tree 8b3f67e531966d25fece1280e96958d88a97e028
parent 33c2dbf38023a9d7e4263fa0d0c5681c7d5d545f
author Alan Donovan <adonovan@google.com> 1664561917 -0400
committer Alan Donovan <adonovan@google.com> 1665001846 +0000

internal/diff: abolish errors

Computing the difference between two strings is logically an
infallible operation. This change makes the code reflect that. The
actual failures were unreachable given consistent inputs, but that was
hard to see from the complexity of the logic surrounding span.Span.
(The problem only occurs when converting offsets beyond the end of the
file to Spans, but the code preserves the integrity of offsets.)

gopls' "old" hooks.ComputeEdits impl (based on sergi/go-diff) now
reports a bug and returns a single diff for the entire file if it
panics.

Also, first steps towards simpler API and a
reusable diff package in x/tools:

- add TODO for new API. In particular, the diff package shouldn't care
  about filenames, spans, and URIs. These are gopls concerns.
- diff.String is the main diff function.
- diff.Unified prints edits in unified form;
  all its internals are now hidden.
- the ComputeEdits func type is moved to gopls (source.DiffFunction)
- remove all non-critical uses of myers.ComputeEdits. The only
  remaining one is in gopls' defaults, but perhaps that gets
  overridden by the default GoDiff setting in hooks, to BothDiffs
  (sergi + pjw impls), so maybe it's now actually unused in practice?

Change-Id: I6ceb5c670897abbf285b243530a7372dfa41edf6
Reviewed-on: https://go-review.googlesource.com/c/tools/+/436778
Run-TryBot: Alan Donovan <adonovan@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>