Fallback to full clone if git fetch fails

[szphie]

fixes #1452

#857 changed api/internal/git/cloner to only fetch the specified ref rather than cloning the whole repository, this means refs which are not a branch HEAD or tag are not reachable. This PR adds a flag to bring back the old behaviour fallback to pull master and checkout the ref if the fetch fails

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[szphie]

/assign @droot

[monopole]

great PR thanks.

Flags become part of the API, so would prefer flag use only for exceptional behavior.

Given the statements about github functionality in the referenced bug, i'm inclined to think that supporting access to specific git hashes should be the 'normal' (no flag required) behavior. "Fast" clone behavior (which only allows tags or HEAD) should require a flag.

i.e. add a flag like --speedy_git_clone to use ClonerUsingGitExec (which cloud be renamed), and otherwise use DeepClonerUsingGitExec by default.

WDYT?

[monopole]

thanks

[szphie]

great PR thanks.

Flags become part of the API, so would prefer flag use only for exceptional behavior.

Given the statements about github functionality in the referenced bug, i'm inclined to think that supporting access to specific git hashes should be the 'normal' (no flag required) behavior. "Fast" clone behavior (which only allows tags or HEAD) should require a flag.

i.e. add a flag like --speedy_git_clone to use ClonerUsingGitExec (which cloud be renamed), and otherwise use DeepClonerUsingGitExec by default.

WDYT?

@monopole That certainly works for my purposes but I'd feel a bit off about hiding that behaviour for people whose workflows are currently okay. Wonder if we could get the best of both worlds - how would you feel about attempting the fetch and then falling back to clone/checkout in case of an error? Then I can abandon all the flag logic entirely

        // ...
        cmd = exec.Command(
		gitProgram,
		"fetch",
		"--depth=1",
		"origin",
		repoSpec.Ref)
	cmd.Stdout = &out
	cmd.Stderr = &out
	cmd.Dir = repoSpec.Dir.String()
	err = cmd.Run()
	if err != nil {
		cmd = exec.Command(
			gitProgram,
			"pull",
			"origin",
			"master")
		var out bytes.Buffer
		cmd.Stdout = &out
		cmd.Dir = repoSpec.Dir.String()
		err := cmd.Run()
		if err != nil {
			return errors.Wrapf(err, "trouble pulling %s", repoSpec.OrgRepo)
		}
		if repoSpec.Ref == "" {
			repoSpec.Ref = "master"
		}
		cmd = exec.Command(gitProgram, "checkout", repoSpec.Ref)
		cmd.Dir = repoSpec.Dir.String()
		err = cmd.Run()
		if err != nil {
			return errors.Wrapf(
				err, "trouble checking out href %s", repoSpec.Ref)
		}
	}
        // ...

[monopole]

simpler, less code, less disruption, no api change. great!