Report mismatched type errors for bound region errors in NLL

matthewjasper · lqd · commit 0c388b0261d7 · 2021-08-15T09:11:00.000+02:00
diff --git a/compiler/rustc_mir/src/borrow_check/diagnostics/bound_region_errors.rs b/compiler/rustc_mir/src/borrow_check/diagnostics/bound_region_errors.rs
@@ -1,4 +1,6 @@
 use rustc_infer::infer::canonical::Canonical;
+use rustc_infer::traits::ObligationCause;
+use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::{self, Ty, TypeFoldable};
 use rustc_span::Span;
 use rustc_trait_selection::traits::query::type_op;
@@ -32,14 +34,33 @@ impl UniverseInfo<'tcx> {
         UniverseInfo(UniverseInfoInner::RelateTys { expected, found })
     }
 
-    crate fn _report_error(
+    crate fn report_error(
         &self,
-        _mbcx: &mut MirBorrowckCtxt<'_, 'tcx>,
+        mbcx: &mut MirBorrowckCtxt<'_, 'tcx>,
         _placeholder: ty::PlaceholderRegion,
         _error_element: RegionElement,
-        _span: Span,
+        span: Span,
     ) {
-        todo!();
+        // FIXME: improve this error message
+        match self.0 {
+            UniverseInfoInner::RelateTys { expected, found } => {
+                let body_id = mbcx.infcx.tcx.hir().local_def_id_to_hir_id(mbcx.mir_def_id());
+                let err = mbcx.infcx.report_mismatched_types(
+                    &ObligationCause::misc(span, body_id),
+                    expected,
+                    found,
+                    TypeError::RegionsPlaceholderMismatch,
+                );
+                err.buffer(&mut mbcx.errors_buffer);
+            }
+            UniverseInfoInner::TypeOp(_) | UniverseInfoInner::Other => {
+                mbcx.infcx
+                    .tcx
+                    .sess
+                    .struct_span_err(span, "higher-ranked subtype error")
+                    .buffer(&mut mbcx.errors_buffer);
+            }
+        }
     }
 }
 
diff --git a/compiler/rustc_mir/src/borrow_check/diagnostics/region_errors.rs b/compiler/rustc_mir/src/borrow_check/diagnostics/region_errors.rs
@@ -223,12 +223,10 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                         error_vid,
                     );
 
-                    // FIXME: improve this error message
-                    self.infcx
-                        .tcx
-                        .sess
-                        .struct_span_err(span, "higher-ranked subtype error")
-                        .buffer(&mut self.errors_buffer);
+                    let universe = placeholder.universe;
+                    let universe_info = self.regioncx.universe_info(universe);
+
+                    universe_info.report_error(self, placeholder, error_element, span);
                 }
 
                 RegionErrorKind::RegionError { fr_origin, longer_fr, shorter_fr, is_reported } => {
diff --git a/compiler/rustc_mir/src/borrow_check/region_infer/mod.rs b/compiler/rustc_mir/src/borrow_check/region_infer/mod.rs
@@ -85,7 +85,7 @@ pub struct RegionInferenceContext<'tcx> {
         FxHashMap<Location, FxHashMap<(RegionVid, RegionVid), (ConstraintCategory, Span)>>,
 
     /// Map universe indexes to information on why we created it.
-    _universe_causes: IndexVec<ty::UniverseIndex, UniverseInfo<'tcx>>,
+    universe_causes: IndexVec<ty::UniverseIndex, UniverseInfo<'tcx>>,
 
     /// Contains the minimum universe of any variable within the same
     /// SCC. We will ensure that no SCC contains values that are not
@@ -297,7 +297,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
             member_constraints,
             member_constraints_applied: Vec::new(),
             closure_bounds_mapping,
-            _universe_causes: universe_causes,
+            universe_causes,
             scc_universes,
             scc_representatives,
             scc_values,
@@ -2143,6 +2143,10 @@ impl<'tcx> RegionInferenceContext<'tcx> {
 
         categorized_path.remove(0)
     }
+
+    crate fn universe_info(&self, universe: ty::UniverseIndex) -> UniverseInfo<'tcx> {
+        self.universe_causes[universe].clone()
+    }
 }
 
 impl<'tcx> RegionDefinition<'tcx> {
diff --git a/src/test/ui/closure-expected-type/expect-fn-supply-fn.nll.stderr b/src/test/ui/closure-expected-type/expect-fn-supply-fn.nll.stderr
@@ -21,23 +21,33 @@ LL |     with_closure_expecting_fn_with_free_region(|x: fn(&'x u32), y| {});
    |
    = help: consider replacing `'x` with `'static`
 
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/expect-fn-supply-fn.rs:32:49
    |
 LL |     with_closure_expecting_fn_with_free_region(|x: fn(&u32), y| {});
-   |                                                 ^
+   |                                                 ^ one type is more general than the other
+   |
+   = note: expected fn pointer `for<'r> fn(&'r u32)`
+              found fn pointer `fn(&u32)`
 
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/expect-fn-supply-fn.rs:39:50
    |
 LL |     with_closure_expecting_fn_with_bound_region(|x: fn(&'x u32), y| {});
-   |                                                  ^
+   |                                                  ^ one type is more general than the other
+   |
+   = note: expected fn pointer `fn(&'x u32)`
+              found fn pointer `for<'r> fn(&'r u32)`
 
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/expect-fn-supply-fn.rs:48:50
    |
 LL |     with_closure_expecting_fn_with_bound_region(|x: Foo<'_>, y| {
-   |                                                  ^
+   |                                                  ^ one type is more general than the other
+   |
+   = note: expected fn pointer `fn(&u32)`
+              found fn pointer `for<'r> fn(&'r u32)`
 
 error: aborting due to 5 previous errors
 
+For more information about this error, try `rustc --explain E0308`.
diff --git a/src/test/ui/hr-subtype/hr-subtype.bound_a_b_ret_a_vs_bound_a_ret_a.nll.stderr b/src/test/ui/hr-subtype/hr-subtype.bound_a_b_ret_a_vs_bound_a_ret_a.nll.stderr
@@ -1,14 +1,17 @@
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/hr-subtype.rs:45:13
    |
 LL |               gimme::<$t1>(None::<$t2>);
-   |               ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
 ...
 LL | / check! { bound_a_b_ret_a_vs_bound_a_ret_a: (for<'a,'b> fn(&'a u32, &'b u32) -> &'a u32,
 LL | | for<'a>    fn(&'a u32, &'a u32) -> &'a u32) }
    | |_____________________________________________- in this macro invocation
    |
+   = note: expected enum `Option<for<'r, 's> fn(&'r u32, &'s u32) -> &'r u32>`
+              found enum `Option<for<'r> fn(&'r u32, &'r u32) -> &'r u32>`
    = note: this error originates in the macro `check` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0308`.
diff --git a/src/test/ui/hr-subtype/hr-subtype.bound_a_vs_free_x.nll.stderr b/src/test/ui/hr-subtype/hr-subtype.bound_a_vs_free_x.nll.stderr
@@ -1,14 +1,17 @@
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/hr-subtype.rs:45:13
    |
 LL |               gimme::<$t1>(None::<$t2>);
-   |               ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
 ...
 LL | / check! { bound_a_vs_free_x: (for<'a> fn(&'a u32),
 LL | | fn(&'x u32)) }
    | |______________- in this macro invocation
    |
+   = note: expected enum `Option<for<'r> fn(&'r u32)>`
+              found enum `Option<fn(&u32)>`
    = note: this error originates in the macro `check` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0308`.
diff --git a/src/test/ui/hr-subtype/hr-subtype.bound_inv_a_b_vs_bound_inv_a.nll.stderr b/src/test/ui/hr-subtype/hr-subtype.bound_inv_a_b_vs_bound_inv_a.nll.stderr
@@ -1,26 +1,31 @@
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/hr-subtype.rs:45:13
    |
 LL |               gimme::<$t1>(None::<$t2>);
-   |               ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
 ...
 LL | / check! { bound_inv_a_b_vs_bound_inv_a: (for<'a,'b> fn(Inv<'a>, Inv<'b>),
 LL | | for<'a>    fn(Inv<'a>, Inv<'a>)) }
    | |__________________________________- in this macro invocation
    |
+   = note: expected enum `Option<for<'r, 's> fn(Inv<'r>, Inv<'s>)>`
+              found enum `Option<for<'r> fn(Inv<'r>, Inv<'r>)>`
    = note: this error originates in the macro `check` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/hr-subtype.rs:45:13
    |
 LL |               gimme::<$t1>(None::<$t2>);
-   |               ^^^^^^^^^^^^^^^^^^^^^^^^^
+   |               ^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
 ...
 LL | / check! { bound_inv_a_b_vs_bound_inv_a: (for<'a,'b> fn(Inv<'a>, Inv<'b>),
 LL | | for<'a>    fn(Inv<'a>, Inv<'a>)) }
    | |__________________________________- in this macro invocation
    |
+   = note: expected enum `Option<for<'r, 's> fn(Inv<'r>, Inv<'s>)>`
+              found enum `Option<for<'r> fn(Inv<'r>, Inv<'r>)>`
    = note: this error originates in the macro `check` (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 E0308`.
diff --git a/src/test/ui/hrtb/hrtb-exists-forall-fn.nll.stderr b/src/test/ui/hrtb/hrtb-exists-forall-fn.nll.stderr
@@ -1,8 +1,12 @@
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/hrtb-exists-forall-fn.rs:17:12
    |
 LL |     let _: for<'b> fn(&'b u32) = foo();
-   |            ^^^^^^^^^^^^^^^^^^^
+   |            ^^^^^^^^^^^^^^^^^^^ one type is more general than the other
+   |
+   = note: expected fn pointer `for<'b> fn(&'b u32)`
+              found fn pointer `fn(&u32)`
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0308`.
diff --git a/src/test/ui/lub-glb/old-lub-glb-hr-noteq1.nll.stderr b/src/test/ui/lub-glb/old-lub-glb-hr-noteq1.nll.stderr
@@ -1,8 +1,12 @@
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/old-lub-glb-hr-noteq1.rs:11:14
    |
 LL |         _ => y,
-   |              ^
+   |              ^ one type is more general than the other
+   |
+   = note: expected fn pointer `for<'r, 's> fn(&'r u8, &'s u8) -> &'r u8`
+              found fn pointer `for<'r> fn(&'r u8, &'r u8) -> &'r u8`
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0308`.
diff --git a/src/test/ui/nll/relate_tys/fn-subtype.rs b/src/test/ui/nll/relate_tys/fn-subtype.rs
@@ -6,5 +6,5 @@
 
 fn main() {
     let x: fn(&'static ()) = |_| {};
-    let y: for<'a> fn(&'a ()) = x; //~ ERROR higher-ranked subtype error
+    let y: for<'a> fn(&'a ()) = x; //~ ERROR mismatched types [E0308]
 }
diff --git a/src/test/ui/nll/relate_tys/fn-subtype.stderr b/src/test/ui/nll/relate_tys/fn-subtype.stderr
@@ -1,8 +1,12 @@
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/fn-subtype.rs:9:33
    |
 LL |     let y: for<'a> fn(&'a ()) = x;
-   |                                 ^
+   |                                 ^ one type is more general than the other
+   |
+   = note: expected fn pointer `for<'r> fn(&'r ())`
+              found fn pointer `fn(&())`
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0308`.
diff --git a/src/test/ui/nll/relate_tys/hr-fn-aaa-as-aba.rs b/src/test/ui/nll/relate_tys/hr-fn-aaa-as-aba.rs
@@ -12,15 +12,15 @@ fn make_it() -> for<'a> fn(&'a u32, &'a u32) -> &'a u32 {
 
 fn foo() {
     let a: for<'a, 'b> fn(&'a u32, &'b u32) -> &'a u32 = make_it();
-    //~^ ERROR higher-ranked subtype error
+    //~^ ERROR mismatched types [E0308]
     drop(a);
 }
 
 fn bar() {
     // The code path for patterns is mildly different, so go ahead and
     // test that too:
     let _: for<'a, 'b> fn(&'a u32, &'b u32) -> &'a u32 = make_it();
-    //~^ ERROR higher-ranked subtype error
+    //~^ ERROR mismatched types [E0308]
 }
 
-fn main() { }
+fn main() {}
diff --git a/src/test/ui/nll/relate_tys/hr-fn-aaa-as-aba.stderr b/src/test/ui/nll/relate_tys/hr-fn-aaa-as-aba.stderr
@@ -1,14 +1,21 @@
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/hr-fn-aaa-as-aba.rs:14:58
    |
 LL |     let a: for<'a, 'b> fn(&'a u32, &'b u32) -> &'a u32 = make_it();
-   |                                                          ^^^^^^^^^
+   |                                                          ^^^^^^^^^ one type is more general than the other
+   |
+   = note: expected fn pointer `for<'r, 's> fn(&'r u32, &'s u32) -> &'r u32`
+              found fn pointer `for<'a> fn(&'a u32, &'a u32) -> &'a u32`
 
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/hr-fn-aaa-as-aba.rs:22:12
    |
 LL |     let _: for<'a, 'b> fn(&'a u32, &'b u32) -> &'a u32 = make_it();
-   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
+   |
+   = note: expected fn pointer `for<'a, 'b> fn(&'a u32, &'b u32) -> &'a u32`
+              found fn pointer `for<'r> fn(&'r u32, &'r u32) -> &'r u32`
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0308`.
diff --git a/src/test/ui/nll/relate_tys/universe-violation.rs b/src/test/ui/nll/relate_tys/universe-violation.rs
@@ -12,6 +12,6 @@ fn make_it() -> fn(&'static u32) -> &'static u32 {
 
 fn main() {
     let a: fn(_) -> _ = make_it();
-    let b: fn(&u32) -> &u32 = a; //~ ERROR higher-ranked subtype error
+    let b: fn(&u32) -> &u32 = a; //~ ERROR mismatched types [E0308]
     drop(a);
 }
diff --git a/src/test/ui/nll/relate_tys/universe-violation.stderr b/src/test/ui/nll/relate_tys/universe-violation.stderr
@@ -1,8 +1,12 @@
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/universe-violation.rs:15:31
    |
 LL |     let b: fn(&u32) -> &u32 = a;
-   |                               ^
+   |                               ^ one type is more general than the other
+   |
+   = note: expected fn pointer `for<'r> fn(&'r u32) -> &'r u32`
+              found fn pointer `fn(&u32) -> &u32`
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0308`.
diff --git a/src/test/ui/regions/region-lifetime-bounds-on-fns-where-clause.nll.stderr b/src/test/ui/regions/region-lifetime-bounds-on-fns-where-clause.nll.stderr
@@ -27,17 +27,24 @@ LL |     a(x, y);
    = note: mutable references are invariant over their type parameter
    = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/region-lifetime-bounds-on-fns-where-clause.rs:20:12
    |
 LL |     let _: fn(&mut &isize, &mut &isize) = a;
-   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
+   |
+   = note: expected fn pointer `for<'r, 's, 't0, 't1> fn(&'r mut &'s isize, &'t0 mut &'t1 isize)`
+              found fn pointer `for<'r, 's> fn(&'r mut &isize, &'s mut &isize)`
 
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/region-lifetime-bounds-on-fns-where-clause.rs:20:12
    |
 LL |     let _: fn(&mut &isize, &mut &isize) = a;
-   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
+   |
+   = note: expected fn pointer `for<'r, 's, 't0, 't1> fn(&'r mut &'s isize, &'t0 mut &'t1 isize)`
+              found fn pointer `for<'r, 's> fn(&'r mut &isize, &'s mut &isize)`
 
 error: aborting due to 4 previous errors
 
+For more information about this error, try `rustc --explain E0308`.
diff --git a/src/test/ui/regions/region-multiple-lifetime-bounds-on-fns-where-clause.nll.stderr b/src/test/ui/regions/region-multiple-lifetime-bounds-on-fns-where-clause.nll.stderr
@@ -27,23 +27,33 @@ LL |     a(x, y, z);
    = note: mutable references are invariant over their type parameter
    = help: see <https://doc.rust-lang.org/nomicon/subtyping.html> for more information about variance
 
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/region-multiple-lifetime-bounds-on-fns-where-clause.rs:22:12
    |
 LL |     let _: fn(&mut &isize, &mut &isize, &mut &isize) = a;
-   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
+   |
+   = note: expected fn pointer `for<'r, 's, 't0, 't1, 't2, 't3> fn(&'r mut &'s isize, &'t0 mut &'t1 isize, &'t2 mut &'t3 isize)`
+              found fn pointer `for<'r, 's, 't0> fn(&'r mut &isize, &'s mut &isize, &'t0 mut &isize)`
 
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/region-multiple-lifetime-bounds-on-fns-where-clause.rs:22:12
    |
 LL |     let _: fn(&mut &isize, &mut &isize, &mut &isize) = a;
-   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
+   |
+   = note: expected fn pointer `for<'r, 's, 't0, 't1, 't2, 't3> fn(&'r mut &'s isize, &'t0 mut &'t1 isize, &'t2 mut &'t3 isize)`
+              found fn pointer `for<'r, 's, 't0> fn(&'r mut &isize, &'s mut &isize, &'t0 mut &isize)`
 
-error: higher-ranked subtype error
+error[E0308]: mismatched types
   --> $DIR/region-multiple-lifetime-bounds-on-fns-where-clause.rs:22:12
    |
 LL |     let _: fn(&mut &isize, &mut &isize, &mut &isize) = a;
-   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ one type is more general than the other
+   |
+   = note: expected fn pointer `for<'r, 's, 't0, 't1, 't2, 't3> fn(&'r mut &'s isize, &'t0 mut &'t1 isize, &'t2 mut &'t3 isize)`
+              found fn pointer `for<'r, 's, 't0> fn(&'r mut &isize, &'s mut &isize, &'t0 mut &isize)`
 
 error: aborting due to 5 previous errors
 
+For more information about this error, try `rustc --explain E0308`.
diff --git a/src/test/ui/regions/regions-fn-subtyping-return-static-fail.nll.stderr b/src/test/ui/regions/regions-fn-subtyping-return-static-fail.nll.stderr
diff --git a/src/test/ui/regions/regions-lifetime-bounds-on-fns.nll.stderr b/src/test/ui/regions/regions-lifetime-bounds-on-fns.nll.stderr

Original file line number	Diff line number	Diff line change
`@@ -6,5 +6,5 @@`
`6`	`6`
`7`	`7`	`fn main() {`
`8`	`8`	`let x: fn(&'static ()) = \|_\| {};`
`9`		`- let y: for<'a> fn(&'a ()) = x; //~ ERROR higher-ranked subtype error`
	`9`	`+ let y: for<'a> fn(&'a ()) = x; //~ ERROR mismatched types [E0308]`
`10`	`10`	`}`
Original file line number	Diff line number	Diff line change
`@@ -12,6 +12,6 @@ fn make_it() -> fn(&'static u32) -> &'static u32 {`
`12`	`12`
`13`	`13`	`fn main() {`
`14`	`14`	`let a: fn(_) -> _ = make_it();`
`15`		`- let b: fn(&u32) -> &u32 = a; //~ ERROR higher-ranked subtype error`
	`15`	`+ let b: fn(&u32) -> &u32 = a; //~ ERROR mismatched types [E0308]`
`16`	`16`	`drop(a);`
`17`	`17`	`}`