libgit2: add remaining checkout strategy tests

This commit is a follow up on 4dc3185
and adds tests for the remaining checkout strategies, while
consolidating some of the logic.

The consolidated logic ensures that (SemVer) tag and commit checkouts
happen using the same "checkout detached HEAD" logic.
The branch checkout is left unmodified, and simply checks out at the
current HEAD of the given branch.

Signed-off-by: Hidde Beydals <[email protected]>

Author: hiddeco

pkg/git/libgit2/checkout.go

@@ -98,31 +98,12 @@ func (c *CheckoutTag) Checkout(ctx context.Context, path, url string, auth *git.
 		},
 	})
 	if err != nil {
-		return nil, "", fmt.Errorf("unable to clone '%s', error: %w", url, err)
-	}
-	ref, err := repo.References.Dwim(c.tag)
-	if err != nil {
-		return nil, "", fmt.Errorf("unable to find tag '%s': %w", c.tag, err)
-	}
-	err = repo.SetHeadDetached(ref.Target())
-	if err != nil {
-		return nil, "", fmt.Errorf("git checkout error: %w", err)
-	}
-	head, err := repo.Head()
-	if err != nil {
-		return nil, "", fmt.Errorf("git resolve HEAD error: %w", err)
+		return nil, "", fmt.Errorf("unable to clone '%s', error: %w", url, gitutil.LibGit2Error(err))
 	}
-	commit, err := repo.LookupCommit(head.Target())
+	commit, err := checkoutDetachedDwim(repo, c.tag)
 	if err != nil {
-		return nil, "", fmt.Errorf("git commit '%s' not found: %w", head.Target(), err)
-	}
-	err = repo.CheckoutHead(&git2go.CheckoutOptions{
-		Strategy: git2go.CheckoutForce,
-	})
-	if err != nil {
-		return nil, "", fmt.Errorf("git checkout error: %w", err)
+		return nil, "", err
 	}
-
 	return &Commit{commit}, fmt.Sprintf("%s/%s", c.tag, commit.Id().String()), nil
 }
 
@@ -140,30 +121,19 @@ func (c *CheckoutCommit) Checkout(ctx context.Context, path, url string, auth *g
 				CertificateCheckCallback: auth.CertCallback,
 			},
 		},
-		CheckoutBranch: c.branch,
 	})
 	if err != nil {
-		return nil, "", fmt.Errorf("unable to clone '%s', error: %w", url, err)
+		return nil, "", fmt.Errorf("unable to clone '%s', error: %w", url, gitutil.LibGit2Error(err))
 	}
+
 	oid, err := git2go.NewOid(c.commit)
 	if err != nil {
-		return nil, "", fmt.Errorf("git commit '%s' could not be parsed", c.commit)
-	}
-	commit, err := repo.LookupCommit(oid)
-	if err != nil {
-		return nil, "", fmt.Errorf("git commit '%s' not found: %w", c.commit, err)
-	}
-	tree, err := repo.LookupTree(commit.TreeId())
-	if err != nil {
-		return nil, "", fmt.Errorf("git worktree error: %w", err)
+		return nil, "", fmt.Errorf("could not create oid for '%s': %w", c.commit, err)
 	}
-	err = repo.CheckoutTree(tree, &git2go.CheckoutOptions{
-		Strategy: git2go.CheckoutForce,
-	})
+	commit, err := checkoutDetachedHEAD(repo, oid)
 	if err != nil {
 		return nil, "", fmt.Errorf("git checkout error: %w", err)
 	}
-
 	return &Commit{commit}, fmt.Sprintf("%s/%s", c.branch, commit.Id().String()), nil
 }
 
@@ -187,7 +157,7 @@ func (c *CheckoutSemVer) Checkout(ctx context.Context, path, url string, auth *g
 		},
 	})
 	if err != nil {
-		return nil, "", fmt.Errorf("unable to clone '%s', error: %w", url, err)
+		return nil, "", fmt.Errorf("unable to clone '%s', error: %w", url, gitutil.LibGit2Error(err))
 	}
 
 	tags := make(map[string]string)
@@ -255,28 +225,62 @@ func (c *CheckoutSemVer) Checkout(ctx context.Context, path, url string, auth *g
 	v := matchedVersions[len(matchedVersions)-1]
 	t := v.Original()
 
-	ref, err := repo.References.Dwim(t)
+	commit, err := checkoutDetachedDwim(repo, t)
+	return &Commit{commit}, fmt.Sprintf("%s/%s", t, commit.Id().String()), nil
+}
+
+// checkoutDetachedDwim attempts to perform a detached HEAD checkout by first DWIMing the short name
+// to get a concrete reference, and then calling checkoutDetachedHEAD.
+func checkoutDetachedDwim(repo *git2go.Repository, name string) (*git2go.Commit, error) {
+	ref, err := repo.References.Dwim(name)
 	if err != nil {
-		return nil, "", fmt.Errorf("unable to find tag '%s': %w", t, err)
+		return nil, fmt.Errorf("unable to find '%s': %w", name, err)
 	}
-	err = repo.SetHeadDetached(ref.Target())
+	defer ref.Free()
+	c, err := ref.Peel(git2go.ObjectCommit)
 	if err != nil {
-		return nil, "", fmt.Errorf("git checkout error: %w", err)
+		return nil, fmt.Errorf("could not get commit for ref '%s': %w", ref.Name(), err)
 	}
-	head, err := repo.Head()
+	defer c.Free()
+	commit, err := c.AsCommit()
 	if err != nil {
-		return nil, "", fmt.Errorf("git resolve HEAD error: %w", err)
+		return nil, fmt.Errorf("could not get commit object for ref '%s': %w", ref.Name(), err)
 	}
-	commit, err := repo.LookupCommit(head.Target())
+	defer commit.Free()
+	return checkoutDetachedHEAD(repo, commit.Id())
+}
+
+// checkoutDetachedHEAD attempts to perform a detached HEAD checkout for the given commit.
+func checkoutDetachedHEAD(repo *git2go.Repository, oid *git2go.Oid) (*git2go.Commit, error) {
+	commit, err := repo.LookupCommit(oid)
 	if err != nil {
-		return nil, "", fmt.Errorf("git commit '%s' not found: %w", head.Target().String(), err)
+		return nil, fmt.Errorf("git commit '%s' not found: %w", oid.String(), err)
 	}
-	err = repo.CheckoutHead(&git2go.CheckoutOptions{
+	if err = repo.SetHeadDetached(commit.Id()); err != nil {
+		commit.Free()
+		return nil, fmt.Errorf("could not detach HEAD at '%s': %w", oid.String(), err)
+	}
+	if err = repo.CheckoutHead(&git2go.CheckoutOptions{
 		Strategy: git2go.CheckoutForce,
-	})
+	}); err != nil {
+		commit.Free()
+		return nil, fmt.Errorf("git checkout error: %w", err)
+	}
+	return commit, nil
+}
+
+// headCommit returns the current HEAD of the repository, or an error.
+func headCommit(repo *git2go.Repository) (*git2go.Commit, error) {
+	head, err := repo.Head()
 	if err != nil {
-		return nil, "", fmt.Errorf("git checkout error: %w", err)
+		return nil, err
 	}
+	defer head.Free()
 
-	return &Commit{commit}, fmt.Sprintf("%s/%s", t, commit.Id().String()), nil
+	commit, err := repo.LookupCommit(head.Target())
+	if err != nil {
+		return nil, err
+	}
+
+	return commit, nil
 }