tree 3646a7e0f5dd1081324c1c7f27ffe756852a5e5a
parent 0a9753308f1f0f4fb8370ece79c5cfde17d02160
author Marcel van Lohuizen <mpvl@golang.org> 1562264221 +0200
committer Marcel van Lohuizen <mpvl@golang.org> 1562264772 +0000

cue/errors: make List implement Error

The semants is for List to adopt the features of the first
error. This is consistent with the default error message
being printed.

Advantages:
- Allows improved type checking.
- Avoids the nil-error return issues for List.
- Simplifies combining code.

Also:
- get rid of E
- Implement: Promote, Append
- clean up code accordingly
- tighten type checking

Change-Id: Iea90ab001111d914aad93731d4ebb50e91865e1d
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/2480
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>