What would you like to be improved?

When changing a tag name to one that already exists in the same metalake, the server returns an internal error instead of an already exists response.

Observed code path

• TagManager.java (line 175) catches EntityAlreadyExistsException during alterTag(...) and wraps it in a generic RuntimeException.
• ExceptionHandlers.java (line 718) only maps TagAlreadyExistsException to an already-exists response.
• Generic RuntimeException falls through to internal error handling in ExceptionHandlers.java (line 1044).
  Impact

A valid user mistake, renaming a tag to an existing tag name, is surfaced as HTTP 500. Clients then receive a generic runtime failure instead of a domain-specific conflict like TagAlreadyExistsException.

How should we improve?

In TagManager.alterTag(...), convert EntityAlreadyExistsException to TagAlreadyExistsException, similar to createTag(...), for example:

} catch (EntityAlreadyExistsException e) {
  throw new TagAlreadyExistsException(
      e, "Tag with name %s under metalake %s already exists", newName, metalake);
}

Here's a unit test to help:

  @Test
  public void testAlterTagRenameToExistingTag() {
    tagManager.createTag(METALAKE, "tag1", null, null);
    tagManager.createTag(METALAKE, "tag2", null, null);

    TagAlreadyExistsException exception =
        Assertions.assertThrows(
            TagAlreadyExistsException.class,
            () -> tagManager.alterTag(METALAKE, "tag1", TagChange.rename("tag2")));

    Assertions.assertEquals(
        "Tag with name tag2 under metalake metalake_for_tag_test already exists",
        exception.getMessage());

    Assertions.assertEquals("tag1", tagManager.getTag(METALAKE, "tag1").name());
    Assertions.assertEquals("tag2", tagManager.getTag(METALAKE, "tag2").name());
  }