Rename `unused_loop_label` to `unused_label` and fix/clean up lint logic

src/librustc_lint/lib.rs

@@ -110,7 +110,7 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
 
     add_early_builtin_with_new!(sess,
                                 DeprecatedAttr,
-                                UnusedLoopLabel,
+                                UnusedLabel,
                                 );
 
     add_builtin!(sess,
@@ -178,8 +178,8 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
                     UNUSED_DOC_COMMENT,
                     UNUSED_EXTERN_CRATES,
                     UNUSED_FEATURES,
-                    UNUSED_PARENS,
-                    UNUSED_LOOP_LABEL);
+                    UNUSED_LABEL,
+                    UNUSED_PARENS);
 
     add_lint_group!(sess,
                     "rust_2018_idioms",

src/librustc_lint/unused.rs

@@ -25,8 +25,6 @@
 
 use rustc::hir;
 
-use std::vec;
-
 declare_lint! {
     pub UNUSED_MUST_USE,
     Warn,
@@ -468,41 +466,38 @@ fn check_expr(&mut self, cx: &LateContext, e: &hir::Expr) {
 }
 
 declare_lint! {
-    pub(super) UNUSED_LOOP_LABEL,
+    pub(super) UNUSED_LABEL,
     Warn,
-    "warns on unused labels for loops"
+    "warns on unused labels"
 }
 
 #[derive(Clone)]
-pub struct UnusedLoopLabel(pub vec::Vec<ast::Label>);
+pub struct UnusedLabel(pub Vec<ast::Label>);
 
-impl UnusedLoopLabel {
+impl UnusedLabel {
     pub fn new() -> Self {
-        UnusedLoopLabel(vec![])
+        UnusedLabel(vec![])
     }
 }
 
-impl LintPass for UnusedLoopLabel {
+impl LintPass for UnusedLabel {
     fn get_lints(&self) -> LintArray {
-        lint_array!(UNUSED_LOOP_LABEL)
+        lint_array!(UNUSED_LABEL)
     }
 }
 
-impl EarlyLintPass for UnusedLoopLabel {
+impl EarlyLintPass for UnusedLabel {
     fn check_expr(&mut self, _: &EarlyContext, expr: &ast::Expr) {
         match expr.node {
-            ast::ExprKind::While(_, _, Some(ref label))
-            | ast::ExprKind::WhileLet(_, _, _, Some(ref label))
-            | ast::ExprKind::ForLoop(_, _, _, Some(ref label))
-            | ast::ExprKind::Loop(_, Some(ref label)) => {
-                self.0.push(*label);
+            ast::ExprKind::While(_, _, Some(label))
+            | ast::ExprKind::WhileLet(_, _, _, Some(label))
+            | ast::ExprKind::ForLoop(_, _, _, Some(label))
+            | ast::ExprKind::Loop(_, Some(label)) => {
+                self.0.push(label);
             }
-            ast::ExprKind::Break(Some(ref label), _) | ast::ExprKind::Continue(Some(ref label)) => {
-                'remove_used_label: for i in (0..self.0.len()).rev() {
-                    if self.0.get(i).unwrap().ident.name == label.ident.name {
-                        self.0.remove(i);
-                        break 'remove_used_label;
-                    }
+            ast::ExprKind::Break(Some(label), _) | ast::ExprKind::Continue(Some(label)) => {
+                if let Some(index) = self.0.iter().rposition(|&l| l.ident == label.ident) {
+                    self.0.remove(index);
                 }
             }
             _ => {}
@@ -511,17 +506,17 @@ fn check_expr(&mut self, _: &EarlyContext, expr: &ast::Expr) {
 
     fn check_expr_post(&mut self, ctxt: &EarlyContext, expr: &ast::Expr) {
         match expr.node {
-            ast::ExprKind::While(_, _, Some(ref label))
-            | ast::ExprKind::WhileLet(_, _, _, Some(ref label))
-            | ast::ExprKind::ForLoop(_, _, _, Some(ref label))
-            | ast::ExprKind::Loop(_, Some(ref label)) => if !self.0.is_empty() {
-                {
-                    let unused_label = self.0.last().unwrap();
-                    if label.ident.name == unused_label.ident.name {
-                        ctxt.span_lint(UNUSED_LOOP_LABEL, label.ident.span, "unused loop label");
+            ast::ExprKind::While(_, _, Some(label))
+            | ast::ExprKind::WhileLet(_, _, _, Some(label))
+            | ast::ExprKind::ForLoop(_, _, _, Some(label))
+            | ast::ExprKind::Loop(_, Some(label)) => {
+                if let Some(unused_label) = self.0.pop() {
+                    if label.ident == unused_label.ident {
+                        ctxt.span_lint(UNUSED_LABEL, label.ident.span, "unused label");
+                    } else {
+                        self.0.push(unused_label);
                     }
                 }
-                self.0.pop();
             },
             _ => {}
         }

src/test/ui/lint/unused_label.rs

@@ -13,20 +13,20 @@
 // within nested loops
 
 // compile-pass
-// compile-flags: -W unused_loop_label
+// compile-flags: -W unused-label
 
 fn main() {
     'unused_while_label: while 0 == 0 {
-        //~^ WARN unused loop label
+        //~^ WARN unused label
     }
 
     let opt = Some(0);
     'unused_while_let_label: while let Some(_) = opt {
-        //~^ WARN unused loop label
+        //~^ WARN unused label
     }
 
     'unused_for_label: for _ in 0..10 {
-        //~^ WARN unused loop label
+        //~^ WARN unused label
     }
 
     'used_loop_label: loop {
@@ -42,14 +42,14 @@ fn main() {
 
     'used_loop_label_outer_2: loop {
         'unused_loop_label_inner_2: loop {
-            //~^ WARN unused loop label
+            //~^ WARN unused label
             break 'used_loop_label_outer_2;
         }
     }
 
     'unused_loop_label_outer_3: loop {
+        //~^ WARN unused label
         'used_loop_label_inner_3: loop {
-            //~^ WARN unused loop label
             break 'used_loop_label_inner_3;
         }
     }
@@ -57,6 +57,6 @@ fn main() {
     // This is diverging, so put it at the end so we don't get
     // unreachable_code errors everywhere else
     'unused_loop_label: loop {
-        //~^ WARN unused loop label
+        //~^ WARN unused label
     }
 }

src/test/ui/lint/unused_label.stderr

@@ -25,13 +25,13 @@ LL |         'unused_loop_label_inner_2: loop {
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused label
-  --> $DIR/unused_label.rs:50:9
+  --> $DIR/unused_label.rs:50:5
    |
 LL |     'unused_loop_label_outer_3: loop {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: unused label
-  --> $DIR/unused_label.rs:52:5
+  --> $DIR/unused_label.rs:59:5
    |
 LL |     'unused_loop_label: loop {
    |     ^^^^^^^^^^^^^^^^^^