Revert "Add lint checks for unused loop labels"

This functionality is being reimplemented in the resolver phase

This reverts commit 503a69e844970476b27bf1ac7be951bb22194f50.

Author: kylestach

src/librustc_lint/lib.rs

@@ -110,7 +110,6 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
 
     add_early_builtin_with_new!(sess,
                                 DeprecatedAttr,
-                                UnusedLabel,
                                 );
 
     add_builtin!(sess,
@@ -178,7 +177,6 @@ pub fn register_builtins(store: &mut lint::LintStore, sess: Option<&Session>) {
                     UNUSED_DOC_COMMENT,
                     UNUSED_EXTERN_CRATES,
                     UNUSED_FEATURES,
-                    UNUSED_LABEL,
                     UNUSED_PARENS);
 
     add_lint_group!(sess,

src/librustc_lint/unused.rs

@@ -464,61 +464,3 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnusedAllocation {
         }
     }
 }
-
-declare_lint! {
-    pub(super) UNUSED_LABEL,
-    Warn,
-    "warns on unused labels"
-}
-
-#[derive(Clone)]
-pub struct UnusedLabel(pub Vec<(ast::Label, bool)>);
-
-impl UnusedLabel {
-    pub fn new() -> Self {
-        UnusedLabel(vec![])
-    }
-}
-
-impl LintPass for UnusedLabel {
-    fn get_lints(&self) -> LintArray {
-        lint_array!(UNUSED_LABEL)
-    }
-}
-
-impl EarlyLintPass for UnusedLabel {
-    fn check_expr(&mut self, _: &EarlyContext, expr: &ast::Expr) {
-        match expr.node {
-            ast::ExprKind::While(_, _, Some(label))
-            | ast::ExprKind::WhileLet(_, _, _, Some(label))
-            | ast::ExprKind::ForLoop(_, _, _, Some(label))
-            | ast::ExprKind::Loop(_, Some(label)) => {
-                self.0.push((label, false));
-            }
-            ast::ExprKind::Break(Some(label), _) | ast::ExprKind::Continue(Some(label)) => {
-                if let Some((_, ref mut was_used)) =
-                    self.0.iter_mut().rev().find(|(l, _)| label == *l)
-                {
-                    *was_used = true;
-                }
-            }
-            _ => {}
-        }
-    }
-
-    fn check_expr_post(&mut self, ctxt: &EarlyContext, expr: &ast::Expr) {
-        match expr.node {
-            ast::ExprKind::While(_, _, Some(label))
-            | ast::ExprKind::WhileLet(_, _, _, Some(label))
-            | ast::ExprKind::ForLoop(_, _, _, Some(label))
-            | ast::ExprKind::Loop(_, Some(label)) => {
-                if let Some((_, was_used)) = self.0.pop() {
-                    if !was_used {
-                        ctxt.span_lint(UNUSED_LABEL, label.ident.span, "unused label");
-                    }
-                }
-            }
-            _ => {}
-        }
-    }
-}

src/librustc_mir/interpret/eval_context.rs

@@ -1705,7 +1705,7 @@ impl<'a, 'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> EvalContext<'a, 'mir, 'tcx, M
             let mut trace_text = "\n\nAn error occurred in miri:\n".to_string();
             backtrace.resolve();
             write!(trace_text, "backtrace frames: {}\n", backtrace.frames().len()).unwrap();
-            for (i, frame) in backtrace.frames().iter().enumerate() {
+            'frames: for (i, frame) in backtrace.frames().iter().enumerate() {
                 if frame.symbols().is_empty() {
                     write!(trace_text, "{}: no symbols\n", i).unwrap();
                 }