Fix unnamed lifetime spans

compiler/rustc_hir/src/hir.rs

@@ -571,6 +571,10 @@ impl<'hir> Generics<'hir> {
         self.params.iter().find(|&param| name == param.name.ident().name)
     }
 
+    pub fn get_with_def_id(&self, id: DefId) -> Option<&GenericParam<'hir>> {
+        self.params.iter().find(|&param| id.index == param.def_id.local_def_index)
+    }
+
     /// If there are generic parameters, return where to introduce a new one.
     pub fn span_for_lifetime_suggestion(&self) -> Option<Span> {
         if let Some(first) = self.params.first()

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -201,8 +201,10 @@ fn msg_span_from_named_region<'tcx>(
     match *region {
         ty::ReEarlyParam(ref br) => {
             let scope = region.free_region_binding_scope(tcx).expect_local();
-            let span = if let Some(param) =
-                tcx.hir().get_generics(scope).and_then(|generics| generics.get_named(br.name))
+            let span = if let Some(param) = tcx
+                .hir()
+                .get_generics(scope)
+                .and_then(|generics| generics.get_with_def_id(br.def_id))
             {
                 param.span
             } else {

tests/ui/inference/unnamed-lifetime-span-mixup-125143.rs

@@ -0,0 +1,42 @@
+struct X;
+
+// Test that the error correctly differentiate between the two unnamed lifetimes
+impl std::ops::Add<&X> for &X {
+    type Output = X;
+
+    fn add(self, _rhs: Self) -> Self::Output {
+        X
+    }
+}
+//~^^^^ ERROR method not compatible with trait
+
+// Test that the error correctly differentiate between named and the unnamed lifetimes
+impl<'a> std::ops::Mul<&'a X> for &X {
+    type Output = X;
+
+    fn mul(self, _rhs: Self) -> Self::Output {
+        X
+    }
+}
+//~^^^^ ERROR method not compatible with trait
+
+// Test that the error correctly differentiate between named and the unnamed lifetimes
+impl<'a> std::ops::Sub<&X> for &'a X {
+    type Output = X;
+
+    fn sub(self, _rhs: Self) -> Self::Output {
+        X
+    }
+}
+//~^^^^ ERROR method not compatible with trait
+
+// This should pass since the lifetime subtyping will pass typecheck
+impl<'a, 'b> std::ops::Div<&'a X> for &'b X where 'a : 'b {
+    type Output = X;
+
+    fn div(self, _rhs: Self) -> Self::Output {
+        X
+    }
+}
+
+fn main() {}

tests/ui/inference/unnamed-lifetime-span-mixup-125143.stderr

@@ -0,0 +1,60 @@
+error[E0308]: method not compatible with trait
+  --> $DIR/unnamed-lifetime-span-mixup-125143.rs:7:5
+   |
+LL |     fn add(self, _rhs: Self) -> Self::Output {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
+   |
+   = note: expected signature `fn(&X, &X) -> X`
+              found signature `fn(&X, &X) -> X`
+note: the anonymous lifetime as defined here...
+  --> $DIR/unnamed-lifetime-span-mixup-125143.rs:4:20
+   |
+LL | impl std::ops::Add<&X> for &X {
+   |                    ^
+note: ...does not necessarily outlive the anonymous lifetime as defined here
+  --> $DIR/unnamed-lifetime-span-mixup-125143.rs:4:28
+   |
+LL | impl std::ops::Add<&X> for &X {
+   |                            ^
+
+error[E0308]: method not compatible with trait
+  --> $DIR/unnamed-lifetime-span-mixup-125143.rs:17:5
+   |
+LL |     fn mul(self, _rhs: Self) -> Self::Output {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
+   |
+   = note: expected signature `fn(&X, &'a X) -> X`
+              found signature `fn(&X, &X) -> X`
+note: the lifetime `'a` as defined here...
+  --> $DIR/unnamed-lifetime-span-mixup-125143.rs:14:6
+   |
+LL | impl<'a> std::ops::Mul<&'a X> for &X {
+   |      ^^
+note: ...does not necessarily outlive the anonymous lifetime as defined here
+  --> $DIR/unnamed-lifetime-span-mixup-125143.rs:14:35
+   |
+LL | impl<'a> std::ops::Mul<&'a X> for &X {
+   |                                   ^
+
+error[E0308]: method not compatible with trait
+  --> $DIR/unnamed-lifetime-span-mixup-125143.rs:27:5
+   |
+LL |     fn sub(self, _rhs: Self) -> Self::Output {
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ lifetime mismatch
+   |
+   = note: expected signature `fn(&'a X, &X) -> X`
+              found signature `fn(&'a X, &'a X) -> X`
+note: the anonymous lifetime as defined here...
+  --> $DIR/unnamed-lifetime-span-mixup-125143.rs:24:24
+   |
+LL | impl<'a> std::ops::Sub<&X> for &'a X {
+   |                        ^
+note: ...does not necessarily outlive the lifetime `'a` as defined here
+  --> $DIR/unnamed-lifetime-span-mixup-125143.rs:24:6
+   |
+LL | impl<'a> std::ops::Sub<&X> for &'a X {
+   |      ^^
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0308`.