have coercion supply back the target type

The `try_coerce` method coerces from a source to a target
type, possibly inserting adjustments. It should guarantee
that the post-adjustment type is a subtype of the target type
(or else that some side-constraint has been registered which will lead
to an error). However, it used to return the (possibly adjusted) source
as the type of the expression rather than the target. This led to
less good downstream errors.

To work around this, the code around blocks -- and particular tail
expressions in blocks -- had some special case manipulation. However,
since that code is now using the more general `CoerceMany` construct (to
account for breaks), it can no longer take advantage of that. This lead
to some regressions in compile-fail tests were errors were reported at
"less good" locations than before.

This change modifies coercions to return the target type when successful
rather the source type. This extends the behavior from blocks to all
coercions. Typically this has limited effect but on a few tests yielded
better errors results (and avoided regressions, of course).

This change also restores the hint about removing semicolons which went
missing (by giving 'force-unit' coercions a chance to add notes etc).

4 files changed, 4 insertions, 7 deletions

diff --git a/src/test/compile-fail/issue-15965.rs b/src/test/compile-fail/issue-15965.rs
index d5d597c190e..08b896f387b 100644
--- a/src/test/compile-fail/issue-15965.rs
+++ b/src/test/compile-fail/issue-15965.rs
@@ -11,7 +11,7 @@
 fn main() {
     return
         { return () }
-//~^ ERROR expected function, found `!`
+//~^ ERROR the type of this value must be known in this context
     ()
     ;
 }
diff --git a/src/test/compile-fail/issue-2149.rs b/src/test/compile-fail/issue-2149.rs
index 9143a226a24..256c5d8e6f7 100644
--- a/src/test/compile-fail/issue-2149.rs
+++ b/src/test/compile-fail/issue-2149.rs
@@ -21,5 +21,5 @@ impl<A> vec_monad<A> for Vec<A> {
 }
 fn main() {
     ["hi"].bind(|x| [x] );
-    //~^ ERROR no method named `bind` found for type `[&'static str; 1]` in the current scope
+    //~^ ERROR no method named `bind` found for type `[&str; 1]` in the current scope
 }
diff --git a/src/test/compile-fail/region-invariant-static-error-reporting.rs b/src/test/compile-fail/region-invariant-static-error-reporting.rs
index ac0167e08bd..d25674a74b1 100644
--- a/src/test/compile-fail/region-invariant-static-error-reporting.rs
+++ b/src/test/compile-fail/region-invariant-static-error-reporting.rs
@@ -16,9 +16,6 @@
 // error-pattern:cannot infer
 // error-pattern:cannot outlive the lifetime 'a
 // error-pattern:must be valid for the static lifetime
-// error-pattern:cannot infer
-// error-pattern:cannot outlive the lifetime 'a
-// error-pattern:must be valid for the static lifetime
 
 struct Invariant<'a>(Option<&'a mut &'a mut ()>);
 
diff --git a/src/test/compile-fail/regions-bounds.rs b/src/test/compile-fail/regions-bounds.rs
index 810a8671c53..5ce80be98d9 100644
--- a/src/test/compile-fail/regions-bounds.rs
+++ b/src/test/compile-fail/regions-bounds.rs
@@ -16,11 +16,11 @@ struct an_enum<'a>(&'a isize);
 struct a_class<'a> { x:&'a isize }
 
 fn a_fn1<'a,'b>(e: an_enum<'a>) -> an_enum<'b> {
-    return e; //~^ ERROR mismatched types
+    return e; //~ ERROR mismatched types
 }
 
 fn a_fn3<'a,'b>(e: a_class<'a>) -> a_class<'b> {
-    return e; //~^ ERROR mismatched types
+    return e; //~ ERROR mismatched types
 }
 
 fn main() { }