Auto merge of #50675 - csmoe:var_span, r=oli-obk

Reduce span highlighted code in unused_variables lint

Fixes #50472
- [X] reduce var span
- [ ] mark applicable

Before:
```
mut unused_mut_var
^^^^^^^^^^^^^^^^^^
```
After:
```
mut unused_mut_var
    ^^^^^^^^^^^^^^
```

src/librustc/hir/pat_util.rs

@@ -141,6 +141,15 @@ impl hir::Pat {
  }
  }
 
+ pub fn simple_span(&self) -> Option<Span> {
+ match self.node {
+ PatKind::Binding(hir::BindingAnnotation::Unannotated, _, ref path1, None) |
+ PatKind::Binding(hir::BindingAnnotation::Mutable, _, ref path1, None) =>
+ Some(path1.span),
+ _ => None,
+ }
+ }
+
  /// Return variants that are necessary to exist for the pattern to match.
  pub fn necessary_variants(&self) -> Vec<DefId> {
  let mut variants = vec![];

src/librustc/middle/liveness.rs

@@ -453,11 +453,11 @@ fn visit_arm<'a, 'tcx>(ir: &mut IrMaps<'a, 'tcx>, arm: &'tcx hir::Arm) {
  }
  }
 
- pat.each_binding(|bm, p_id, sp, path1| {
+ pat.each_binding(|bm, p_id, _sp, path1| {
  debug!("adding local variable {} from match with bm {:?}",
  p_id, bm);
  let name = path1.node;
- ir.add_live_node_for_node(p_id, VarDefNode(sp));
+ ir.add_live_node_for_node(p_id, VarDefNode(path1.span));
  ir.add_variable(Local(LocalInfo {
  id: p_id,
  name: name,
@@ -628,10 +628,10 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
  fn pat_bindings<F>(&mut self, pat: &hir::Pat, mut f: F) where
  F: FnMut(&mut Liveness<'a, 'tcx>, LiveNode, Variable, Span, NodeId),
  {
- pat.each_binding(|_bm, p_id, sp, _n| {
+ pat.each_binding(|_bm, p_id, sp, n| {
  let ln = self.live_node(p_id, sp);
- let var = self.variable(p_id, sp);
- f(self, ln, var, sp, p_id);
+ let var = self.variable(p_id, n.span);
+ f(self, ln, var, n.span, p_id);
  })
  }
 
@@ -1398,7 +1398,8 @@ fn check_local<'a, 'tcx>(this: &mut Liveness<'a, 'tcx>, local: &'tcx hir::Local)
  },
  None => {
  this.pat_bindings(&local.pat, |this, ln, var, sp, id| {
- this.warn_about_unused(sp, id, ln, var);
+ let span = local.pat.simple_span().unwrap_or(sp);
+ this.warn_about_unused(span, id, ln, var);
  })
  }
  }
@@ -1497,7 +1498,8 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
 
  fn warn_about_unused_args(&self, body: &hir::Body, entry_ln: LiveNode) {
  for arg in &body.arguments {
- arg.pat.each_binding(|_bm, p_id, sp, path1| {
+ arg.pat.each_binding(|_bm, p_id, _, path1| {
+ let sp = path1.span;
  let var = self.variable(p_id, sp);
  // Ignore unused self.
  let name = path1.node;
@@ -1541,6 +1543,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
 
  let suggest_underscore_msg = format!("consider using `_{}` instead",
  name);
+
  if is_assigned {
  self.ir.tcx
  .lint_node_note(lint::builtin::UNUSED_VARIABLES, id, sp,

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

@@ -35,6 +35,10 @@ fn main() {
  endless_and_singing: true
  };
 
+ let mut mut_unused_var = 1;
+
+ let (mut var, unused_var) = (1, 2);
+
  if let SoulHistory { corridors_of_light,
  mut hours_are_suns,
  endless_and_singing: true } = who_from_the_womb_remembered {

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

@@ -11,22 +11,40 @@ LL | #![warn(unused)] // UI tests pass `-A unused` (#43896)
  | ^^^^^^
  = note: #[warn(unused_variables)] implied by #[warn(unused)]
 
+warning: unused variable: `mut_unused_var`
+ --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:38:13
+ |
+LL | let mut mut_unused_var = 1;
+ | ^^^^^^^^^^^^^^ help: consider using `_mut_unused_var` instead
+
+warning: unused variable: `var`
+ --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:40:14
+ |
+LL | let (mut var, unused_var) = (1, 2);
+ | ^^^ help: consider using `_var` instead
+
+warning: unused variable: `unused_var`
+ --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:40:19
+ |
+LL | let (mut var, unused_var) = (1, 2);
+ | ^^^^^^^^^^ help: consider using `_unused_var` instead
+
 warning: unused variable: `corridors_of_light`
- --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:38:26
+ --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:42:26
  |
 LL | if let SoulHistory { corridors_of_light,
  | ^^^^^^^^^^^^^^^^^^ help: try ignoring the field: `corridors_of_light: _`
 
 warning: variable `hours_are_suns` is assigned to, but never used
- --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:39:26
+ --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:43:30
  |
 LL | mut hours_are_suns,
- | ^^^^^^^^^^^^^^^^^^
+ |  ^^^^^^^^^^^^^^
  |
  = note: consider using `_hours_are_suns` instead
 
 warning: value assigned to `hours_are_suns` is never read
- --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:41:9
+ --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:45:9
  |
 LL | hours_are_suns = false;
  | ^^^^^^^^^^^^^^
@@ -39,38 +57,61 @@ LL | #![warn(unused)] // UI tests pass `-A unused` (#43896)
  = note: #[warn(unused_assignments)] implied by #[warn(unused)]
 
 warning: unused variable: `case`
- --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:50:23
+ --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:54:23
  |
 LL | Large::Suit { case } => {}
  | ^^^^ help: try ignoring the field: `case: _`
 
 warning: unused variable: `case`
- --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:55:24
+ --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:59:24
  |
 LL | &Large::Suit { case } => {}
  | ^^^^ help: try ignoring the field: `case: _`
 
 warning: unused variable: `case`
- --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:60:27
+ --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:64:27
  |
 LL | box Large::Suit { case } => {}
  | ^^^^ help: try ignoring the field: `case: _`
 
 warning: unused variable: `case`
- --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:65:24
+ --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:69:24
  |
 LL | (Large::Suit { case },) => {}
  | ^^^^ help: try ignoring the field: `case: _`
 
 warning: unused variable: `case`
- --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:70:24
+ --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:74:24
  |
 LL | [Large::Suit { case }] => {}
  | ^^^^ help: try ignoring the field: `case: _`
 
 warning: unused variable: `case`
- --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:75:29
+ --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:79:29
  |
 LL | Tuple(Large::Suit { case }, ()) => {}
  | ^^^^ help: try ignoring the field: `case: _`
 
+warning: variable does not need to be mutable
+ --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:38:9
+ |
+LL | let mut mut_unused_var = 1;
+ | ----^^^^^^^^^^^^^^
+ | |
+ | help: remove this `mut`
+ |
+note: lint level defined here
+ --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:15:9
+ |
+LL | #![warn(unused)] // UI tests pass `-A unused` (#43896)
+ | ^^^^^^
+ = note: #[warn(unused_mut)] implied by #[warn(unused)]
+
+warning: variable does not need to be mutable
+ --> $DIR/issue-47390-unused-variable-in-struct-pattern.rs:40:10
+ |
+LL | let (mut var, unused_var) = (1, 2);
+ | ----^^^
+ | |
+ | help: remove this `mut`
+