'tcx>(
     infcx: &InferCtxt<'a, 'tcx>,
     input_body: &Body<'tcx>,
     input_promoted: &IndexVec<Promoted, Body<'tcx>>,
+    unused_variables_spans: &Option<FxIndexSet<Span>>,
     return_body_with_facts: bool,
 ) -> (BorrowCheckResult<'tcx>, Option<Box<BodyWithBorrowckFacts<'tcx>>>) {
     let def = input_body.source.with_opt_param().as_local().unwrap();
@@ -428,6 +435,14 @@ fn do_mir_borrowck<'a, 'tcx>(
         }
 
         let mut_span = tcx.sess.source_map().span_until_non_whitespace(span);
+        let ident_span = span.with_lo(mut_span.hi());
+
+        // Suppress lints if we already reported unused variables
+        if let Some(unused_variables_spans) = unused_variables_spans {
+            if unused_variables_spans.contains(&ident_span) {
+                continue;
+            }
+        }
 
         tcx.emit_spanned_lint(UNUSED_MUT, lint_root, span, VarNeedNotMut { span: mut_span })
     }

compiler/rustc_lint_defs/src/builtin.rs

@@ -1558,6 +1558,7 @@ declare_lint! {
     ///
     /// ```rust
     /// let mut x = 5;
+    /// drop(x);
     /// ```
     ///
     /// {{produces}}

compiler/rustc_middle/src/query/mod.rs

@@ -830,7 +830,8 @@ rustc_queries! {
         desc { |tcx| "checking privacy in {}", describe_as_module(key, tcx) }
     }
 
-    query check_liveness(key: DefId) {
+    query check_liveness(key: DefId) -> Option<FxIndexSet<Span>> {
+        arena_cache
         desc { |tcx| "checking liveness of variables in {}", tcx.def_path_str(key) }
     }
 

compiler/rustc_passes/src/liveness.rs

@@ -85,7 +85,7 @@ use self::LiveNodeKind::*;
 use self::VarKind::*;
 
 use rustc_ast::InlineAsmOptions;
-use rustc_data_structures::fx::FxIndexMap;
+use rustc_data_structures::fx::{FxIndexMap, FxIndexSet};
 use rustc_errors::Applicability;
 use rustc_hir as hir;
 use rustc_hir::def::*;
@@ -99,6 +99,7 @@ use rustc_session::lint;
 use rustc_span::symbol::{kw, sym, Symbol};
 use rustc_span::{BytePos, Span};
 
+use std::cell::RefCell;
 use std::collections::VecDeque;
 use std::io;
 use std::io::prelude::*;
@@ -138,9 +139,9 @@ fn live_node_kind_to_string(lnk: LiveNodeKind, tcx: TyCtxt<'_>) -> String {
     }
 }
 
-fn check_liveness(tcx: TyCtxt<'_>, def_id: DefId) {
+fn check_liveness(tcx: TyCtxt<'_>, def_id: DefId) -> Option<FxIndexSet<Span>> {
     let local_def_id = match def_id.as_local() {
-        None => return,
+        None => return None,
         Some(def_id) => def_id,
     };
 
@@ -149,12 +150,12 @@ fn check_liveness(tcx: TyCtxt<'_>, def_id: DefId) {
     if let DefKind::Impl = tcx.def_kind(parent)
         && tcx.has_attr(parent.to_def_id(), sym::automatically_derived)
     {
-        return;
+        return None;
     }
 
     // Don't run unused pass for #[naked]
     if tcx.has_attr(def_id, sym::naked) {
-        return;
+        return None;
     }
 
     let mut maps = IrMaps::new(tcx);
@@ -182,6 +183,8 @@ fn check_liveness(tcx: TyCtxt<'_>, def_id: DefId) {
     lsets.visit_body(body);
     lsets.warn_about_unused_upvars(entry_ln);
     lsets.warn_about_unused_args(body, entry_ln);
+
+    Some(lsets.unused_variables_spans.into_inner())
 }
 
 pub fn provide(providers: &mut Providers) {
@@ -517,6 +520,8 @@ struct Liveness<'a, 'tcx> {
     // it probably doesn't now)
     break_ln: HirIdMap<LiveNode>,
     cont_ln: HirIdMap<LiveNode>,
+
+    unused_variables_spans: RefCell<FxIndexSet<Span>>,
 }
 
 impl<'a, 'tcx> Liveness<'a, 'tcx> {
@@ -541,6 +546,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
             exit_ln,
             break_ln: Default::default(),
             cont_ln: Default::default(),
+            unused_variables_spans: Default::default(),
         }
     }
 
@@ -1504,6 +1510,7 @@ impl<'tcx> Liveness<'_, 'tcx> {
                     }
                 } else {
                     if let Some(name) = self.should_warn(var) {
+                        self.unused_variables_spans.borrow_mut().insert(span);
                         self.ir.tcx.struct_span_lint_hir(
                             lint::builtin::UNUSED_VARIABLES,
                             var_hir_id,
@@ -1594,24 +1601,29 @@ impl<'tcx> Liveness<'_, 'tcx> {
                 if ln == self.exit_ln { false } else { self.assigned_on_exit(ln, var) };
 
             if is_assigned {
+                let spans = hir_ids_and_spans
+                    .into_iter()
+                    .map(|(_, _, ident_span)| ident_span)
+                    .collect::<Vec<_>>();
+                self.unused_variables_spans.borrow_mut().extend(&spans);
                 self.ir.tcx.struct_span_lint_hir(
                     lint::builtin::UNUSED_VARIABLES,
                     first_hir_id,
-                    hir_ids_and_spans
-                        .into_iter()
-                        .map(|(_, _, ident_span)| ident_span)
-                        .collect::<Vec<_>>(),
+                    spans,
                     |lint| {
                         lint.build(&format!("variable `{}` is assigned to, but never used", name))
                             .note(&format!("consider using `_{}` instead", name))
                             .emit();
                     },
                 )
             } else if can_remove {
+                let spans =
+                    hir_ids_and_spans.iter().map(|(_, pat_span, _)| *pat_span).collect::<Vec<_>>();
+                self.unused_variables_spans.borrow_mut().extend(&spans);
                 self.ir.tcx.struct_span_lint_hir(
                     lint::builtin::UNUSED_VARIABLES,
                     first_hir_id,
-                    hir_ids_and_spans.iter().map(|(_, pat_span, _)| *pat_span).collect::<Vec<_>>(),
+                    spans,
                     |lint| {
                         let mut err = lint.build(&format!("unused variable: `{}`", name));
                         err.multipart_suggestion(
@@ -1654,13 +1666,15 @@ impl<'tcx> Liveness<'_, 'tcx> {
                         )
                         .collect::<Vec<_>>();
 
+                    let spans = hir_ids_and_spans
+                        .iter()
+                        .map(|(_, pat_span, _)| *pat_span)
+                        .collect::<Vec<_>>();
+                    self.unused_variables_spans.borrow_mut().extend(&spans);
                     self.ir.tcx.struct_span_lint_hir(
                         lint::builtin::UNUSED_VARIABLES,
                         first_hir_id,
-                        hir_ids_and_spans
-                            .iter()
-                            .map(|(_, pat_span, _)| *pat_span)
-                            .collect::<Vec<_>>(),
+                        spans,
                         |lint| {
                             let mut err = lint.build(&format!("unused variable: `{}`", name));
                             err.multipart_suggestion(
@@ -1677,13 +1691,15 @@ impl<'tcx> Liveness<'_, 'tcx> {
                         .map(|(_, _, ident_span)| (ident_span, format!("_{}", name)))
                         .collect::<Vec<_>>();
 
+                    let spans = hir_ids_and_spans
+                        .iter()
+                        .map(|(_, _, ident_span)| *ident_span)
+                        .collect::<Vec<_>>();
+                    self.unused_variables_spans.borrow_mut().extend(&spans);
                     self.ir.tcx.struct_span_lint_hir(
                         lint::builtin::UNUSED_VARIABLES,
                         first_hir_id,
-                        hir_ids_and_spans
-                            .iter()
-                            .map(|(_, _, ident_span)| *ident_span)
-                            .collect::<Vec<_>>(),
+                        spans,
                         |lint| {
                             let mut err = lint.build(&format!("unused variable: `{}`", name));
                             if self.has_added_lit_match_name_span(&name, opt_body, &mut err) {

src/test/ui/lint/rfc-2383-lint-reason/expect_nested_lint_levels.rs

@@ -21,22 +21,22 @@ mod foo {
 }
 
 #[expect(
-    unused_mut,
+    unused_variables,
     //~^ WARNING this lint expectation is unfulfilled [unfulfilled_lint_expectations]
-    //~| NOTE this `expect` is overridden by a `warn` attribute before the `unused_mut` lint is triggered
-    reason = "this `expect` is overridden by a `warn` attribute before the `unused_mut` lint is triggered"
+    //~| NOTE this `expect` is overridden by a `warn` attribute before the `unused_variables` lint is triggered
+    reason = "this `expect` is overridden by a `warn` attribute before the `unused_variables` lint is triggered"
 )]
 mod oof {
     #[warn(
-        unused_mut,
+        unused_variables,
         //~^ NOTE the lint level is defined here
-        reason = "this overrides the previous `expect` lint level and warns about the `unused_mut` lint here"
+        reason = "this overrides the previous `expect` lint level and warns about the `unused_variables` lint here"
     )]
     fn bar() {
         let mut v = 0;
-        //~^ WARNING variable does not need to be mutable [unused_mut]
-        //~| NOTE this overrides the previous `expect` lint level and warns about the `unused_mut` lint here
-        //~| HELP remove this `mut`
+        //~^ WARNING unused variable: `v` [unused_variables]
+        //~| NOTE this overrides the previous `expect` lint level and warns about the `unused_variables` lint here
+        //~| HELP if this is intentional, prefix it with an underscore
     }
 }
 

src/test/ui/lint/rfc-2383-lint-reason/expect_nested_lint_levels.stderr

@@ -1,3 +1,16 @@
+warning: unused variable: `v`
+  --> $DIR/expect_nested_lint_levels.rs:36:17
+   |
+LL |         let mut v = 0;
+   |                 ^ help: if this is intentional, prefix it with an underscore: `_v`
+   |
+   = note: this overrides the previous `expect` lint level and warns about the `unused_variables` lint here
+note: the lint level is defined here
+  --> $DIR/expect_nested_lint_levels.rs:31:9
+   |
+LL |         unused_variables,
+   |         ^^^^^^^^^^^^^^^^
+
 error: unused variable: `this_is_my_function`
   --> $DIR/expect_nested_lint_levels.rs:48:9
    |
@@ -10,21 +23,6 @@ note: the lint level is defined here
 LL | #[forbid(unused_variables)]
    |          ^^^^^^^^^^^^^^^^
 
-warning: variable does not need to be mutable
-  --> $DIR/expect_nested_lint_levels.rs:36:13
-   |
-LL |         let mut v = 0;
-   |             ----^
-   |             |
-   |             help: remove this `mut`
-   |
-   = note: this overrides the previous `expect` lint level and warns about the `unused_mut` lint here
-note: the lint level is defined here
-  --> $DIR/expect_nested_lint_levels.rs:31:9
-   |
-LL |         unused_mut,
-   |         ^^^^^^^^^^
-
 warning: this lint expectation is unfulfilled
   --> $DIR/expect_nested_lint_levels.rs:7:5
    |
@@ -37,10 +35,10 @@ LL |     unused_mut,
 warning: this lint expectation is unfulfilled
   --> $DIR/expect_nested_lint_levels.rs:24:5
    |
-LL |     unused_mut,
-   |     ^^^^^^^^^^
+LL |     unused_variables,
+   |     ^^^^^^^^^^^^^^^^
    |
-   = note: this `expect` is overridden by a `warn` attribute before the `unused_mut` lint is triggered
+   = note: this `expect` is overridden by a `warn` attribute before the `unused_variables` lint is triggered
 
 warning: this lint expectation is unfulfilled
   --> $DIR/expect_nested_lint_levels.rs:43:10

src/test/ui/lint/unused/issue-47390-unused-variable-in-struct-pattern.rs

@@ -32,12 +32,10 @@ fn main() {
 
     let mut mut_unused_var = 1;
     //~^ WARNING unused variable: `mut_unused_var`
-    //~| WARNING variable does not need to be mutable
 
     let (mut var, unused_var) = (1, 2);
     //~^ WARNING unused variable: `var`
     //~| WARNING unused variable: `unused_var`
-    //~| WARNING variable does not need to be mutable
     // NOTE: `var` comes after `unused_var` lexicographically yet the warning
     // for `var` will be emitted before the one for `unused_var`. We use an
     // `IndexMap` to ensure this is the case instead of a `BTreeMap`.