closes 2462. better implicit error messages.

@implicitNotFound(msg="Custom error message that may refer to type parameters ${T} and ${U}")
trait Constraint[T, U]

whenever an implicit argument of type Constraint[A, B] cannot be found,
the custom error message will be used, where the type arguments are
interpolated in the obvious way

note: if the msg in the annotation references non-existing type params,
a warning is emitted

the patch also cleans up annotation argument retrieval (moved it to
AnnotationInfo from Symbol)

review by odersky

1 files changed, 14 insertions, 0 deletions

diff --git a/test/files/neg/t2462b.check b/test/files/neg/t2462b.check
new file mode 100644
index 0000000000..ac9563878c
--- /dev/null
+++ b/test/files/neg/t2462b.check
@@ -0,0 +1,14 @@
+implicitNotFound_syntax.scala:6: warning: Invalid implicitNotFound message for trait Meh in package test:
+The type parameters Too, Elem referenced in the message of the @implicitNotFound annotation are not defined by trait Meh.
+trait Meh[-From, +To]
+      ^
+implicitNotFound_syntax.scala:9: warning: Invalid implicitNotFound message for trait Meh2 in package test:
+The type parameter Elem referenced in the message of the @implicitNotFound annotation is not defined by trait Meh2.
+trait Meh2[-From, +To]
+      ^
+implicitNotFound_syntax.scala:12: error: overriding method x in class thankyoupartest of type => Int;
+ method x needs `override' modifier
+class testmustfail extends thankyoupartest { def x = 43 }
+                                                 ^
+two warnings found
+one error found