Rollup merge of rust-lang#44124 - gaurikholkar:return_self, r=arielb1

adding E0623 for return types - both parameters are anonymous

This is a fix for rust-lang#44018
```
error[E0621]: explicit lifetime required in the type of `self`
  --> $DIR/ex3-both-anon-regions-return-type-is-anon.rs:17:5
   |
16 |   fn foo<'a>(&self, x: &i32) -> &i32 {
   |                        ----     ----
   |                        |
   |                        this parameter and the return type are
                            declared with different lifetimes...
17 |     x
   |     ^ ...but data from `x` is returned here

error: aborting due to previous error
```
It also works for the below case where we have self as anonymous

```
error[E0623]: lifetime mismatch
  --> src/test/ui/lifetime-errors/ex3-both-anon-regions-self-is-anon.rs:17:19
   |
16 |     fn foo<'a>(&self, x: &Foo) -> &Foo {
   |                          ----     ----
   |                          |
   |                          this parameter and the return type are
                            declared with different lifetimes...
17 |         if true { x } else { self }
   |                   ^ ...but data from `x` is returned here

error: aborting due to previous error
```
r? @nikomatsakis

Currently, I have enabled E0621 where return type and self are anonymous, hence WIP.

Author: Mark-Simulacrum

src/librustc/diagnostics.rs

@@ -1351,74 +1351,6 @@ struct Foo<T: 'static> {
 ```
 "##,
 
-E0312: r##"
-A lifetime of reference outlives lifetime of borrowed content.
-
-Erroneous code example:
-
-```compile_fail,E0312
-fn make_child<'tree, 'human>(
-  x: &'human i32,
-  y: &'tree i32
-) -> &'human i32 {
-    if x > y
-       { x }
-    else
-       { y }
-       // error: lifetime of reference outlives lifetime of borrowed content
-}
-```
-
-The function declares that it returns a reference with the `'human`
-lifetime, but it may return data with the `'tree` lifetime. As neither
-lifetime is declared longer than the other, this results in an
-error. Sometimes, this error is because the function *body* is
-incorrect -- that is, maybe you did not *mean* to return data from
-`y`. In that case, you should fix the function body.
-
-Often, however, the body is correct. In that case, the function
-signature needs to be altered to match the body, so that the caller
-understands that data from either `x` or `y` may be returned. The
-simplest way to do this is to give both function parameters the *same*
-named lifetime:
-
-```
-fn make_child<'human>(
-  x: &'human i32,
-  y: &'human i32
-) -> &'human i32 {
-    if x > y
-       { x }
-    else
-       { y } // ok!
-}
-```
-
-However, in some cases, you may prefer to explicitly declare that one lifetime
-outlives another using a `where` clause:
-
-```
-fn make_child<'tree, 'human>(
-  x: &'human i32,
-  y: &'tree i32
-) -> &'human i32
-where
-  'tree: 'human
-{
-    if x > y
-       { x }
-    else
-       { y } // ok!
-}
-```
-
-Here, the where clause `'tree: 'human` can be read as "the lifetime
-'tree outlives the lifetime 'human" -- meaning, references with the
-`'tree` lifetime live *at least as long as* references with the
-`'human` lifetime. Therefore, it is safe to return data with lifetime
-`'tree` when data with the lifetime `'human` is needed.
-"##,
-
 E0317: r##"
 This error occurs when an `if` expression without an `else` block is used in a
 context where a type other than `()` is expected, for example a `let`
@@ -2028,6 +1960,7 @@ register_diagnostics! {
 //  E0304, // expected signed integer constant
 //  E0305, // expected constant
     E0311, // thing may not live long enough
+    E0312, // lifetime of reference outlives lifetime of borrowed content
     E0313, // lifetime of borrowed pointer outlives lifetime of captured variable
     E0314, // closure outlives stack frame
     E0315, // cannot invoke closure outside of its lifetime

src/librustc/infer/error_reporting/different_lifetimes.rs

@@ -18,6 +18,7 @@ use infer::region_inference::RegionResolutionError;
 use hir::map as hir_map;
 use middle::resolve_lifetime as rl;
 use hir::intravisit::{self, Visitor, NestedVisitorMap};
+use infer::error_reporting::util::AnonymousArgInfo;
 
 impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     // This method prints the error message for lifetime errors when both the concerned regions
@@ -57,6 +58,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         let ty_sup = or_false!(self.find_anon_type(sup, &bregion_sup));
 
         let ty_sub = or_false!(self.find_anon_type(sub, &bregion_sub));
+
         debug!("try_report_anon_anon_conflict: found_arg1={:?} sup={:?} br1={:?}",
                ty_sub,
                sup,
@@ -66,56 +68,70 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                sub,
                bregion_sub);
 
-        let (main_label, label1, label2) = if let (Some(sup_arg), Some(sub_arg)) =
-            (self.find_arg_with_region(sup, sup), self.find_arg_with_region(sub, sub)) {
+        let (ty_sup, ty_fndecl_sup) = ty_sup;
+        let (ty_sub, ty_fndecl_sub) = ty_sub;
 
-            let (anon_arg_sup, is_first_sup, anon_arg_sub, is_first_sub) =
-                (sup_arg.arg, sup_arg.is_first, sub_arg.arg, sub_arg.is_first);
-            if self.is_self_anon(is_first_sup, scope_def_id_sup) ||
-               self.is_self_anon(is_first_sub, scope_def_id_sub) {
-                return false;
-            }
+        let AnonymousArgInfo { arg: anon_arg_sup, .. } =
+            or_false!(self.find_arg_with_region(sup, sup));
+        let AnonymousArgInfo { arg: anon_arg_sub, .. } =
+            or_false!(self.find_arg_with_region(sub, sub));
 
-            if self.is_return_type_anon(scope_def_id_sup, bregion_sup) ||
-               self.is_return_type_anon(scope_def_id_sub, bregion_sub) {
-                return false;
-            }
+        let sup_is_ret_type =
+            self.is_return_type_anon(scope_def_id_sup, bregion_sup, ty_fndecl_sup);
+        let sub_is_ret_type =
+            self.is_return_type_anon(scope_def_id_sub, bregion_sub, ty_fndecl_sub);
 
-            if anon_arg_sup == anon_arg_sub {
-                (format!("this type was declared with multiple lifetimes..."),
-                 format!(" with one lifetime"),
-                 format!(" into the other"))
-            } else {
-                let span_label_var1 = if let Some(simple_name) = anon_arg_sup.pat.simple_name() {
-                    format!(" from `{}`", simple_name)
-                } else {
-                    format!("")
-                };
+        let span_label_var1 = if let Some(simple_name) = anon_arg_sup.pat.simple_name() {
+            format!(" from `{}`", simple_name)
+        } else {
+            format!("")
+        };
+
+        let span_label_var2 = if let Some(simple_name) = anon_arg_sub.pat.simple_name() {
+            format!(" into `{}`", simple_name)
+        } else {
+            format!("")
+        };
+
+
+        let (span_1, span_2, main_label, span_label) = match (sup_is_ret_type, sub_is_ret_type) {
+            (None, None) => {
+                let (main_label_1, span_label_1) = if ty_sup == ty_sub {
 
-                let span_label_var2 = if let Some(simple_name) = anon_arg_sub.pat.simple_name() {
-                    format!(" into `{}`", simple_name)
+                    (format!("this type is declared with multiple lifetimes..."),
+                     format!("...but data{} flows{} here",
+                             format!(" with one lifetime"),
+                             format!(" into the other")))
                 } else {
-                    format!("")
+                    (format!("these two types are declared with different lifetimes..."),
+                     format!("...but data{} flows{} here",
+                             span_label_var1,
+                             span_label_var2))
                 };
+                (ty_sup.span, ty_sub.span, main_label_1, span_label_1)
+            }
 
-                let span_label =
-                    format!("these two types are declared with different lifetimes...",);
-
-                (span_label, span_label_var1, span_label_var2)
+            (Some(ret_span), _) => {
+                (ty_sub.span,
+                 ret_span,
+                 format!("this parameter and the return type are declared \
+                          with different lifetimes...",),
+                 format!("...but data{} is returned here", span_label_var1))
+            }
+            (_, Some(ret_span)) => {
+                (ty_sup.span,
+                 ret_span,
+                 format!("this parameter and the return type are declared \
+                          with different lifetimes...",),
+                 format!("...but data{} is returned here", span_label_var1))
             }
-        } else {
-            debug!("no arg with anon region found");
-            debug!("try_report_anon_anon_conflict: is_suitable(sub) = {:?}",
-                   self.is_suitable_region(sub));
-            debug!("try_report_anon_anon_conflict: is_suitable(sup) = {:?}",
-                   self.is_suitable_region(sup));
-            return false;
         };
 
+
         struct_span_err!(self.tcx.sess, span, E0623, "lifetime mismatch")
-            .span_label(ty_sup.span, main_label)
-            .span_label(ty_sub.span, format!(""))
-            .span_label(span, format!("...but data{} flows{} here", label1, label2))
+            .span_label(span_1, main_label)
+            .span_label(span_2, format!(""))
+            .span_label(span, span_label)
             .emit();
         return true;
     }
@@ -135,28 +151,32 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     /// ```
     /// The function returns the nested type corresponding to the anonymous region
     /// for e.g. `&u8` and Vec<`&u8`.
-    pub fn find_anon_type(&self, region: Region<'tcx>, br: &ty::BoundRegion) -> Option<&hir::Ty> {
+    pub fn find_anon_type(&self,
+                          region: Region<'tcx>,
+                          br: &ty::BoundRegion)
+                          -> Option<(&hir::Ty, &hir::FnDecl)> {
         if let Some(anon_reg) = self.is_suitable_region(region) {
             let def_id = anon_reg.def_id;
             if let Some(node_id) = self.tcx.hir.as_local_node_id(def_id) {
-                let inputs: &[_] = match self.tcx.hir.get(node_id) {
+                let fndecl = match self.tcx.hir.get(node_id) {
                     hir_map::NodeItem(&hir::Item { node: hir::ItemFn(ref fndecl, ..), .. }) => {
-                        &fndecl.inputs
+                        &fndecl
                     }
                     hir_map::NodeTraitItem(&hir::TraitItem {
-                                               node: hir::TraitItemKind::Method(ref fndecl, ..), ..
-                                           }) => &fndecl.decl.inputs,
+                                               node: hir::TraitItemKind::Method(ref m, ..), ..
+                                           }) |
                     hir_map::NodeImplItem(&hir::ImplItem {
-                                              node: hir::ImplItemKind::Method(ref fndecl, ..), ..
-                                          }) => &fndecl.decl.inputs,
-
-                    _ => &[],
+                                              node: hir::ImplItemKind::Method(ref m, ..), ..
+                                          }) => &m.decl,
+                    _ => return None,
                 };
 
-                return inputs
+                return fndecl
+                           .inputs
                            .iter()
-                           .filter_map(|arg| self.find_component_for_bound_region(&**arg, br))
-                           .next();
+                           .filter_map(|arg| self.find_component_for_bound_region(arg, br))
+                           .next()
+                           .map(|ty| (ty, &**fndecl));
             }
         }
         None

src/librustc/infer/error_reporting/named_anon_conflict.rs

@@ -35,15 +35,17 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         // only introduced anonymous regions in parameters) as well as a
         // version new_ty of its type where the anonymous region is replaced
         // with the named one.//scope_def_id
-        let (named, anon_arg_info, region_info) =
+        let (named, anon, anon_arg_info, region_info) =
             if self.is_named_region(sub) && self.is_suitable_region(sup).is_some() &&
                self.find_arg_with_region(sup, sub).is_some() {
                 (sub,
+                 sup,
                  self.find_arg_with_region(sup, sub).unwrap(),
                  self.is_suitable_region(sup).unwrap())
             } else if self.is_named_region(sup) && self.is_suitable_region(sub).is_some() &&
                       self.find_arg_with_region(sub, sup).is_some() {
                 (sup,
+                 sub,
                  self.find_arg_with_region(sub, sup).unwrap(),
                  self.is_suitable_region(sub).unwrap())
             } else {
@@ -76,33 +78,29 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             return false;
         }
 
-        if self.is_return_type_anon(scope_def_id, br) {
-            debug!("try_report_named_anon_conflict: is_return_type_anon({:?}, {:?}) = true",
-                   scope_def_id,
-                   br);
-            return false;
-        } else if self.is_self_anon(is_first, scope_def_id) {
-            debug!("try_report_named_anon_conflict: is_self_anon({:?}, {:?}) = true",
-                   is_first,
-                   scope_def_id);
-            return false;
+        if let Some((_, fndecl)) = self.find_anon_type(anon, &br) {
+            if self.is_return_type_anon(scope_def_id, br, fndecl).is_some() ||
+               self.is_self_anon(is_first, scope_def_id) {
+                return false;
+            }
+        }
+
+        let (error_var, span_label_var) = if let Some(simple_name) = arg.pat.simple_name() {
+            (format!("the type of `{}`", simple_name), format!("the type of `{}`", simple_name))
         } else {
-            let (error_var, span_label_var) = if let Some(simple_name) = arg.pat.simple_name() {
-                (format!("the type of `{}`", simple_name), format!("the type of `{}`", simple_name))
-            } else {
-                ("parameter type".to_owned(), "type".to_owned())
-            };
+            ("parameter type".to_owned(), "type".to_owned())
+        };
+
+        struct_span_err!(self.tcx.sess,
+                         span,
+                         E0621,
+                         "explicit lifetime required in {}",
+                         error_var)
+                .span_label(arg.pat.span,
+                            format!("consider changing {} to `{}`", span_label_var, new_ty))
+                .span_label(span, format!("lifetime `{}` required", named))
+                .emit();
+        return true;
 
-            struct_span_err!(self.tcx.sess,
-                             span,
-                             E0621,
-                             "explicit lifetime required in {}",
-                             error_var)
-                    .span_label(arg.pat.span,
-                                format!("consider changing {} to `{}`", span_label_var, new_ty))
-                    .span_label(span, format!("lifetime `{}` required", named))
-                    .emit();
-            return true;
-        }
     }
 }

src/librustc/infer/error_reporting/util.rs

@@ -15,6 +15,7 @@ use infer::InferCtxt;
 use ty::{self, Region, Ty};
 use hir::def_id::DefId;
 use hir::map as hir_map;
+use syntax_pos::Span;
 
 macro_rules! or_false {
      ($v:expr) => {
@@ -163,20 +164,24 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     // Here, we check for the case where the anonymous region
     // is in the return type.
     // FIXME(#42703) - Need to handle certain cases here.
-    pub fn is_return_type_anon(&self, scope_def_id: DefId, br: ty::BoundRegion) -> bool {
+    pub fn is_return_type_anon(&self,
+                               scope_def_id: DefId,
+                               br: ty::BoundRegion,
+                               decl: &hir::FnDecl)
+                               -> Option<Span> {
         let ret_ty = self.tcx.type_of(scope_def_id);
         match ret_ty.sty {
             ty::TyFnDef(_, _) => {
                 let sig = ret_ty.fn_sig(self.tcx);
                 let late_bound_regions = self.tcx
                     .collect_referenced_late_bound_regions(&sig.output());
                 if late_bound_regions.iter().any(|r| *r == br) {
-                    return true;
+                    return Some(decl.output.span());
                 }
             }
             _ => {}
         }
-        false
+        None
     }
     // Here we check for the case where anonymous region
     // corresponds to self and if yes, we display E0312.

src/test/compile-fail/object-lifetime-default-mybox.rs

@@ -34,7 +34,7 @@ fn load1<'a,'b>(a: &'a MyBox<SomeTrait>,
                 b: &'b MyBox<SomeTrait>)
                 -> &'b MyBox<SomeTrait>
 {
-    a //~ ERROR E0312
+    a //~ ERROR lifetime mismatch
 }
 
 fn load2<'a>(ss: &MyBox<SomeTrait+'a>) -> MyBox<SomeTrait+'a> {