gitserver: grpc: port GetBehindAhead from client to gitcli backend

[ggilmore]

Part of #62101

This PR ports the GetBehindAhead implementation from the gitserver client to the new gitserver.Backend interface.

Here is the original implementation from the client for reference:

// GetBehindAhead returns the behind/ahead commit counts information for right vs. left (both Git
// revspecs).
func (c *clientImplementor) GetBehindAhead(ctx context.Context, repo api.RepoName, left, right string) (_ *gitdomain.BehindAhead, err error) {
	ctx, _, endObservation := c.operations.getBehindAhead.With(ctx, &err, observation.Args{
		MetricLabelValues: []string{c.scope},
		Attrs: []attribute.KeyValue{
			repo.Attr(),
			attribute.String("left", left),
			attribute.String("right", right),
		},
	})
	defer endObservation(1, observation.Args{})

	if err := checkSpecArgSafety(left); err != nil {
		return nil, err
	}
	if err := checkSpecArgSafety(right); err != nil {
		return nil, err
	}

	cmd := c.gitCommand(repo, "rev-list", "--count", "--left-right", fmt.Sprintf("%s...%s", left, right))
	out, err := cmd.Output(ctx)
	if err != nil {
		return nil, err
	}
	behindAhead := strings.Split(strings.TrimSuffix(string(out), "\n"), "\t")
	b, err := strconv.ParseUint(behindAhead[0], 10, 0)
	if err != nil {
		return nil, err
	}
	a, err := strconv.ParseUint(behindAhead[1], 10, 0)
	if err != nil {
		return nil, err
	}
	return &gitdomain.BehindAhead{Behind: uint32(b), Ahead: uint32(a)}, nil
}

Test plan

New unit tests

[ggilmore]

• searcher: remove unused diff.ParseGitDiffNameStatus package #62363
• gitserver: grpc: remove now unused DiffSymbols func #62360
• worker: embeddings: replace usage of old gitserver.DiffSymbols client method with new gitserver.ChangedFiles method #62359
• searcher: replace usage of gitserver.DiffSymbols with new gitserver.ChangedFiles client method #62358
• symbols: replace usage of gitserver client's DiffSymbols method with new ChangedFiles method #62355
• gitserver: grpc: add new ChangedFiles method to gitserver client #62354
• gitserver: grpc: create changed files RPC implementation for gRPC server #62262
• gitserver: grpc: port DiffSymbols from client as new GitBackend.ChangedFiles() func #62252
• gitserver: grpc: swap client implementation of GetAheadBehind from Exec to bespoke gRPC endpoint #62217
• gitserver: grpc: create server implementation for GetBehindAhead #62216
• gitserver: grpc: port GetBehindAhead from client to gitcli backend #62212 👈
• codeinsights: remove now useless empty repo string error check #62302
• gitserver: grpc: switch clientImplementor to use new dedicated gRPC method for FirstEverCommit #62173
• gitserver: grpc: create FirstEverCommit RPC method and server implementation #62169
• gitserver: port FirstEverCommit functionality from client to git cli backend #62165
• gitserver: grpc: create exhaustive logger for repository service #62158
• main

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[eseliger]

<3 for diagram!

[graphite-app]

[graphite-app]

Graphite Automations

"Post a GIF when PR approved" took an action on this PR • (05/02/24)

1 gif was posted to this PR based on Geoffrey Gilmore's automation.