Print the generic parameter along with the variance in dumps.

compiler/rustc_hir_analysis/src/variance/dump.rs

@@ -1,18 +1,36 @@
+use std::fmt::Write;
+
 use rustc_hir::def::DefKind;
-use rustc_hir::def_id::CRATE_DEF_ID;
-use rustc_middle::ty::TyCtxt;
+use rustc_hir::def_id::{LocalDefId, CRATE_DEF_ID};
+use rustc_middle::ty::{GenericArgs, TyCtxt};
 use rustc_span::symbol::sym;
 
+fn format_variances(tcx: TyCtxt<'_>, def_id: LocalDefId) -> String {
+    let variances = tcx.variances_of(def_id);
+    let generics = GenericArgs::identity_for_item(tcx, def_id);
+    // 7 = 2-letter parameter + ": " + 1-letter variance + ", "
+    let mut ret = String::with_capacity(2 + 7 * variances.len());
+    ret.push('[');
+    for (arg, variance) in generics.iter().zip(variances.iter()) {
+        write!(ret, "{arg}: {variance:?}, ").unwrap();
+    }
+    // Remove trailing `, `.
+    if !variances.is_empty() {
+        ret.pop();
+        ret.pop();
+    }
+    ret.push(']');
+    ret
+}
+
 pub(crate) fn variances(tcx: TyCtxt<'_>) {
     if tcx.has_attr(CRATE_DEF_ID, sym::rustc_variance_of_opaques) {
         for id in tcx.hir().items() {
             let DefKind::OpaqueTy = tcx.def_kind(id.owner_id) else { continue };
 
-            let variances = tcx.variances_of(id.owner_id);
-
             tcx.dcx().emit_err(crate::errors::VariancesOf {
                 span: tcx.def_span(id.owner_id),
-                variances: format!("{variances:?}"),
+                variances: format_variances(tcx, id.owner_id.def_id),
             });
         }
     }
@@ -22,11 +40,9 @@ pub(crate) fn variances(tcx: TyCtxt<'_>) {
             continue;
         }
 
-        let variances = tcx.variances_of(id.owner_id);
-
         tcx.dcx().emit_err(crate::errors::VariancesOf {
             span: tcx.def_span(id.owner_id),
-            variances: format!("{variances:?}"),
+            variances: format_variances(tcx, id.owner_id.def_id),
         });
     }
 }

tests/ui/error-codes/E0208.rs

@@ -1,7 +1,7 @@
 #![feature(rustc_attrs)]
 
 #[rustc_variance]
-struct Foo<'a, T> { //~ ERROR [+, o]
+struct Foo<'a, T> { //~ ERROR ['a: +, T: o]
     t: &'a mut T,
 }
 

tests/ui/error-codes/E0208.stderr

@@ -1,4 +1,4 @@
-error: [+, o]
+error: ['a: +, T: o]
   --> $DIR/E0208.rs:4:1
    |
 LL | struct Foo<'a, T> {

tests/ui/impl-trait/capture-lifetime-not-in-hir.rs

@@ -6,13 +6,13 @@ trait Bar<'a> {
 }
 
 fn foo<'a, T: Bar<'a>>() -> impl Into<T::Assoc> {
-    //~^ ERROR [o, o]
+    //~^ ERROR ['a: o, T: o]
     // captures both T and 'a invariantly
     ()
 }
 
 fn foo2<'a, T: Bar<'a>>() -> impl Into<T::Assoc> + 'a {
-    //~^ ERROR [o, o, o]
+    //~^ ERROR ['a: o, T: o, 'a: o]
     // captures both T and 'a invariantly, and also duplicates `'a`
     // i.e. the opaque looks like `impl Into<<T as Bar<'a>>::Assoc> + 'a_duplicated`
     ()

tests/ui/impl-trait/capture-lifetime-not-in-hir.stderr

@@ -1,10 +1,10 @@
-error: [o, o]
+error: ['a: o, T: o]
   --> $DIR/capture-lifetime-not-in-hir.rs:8:29
    |
 LL | fn foo<'a, T: Bar<'a>>() -> impl Into<T::Assoc> {
    |                             ^^^^^^^^^^^^^^^^^^^
 
-error: [o, o, o]
+error: ['a: o, T: o, 'a: o]
   --> $DIR/capture-lifetime-not-in-hir.rs:14:30
    |
 LL | fn foo2<'a, T: Bar<'a>>() -> impl Into<T::Assoc> + 'a {

tests/ui/impl-trait/implicit-capture-late.stderr

@@ -10,7 +10,7 @@ note: lifetime declared here
 LL | fn foo(x: Vec<i32>) -> Box<dyn for<'a> Deref<Target = impl ?Sized>> {
    |                                    ^^
 
-error: [o]
+error: ['a: o]
   --> $DIR/implicit-capture-late.rs:10:55
    |
 LL | fn foo(x: Vec<i32>) -> Box<dyn for<'a> Deref<Target = impl ?Sized>> {

tests/ui/impl-trait/in-trait/variance.rs

@@ -7,14 +7,16 @@ impl<T> Captures<'_> for T {}
 
 trait Foo<'i> {
     fn implicit_capture_early<'a: 'a>() -> impl Sized {}
-    //~^ [o, *, *, o, o]
-    // Self, 'i, 'a, 'i_duplicated, 'a_duplicated
+    //~^ [Self: o, 'i: *, 'a: *, 'a: o, 'i: o]
 
-    fn explicit_capture_early<'a: 'a>() -> impl Sized + Captures<'a> {} //~ [o, *, *, o, o]
+    fn explicit_capture_early<'a: 'a>() -> impl Sized + Captures<'a> {}
+    //~^ [Self: o, 'i: *, 'a: *, 'a: o, 'i: o]
 
-    fn implicit_capture_late<'a>(_: &'a ()) -> impl Sized {} //~ [o, *, o, o]
+    fn implicit_capture_late<'a>(_: &'a ()) -> impl Sized {}
+    //~^ [Self: o, 'i: *, 'a: o, 'i: o]
 
-    fn explicit_capture_late<'a>(_: &'a ()) -> impl Sized + Captures<'a> {} //~ [o, *, o, o]
+    fn explicit_capture_late<'a>(_: &'a ()) -> impl Sized + Captures<'a> {}
+    //~^ [Self: o, 'i: *, 'a: o, 'i: o]
 }
 
 fn main() {}

tests/ui/impl-trait/in-trait/variance.stderr

@@ -1,23 +1,23 @@
-error: [o, *, *, o, o]
+error: [Self: o, 'i: *, 'a: *, 'a: o, 'i: o]
   --> $DIR/variance.rs:9:44
    |
 LL |     fn implicit_capture_early<'a: 'a>() -> impl Sized {}
    |                                            ^^^^^^^^^^
 
-error: [o, *, *, o, o]
-  --> $DIR/variance.rs:13:44
+error: [Self: o, 'i: *, 'a: *, 'a: o, 'i: o]
+  --> $DIR/variance.rs:12:44
    |
 LL |     fn explicit_capture_early<'a: 'a>() -> impl Sized + Captures<'a> {}
    |                                            ^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: [o, *, o, o]
+error: [Self: o, 'i: *, 'a: o, 'i: o]
   --> $DIR/variance.rs:15:48
    |
 LL |     fn implicit_capture_late<'a>(_: &'a ()) -> impl Sized {}
    |                                                ^^^^^^^^^^
 
-error: [o, *, o, o]
-  --> $DIR/variance.rs:17:48
+error: [Self: o, 'i: *, 'a: o, 'i: o]
+  --> $DIR/variance.rs:18:48
    |
 LL |     fn explicit_capture_late<'a>(_: &'a ()) -> impl Sized + Captures<'a> {}
    |                                                ^^^^^^^^^^^^^^^^^^^^^^^^^

tests/ui/impl-trait/variance.e2024.stderr

@@ -1,22 +1,22 @@
-error: [*, o]
+error: ['a: *, 'a: o]
   --> $DIR/variance.rs:14:36
    |
 LL | fn not_captured_early<'a: 'a>() -> impl Sized {}
    |                                    ^^^^^^^^^^
 
-error: [*, o]
+error: ['a: *, 'a: o]
   --> $DIR/variance.rs:19:32
    |
 LL | fn captured_early<'a: 'a>() -> impl Sized + Captures<'a> {}
    |                                ^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: [o]
+error: ['a: o]
   --> $DIR/variance.rs:21:40
    |
 LL | fn not_captured_late<'a>(_: &'a ()) -> impl Sized {}
    |                                        ^^^^^^^^^^
 
-error: [o]
+error: ['a: o]
   --> $DIR/variance.rs:26:36
    |
 LL | fn captured_late<'a>(_: &'a ()) -> impl Sized + Captures<'a> {}

tests/ui/impl-trait/variance.new.stderr

@@ -1,22 +1,22 @@
-error: [*, o]
+error: ['a: *, 'a: o]
   --> $DIR/variance.rs:14:36
    |
 LL | fn not_captured_early<'a: 'a>() -> impl Sized {}
    |                                    ^^^^^^^^^^
 
-error: [*, o]
+error: ['a: *, 'a: o]
   --> $DIR/variance.rs:19:32
    |
 LL | fn captured_early<'a: 'a>() -> impl Sized + Captures<'a> {}
    |                                ^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: [o]
+error: ['a: o]
   --> $DIR/variance.rs:21:40
    |
 LL | fn not_captured_late<'a>(_: &'a ()) -> impl Sized {}
    |                                        ^^^^^^^^^^
 
-error: [o]
+error: ['a: o]
   --> $DIR/variance.rs:26:36
    |
 LL | fn captured_late<'a>(_: &'a ()) -> impl Sized + Captures<'a> {}

tests/ui/impl-trait/variance.old.stderr

@@ -1,10 +1,10 @@
-error: [*]
+error: ['a: *]
   --> $DIR/variance.rs:14:36
    |
 LL | fn not_captured_early<'a: 'a>() -> impl Sized {}
    |                                    ^^^^^^^^^^
 
-error: [*, o]
+error: ['a: *, 'a: o]
   --> $DIR/variance.rs:19:32
    |
 LL | fn captured_early<'a: 'a>() -> impl Sized + Captures<'a> {}
@@ -16,7 +16,7 @@ error: []
 LL | fn not_captured_late<'a>(_: &'a ()) -> impl Sized {}
    |                                        ^^^^^^^^^^
 
-error: [o]
+error: ['a: o]
   --> $DIR/variance.rs:26:36
    |
 LL | fn captured_late<'a>(_: &'a ()) -> impl Sized + Captures<'a> {}

tests/ui/impl-trait/variance.rs

@@ -12,17 +12,17 @@ trait Captures<'a> {}
 impl<T> Captures<'_> for T {}
 
 fn not_captured_early<'a: 'a>() -> impl Sized {}
-//[old]~^ [*]
-//[new]~^^ [*, o]
-//[e2024]~^^^ [*, o]
+//[old]~^ ['a: *]
+//[new]~^^ ['a: *, 'a: o]
+//[e2024]~^^^ ['a: *, 'a: o]
 
-fn captured_early<'a: 'a>() -> impl Sized + Captures<'a> {} //~ [*, o]
+fn captured_early<'a: 'a>() -> impl Sized + Captures<'a> {} //~ ['a: *, 'a: o]
 
 fn not_captured_late<'a>(_: &'a ()) -> impl Sized {}
 //[old]~^ []
-//[new]~^^ [o]
-//[e2024]~^^^ [o]
+//[new]~^^ ['a: o]
+//[e2024]~^^^ ['a: o]
 
-fn captured_late<'a>(_: &'a ()) -> impl Sized + Captures<'a> {} //~ [o]
+fn captured_late<'a>(_: &'a ()) -> impl Sized + Captures<'a> {} //~ ['a: o]
 
 fn main() {}

tests/ui/type-alias-impl-trait/variance.rs

@@ -5,21 +5,21 @@
 trait Captures<'a> {}
 impl<T> Captures<'_> for T {}
 
-type NotCapturedEarly<'a> = impl Sized; //~ [*, o]
+type NotCapturedEarly<'a> = impl Sized; //~ ['a: *, 'a: o]
 //~^ ERROR: unconstrained opaque type
 
-type CapturedEarly<'a> = impl Sized + Captures<'a>; //~ [*, o]
+type CapturedEarly<'a> = impl Sized + Captures<'a>; //~ ['a: *, 'a: o]
 //~^ ERROR: unconstrained opaque type
 
-type NotCapturedLate<'a> = dyn for<'b> Iterator<Item = impl Sized>; //~ [*, o, o]
+type NotCapturedLate<'a> = dyn for<'b> Iterator<Item = impl Sized>; //~ ['a: *, 'b: o, 'a: o]
 //~^ ERROR `impl Trait` cannot capture higher-ranked lifetime from `dyn` type
 //~| ERROR: unconstrained opaque type
 
-type Captured<'a> = dyn for<'b> Iterator<Item = impl Sized + Captures<'a>>; //~ [*, o, o]
+type Captured<'a> = dyn for<'b> Iterator<Item = impl Sized + Captures<'a>>; //~ ['a: *, 'b: o, 'a: o]
 //~^ ERROR `impl Trait` cannot capture higher-ranked lifetime from `dyn` type
 //~| ERROR: unconstrained opaque type
 
-type Bar<'a, 'b: 'b, T> = impl Sized; //~ ERROR [*, *, o, o, o]
+type Bar<'a, 'b: 'b, T> = impl Sized; //~ ERROR ['a: *, 'b: *, T: o, 'a: o, 'b: o]
 //~^ ERROR: unconstrained opaque type
 
 trait Foo<'i> {
@@ -31,24 +31,24 @@ trait Foo<'i> {
 }
 
 impl<'i> Foo<'i> for &'i () {
-    type ImplicitCapture<'a> = impl Sized; //~ [*, *, o, o]
+    type ImplicitCapture<'a> = impl Sized; //~ ['i: *, 'a: *, 'a: o, 'i: o]
     //~^ ERROR: unconstrained opaque type
 
-    type ExplicitCaptureFromHeader<'a> = impl Sized + Captures<'i>; //~ [*, *, o, o]
+    type ExplicitCaptureFromHeader<'a> = impl Sized + Captures<'i>; //~ ['i: *, 'a: *, 'a: o, 'i: o]
     //~^ ERROR: unconstrained opaque type
 
-    type ExplicitCaptureFromGat<'a> = impl Sized + Captures<'a>; //~ [*, *, o, o]
+    type ExplicitCaptureFromGat<'a> = impl Sized + Captures<'a>; //~ ['i: *, 'a: *, 'a: o, 'i: o]
     //~^ ERROR: unconstrained opaque type
 }
 
 impl<'i> Foo<'i> for () {
-    type ImplicitCapture<'a> = impl Sized; //~ [*, *, o, o]
+    type ImplicitCapture<'a> = impl Sized; //~ ['i: *, 'a: *, 'a: o, 'i: o]
     //~^ ERROR: unconstrained opaque type
 
-    type ExplicitCaptureFromHeader<'a> = impl Sized + Captures<'i>; //~ [*, *, o, o]
+    type ExplicitCaptureFromHeader<'a> = impl Sized + Captures<'i>; //~ ['i: *, 'a: *, 'a: o, 'i: o]
     //~^ ERROR: unconstrained opaque type
 
-    type ExplicitCaptureFromGat<'a> = impl Sized + Captures<'a>; //~ [*, *, o, o]
+    type ExplicitCaptureFromGat<'a> = impl Sized + Captures<'a>; //~ ['i: *, 'a: *, 'a: o, 'i: o]
     //~^ ERROR: unconstrained opaque type
 }
 
@@ -59,15 +59,15 @@ impl<'a> Nesting<'a> for &'a () {
     type Output = &'a ();
 }
 type NestedDeeply<'a> =
-    impl Nesting< //~ [*, o]
+    impl Nesting< //~ ['a: *, 'a: o]
         'a,
-        Output = impl Nesting< //~ [*, o]
+        Output = impl Nesting< //~ ['a: *, 'a: o]
             'a,
-            Output = impl Nesting< //~ [*, o]
+            Output = impl Nesting< //~ ['a: *, 'a: o]
                 'a,
-                Output = impl Nesting< //~ [*, o]
+                Output = impl Nesting< //~ ['a: *, 'a: o]
                     'a,
-                    Output = impl Nesting<'a> //~ [*, o]
+                    Output = impl Nesting<'a> //~ ['a: *, 'a: o]
                 >
             >,
         >,