Auto merge of #47791 - estebank:mismatched-trait-impl, r=nikomatsakis

Tweak presentation on lifetime trait mismatch

 - On trait/impl method discrepancy, add label pointing at trait signature.
 - Point only at method definition when referring to named lifetimes on lifetime mismatch.
 - When the sub and sup expectations are the same, tweak the output to avoid repeated spans.

Fix #30790, CC #18759.

Author: bors

src/librustc/infer/error_reporting/mod.rs

@@ -175,25 +175,6 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             ty::ReEarlyBound(_) |
             ty::ReFree(_) => {
                 let scope = region.free_region_binding_scope(self);
-                let prefix = match *region {
-                    ty::ReEarlyBound(ref br) => {
-                        format!("the lifetime {} as defined on", br.name)
-                    }
-                    ty::ReFree(ref fr) => {
-                        match fr.bound_region {
-                            ty::BrAnon(idx) => {
-                                format!("the anonymous lifetime #{} defined on", idx + 1)
-                            }
-                            ty::BrFresh(_) => "an anonymous lifetime defined on".to_owned(),
-                            _ => {
-                                format!("the lifetime {} as defined on",
-                                        fr.bound_region)
-                            }
-                        }
-                    }
-                    _ => bug!()
-                };
-
                 let node = self.hir.as_local_node_id(scope)
                                    .unwrap_or(DUMMY_NODE_ID);
                 let unknown;
@@ -218,7 +199,26 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
                         &unknown
                     }
                 };
-                let (msg, opt_span) = explain_span(self, tag, self.hir.span(node));
+                let (prefix, span) = match *region {
+                    ty::ReEarlyBound(ref br) => {
+                        (format!("the lifetime {} as defined on", br.name),
+                         self.sess.codemap().def_span(self.hir.span(node)))
+                    }
+                    ty::ReFree(ref fr) => {
+                        match fr.bound_region {
+                            ty::BrAnon(idx) => {
+                                (format!("the anonymous lifetime #{} defined on", idx + 1),
+                                 self.hir.span(node))
+                            }
+                            ty::BrFresh(_) => ("an anonymous lifetime defined on".to_owned(),
+                                               self.hir.span(node)),
+                            _ => (format!("the lifetime {} as defined on", fr.bound_region),
+                                  self.sess.codemap().def_span(self.hir.span(node))),
+                        }
+                    }
+                    _ => bug!()
+                };
+                let (msg, opt_span) = explain_span(self, tag, span);
                 (format!("{} {}", prefix, msg), opt_span)
             }
 
@@ -807,7 +807,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             }
         };
 
-        let span = cause.span;
+        let span = cause.span(&self.tcx);
 
         diag.span_label(span, terr.to_string());
         if let Some((sp, msg)) = secondary_span {
@@ -842,7 +842,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                                     "did you mean `{}(/* fields */)`?",
                                     self.tcx.item_path_str(def_id)
                                 );
-                                diag.span_label(cause.span, message);
+                                diag.span_label(span, message);
                             }
                         }
                     }
@@ -870,7 +870,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                trace,
                terr);
 
-        let span = trace.cause.span;
+        let span = trace.cause.span(&self.tcx);
         let failure_code = trace.cause.as_failure_code(terr);
         let mut diag = match failure_code {
             FailureCode::Error0317(failure_str) => {
@@ -1076,6 +1076,31 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             sup_region,
             "...");
 
+        match (&sup_origin, &sub_origin) {
+            (&infer::Subtype(ref sup_trace), &infer::Subtype(ref sub_trace)) => {
+                if let (Some((sup_expected, sup_found)),
+                        Some((sub_expected, sub_found))) = (self.values_str(&sup_trace.values),
+                                                            self.values_str(&sub_trace.values)) {
+                    if sub_expected == sup_expected && sub_found == sup_found {
+                        self.tcx.note_and_explain_region(
+                            region_scope_tree,
+                            &mut err,
+                            "...but the lifetime must also be valid for ",
+                            sub_region,
+                            "...",
+                        );
+                        err.note(&format!("...so that the {}:\nexpected {}\n   found {}",
+                                          sup_trace.cause.as_requirement_str(),
+                                          sup_expected.content(),
+                                          sup_found.content()));
+                        err.emit();
+                        return;
+                    }
+                }
+            }
+            _ => {}
+        }
+
         self.note_region_origin(&mut err, &sup_origin);
 
         self.tcx.note_and_explain_region(region_scope_tree, &mut err,

src/librustc/infer/error_reporting/note.rs

@@ -23,12 +23,10 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                 if let Some((expected, found)) = self.values_str(&trace.values) {
                     let expected = expected.content();
                     let found = found.content();
-                    // FIXME: do we want a "the" here?
-                    err.span_note(trace.cause.span,
-                                  &format!("...so that {} (expected {}, found {})",
-                                           trace.cause.as_requirement_str(),
-                                           expected,
-                                           found));
+                    err.note(&format!("...so that the {}:\nexpected {}\n   found {}",
+                                      trace.cause.as_requirement_str(),
+                                      expected,
+                                      found));
                 } else {
                     // FIXME: this really should be handled at some earlier stage. Our
                     // handling of region checking when type errors are present is

src/librustc/traits/mod.rs

@@ -100,6 +100,19 @@ pub struct ObligationCause<'tcx> {
     pub code: ObligationCauseCode<'tcx>
 }
 
+impl<'tcx> ObligationCause<'tcx> {
+    pub fn span<'a, 'gcx>(&self, tcx: &TyCtxt<'a, 'gcx, 'tcx>) -> Span {
+        match self.code {
+            ObligationCauseCode::CompareImplMethodObligation { .. } |
+            ObligationCauseCode::MainFunctionType |
+            ObligationCauseCode::StartFunctionType => {
+                tcx.sess.codemap().def_span(self.span)
+            }
+            _ => self.span,
+        }
+    }
+}
+
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum ObligationCauseCode<'tcx> {
     /// Not well classified or should be obvious from span.

src/librustc_typeck/check/compare_method.rs

@@ -40,6 +40,8 @@ pub fn compare_impl_method<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     debug!("compare_impl_method(impl_trait_ref={:?})",
            impl_trait_ref);
 
+    let impl_m_span = tcx.sess.codemap().def_span(impl_m_span);
+
     if let Err(ErrorReported) = compare_self_type(tcx,
                                                   impl_m,
                                                   impl_m_span,
@@ -186,6 +188,7 @@ fn compare_predicate_entailment<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     check_region_bounds_on_impl_method(tcx,
                                        impl_m_span,
                                        impl_m,
+                                       trait_m,
                                        &trait_m_generics,
                                        &impl_m_generics,
                                        trait_to_skol_substs)?;
@@ -310,7 +313,7 @@ fn compare_predicate_entailment<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
             };
 
             let mut diag = struct_span_err!(tcx.sess,
-                                            cause.span,
+                                            cause.span(&tcx),
                                             E0053,
                                             "method `{}` has an incompatible type for trait",
                                             trait_m.name);
@@ -346,10 +349,12 @@ fn compare_predicate_entailment<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 fn check_region_bounds_on_impl_method<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                                 span: Span,
                                                 impl_m: &ty::AssociatedItem,
+                                                trait_m: &ty::AssociatedItem,
                                                 trait_generics: &ty::Generics,
                                                 impl_generics: &ty::Generics,
                                                 trait_to_skol_substs: &Substs<'tcx>)
                                                 -> Result<(), ErrorReported> {
+    let span = tcx.sess.codemap().def_span(span);
     let trait_params = &trait_generics.regions[..];
     let impl_params = &impl_generics.regions[..];
 
@@ -371,14 +376,18 @@ fn check_region_bounds_on_impl_method<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     // are zero. Since I don't quite know how to phrase things at
     // the moment, give a kind of vague error message.
     if trait_params.len() != impl_params.len() {
-        struct_span_err!(tcx.sess,
-                         span,
-                         E0195,
-                         "lifetime parameters or bounds on method `{}` do not match the \
-                          trait declaration",
-                         impl_m.name)
-            .span_label(span, "lifetimes do not match trait")
-            .emit();
+        let mut err = struct_span_err!(tcx.sess,
+                                       span,
+                                       E0195,
+                                       "lifetime parameters or bounds on method `{}` do not match \
+                                        the trait declaration",
+                                       impl_m.name);
+        err.span_label(span, "lifetimes do not match method in trait");
+        if let Some(sp) = tcx.hir.span_if_local(trait_m.def_id) {
+            err.span_label(tcx.sess.codemap().def_span(sp),
+                           "lifetimes in impl do not match this method in trait");
+        }
+        err.emit();
         return Err(ErrorReported);
     }
 
@@ -424,9 +433,9 @@ fn extract_spans_for_error_reporting<'a, 'gcx, 'tcx>(infcx: &infer::InferCtxt<'a
                 }).map(|(ref impl_arg, ref trait_arg)| {
                     (impl_arg.span, Some(trait_arg.span))
                 })
-                .unwrap_or_else(|| (cause.span, tcx.hir.span_if_local(trait_m.def_id)))
+                .unwrap_or_else(|| (cause.span(&tcx), tcx.hir.span_if_local(trait_m.def_id)))
             } else {
-                (cause.span, tcx.hir.span_if_local(trait_m.def_id))
+                (cause.span(&tcx), tcx.hir.span_if_local(trait_m.def_id))
             }
         }
         TypeError::Sorts(ExpectedFound { .. }) => {
@@ -459,14 +468,14 @@ fn extract_spans_for_error_reporting<'a, 'gcx, 'tcx>(infcx: &infer::InferCtxt<'a
                              {
                                  (impl_m_output.span(), Some(trait_m_output.span()))
                              } else {
-                                 (cause.span, tcx.hir.span_if_local(trait_m.def_id))
+                                 (cause.span(&tcx), tcx.hir.span_if_local(trait_m.def_id))
                              }
                          })
             } else {
-                (cause.span, tcx.hir.span_if_local(trait_m.def_id))
+                (cause.span(&tcx), tcx.hir.span_if_local(trait_m.def_id))
             }
         }
-        _ => (cause.span, tcx.hir.span_if_local(trait_m.def_id)),
+        _ => (cause.span(&tcx), tcx.hir.span_if_local(trait_m.def_id)),
     }
 }
 

src/test/compile-fail/E0195.rs

@@ -10,13 +10,14 @@
 
 trait Trait {
     fn bar<'a,'b:'a>(x: &'a str, y: &'b str);
+    //~^ NOTE lifetimes in impl do not match this method in trait
 }
 
 struct Foo;
 
 impl Trait for Foo {
     fn bar<'a,'b>(x: &'a str, y: &'b str) { //~ ERROR E0195
-                                            //~^ lifetimes do not match trait
+    //~^ NOTE lifetimes do not match method in trait
     }
 }
 

src/test/compile-fail/issue-16048.rs

@@ -10,6 +10,7 @@
 
 trait NoLifetime {
     fn get<'p, T : Test<'p>>(&self) -> T;
+    //~^ NOTE lifetimes in impl do not match this method in trait
 }
 
 trait Test<'p> {
@@ -28,8 +29,8 @@ impl<'a> Test<'a> for Foo<'a> {
 
 impl<'a> NoLifetime for Foo<'a> {
     fn get<'p, T : Test<'a>>(&self) -> T {
-//~^ ERROR E0195
-//~| lifetimes do not match trait
+    //~^ ERROR E0195
+    //~| NOTE lifetimes do not match method in trait
         return *self as T;
     }
 }

src/test/ui/associated-const-impl-wrong-lifetime.stderr

@@ -9,11 +9,8 @@ error[E0308]: mismatched types
 note: the lifetime 'a as defined on the impl at 17:1...
   --> $DIR/associated-const-impl-wrong-lifetime.rs:17:1
    |
-17 | / impl<'a> Foo for &'a () {
-18 | |     const NAME: &'a str = "unit";
-19 | |     //~^ ERROR mismatched types [E0308]
-20 | | }
-   | |_^
+17 | impl<'a> Foo for &'a () {
+   | ^^^^^^^^^^^^^^^^^^^^^^^
    = note: ...does not necessarily outlive the static lifetime
 
 error: aborting due to previous error

src/test/compile-fail/regions-bound-missing-bound-in-impl.rs renamed to src/test/ui/borrowck/regions-bound-missing-bound-in-impl.rs

@@ -0,0 +1,48 @@
+error[E0195]: lifetime parameters or bounds on method `no_bound` do not match the trait declaration
+  --> $DIR/regions-bound-missing-bound-in-impl.rs:28:5
+   |
+20 |     fn no_bound<'b>(self, b: Inv<'b>);
+   |     ---------------------------------- lifetimes in impl do not match this method in trait
+...
+28 |     fn no_bound<'b:'a>(self, b: Inv<'b>) {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ lifetimes do not match method in trait
+
+error[E0195]: lifetime parameters or bounds on method `has_bound` do not match the trait declaration
+  --> $DIR/regions-bound-missing-bound-in-impl.rs:32:5
+   |
+21 |     fn has_bound<'b:'a>(self, b: Inv<'b>);
+   |     -------------------------------------- lifetimes in impl do not match this method in trait
+...
+32 |     fn has_bound<'b>(self, b: Inv<'b>) {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ lifetimes do not match method in trait
+
+error[E0308]: method not compatible with trait
+  --> $DIR/regions-bound-missing-bound-in-impl.rs:36:5
+   |
+36 |     fn wrong_bound1<'b,'c,'d:'a+'c>(self, b: Inv<'b>, c: Inv<'c>, d: Inv<'d>) {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
+   |
+   = note: expected type `fn(&'a isize, Inv<'c>, Inv<'c>, Inv<'d>)`
+              found type `fn(&'a isize, Inv<'_>, Inv<'c>, Inv<'d>)`
+note: the lifetime 'c as defined on the method body at 36:5...
+  --> $DIR/regions-bound-missing-bound-in-impl.rs:36:5
+   |
+36 |     fn wrong_bound1<'b,'c,'d:'a+'c>(self, b: Inv<'b>, c: Inv<'c>, d: Inv<'d>) {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+note: ...does not necessarily outlive the lifetime 'c as defined on the method body at 36:5
+  --> $DIR/regions-bound-missing-bound-in-impl.rs:36:5
+   |
+36 |     fn wrong_bound1<'b,'c,'d:'a+'c>(self, b: Inv<'b>, c: Inv<'c>, d: Inv<'d>) {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0276]: impl has stricter requirements than trait
+  --> $DIR/regions-bound-missing-bound-in-impl.rs:53:5
+   |
+24 |     fn another_bound<'x: 'a>(self, x: Inv<'x>, y: Inv<'t>);
+   |     ------------------------------------------------------- definition of `another_bound` from trait
+...
+53 |     fn another_bound<'x: 't>(self, x: Inv<'x>, y: Inv<'t>) {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ impl has extra requirement `'x: 't`
+
+error: aborting due to 4 previous errors
+

src/test/ui/borrowck/regions-bound-missing-bound-in-impl.stderr

@@ -41,14 +41,8 @@ note: the anonymous lifetime #2 defined on the body at 47:29...
 note: ...does not necessarily outlive the lifetime 'x as defined on the function body at 42:1
   --> $DIR/expect-region-supply-region.rs:42:1
    |
-42 | / fn expect_bound_supply_named<'x>() {
-43 | |     let mut f: Option<&u32> = None;
-44 | |
-45 | |     // Here we give a type annotation that `x` should be free. We get
-...  |
-54 | |     });
-55 | | }
-   | |_^
+42 | fn expect_bound_supply_named<'x>() {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0308]: mismatched types
   --> $DIR/expect-region-supply-region.rs:47:33
@@ -61,14 +55,8 @@ error[E0308]: mismatched types
 note: the lifetime 'x as defined on the function body at 42:1...
   --> $DIR/expect-region-supply-region.rs:42:1
    |
-42 | / fn expect_bound_supply_named<'x>() {
-43 | |     let mut f: Option<&u32> = None;
-44 | |
-45 | |     // Here we give a type annotation that `x` should be free. We get
-...  |
-54 | |     });
-55 | | }
-   | |_^
+42 | fn expect_bound_supply_named<'x>() {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 note: ...does not necessarily outlive the anonymous lifetime #2 defined on the body at 47:29
   --> $DIR/expect-region-supply-region.rs:47:29
    |