RFR: 7039014: Confusing error message for method conflict [v2]

[Archie L. Cobbs]

> This fixes a confusing error message.
> 
> Currently, this input:
> 
> interface A<T> {
>     byte m(String x);
>     char m(T x);
> }
> 
> interface B extends A<String> {
> }
> 
> produces this error:
> 
> A.java:6: error: types A<String> and A<String> are incompatible;
> interface B extends A<String> {
> ^
>   both define m(String), but with unrelated return types
> 1 error
> 
> This patch detects when the two types are actually the same type and gives this error message instead:
> 
> A.java:6: error: type A<String> defines m(String) more than once with unrelated return types
> interface B extends A<String> {
> ^
> 1 error

Archie L. Cobbs has updated the pull request incrementally with one additional commit since the last revision:

  Add a few more unit tests.

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/10752/files
  - new: https://git.openjdk.org/jdk/pull/10752/files/a233f6de..4404568c

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10752&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10752&range=00-01

  Stats: 83 lines in 5 files changed: 83 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/10752.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10752/head:pull/10752

PR: https://git.openjdk.org/jdk/pull/10752