Gate stability attrs with other attributes.

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -420,6 +420,31 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 }
             }
         }
+
+        // Emit errors for non-staged-api crates.
+        if !self.features.staged_api {
+            if attr.has_name(sym::rustc_deprecated)
+                || attr.has_name(sym::unstable)
+                || attr.has_name(sym::stable)
+                || attr.has_name(sym::rustc_const_unstable)
+                || attr.has_name(sym::rustc_const_stable)
+            {
+                struct_span_err!(
+                    self.sess,
+                    attr.span,
+                    E0734,
+                    "stability attributes may not be used outside of the standard library",
+                )
+                .emit();
+            }
+        } else {
+            if attr.has_name(sym::deprecated) {
+                self.sess
+                    .struct_span_err(attr.span, "`#[deprecated]` cannot be used in staged API")
+                    .span_label(attr.span, "use `#[rustc_deprecated]` instead")
+                    .emit();
+            }
+        }
     }
 
     fn visit_item(&mut self, i: &'a ast::Item) {

compiler/rustc_passes/src/stability.rs

@@ -1,7 +1,6 @@
 //! A pass that annotates every item and method with its stability level,
 //! propagating default levels lexically from parent to children ast nodes.
 
-use rustc_ast::Attribute;
 use rustc_attr::{self as attr, ConstStability, Stability};
 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::struct_span_err;
@@ -113,12 +112,8 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
     {
         let attrs = self.tcx.get_attrs(def_id.to_def_id());
         debug!("annotate(id = {:?}, attrs = {:?})", def_id, attrs);
-        let mut did_error = false;
-        if !self.tcx.features().staged_api {
-            did_error = self.forbid_staged_api_attrs(def_id, attrs, inherit_deprecation.clone());
-        }
 
-        let depr = if did_error { None } else { attr::find_deprecation(&self.tcx.sess, attrs) };
+        let depr = attr::find_deprecation(&self.tcx.sess, attrs);
         let mut is_deprecated = false;
         if let Some((depr, span)) = &depr {
             is_deprecated = true;
@@ -148,16 +143,15 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
             }
         }
 
-        if self.tcx.features().staged_api {
+        if !self.tcx.features().staged_api {
-            if let Some(a) = attrs.iter().find(|a| a.has_name(sym::deprecated)) {
+            // Propagate unstability.  This can happen even for non-staged-api crates in case
-                self.tcx
+            // -Zforce-unstable-if-unmarked is set.
-                    .sess
+            if let Some(stab) = self.parent_stab {
-                    .struct_span_err(a.span, "`#[deprecated]` cannot be used in staged API")
+                if inherit_deprecation.yes() && stab.level.is_unstable() {
-                    .span_label(a.span, "use `#[rustc_deprecated]` instead")
+                    self.index.stab_map.insert(def_id, stab);
-                    .span_label(item_sp, "")
-                    .emit();
                 }
-        } else {
+            }
+
             self.recurse_with_stability_attrs(
                 depr.map(|(d, _)| DeprecationEntry::local(d, def_id)),
                 None,
@@ -329,47 +323,6 @@ impl<'a, 'tcx> Annotator<'a, 'tcx> {
             self.parent_const_stab = orig_parent_const_stab;
         }
     }
-
-    // returns true if an error occurred, used to suppress some spurious errors
-    fn forbid_staged_api_attrs(
-        &mut self,
-        def_id: LocalDefId,
-        attrs: &[Attribute],
-        inherit_deprecation: InheritDeprecation,
-    ) -> bool {
-        // Emit errors for non-staged-api crates.
-        let unstable_attrs = [
-            sym::unstable,
-            sym::stable,
-            sym::rustc_deprecated,
-            sym::rustc_const_unstable,
-            sym::rustc_const_stable,
-        ];
-        let mut has_error = false;
-        for attr in attrs {
-            let name = attr.name_or_empty();
-            if unstable_attrs.contains(&name) {
-                struct_span_err!(
-                    self.tcx.sess,
-                    attr.span,
-                    E0734,
-                    "stability attributes may not be used outside of the standard library",
-                )
-                .emit();
-                has_error = true;
-            }
-        }
-
-        // Propagate unstability.  This can happen even for non-staged-api crates in case
-        // -Zforce-unstable-if-unmarked is set.
-        if let Some(stab) = self.parent_stab {
-            if inherit_deprecation.yes() && stab.level.is_unstable() {
-                self.index.stab_map.insert(def_id, stab);
-            }
-        }
-
-        has_error
-    }
 }
 
 impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {

src/test/ui/deprecation/deprecation-in-staged-api.stderr

@@ -3,8 +3,6 @@ error: `#[deprecated]` cannot be used in staged API
    |
 LL | #[deprecated]
    | ^^^^^^^^^^^^^ use `#[rustc_deprecated]` instead
-LL | fn main() {}
-   | ------------
 
 error: aborting due to previous error
 

src/test/ui/feature-gates/feature-gate-staged_api.stderr

@@ -1,15 +1,15 @@
-error[E0734]: stability attributes may not be used outside of the standard library
-  --> $DIR/feature-gate-staged_api.rs:1:1
-   |
-LL | #![stable(feature = "a", since = "b")]
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
 error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/feature-gate-staged_api.rs:8:1
    |
 LL | #[stable(feature = "a", since = "b")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
+error[E0734]: stability attributes may not be used outside of the standard library
+  --> $DIR/feature-gate-staged_api.rs:1:1
+   |
+LL | #![stable(feature = "a", since = "b")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
 error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0734`.

src/test/ui/feature-gates/issue-43106-gating-of-rustc_deprecated.rs

@@ -6,25 +6,38 @@
 
 #![rustc_deprecated()]
 //~^ ERROR stability attributes may not be used outside of the standard library
+//~| ERROR missing 'since' [E0542]
 
 #[rustc_deprecated()]
 //~^ ERROR stability attributes may not be used outside of the standard library
+//~| ERROR missing 'since' [E0542]
 mod rustc_deprecated {
-    mod inner { #![rustc_deprecated()] }
+    mod inner {
+        #![rustc_deprecated()]
         //~^ ERROR stability attributes may not be used outside of the standard library
+        //~| ERROR missing 'since' [E0542]
+    }
 
-    #[rustc_deprecated()] fn f() { }
+    #[rustc_deprecated()]
     //~^ ERROR stability attributes may not be used outside of the standard library
+    //~| ERROR missing 'since' [E0542]
+    fn f() {}
 
-    #[rustc_deprecated()] struct S;
+    #[rustc_deprecated()]
     //~^ ERROR stability attributes may not be used outside of the standard library
-    //~| ERROR stability attributes may not be used outside of the standard library
+    //~| ERROR missing 'since' [E0542]
+    //~| ERROR missing 'since' [E0542]
+    struct S;
 
-    #[rustc_deprecated()] type T = S;
+    #[rustc_deprecated()]
     //~^ ERROR stability attributes may not be used outside of the standard library
+    //~| ERROR missing 'since' [E0542]
+    type T = S;
 
-    #[rustc_deprecated()] impl S { }
+    #[rustc_deprecated()]
     //~^ ERROR stability attributes may not be used outside of the standard library
+    //~| ERROR missing 'since' [E0542]
+    impl S {}
 }
 
 fn main() {}

src/test/ui/feature-gates/issue-43106-gating-of-rustc_deprecated.stderr

@@ -1,51 +1,94 @@
+error[E0734]: stability attributes may not be used outside of the standard library
+  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:16:9
+   |
+LL |         #![rustc_deprecated()]
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0734]: stability attributes may not be used outside of the standard library
+  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:21:5
+   |
+LL |     #[rustc_deprecated()]
+   |     ^^^^^^^^^^^^^^^^^^^^^
+
+error[E0734]: stability attributes may not be used outside of the standard library
+  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:26:5
+   |
+LL |     #[rustc_deprecated()]
+   |     ^^^^^^^^^^^^^^^^^^^^^
+
+error[E0734]: stability attributes may not be used outside of the standard library
+  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:32:5
+   |
+LL |     #[rustc_deprecated()]
+   |     ^^^^^^^^^^^^^^^^^^^^^
+
+error[E0734]: stability attributes may not be used outside of the standard library
+  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:37:5
+   |
+LL |     #[rustc_deprecated()]
+   |     ^^^^^^^^^^^^^^^^^^^^^
+
+error[E0734]: stability attributes may not be used outside of the standard library
+  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:11:1
+   |
+LL | #[rustc_deprecated()]
+   | ^^^^^^^^^^^^^^^^^^^^^
+
 error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:7:1
    |
 LL | #![rustc_deprecated()]
    | ^^^^^^^^^^^^^^^^^^^^^^
 
-error[E0734]: stability attributes may not be used outside of the standard library
+error[E0542]: missing 'since'
-  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:10:1
+  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:7:1
+   |
+LL | #![rustc_deprecated()]
+   | ^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0542]: missing 'since'
+  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:11:1
    |
 LL | #[rustc_deprecated()]
    | ^^^^^^^^^^^^^^^^^^^^^
 
-error[E0734]: stability attributes may not be used outside of the standard library
+error[E0542]: missing 'since'
-  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:13:17
+  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:16:9
    |
-LL |     mod inner { #![rustc_deprecated()] }
+LL |         #![rustc_deprecated()]
    |         ^^^^^^^^^^^^^^^^^^^^^^
 
-error[E0734]: stability attributes may not be used outside of the standard library
+error[E0542]: missing 'since'
-  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:16:5
+  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:21:5
    |
-LL |     #[rustc_deprecated()] fn f() { }
+LL |     #[rustc_deprecated()]
    |     ^^^^^^^^^^^^^^^^^^^^^
 
-error[E0734]: stability attributes may not be used outside of the standard library
+error[E0542]: missing 'since'
-  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:19:5
-   |
-LL |     #[rustc_deprecated()] struct S;
-   |     ^^^^^^^^^^^^^^^^^^^^^
-
-error[E0734]: stability attributes may not be used outside of the standard library
-  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:19:5
-   |
-LL |     #[rustc_deprecated()] struct S;
-   |     ^^^^^^^^^^^^^^^^^^^^^
-
-error[E0734]: stability attributes may not be used outside of the standard library
-  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:23:5
-   |
-LL |     #[rustc_deprecated()] type T = S;
-   |     ^^^^^^^^^^^^^^^^^^^^^
-
-error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:26:5
    |
-LL |     #[rustc_deprecated()] impl S { }
+LL |     #[rustc_deprecated()]
    |     ^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 8 previous errors
+error[E0542]: missing 'since'
+  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:26:5
+   |
+LL |     #[rustc_deprecated()]
+   |     ^^^^^^^^^^^^^^^^^^^^^
 
-For more information about this error, try `rustc --explain E0734`.
+error[E0542]: missing 'since'
+  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:32:5
+   |
+LL |     #[rustc_deprecated()]
+   |     ^^^^^^^^^^^^^^^^^^^^^
+
+error[E0542]: missing 'since'
+  --> $DIR/issue-43106-gating-of-rustc_deprecated.rs:37:5
+   |
+LL |     #[rustc_deprecated()]
+   |     ^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 15 previous errors
+
+Some errors have detailed explanations: E0542, E0734.
+For more information about an error, try `rustc --explain E0542`.

src/test/ui/feature-gates/issue-43106-gating-of-stable.rs

@@ -10,21 +10,26 @@
 #[stable()]
 //~^ ERROR stability attributes may not be used outside of the standard library
 mod stable {
-    mod inner { #![stable()] }
+    mod inner {
-    //~^ ERROR stability attributes may not be used outside of the standard library
+        #![stable()]
-
-    #[stable()] fn f() { }
-    //~^ ERROR stability attributes may not be used outside of the standard library
-
-    #[stable()] struct S;
-    //~^ ERROR stability attributes may not be used outside of the standard library
-    //~| ERROR stability attributes may not be used outside of the standard library
-
-    #[stable()] type T = S;
-    //~^ ERROR stability attributes may not be used outside of the standard library
-
-    #[stable()] impl S { }
         //~^ ERROR stability attributes may not be used outside of the standard library
     }
 
+    #[stable()]
+    //~^ ERROR stability attributes may not be used outside of the standard library
+    fn f() {}
+
+    #[stable()]
+    //~^ ERROR stability attributes may not be used outside of the standard library
+    struct S;
+
+    #[stable()]
+    //~^ ERROR stability attributes may not be used outside of the standard library
+    type T = S;
+
+    #[stable()]
+    //~^ ERROR stability attributes may not be used outside of the standard library
+    impl S {}
+}
+
 fn main() {}

src/test/ui/feature-gates/issue-43106-gating-of-stable.stderr

@@ -1,9 +1,33 @@
 error[E0734]: stability attributes may not be used outside of the standard library
-  --> $DIR/issue-43106-gating-of-stable.rs:7:1
+  --> $DIR/issue-43106-gating-of-stable.rs:14:9
    |
 LL |         #![stable()]
    |         ^^^^^^^^^^^^
 
+error[E0734]: stability attributes may not be used outside of the standard library
+  --> $DIR/issue-43106-gating-of-stable.rs:18:5
+   |
+LL |     #[stable()]
+   |     ^^^^^^^^^^^
+
+error[E0734]: stability attributes may not be used outside of the standard library
+  --> $DIR/issue-43106-gating-of-stable.rs:22:5
+   |
+LL |     #[stable()]
+   |     ^^^^^^^^^^^
+
+error[E0734]: stability attributes may not be used outside of the standard library
+  --> $DIR/issue-43106-gating-of-stable.rs:26:5
+   |
+LL |     #[stable()]
+   |     ^^^^^^^^^^^
+
+error[E0734]: stability attributes may not be used outside of the standard library
+  --> $DIR/issue-43106-gating-of-stable.rs:30:5
+   |
+LL |     #[stable()]
+   |     ^^^^^^^^^^^
+
 error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-stable.rs:10:1
    |
@@ -11,41 +35,11 @@ LL | #[stable()]
    | ^^^^^^^^^^^
 
 error[E0734]: stability attributes may not be used outside of the standard library
-  --> $DIR/issue-43106-gating-of-stable.rs:13:17
+  --> $DIR/issue-43106-gating-of-stable.rs:7:1
    |
-LL |     mod inner { #![stable()] }
+LL | #![stable()]
    | ^^^^^^^^^^^^
 
-error[E0734]: stability attributes may not be used outside of the standard library
+error: aborting due to 7 previous errors
-  --> $DIR/issue-43106-gating-of-stable.rs:16:5
-   |
-LL |     #[stable()] fn f() { }
-   |     ^^^^^^^^^^^
-
-error[E0734]: stability attributes may not be used outside of the standard library
-  --> $DIR/issue-43106-gating-of-stable.rs:19:5
-   |
-LL |     #[stable()] struct S;
-   |     ^^^^^^^^^^^
-
-error[E0734]: stability attributes may not be used outside of the standard library
-  --> $DIR/issue-43106-gating-of-stable.rs:19:5
-   |
-LL |     #[stable()] struct S;
-   |     ^^^^^^^^^^^
-
-error[E0734]: stability attributes may not be used outside of the standard library
-  --> $DIR/issue-43106-gating-of-stable.rs:23:5
-   |
-LL |     #[stable()] type T = S;
-   |     ^^^^^^^^^^^
-
-error[E0734]: stability attributes may not be used outside of the standard library
-  --> $DIR/issue-43106-gating-of-stable.rs:26:5
-   |
-LL |     #[stable()] impl S { }
-   |     ^^^^^^^^^^^
-
-error: aborting due to 8 previous errors
 
 For more information about this error, try `rustc --explain E0734`.

src/test/ui/feature-gates/issue-43106-gating-of-unstable.rs

@@ -10,21 +10,26 @@
 #[unstable()]
 //~^ ERROR stability attributes may not be used outside of the standard library
 mod unstable {
-    mod inner { #![unstable()] }
+    mod inner {
-    //~^ ERROR stability attributes may not be used outside of the standard library
+        #![unstable()]
-
-    #[unstable()] fn f() { }
-    //~^ ERROR stability attributes may not be used outside of the standard library
-
-    #[unstable()] struct S;
-    //~^ ERROR stability attributes may not be used outside of the standard library
-    //~| ERROR stability attributes may not be used outside of the standard library
-
-    #[unstable()] type T = S;
-    //~^ ERROR stability attributes may not be used outside of the standard library
-
-    #[unstable()] impl S { }
         //~^ ERROR stability attributes may not be used outside of the standard library
     }
 
+    #[unstable()]
+    //~^ ERROR stability attributes may not be used outside of the standard library
+    fn f() {}
+
+    #[unstable()]
+    //~^ ERROR stability attributes may not be used outside of the standard library
+    struct S;
+
+    #[unstable()]
+    //~^ ERROR stability attributes may not be used outside of the standard library
+    type T = S;
+
+    #[unstable()]
+    //~^ ERROR stability attributes may not be used outside of the standard library
+    impl S {}
+}
+
 fn main() {}

src/test/ui/feature-gates/issue-43106-gating-of-unstable.stderr

@@ -1,9 +1,33 @@
 error[E0734]: stability attributes may not be used outside of the standard library
-  --> $DIR/issue-43106-gating-of-unstable.rs:7:1
+  --> $DIR/issue-43106-gating-of-unstable.rs:14:9
    |
 LL |         #![unstable()]
    |         ^^^^^^^^^^^^^^
 
+error[E0734]: stability attributes may not be used outside of the standard library
+  --> $DIR/issue-43106-gating-of-unstable.rs:18:5
+   |
+LL |     #[unstable()]
+   |     ^^^^^^^^^^^^^
+
+error[E0734]: stability attributes may not be used outside of the standard library
+  --> $DIR/issue-43106-gating-of-unstable.rs:22:5
+   |
+LL |     #[unstable()]
+   |     ^^^^^^^^^^^^^
+
+error[E0734]: stability attributes may not be used outside of the standard library
+  --> $DIR/issue-43106-gating-of-unstable.rs:26:5
+   |
+LL |     #[unstable()]
+   |     ^^^^^^^^^^^^^
+
+error[E0734]: stability attributes may not be used outside of the standard library
+  --> $DIR/issue-43106-gating-of-unstable.rs:30:5
+   |
+LL |     #[unstable()]
+   |     ^^^^^^^^^^^^^
+
 error[E0734]: stability attributes may not be used outside of the standard library
   --> $DIR/issue-43106-gating-of-unstable.rs:10:1
    |
@@ -11,41 +35,11 @@ LL | #[unstable()]
    | ^^^^^^^^^^^^^
 
 error[E0734]: stability attributes may not be used outside of the standard library
-  --> $DIR/issue-43106-gating-of-unstable.rs:13:17
+  --> $DIR/issue-43106-gating-of-unstable.rs:7:1
    |
-LL |     mod inner { #![unstable()] }
+LL | #![unstable()]
    | ^^^^^^^^^^^^^^
 
-error[E0734]: stability attributes may not be used outside of the standard library
+error: aborting due to 7 previous errors
-  --> $DIR/issue-43106-gating-of-unstable.rs:16:5
-   |
-LL |     #[unstable()] fn f() { }
-   |     ^^^^^^^^^^^^^
-
-error[E0734]: stability attributes may not be used outside of the standard library
-  --> $DIR/issue-43106-gating-of-unstable.rs:19:5
-   |
-LL |     #[unstable()] struct S;
-   |     ^^^^^^^^^^^^^
-
-error[E0734]: stability attributes may not be used outside of the standard library
-  --> $DIR/issue-43106-gating-of-unstable.rs:19:5
-   |
-LL |     #[unstable()] struct S;
-   |     ^^^^^^^^^^^^^
-
-error[E0734]: stability attributes may not be used outside of the standard library
-  --> $DIR/issue-43106-gating-of-unstable.rs:23:5
-   |
-LL |     #[unstable()] type T = S;
-   |     ^^^^^^^^^^^^^
-
-error[E0734]: stability attributes may not be used outside of the standard library
-  --> $DIR/issue-43106-gating-of-unstable.rs:26:5
-   |
-LL |     #[unstable()] impl S { }
-   |     ^^^^^^^^^^^^^
-
-error: aborting due to 8 previous errors
 
 For more information about this error, try `rustc --explain E0734`.

src/test/ui/stability-attribute/stability-attribute-non-staged-force-unstable.rs

@@ -3,4 +3,5 @@
 #[unstable()] //~ ERROR: stability attributes may not be used
 #[stable()] //~ ERROR: stability attributes may not be used
 #[rustc_deprecated()] //~ ERROR: stability attributes may not be used
+//~^ ERROR missing 'since'
 fn main() {}

src/test/ui/stability-attribute/stability-attribute-non-staged-force-unstable.stderr

@@ -16,6 +16,13 @@ error[E0734]: stability attributes may not be used outside of the standard libra
 LL | #[rustc_deprecated()]
    | ^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 3 previous errors
+error[E0542]: missing 'since'
+  --> $DIR/stability-attribute-non-staged-force-unstable.rs:5:1
+   |
+LL | #[rustc_deprecated()]
+   | ^^^^^^^^^^^^^^^^^^^^^
 
-For more information about this error, try `rustc --explain E0734`.
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0542, E0734.
+For more information about an error, try `rustc --explain E0542`.

src/test/ui/stability-attribute/stability-attribute-non-staged.rs

@@ -1,4 +1,5 @@
 #[unstable()] //~ ERROR: stability attributes may not be used
 #[stable()] //~ ERROR: stability attributes may not be used
 #[rustc_deprecated()] //~ ERROR: stability attributes may not be used
+//~^ ERROR missing 'since'
 fn main() {}

src/test/ui/stability-attribute/stability-attribute-non-staged.stderr

@@ -16,6 +16,13 @@ error[E0734]: stability attributes may not be used outside of the standard libra
 LL | #[rustc_deprecated()]
    | ^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 3 previous errors
+error[E0542]: missing 'since'
+  --> $DIR/stability-attribute-non-staged.rs:3:1
+   |
+LL | #[rustc_deprecated()]
+   | ^^^^^^^^^^^^^^^^^^^^^
 
-For more information about this error, try `rustc --explain E0734`.
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0542, E0734.
+For more information about an error, try `rustc --explain E0542`.