Explicitly label any named lifetimes mentioned in error messages.

src/librustc_mir/borrow_check/nll/region_infer/error_reporting/region_name.rs

@@ -15,10 +15,10 @@ use rustc::hir::def_id::DefId;
 use rustc::infer::InferCtxt;
 use rustc::mir::Mir;
 use rustc::ty::subst::{Substs, UnpackedKind};
-use rustc::ty::{self, RegionVid, Ty, TyCtxt};
+use rustc::ty::{self, RegionKind, RegionVid, Ty, TyCtxt};
 use rustc::util::ppaux::with_highlight_region;
 use rustc_errors::DiagnosticBuilder;
-use syntax::ast::Name;
+use syntax::ast::{Name, DUMMY_NODE_ID};
 use syntax::symbol::keywords;
 use syntax_pos::symbol::InternedString;
 
@@ -90,14 +90,21 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         diag: &mut DiagnosticBuilder<'_>,
     ) -> Option<InternedString> {
         let error_region = self.to_error_region(fr)?;
+
         debug!("give_region_a_name: error_region = {:?}", error_region);
         match error_region {
-            ty::ReEarlyBound(ebr) => Some(ebr.name),
+            ty::ReEarlyBound(ebr) => {
+                self.highlight_named_span(tcx, error_region, &ebr.name, diag);
+                Some(ebr.name)
+            },
 
             ty::ReStatic => Some(keywords::StaticLifetime.name().as_interned_str()),
 
             ty::ReFree(free_region) => match free_region.bound_region {
-                ty::BoundRegion::BrNamed(_, name) => Some(name),
+                ty::BoundRegion::BrNamed(_, name) => {
+                    self.highlight_named_span(tcx, error_region, &name, diag);
+                    Some(name)
+                },
 
                 ty::BoundRegion::BrEnv => {
                     let closure_span = tcx.hir.span_if_local(mir_def_id).unwrap();
@@ -123,6 +130,45 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         }
     }
 
+    /// Highlight a named span to provide context for error messages that
+    /// mention that span, for example:
+    ///
+    /// ```
+    ///  |
+    ///  | fn two_regions<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
+    ///  |                --  -- lifetime `'b` defined here
+    ///  |                |
+    ///  |                lifetime `'a` defined here
+    ///  |
+    ///  |     with_signature(cell, t, |cell, t| require(cell, t));
+    ///  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'b` must
+    ///  |                                                         outlive `'a`
+    /// ```
+    fn highlight_named_span(
+        &self,
+        tcx: TyCtxt<'_, '_, 'tcx>,
+        error_region: &RegionKind,
+        name: &InternedString,
+        diag: &mut DiagnosticBuilder<'_>,
+    ) {
+        let cm = tcx.sess.codemap();
+
+        let scope = error_region.free_region_binding_scope(tcx);
+        let node = tcx.hir.as_local_node_id(scope).unwrap_or(DUMMY_NODE_ID);
+
+        let mut sp = cm.def_span(tcx.hir.span(node));
+        if let Some(param) = tcx.hir.get_generics(scope).and_then(|generics| {
+            generics.get_named(name)
+        }) {
+            sp = param.span;
+        }
+
+        diag.span_label(
+            sp,
+            format!("lifetime `{}` defined here", name),
+        );
+    }
+
     /// Find an argument that contains `fr` and label it with a fully
     /// elaborated type, returning something like `'1`. Result looks
     /// like:

src/test/ui/impl-trait/static-return-lifetime-infered.nll.stderr

@@ -21,6 +21,8 @@ LL |         self.x.iter().map(|a| a.0)
 error: unsatisfied lifetime constraints
   --> $DIR/static-return-lifetime-infered.rs:21:9
    |
+LL |     fn iter_values<'a>(&'a self) -> impl Iterator<Item=u32> {
+   |                    -- lifetime `'a` defined here
 LL |         self.x.iter().map(|a| a.0)
    |         ^^^^^^^^^^^^^ requires that `'a` must outlive `'static`
 

src/test/ui/issue-10291.nll.stderr

@@ -7,6 +7,8 @@ LL |         x //~ ERROR E0312
 error: unsatisfied lifetime constraints
   --> $DIR/issue-10291.rs:12:5
    |
+LL | fn test<'x>(x: &'x isize) {
+   |         -- lifetime `'x` defined here
 LL |     drop::<Box<for<'z> FnMut(&'z isize) -> &'z isize>>(Box::new(|z| {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ requires that `'x` must outlive `'static`
 

src/test/ui/issue-52213.nll.stderr

@@ -7,6 +7,11 @@ LL |     match (&t,) { //~ ERROR cannot infer an appropriate lifetime
 error: unsatisfied lifetime constraints
   --> $DIR/issue-52213.rs:13:11
    |
+LL | fn transmute_lifetime<'a, 'b, T>(t: &'a (T,)) -> &'b T {
+   |                       --  -- lifetime `'b` defined here
+   |                       |
+   |                       lifetime `'a` defined here
+LL |     match (&t,) { //~ ERROR cannot infer an appropriate lifetime
 LL |         ((u,),) => u,
    |           ^ requires that `'a` must outlive `'b`
 

src/test/ui/nll/closure-requirements/region-lbr-named-does-not-outlive-static.stderr

@@ -7,6 +7,8 @@ LL |     &*x
 error: unsatisfied lifetime constraints
   --> $DIR/region-lbr-named-does-not-outlive-static.rs:19:5
    |
+LL | fn foo<'a>(x: &'a u32) -> &'static u32 {
+   |        -- lifetime `'a` defined here
 LL |     &*x
    |     ^^^ requires that `'a` must outlive `'static`
 

src/test/ui/nll/mir_check_cast_closure.stderr

@@ -7,6 +7,10 @@ LL |     g
 error: unsatisfied lifetime constraints
   --> $DIR/mir_check_cast_closure.rs:16:28
    |
+LL | fn bar<'a, 'b>() -> fn(&'a u32, &'b u32) -> &'a u32 {
+   |        --  -- lifetime `'b` defined here
+   |        |
+   |        lifetime `'a` defined here
 LL |     let g: fn(_, _) -> _ = |_x, y| y;
    |                            ^^^^^^^^^ cast requires that `'b` must outlive `'a`
 

src/test/ui/nll/mir_check_cast_unsize.stderr

@@ -8,7 +8,9 @@ error: unsatisfied lifetime constraints
   --> $DIR/mir_check_cast_unsize.rs:17:46
    |
 LL |   fn bar<'a>(x: &'a u32) -> &'static dyn Debug {
-   |  ______________________________________________^
+   |  ________--____________________________________^
+   | |        |
+   | |        lifetime `'a` defined here
 LL | |     //~^ ERROR unsatisfied lifetime constraints
 LL | |     x
 LL | |     //~^ WARNING not reporting region error due to nll

src/test/ui/nll/ty-outlives/projection-one-region-closure.stderr

@@ -52,6 +52,11 @@ LL | | }
 error: unsatisfied lifetime constraints
   --> $DIR/projection-one-region-closure.rs:55:5
    |
+LL | fn no_relationships_late<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
+   |                          --  -- lifetime `'b` defined here
+   |                          |
+   |                          lifetime `'a` defined here
+...
 LL |     with_signature(cell, t, |cell, t| require(cell, t));
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'b` must outlive `'a`
 
@@ -101,6 +106,11 @@ LL | | }
 error: unsatisfied lifetime constraints
   --> $DIR/projection-one-region-closure.rs:67:5
    |
+LL | fn no_relationships_early<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
+   |                           --  -- lifetime `'b` defined here
+   |                           |
+   |                           lifetime `'a` defined here
+...
 LL |     with_signature(cell, t, |cell, t| require(cell, t));
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'b` must outlive `'a`
 
@@ -150,6 +160,11 @@ LL | | }
 error: unsatisfied lifetime constraints
   --> $DIR/projection-one-region-closure.rs:89:5
    |
+LL | fn projection_outlives<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
+   |                        --  -- lifetime `'b` defined here
+   |                        |
+   |                        lifetime `'a` defined here
+...
 LL |     with_signature(cell, t, |cell, t| require(cell, t));
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'b` must outlive `'a`
 

src/test/ui/nll/ty-outlives/projection-one-region-trait-bound-closure.stderr

@@ -51,6 +51,11 @@ LL | | }
 error: unsatisfied lifetime constraints
   --> $DIR/projection-one-region-trait-bound-closure.rs:47:5
    |
+LL | fn no_relationships_late<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
+   |                          --  -- lifetime `'b` defined here
+   |                          |
+   |                          lifetime `'a` defined here
+...
 LL |     with_signature(cell, t, |cell, t| require(cell, t));
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'b` must outlive `'a`
 
@@ -91,6 +96,11 @@ LL | | }
 error: unsatisfied lifetime constraints
   --> $DIR/projection-one-region-trait-bound-closure.rs:58:5
    |
+LL | fn no_relationships_early<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
+   |                           --  -- lifetime `'b` defined here
+   |                           |
+   |                           lifetime `'a` defined here
+...
 LL |     with_signature(cell, t, |cell, t| require(cell, t));
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'b` must outlive `'a`
 
@@ -131,6 +141,11 @@ LL | | }
 error: unsatisfied lifetime constraints
   --> $DIR/projection-one-region-trait-bound-closure.rs:79:5
    |
+LL | fn projection_outlives<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
+   |                        --  -- lifetime `'b` defined here
+   |                        |
+   |                        lifetime `'a` defined here
+...
 LL |     with_signature(cell, t, |cell, t| require(cell, t));
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'b` must outlive `'a`
 

src/test/ui/nll/ty-outlives/projection-two-region-trait-bound-closure.stderr

@@ -259,6 +259,11 @@ LL | | }
 error: unsatisfied lifetime constraints
   --> $DIR/projection-two-region-trait-bound-closure.rs:108:5
    |
+LL | fn two_regions<'a, 'b, T>(cell: Cell<&'a ()>, t: T)
+   |                --  -- lifetime `'b` defined here
+   |                |
+   |                lifetime `'a` defined here
+...
 LL |     with_signature(cell, t, |cell, t| require(cell, t));
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ argument requires that `'b` must outlive `'a`