[GROOVY-4908] Improved compiler checking/error messages required when checking interfaces with generics

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.4.0-beta-3, 3.0.0-alpha-3, 2.5.2
• Component/s: Compiler
• Assignee: Unassigned
• Reporter: Paul King
• Created: 01/Jul/11 18:09
• Updated: 26/Aug/18 03:09

Description

Given this interface:

interface Base {
  public <T extends CharSequence> T copy1(T arg)
  public <T extends CharSequence> T copy2(T arg)
  public <T extends CharSequence> T copy3(T arg)
  public <T extends CharSequence> T copy4(T arg)
  public <T extends CharSequence> T copy5(T arg)
  public <T extends CharSequence> T copy6(T arg)
}

Then this class doesn't compile with one error (but there should be at least 5 errors):

class Foo implements Base {
  def copy1(arg) { arg }
  CharSequence copy2(arg) { arg }
  def <T> T copy3(T arg) { arg }
  def <T extends Object> T copy4(T arg) { arg }
  def <T extends CharSequence> T copy5(T arg) { arg }
  def <T extends String> T copy6(T arg) { arg }
}

Current behavior:

• copy1 through copy4 would be allowed by Java but would count as overloaded non-interface methods and compile would fail saying Foo wasn't abstract and didn't implement copyN method. Groovy doesn't complain but I think it should. The existence of those methods is fooling the later checks that all interface methods are implemented - we need to tighten the checks
• Java also wouldn't allow copy2 and copy3 above together as they have the same erasure. Again, we should have a check for that.
• copy5 passes as it should for both Groovy and Java.
• copy6 is recognised by Groovy as overloaded method, so we have the correct error message in that case.

Issue Links

• depends upon: GROOVY-4767 Compilation error for generic interface method