SD-128 fix override checks for default methods

The check for inheriting two conflicting members was wrong for default
methods, leading to a missing error message.

We were also not issuing "needs `override' modifier" when overriding a
default method.

Removes two methods:

  - `isDeferredOrJavaDefault` had a single use that is removed in this commit.

  - `isDeferredNotJavaDefault` is redundant with `isDeferred`, because
no default method has the `DEFERRED` flag:
    - For symbols originating in the classfile parser this was the case
      from day one: default methods don't receive the `DEFERRED` flag.
      Only abstract interface methods do, as they have the `JAVA_ACC_ABSTRACT`
      flag in bytecode, which the classfile parser translates to `DEFERRED`.

    - For symbols created by the Java source parser, we don't add the
      `DEFERRED` to default methods anymore since 373db1e.

Fixes scala/scala-dev#128

1 files changed, 17 insertions, 0 deletions

diff --git a/test/files/neg/sd128.check b/test/files/neg/sd128.check
new file mode 100644
index 0000000000..8f6fcb1213
--- /dev/null
+++ b/test/files/neg/sd128.check
@@ -0,0 +1,17 @@
+Test.scala:4: error: class C1 inherits conflicting members:
+  method f in trait A of type ()Int  and
+  method f in trait T of type => Int
+(Note: this can be resolved by declaring an override in class C1.)
+class C1 extends A with T // error
+      ^
+Test.scala:5: error: class C2 inherits conflicting members:
+  method f in trait T of type => Int  and
+  method f in trait A of type ()Int
+(Note: this can be resolved by declaring an override in class C2.)
+class C2 extends T with A // error
+      ^
+Test.scala:14: error: overriding method f in trait A of type ()Int;
+ method f needs `override' modifier
+  def f() = 9999 // need override modifier
+      ^
+three errors found