Auto merge of #96296 - cjgillot:remove-label-lt-shadow, r=petrochenkov

Remove label/lifetime shadowing warnings

This PR removes some pre-1.0 shadowing warnings for labels and lifetimes.

The current behaviour of the compiler is to warn
* labels that shadow unrelated labels in the same function --> removed
```rust
'a: loop {}
'a: loop {} // STOP WARNING
```

* labels that shadow enclosing labels --> kept, but only if shadowing is hygienic
```rust
'a: loop {
  'a: loop {} // KEEP WARNING
}
```

* labels that shadow lifetime --> removed
```rust
fn foo<'a>() {
  'a: loop {} // STOP WARNING
}
```

* lifetimes that shadow labels --> removed
```rust
'a: loop {
  let b = Box::new(|x: &i8| *x) as Box<dyn for <'a> Fn(&'a i8) -> i8>; // STOP WARNING
}
```

* lifetimes that shadow lifetimes --> kept
```rust
fn foo<'a>() {
  let b = Box::new(|x: &i8| *x) as Box<dyn for <'a> Fn(&'a i8) -> i8>; // KEEP WARNING
}
```

Closes #31745.

-----

From `@petrochenkov` in #95781 (comment)
> I think we should remove these silly checks entirely.
> They were introduced long time ago in case some new language features appear and require this space.
> Now we have another mechanism for such language changes - editions, and if "lifetimes in expressions" or something like that needs to be introduced it could be introduced as an edition change.
> However, there was no plans to introduce anything like for years, so it's unlikely that even the edition mechanism will be necessary.

r? rust-lang/lang

Author: bors

compiler/rustc_ast_lowering/src/lib.rs

@@ -1848,14 +1848,15 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     fn lower_generic_param(&mut self, param: &GenericParam) -> hir::GenericParam<'hir> {
         let (name, kind) = match param.kind {
             GenericParamKind::Lifetime => {
-                let param_name = if param.ident.name == kw::StaticLifetime
-                    || param.ident.name == kw::UnderscoreLifetime
-                {
-                    ParamName::Error
-                } else {
-                    let ident = self.lower_ident(param.ident);
-                    ParamName::Plain(ident)
-                };
+                // AST resolution emitted an error on those parameters, so we lower them using
+                // `ParamName::Error`.
+                let param_name =
+                    if let Some(LifetimeRes::Error) = self.resolver.get_lifetime_res(param.id) {
+                        ParamName::Error
+                    } else {
+                        let ident = self.lower_ident(param.ident);
+                        ParamName::Plain(ident)
+                    };
                 let kind =
                     hir::GenericParamKind::Lifetime { kind: hir::LifetimeParamKind::Explicit };
 
@@ -1880,10 +1881,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 )
             }
         };
-        let name = match name {
-            hir::ParamName::Plain(ident) => hir::ParamName::Plain(self.lower_ident(ident)),
-            name => name,
-        };
 
         let hir_id = self.lower_node_id(param.id);
         self.lower_attrs(hir_id, &param.attrs);

compiler/rustc_error_codes/src/error_codes/E0263.md

@@ -1,8 +1,10 @@
+#### Note: this error code is no longer emitted by the compiler.
+
 A lifetime was declared more than once in the same scope.
 
 Erroneous code example:
 
-```compile_fail,E0263
+```compile_fail,E0403
 fn foo<'a, 'b, 'a>(x: &'a str, y: &'b str, z: &'a str) { // error!
 }
 ```

compiler/rustc_resolve/src/late.rs

@@ -172,6 +172,23 @@ impl RibKind<'_> {
             AssocItemRibKind | ItemRibKind(_) | ForwardGenericParamBanRibKind => true,
         }
     }
+
+    /// This rib forbids referring to labels defined in upwards ribs.
+    fn is_label_barrier(self) -> bool {
+        match self {
+            NormalRibKind | MacroDefinition(..) => false,
+
+            AssocItemRibKind
+            | ClosureOrAsyncRibKind
+            | FnItemRibKind
+            | ItemRibKind(..)
+            | ConstantItemRibKind(..)
+            | ModuleRibKind(..)
+            | ForwardGenericParamBanRibKind
+            | ConstParamTyRibKind
+            | InlineAsmSymRibKind => true,
+        }
+    }
 }
 
 /// A single local scope.
@@ -732,7 +749,7 @@ impl<'a: 'ast, 'ast> Visitor<'ast> for LateResolutionVisitor<'a, '_, 'ast> {
         // Create a value rib for the function.
         self.with_rib(ValueNS, rib_kind, |this| {
             // Create a label rib for the function.
-            this.with_label_rib(rib_kind, |this| {
+            this.with_label_rib(FnItemRibKind, |this| {
                 let async_node_id = fn_kind.header().and_then(|h| h.asyncness.opt_return_id());
 
                 if let FnKind::Fn(_, _, _, _, generics, _) = fn_kind {
@@ -1531,13 +1548,9 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
 
     /// Searches the current set of local scopes for labels. Returns the `NodeId` of the resolved
     /// label and reports an error if the label is not found or is unreachable.
-    fn resolve_label(&mut self, mut label: Ident) -> Option<NodeId> {
+    fn resolve_label(&mut self, mut label: Ident) -> Result<(NodeId, Span), ResolutionError<'a>> {
         let mut suggestion = None;
 
-        // Preserve the original span so that errors contain "in this macro invocation"
-        // information.
-        let original_span = label.span;
-
         for i in (0..self.label_ribs.len()).rev() {
             let rib = &self.label_ribs[i];
 
@@ -1553,18 +1566,13 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
             if let Some((ident, id)) = rib.bindings.get_key_value(&ident) {
                 let definition_span = ident.span;
                 return if self.is_label_valid_from_rib(i) {
-                    Some(*id)
+                    Ok((*id, definition_span))
                 } else {
-                    self.report_error(
-                        original_span,
-                        ResolutionError::UnreachableLabel {
-                            name: label.name,
-                            definition_span,
-                            suggestion,
-                        },
-                    );
-
-                    None
+                    Err(ResolutionError::UnreachableLabel {
+                        name: label.name,
+                        definition_span,
+                        suggestion,
+                    })
                 };
             }
 
@@ -1573,34 +1581,16 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
             suggestion = suggestion.or_else(|| self.suggestion_for_label_in_rib(i, label));
         }
 
-        self.report_error(
-            original_span,
-            ResolutionError::UndeclaredLabel { name: label.name, suggestion },
-        );
-        None
+        Err(ResolutionError::UndeclaredLabel { name: label.name, suggestion })
     }
 
     /// Determine whether or not a label from the `rib_index`th label rib is reachable.
     fn is_label_valid_from_rib(&self, rib_index: usize) -> bool {
         let ribs = &self.label_ribs[rib_index + 1..];
 
         for rib in ribs {
-            match rib.kind {
-                NormalRibKind | MacroDefinition(..) => {
-                    // Nothing to do. Continue.
-                }
-
-                AssocItemRibKind
-                | ClosureOrAsyncRibKind
-                | FnItemRibKind
-                | ItemRibKind(..)
-                | ConstantItemRibKind(..)
-                | ModuleRibKind(..)
-                | ForwardGenericParamBanRibKind
-                | ConstParamTyRibKind
-                | InlineAsmSymRibKind => {
-                    return false;
-                }
+            if rib.kind.is_label_barrier() {
+                return false;
             }
         }
 
@@ -1895,6 +1885,8 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
         let mut function_value_rib = Rib::new(kind);
         let mut function_lifetime_rib = LifetimeRib::new(lifetime_kind);
         let mut seen_bindings = FxHashMap::default();
+        // Store all seen lifetimes names from outer scopes.
+        let mut seen_lifetimes = FxHashSet::default();
 
         // We also can't shadow bindings from the parent item
         if let AssocItemRibKind = kind {
@@ -1910,16 +1902,36 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
             add_bindings_for_ns(TypeNS);
         }
 
+        // Forbid shadowing lifetime bindings
+        for rib in self.lifetime_ribs.iter().rev() {
+            seen_lifetimes.extend(rib.bindings.iter().map(|(ident, _)| *ident));
+            if let LifetimeRibKind::Item = rib.kind {
+                break;
+            }
+        }
+
         for param in params {
             let ident = param.ident.normalize_to_macros_2_0();
             debug!("with_generic_param_rib: {}", param.id);
 
+            if let GenericParamKind::Lifetime = param.kind
+                && let Some(&original) = seen_lifetimes.get(&ident)
+            {
+                diagnostics::signal_lifetime_shadowing(self.r.session, original, param.ident);
+                // Record lifetime res, so lowering knows there is something fishy.
+                self.record_lifetime_res(param.id, LifetimeRes::Error);
+                continue;
+            }
+
             match seen_bindings.entry(ident) {
                 Entry::Occupied(entry) => {
                     let span = *entry.get();
                     let err = ResolutionError::NameAlreadyUsedInParameterList(ident.name, span);
-                    if !matches!(param.kind, GenericParamKind::Lifetime) {
-                        self.report_error(param.ident.span, err);
+                    self.report_error(param.ident.span, err);
+                    if let GenericParamKind::Lifetime = param.kind {
+                        // Record lifetime res, so lowering knows there is something fishy.
+                        self.record_lifetime_res(param.id, LifetimeRes::Error);
+                        continue;
                     }
                 }
                 Entry::Vacant(entry) => {
@@ -1936,6 +1948,8 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                 )
                 .span_label(param.ident.span, "`'_` is a reserved lifetime name")
                 .emit();
+                // Record lifetime res, so lowering knows there is something fishy.
+                self.record_lifetime_res(param.id, LifetimeRes::Error);
                 continue;
             }
 
@@ -1949,6 +1963,8 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
                 )
                 .span_label(param.ident.span, "'static is a reserved lifetime name")
                 .emit();
+                // Record lifetime res, so lowering knows there is something fishy.
+                self.record_lifetime_res(param.id, LifetimeRes::Error);
                 continue;
             }
 
@@ -3114,6 +3130,11 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
             if label.ident.as_str().as_bytes()[1] != b'_' {
                 self.diagnostic_metadata.unused_labels.insert(id, label.ident.span);
             }
+
+            if let Ok((_, orig_span)) = self.resolve_label(label.ident) {
+                diagnostics::signal_label_shadowing(self.r.session, orig_span, label.ident)
+            }
+
             self.with_label_rib(NormalRibKind, |this| {
                 let ident = label.ident.normalize_to_macro_rules();
                 this.label_ribs.last_mut().unwrap().bindings.insert(ident, id);
@@ -3219,10 +3240,15 @@ impl<'a: 'ast, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
             }
 
             ExprKind::Break(Some(label), _) | ExprKind::Continue(Some(label)) => {
-                if let Some(node_id) = self.resolve_label(label.ident) {
-                    // Since this res is a label, it is never read.
-                    self.r.label_res_map.insert(expr.id, node_id);
-                    self.diagnostic_metadata.unused_labels.remove(&node_id);
+                match self.resolve_label(label.ident) {
+                    Ok((node_id, _)) => {
+                        // Since this res is a label, it is never read.
+                        self.r.label_res_map.insert(expr.id, node_id);
+                        self.diagnostic_metadata.unused_labels.remove(&node_id);
+                    }
+                    Err(error) => {
+                        self.report_error(label.ident.span, error);
+                    }
                 }
 
                 // visit `break` argument if any

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -25,6 +25,7 @@ use rustc_hir::def_id::{DefId, CRATE_DEF_ID, LOCAL_CRATE};
 use rustc_hir::PrimTy;
 use rustc_session::lint;
 use rustc_session::parse::feature_err;
+use rustc_session::Session;
 use rustc_span::edition::Edition;
 use rustc_span::hygiene::MacroKind;
 use rustc_span::lev_distance::find_best_match_for_name;
@@ -2036,6 +2037,34 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
     }
 }
 
+/// Report lifetime/lifetime shadowing as an error.
+pub fn signal_lifetime_shadowing(sess: &Session, orig: Ident, shadower: Ident) {
+    let mut err = struct_span_err!(
+        sess,
+        shadower.span,
+        E0496,
+        "lifetime name `{}` shadows a lifetime name that is already in scope",
+        orig.name,
+    );
+    err.span_label(orig.span, "first declared here");
+    err.span_label(shadower.span, format!("lifetime `{}` already in scope", orig.name));
+    err.emit();
+}
+
+/// Shadowing involving a label is only a warning for historical reasons.
+//FIXME: make this a proper lint.
+pub fn signal_label_shadowing(sess: &Session, orig: Span, shadower: Ident) {
+    let name = shadower.name;
+    let shadower = shadower.span;
+    let mut err = sess.struct_span_warn(
+        shadower,
+        &format!("label name `{}` shadows a label name that is already in scope", name),
+    );
+    err.span_label(orig, "first declared here");
+    err.span_label(shadower, format!("label `{}` already in scope", name));
+    err.emit();
+}
+
 impl<'tcx> LifetimeContext<'_, 'tcx> {
     pub(crate) fn report_missing_lifetime_specifiers(
         &self,

compiler/rustc_resolve/src/late/lifetimes.rs

@@ -1,5 +1,5 @@
 fn foo<'a, 'b, 'a>(x: &'a str, y: &'b str) {
-    //~^ ERROR E0263
+    //~^ ERROR E0403
 }
 
 fn main() {}

src/test/ui/error-codes/E0263.rs

@@ -1,11 +1,11 @@
-error[E0263]: lifetime name `'a` declared twice in the same scope
+error[E0403]: the name `'a` is already used for a generic parameter in this item's generic parameters
   --> $DIR/E0263.rs:1:16
    |
 LL | fn foo<'a, 'b, 'a>(x: &'a str, y: &'b str) {
-   |        --      ^^ declared twice
+   |        --      ^^ already used
    |        |
-   |        previous declaration here
+   |        first use of `'a`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0263`.
+For more information about this error, try `rustc --explain E0403`.

src/test/ui/error-codes/E0263.stderr

@@ -102,7 +102,7 @@ fn label_break_match(c: u8, xe: u8, ye: i8) {
             0 => break 'a 0,
             v if { if v % 2 == 0 { break 'a 1; }; v % 3 == 0 } => { x += 1; },
             v if { 'b: { break 'b v == 5; } } => { x = 41; },
-            _ => 'b: { //~ WARNING `'b` shadows a label
+            _ => 'b: {
                 break 'b ();
             },
         }
@@ -128,8 +128,8 @@ fn label_break_macro() {
         0
     };
     assert_eq!(x, 0);
-    let x: u8 = 'a: { //~ WARNING `'a` shadows a label
-        'b: { //~ WARNING `'b` shadows a label
+    let x: u8 = 'a: {
+        'b: {
             if true {
                 mac1!('a, 1);
             }

src/test/ui/for-loop-while/label_break_value.rs

@@ -20,14 +20,11 @@ fn lbv_macro_test_hygiene_respected() {
     macro_rules! mac3 {
         ($val:expr) => {
             'a: {
-            //~^ WARNING `'a` shadows a label
-            //~| WARNING `'a` shadows a label
-            //~| WARNING `'a` shadows a label
                 $val
             }
         };
     }
-    let x: u8 = mac3!('b: { //~ WARNING `'b` shadows a label
+    let x: u8 = mac3!('b: {
         if true {
             break 'a 3; //~ ERROR undeclared label `'a` [E0426]
         }

src/test/ui/for-loop-while/label_break_value.stderr

@@ -10,7 +10,7 @@ LL |                 mac2!(2);
    = note: this error originates in the macro `mac2` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0426]: use of undeclared label `'a`
-  --> $DIR/label_break_value_invalid.rs:32:19
+  --> $DIR/label_break_value_invalid.rs:29:19
    |
 LL |     let x: u8 = mac3!('b: {
    |                       -- a label with a similar name is reachable
@@ -22,68 +22,11 @@ LL |             break 'a 3;
    |                   help: try using similarly named label: `'b`
 
 error[E0426]: use of undeclared label `'a`
-  --> $DIR/label_break_value_invalid.rs:37:29
+  --> $DIR/label_break_value_invalid.rs:34:29
    |
 LL |     let x: u8 = mac3!(break 'a 4);
    |                             ^^ undeclared label `'a`
 
-warning: label name `'a` shadows a label name that is already in scope
-  --> $DIR/label_break_value_invalid.rs:22:13
-   |
-LL |       let x: u8 = 'a: {
-   |                   -- first declared here
-...
-LL |               'a: {
-   |               ^^ label `'a` already in scope
-...
-LL |       let x: u8 = mac3!('b: {
-   |  _________________-
-LL | |         if true {
-LL | |             break 'a 3;
-LL | |         }
-LL | |         0
-LL | |     });
-   | |______- in this macro invocation
-   |
-   = note: this warning originates in the macro `mac3` (in Nightly builds, run with -Z macro-backtrace for more info)
-
-warning: label name `'b` shadows a label name that is already in scope
-  --> $DIR/label_break_value_invalid.rs:30:23
-   |
-LL |         'b: {
-   |         -- first declared here
-...
-LL |     let x: u8 = mac3!('b: {
-   |                       ^^ label `'b` already in scope
-
-warning: label name `'a` shadows a label name that is already in scope
-  --> $DIR/label_break_value_invalid.rs:22:13
-   |
-LL |     let x: u8 = 'a: {
-   |                 -- first declared here
-...
-LL |             'a: {
-   |             ^^ label `'a` already in scope
-...
-LL |     let x: u8 = mac3!(break 'a 4);
-   |                 ----------------- in this macro invocation
-   |
-   = note: this warning originates in the macro `mac3` (in Nightly builds, run with -Z macro-backtrace for more info)
-
-warning: label name `'a` shadows a label name that is already in scope
-  --> $DIR/label_break_value_invalid.rs:22:13
-   |
-LL |             'a: {
-   |             ^^
-   |             |
-   |             first declared here
-   |             label `'a` already in scope
-...
-LL |     let x: u8 = mac3!(break 'a 4);
-   |                 ----------------- in this macro invocation
-   |
-   = note: this warning originates in the macro `mac3` (in Nightly builds, run with -Z macro-backtrace for more info)
-
-error: aborting due to 3 previous errors; 4 warnings emitted
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0426`.

src/test/ui/for-loop-while/label_break_value_invalid.rs

@@ -1,3 +1,19 @@
+error[E0496]: lifetime name `'a` shadows a lifetime name that is already in scope
+  --> $DIR/shadowing.rs:4:14
+   |
+LL | trait Shadow<'a> {
+   |              -- first declared here
+LL |     type Bar<'a>;
+   |              ^^ lifetime `'a` already in scope
+
+error[E0496]: lifetime name `'a` shadows a lifetime name that is already in scope
+  --> $DIR/shadowing.rs:13:14
+   |
+LL | impl<'a> NoShadow<'a> for &'a u32 {
+   |      -- first declared here
+LL |     type Bar<'a> = i32;
+   |              ^^ lifetime `'a` already in scope
+
 error[E0403]: the name `T` is already used for a generic parameter in this item's generic parameters
   --> $DIR/shadowing.rs:18:14
    |
@@ -14,22 +30,6 @@ LL | impl<T> NoShadowT<T> for Option<T> {
 LL |     type Bar<T> = i32;
    |              ^ already used
 
-error[E0496]: lifetime name `'a` shadows a lifetime name that is already in scope
-  --> $DIR/shadowing.rs:13:14
-   |
-LL | impl<'a> NoShadow<'a> for &'a u32 {
-   |      -- first declared here
-LL |     type Bar<'a> = i32;
-   |              ^^ lifetime `'a` already in scope
-
-error[E0496]: lifetime name `'a` shadows a lifetime name that is already in scope
-  --> $DIR/shadowing.rs:4:14
-   |
-LL | trait Shadow<'a> {
-   |              -- first declared here
-LL |     type Bar<'a>;
-   |              ^^ lifetime `'a` already in scope
-
 error: aborting due to 4 previous errors
 
 Some errors have detailed explanations: E0403, E0496.

src/test/ui/for-loop-while/label_break_value_invalid.stderr

@@ -5,12 +5,12 @@
 
 #[rustc_macro_transparency = "semitransparent"]
 macro m($a:lifetime) {
-    fn g<$a, 'a>() {} //~ ERROR lifetime name `'a` declared twice
+    fn g<$a, 'a>() {} //~ ERROR the name `'a` is already used for a generic parameter
 }
 
 #[rustc_macro_transparency = "transparent"]
 macro n($a:lifetime) {
-    fn h<$a, 'a>() {} //~ ERROR lifetime name `'a` declared twice
+    fn h<$a, 'a>() {} //~ ERROR the name `'a` is already used for a generic parameter
 }
 
 m!('a);

src/test/ui/generic-associated-types/shadowing.stderr

@@ -1,31 +1,31 @@
-error[E0263]: lifetime name `'a` declared twice in the same scope
+error[E0403]: the name `'a` is already used for a generic parameter in this item's generic parameters
   --> $DIR/duplicate_lifetimes.rs:8:14
    |
 LL |     fn g<$a, 'a>() {}
-   |              ^^ declared twice
+   |              ^^ already used
 ...
 LL | m!('a);
    | ------
    | |  |
-   | |  previous declaration here
+   | |  first use of `'a`
    | in this macro invocation
    |
    = note: this error originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0263]: lifetime name `'a` declared twice in the same scope
+error[E0403]: the name `'a` is already used for a generic parameter in this item's generic parameters
   --> $DIR/duplicate_lifetimes.rs:13:14
    |
 LL |     fn h<$a, 'a>() {}
-   |              ^^ declared twice
+   |              ^^ already used
 ...
 LL | n!('a);
    | ------
    | |  |
-   | |  previous declaration here
+   | |  first use of `'a`
    | in this macro invocation
    |
    = note: this error originates in the macro `n` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0263`.
+For more information about this error, try `rustc --explain E0403`.

src/test/ui/hygiene/duplicate_lifetimes.rs

@@ -13,38 +13,28 @@
 macro_rules! loop_x {
     ($e: expr) => {
         // $e shouldn't be able to interact with this 'x
-        'x: loop { $e }
-        //~^ WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-    }
+        'x: loop {
+            $e
+        }
+    };
 }
 
 macro_rules! while_true {
     ($e: expr) => {
         // $e shouldn't be able to interact with this 'x
-        'x: while 1 + 1 == 2 { $e }
-        //~^ WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-    }
+        'x: while 1 + 1 == 2 {
+            $e
+        }
+    };
 }
 
 macro_rules! run_once {
     ($e: expr) => {
         // ditto
-        'x: for _ in 0..1 { $e }
-        //~^ WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-    }
+        'x: for _ in 0..1 {
+            $e
+        }
+    };
 }
 
 pub fn main() {
@@ -62,8 +52,6 @@ pub fn main() {
 
     let k: isize = {
         'x: for _ in 0..1 {
-            //~^ WARNING shadows a label name that is already in scope
-            //~| WARNING shadows a label name that is already in scope
             // ditto
             loop_x!(break 'x);
             i += 1;
@@ -74,10 +62,6 @@ pub fn main() {
 
     let l: isize = {
         'x: for _ in 0..1 {
-            //~^ WARNING shadows a label name that is already in scope
-            //~| WARNING shadows a label name that is already in scope
-            //~| WARNING shadows a label name that is already in scope
-            //~| WARNING shadows a label name that is already in scope
             // ditto
             while_true!(break 'x);
             i += 1;
@@ -88,12 +72,6 @@ pub fn main() {
 
     let n: isize = {
         'x: for _ in 0..1 {
-            //~^ WARNING shadows a label name that is already in scope
-            //~| WARNING shadows a label name that is already in scope
-            //~| WARNING shadows a label name that is already in scope
-            //~| WARNING shadows a label name that is already in scope
-            //~| WARNING shadows a label name that is already in scope
-            //~| WARNING shadows a label name that is already in scope
             // ditto
             run_once!(continue 'x);
             i += 1;

src/test/ui/hygiene/duplicate_lifetimes.stderr

@@ -10,38 +10,28 @@
 macro_rules! loop_x {
     ($e: expr) => {
         // $e shouldn't be able to interact with this 'x
-        'x: loop { $e }
-        //~^ WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-    }
+        'x: loop {
+            $e
+        }
+    };
 }
 
 macro_rules! run_once {
     ($e: expr) => {
         // ditto
-        'x: for _ in 0..1 { $e }
-        //~^ WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-    }
+        'x: for _ in 0..1 {
+            $e
+        }
+    };
 }
 
 macro_rules! while_x {
     ($e: expr) => {
         // ditto
-        'x: while 1 + 1 == 2 { $e }
-        //~^ WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-    }
+        'x: while 1 + 1 == 2 {
+            $e
+        }
+    };
 }
 
 pub fn main() {
@@ -52,32 +42,17 @@ pub fn main() {
     }
 
     'x: loop {
-        //~^ WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-
         // ditto
         loop_x!(break 'x);
         panic!("break doesn't act hygienically inside infinite loop");
     }
 
     'x: while 1 + 1 == 2 {
-        //~^ WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-
         while_x!(break 'x);
         panic!("break doesn't act hygienically inside infinite while loop");
     }
 
     'x: for _ in 0..1 {
-        //~^ WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-        //~| WARNING shadows a label name that is already in scope
-
         // ditto
         run_once!(continue 'x);
         panic!("continue doesn't act hygienically inside for loop");

src/test/ui/hygiene/hygienic-labels-in-let.rs

@@ -1,3 +1,12 @@
+warning: label name `'many_used_shadowed` shadows a label name that is already in scope
+  --> $DIR/unused_labels.rs:62:9
+   |
+LL |     'many_used_shadowed: for _ in 0..10 {
+   |     ------------------- first declared here
+LL |
+LL |         'many_used_shadowed: for _ in 0..10 {
+   |         ^^^^^^^^^^^^^^^^^^^ label `'many_used_shadowed` already in scope
+
 warning: unused label
   --> $DIR/unused_labels.rs:11:5
    |
@@ -52,14 +61,5 @@ warning: unused label
 LL |     'unused_block_label: {
    |     ^^^^^^^^^^^^^^^^^^^
 
-warning: label name `'many_used_shadowed` shadows a label name that is already in scope
-  --> $DIR/unused_labels.rs:62:9
-   |
-LL |     'many_used_shadowed: for _ in 0..10 {
-   |     ------------------- first declared here
-LL |
-LL |         'many_used_shadowed: for _ in 0..10 {
-   |         ^^^^^^^^^^^^^^^^^^^ label `'many_used_shadowed` already in scope
-
 warning: 9 warnings emitted
 

src/test/ui/hygiene/hygienic-labels-in-let.stderr

@@ -18,7 +18,7 @@ macro_rules! br {
 }
 macro_rules! br2 {
     ($b:lifetime) => {
-        'b: loop { //~ WARNING `'b` shadows a label name that is already in scope
+        'b: loop {
             break $b; // this $b should refer to the outer loop.
         }
     }

src/test/ui/hygiene/hygienic-labels.rs

@@ -1,5 +1,6 @@
-struct Foo<'a, 'a> { //~ ERROR lifetime name `'a` declared twice
-    x: &'a isize
+struct Foo<'a, 'a> {
+    //~^ ERROR the name `'a` is already used for a generic parameter
+    x: &'a isize,
 }
 
 fn main() {}

src/test/ui/hygiene/hygienic-labels.stderr

@@ -1,11 +1,11 @@
-error[E0263]: lifetime name `'a` declared twice in the same scope
+error[E0403]: the name `'a` is already used for a generic parameter in this item's generic parameters
   --> $DIR/regions-name-duplicated.rs:1:16
    |
 LL | struct Foo<'a, 'a> {
-   |            --  ^^ declared twice
+   |            --  ^^ already used
    |            |
-   |            previous declaration here
+   |            first use of `'a`
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0263`.
+For more information about this error, try `rustc --explain E0403`.