Rollup of 3 pull requests

src/librustc/diagnostics.rs

@@ -1946,6 +1946,44 @@ Maybe you just misspelled the lint name or the lint doesn't exist anymore.
 Either way, try to update/remove it in order to fix the error.
 "##,
 
+E0621: r##"
+This error code indicates a mismatch between the function signature (i.e.,
+the parameter types and the return type) and the function body. Most of
+the time, this indicates that the function signature needs to be changed to
+match the body, but it may be that the body needs to be changed to match
+the signature.
+
+Specifically, one or more of the parameters contain borrowed data that
+needs to have a named lifetime in order for the body to type-check. Most of
+the time, this is because the borrowed data is being returned from the
+function, as in this example:
+
+```compile_fail,E0621
+fn foo<'a>(x: &'a i32, y: &i32) -> &'a i32 { // explicit lifetime required
+                                             // in the type of `y`
+    if x > y { x } else { y }
+}
+```
+
+Here, the function is returning data borrowed from either x or y, but the
+'a annotation indicates that it is returning data only from x. We can make
+the signature match the body by changing the type of y to &'a i32, like so:
+
+```
+fn foo<'a>(x: &'a i32, y: &'a i32) -> &'a i32 {
+    if x > y { x } else { y }
+}
+```
+
+Alternatively, you could change the body not to return data from y:
+
+```
+fn foo<'a>(x: &'a i32, y: &i32) -> &'a i32 {
+    x
+}
+```
+"##,
+
 }
 
 

src/librustc/infer/error_reporting/mod.rs

@@ -72,9 +72,11 @@ use ty::error::TypeError;
 use syntax::ast::DUMMY_NODE_ID;
 use syntax_pos::{Pos, Span};
 use errors::{DiagnosticBuilder, DiagnosticStyledString};
-
 mod note;
+
 mod need_type_info;
+mod named_anon_conflict;
+
 
 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     pub fn note_and_explain_region(self,
@@ -255,34 +257,48 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 }
 
 impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
-    pub fn report_region_errors(&self,
-                                errors: &Vec<RegionResolutionError<'tcx>>) {
+
+    pub fn report_region_errors(&self, errors: &Vec<RegionResolutionError<'tcx>>) {
         debug!("report_region_errors(): {} errors to start", errors.len());
 
         // try to pre-process the errors, which will group some of them
         // together into a `ProcessedErrors` group:
         let errors = self.process_errors(errors);
 
-        debug!("report_region_errors: {} errors after preprocessing", errors.len());
+        debug!("report_region_errors: {} errors after preprocessing",
+               errors.len());
 
         for error in errors {
+
             debug!("report_region_errors: error = {:?}", error);
-            match error.clone() {
-                ConcreteFailure(origin, sub, sup) => {
-                    self.report_concrete_failure(origin, sub, sup).emit();
-                }
 
-                GenericBoundFailure(kind, param_ty, sub) => {
-                    self.report_generic_bound_failure(kind, param_ty, sub);
-                }
+            if !self.try_report_named_anon_conflict(&error){
+
+               match error.clone() {
+                  // These errors could indicate all manner of different
+                  // problems with many different solutions. Rather
+                  // than generate a "one size fits all" error, what we
+                  // attempt to do is go through a number of specific
+                  // scenarios and try to find the best way to present
+                  // the error. If all of these fails, we fall back to a rather
+                  // general bit of code that displays the error information
+                  ConcreteFailure(origin, sub, sup) => {
+
+                      self.report_concrete_failure(origin, sub, sup).emit();
+                  }
 
-                SubSupConflict(var_origin,
+                  GenericBoundFailure(kind, param_ty, sub) => {
+                      self.report_generic_bound_failure(kind, param_ty, sub);
+                  }
+
+                  SubSupConflict(var_origin,
                                sub_origin, sub_r,
                                sup_origin, sup_r) => {
-                    self.report_sub_sup_conflict(var_origin,
+                      self.report_sub_sup_conflict(var_origin,
                                                  sub_origin, sub_r,
                                                  sup_origin, sup_r);
-                }
+                  }
+               }
             }
         }
     }