Urgh I made some wrong amends and I'm too tired to separate the commits out this time

ancestor: Split out of reachability
mergebase: Add merge base routines
internal/commitquery: Add commit query context engine thingy
internal/peel: Shared tag peeling
errors: Shared object query errors
internal/testgit: Add rooted repo helpers; remove raw path access
objectstore/memory: Add in-memory object store
objectid: Add Compare helper

4 files changed, 62 insertions, 174 deletions

diff --git a/repository/refs_test.go b/repository/refs_test.go
index 8d8c604e..8b2676a2 100644
--- a/repository/refs_test.go
+++ b/repository/refs_test.go
@@ -1,14 +1,12 @@
 package repository_test
 
 import (
-	"os"
 	"testing"
 
 	"codeberg.org/lindenii/furgit/internal/testgit"
 	"codeberg.org/lindenii/furgit/objectid"
 	"codeberg.org/lindenii/furgit/objecttype"
 	"codeberg.org/lindenii/furgit/ref"
-	"codeberg.org/lindenii/furgit/repository"
 )
 
 func TestOpenFilesRefFormat(t *testing.T) {
@@ -25,19 +23,7 @@ func TestOpenFilesRefFormat(t *testing.T) {
 		repoHarness.UpdateRef(t, "refs/heads/main", commitID)
 		repoHarness.SymbolicRef(t, "HEAD", "refs/heads/main")
 
-		root, err := os.OpenRoot(repoHarness.Dir())
-		if err != nil {
-			t.Fatalf("os.OpenRoot: %v", err)
-		}
-
-		defer func() { _ = root.Close() }()
-
-		repo, err := repository.Open(root)
-		if err != nil {
-			t.Fatalf("repository.Open: %v", err)
-		}
-
-		defer func() { _ = repo.Close() }()
+		repo := repoHarness.OpenRepository(t)
 
 		if repo.Algorithm() != algo {
 			t.Fatalf("Algorithm = %v, want %v", repo.Algorithm(), algo)
@@ -114,19 +100,7 @@ func writeMainAndHead(t *testing.T, repoHarness *testgit.TestRepo) objectid.Obje
 func assertResolveFully(t *testing.T, repoHarness *testgit.TestRepo, name string, want objectid.ObjectID) {
 	t.Helper()
 
-	root, err := os.OpenRoot(repoHarness.Dir())
-	if err != nil {
-		t.Fatalf("os.OpenRoot: %v", err)
-	}
-
-	defer func() { _ = root.Close() }()
-
-	repo, err := repository.Open(root)
-	if err != nil {
-		t.Fatalf("repository.Open: %v", err)
-	}
-
-	defer func() { _ = repo.Close() }()
+	repo := repoHarness.OpenRepository(t)
 
 	resolved, err := repo.Refs().ResolveFully(name)
 	if err != nil {
diff --git a/repository/stored_test.go b/repository/stored_test.go
index 0ca88664..cefb4cbe 100644
--- a/repository/stored_test.go
+++ b/repository/stored_test.go
@@ -2,14 +2,12 @@ package repository_test
 
 import (
 	"fmt"
-	"os"
 	"strings"
 	"testing"
 
 	"codeberg.org/lindenii/furgit/internal/testgit"
 	"codeberg.org/lindenii/furgit/object"
 	"codeberg.org/lindenii/furgit/objectid"
-	"codeberg.org/lindenii/furgit/repository"
 )
 
 func TestReadStoredTyped(t *testing.T) {
@@ -24,19 +22,7 @@ func TestReadStoredTyped(t *testing.T) {
 
 		blobID, treeID, commitID := repoHarness.MakeCommit(t, "stored types")
 
-		root, err := os.OpenRoot(repoHarness.Dir())
-		if err != nil {
-			t.Fatalf("os.OpenRoot: %v", err)
-		}
-
-		defer func() { _ = root.Close() }()
-
-		repo, err := repository.Open(root)
-		if err != nil {
-			t.Fatalf("repository.Open: %v", err)
-		}
-
-		defer func() { _ = repo.Close() }()
+		repo := repoHarness.OpenRepository(t)
 
 		blob, err := repo.ReadStoredBlob(blobID)
 		if err != nil {
@@ -93,19 +79,7 @@ func TestResolveTreeEntry(t *testing.T) {
 		childTreeID := repoHarness.Mktree(t, fmt.Sprintf("100644 blob %s\tleaf.txt\n", blobID))
 		rootTreeID := repoHarness.Mktree(t, fmt.Sprintf("040000 tree %s\tdir\n", childTreeID))
 
-		root, err := os.OpenRoot(repoHarness.Dir())
-		if err != nil {
-			t.Fatalf("os.OpenRoot: %v", err)
-		}
-
-		defer func() { _ = root.Close() }()
-
-		repo, err := repository.Open(root)
-		if err != nil {
-			t.Fatalf("repository.Open: %v", err)
-		}
-
-		defer func() { _ = repo.Close() }()
+		repo := repoHarness.OpenRepository(t)
 
 		rootTree, err := repo.ReadStoredTree(rootTreeID)
 		if err != nil {
@@ -141,19 +115,7 @@ func TestResolveTreeEntryErrors(t *testing.T) {
 			blobID := repoHarness.HashObject(t, "blob", []byte("body\n"))
 			rootTreeID := repoHarness.Mktree(t, fmt.Sprintf("100644 blob %s\tfile.txt\n", blobID))
 
-			root, err := os.OpenRoot(repoHarness.Dir())
-			if err != nil {
-				t.Fatalf("os.OpenRoot: %v", err)
-			}
-
-			defer func() { _ = root.Close() }()
-
-			repo, err := repository.Open(root)
-			if err != nil {
-				t.Fatalf("repository.Open: %v", err)
-			}
-
-			defer func() { _ = repo.Close() }()
+			repo := repoHarness.OpenRepository(t)
 
 			rootTree, err := repo.ReadStoredTree(rootTreeID)
 			if err != nil {
@@ -176,19 +138,7 @@ func TestResolveTreeEntryErrors(t *testing.T) {
 			blobID := repoHarness.HashObject(t, "blob", []byte("body\n"))
 			rootTreeID := repoHarness.Mktree(t, fmt.Sprintf("100644 blob %s\tdir\n", blobID))
 
-			root, err := os.OpenRoot(repoHarness.Dir())
-			if err != nil {
-				t.Fatalf("os.OpenRoot: %v", err)
-			}
-
-			defer func() { _ = root.Close() }()
-
-			repo, err := repository.Open(root)
-			if err != nil {
-				t.Fatalf("repository.Open: %v", err)
-			}
-
-			defer func() { _ = repo.Close() }()
+			repo := repoHarness.OpenRepository(t)
 
 			rootTree, err := repo.ReadStoredTree(rootTreeID)
 			if err != nil {
@@ -227,19 +177,7 @@ func TestResolveTreeEntryDeepPath(t *testing.T) {
 
 		parts = append(parts, []byte("leaf.txt"))
 
-		root, err := os.OpenRoot(repoHarness.Dir())
-		if err != nil {
-			t.Fatalf("os.OpenRoot: %v", err)
-		}
-
-		defer func() { _ = root.Close() }()
-
-		repo, err := repository.Open(root)
-		if err != nil {
-			t.Fatalf("repository.Open: %v", err)
-		}
-
-		defer func() { _ = repo.Close() }()
+		repo := repoHarness.OpenRepository(t)
 
 		rootTree, err := repo.ReadStoredTree(currentTree)
 		if err != nil {
@@ -287,19 +225,7 @@ func TestReadStoredTreeMixedModes(t *testing.T) {
 			),
 		)
 
-		root, err := os.OpenRoot(repoHarness.Dir())
-		if err != nil {
-			t.Fatalf("os.OpenRoot: %v", err)
-		}
-
-		defer func() { _ = root.Close() }()
-
-		repo, err := repository.Open(root)
-		if err != nil {
-			t.Fatalf("repository.Open: %v", err)
-		}
-
-		defer func() { _ = repo.Close() }()
+		repo := repoHarness.OpenRepository(t)
 
 		rootTree, err := repo.ReadStoredTree(rootTreeID)
 		if err != nil {
diff --git a/repository/traversal_test.go b/repository/traversal_test.go
index ff3614dc..d5eaabb4 100644
--- a/repository/traversal_test.go
+++ b/repository/traversal_test.go
@@ -31,7 +31,8 @@ func TestRepositoryDepthFirstEnumerationFromHEAD(t *testing.T) {
 		repoHarness.UpdateRef(t, "refs/heads/main", commit2)
 		repoHarness.SymbolicRef(t, "HEAD", "refs/heads/main")
 
-		walkRepositoryFromHead(t, repoHarness.Dir())
+		root := repoHarness.OpenGitRoot(t)
+		walkRepositoryFromRoot(t, root, "test repo")
 	})
 }
 
@@ -39,38 +40,51 @@ func TestRepositoryDepthFirstEnumerationCurrentWorktree(t *testing.T) {
 	t.Parallel()
 
 	worktreeRoot := filepath.Clean("..")
-	gitPath := filepath.Join(worktreeRoot, ".git")
 
-	info, err := os.Stat(gitPath)
+	worktreeFS, err := os.OpenRoot(worktreeRoot)
 	if err != nil {
-		t.Fatalf("stat %q: %v", gitPath, err)
+		t.Fatalf("os.OpenRoot(%q): %v", worktreeRoot, err)
+	}
+
+	defer func() { _ = worktreeFS.Close() }()
+
+	info, err := worktreeFS.Stat(".git")
+	if err != nil {
+		t.Fatalf("stat %q: %v", filepath.Join(worktreeRoot, ".git"), err)
 	}
 
 	if info.IsDir() {
-		walkRepositoryFromHead(t, gitPath)
+		gitRoot, err := worktreeFS.OpenRoot(".git")
+		if err != nil {
+			t.Fatalf("OpenRoot(.git): %v", err)
+		}
+
+		defer func() { _ = gitRoot.Close() }()
+
+		walkRepositoryFromRoot(t, gitRoot, filepath.Join(worktreeRoot, ".git"))
 
 		return
 	}
 
 	if !info.Mode().IsRegular() {
-		t.Fatalf("%q is neither a directory nor a regular file", gitPath)
+		t.Fatalf("%q is neither a directory nor a regular file", filepath.Join(worktreeRoot, ".git"))
 	}
 
-	content, err := os.ReadFile(gitPath) //#nosec G304
+	content, err := worktreeFS.ReadFile(".git")
 	if err != nil {
-		t.Fatalf("read %q: %v", gitPath, err)
+		t.Fatalf("read %q: %v", filepath.Join(worktreeRoot, ".git"), err)
 	}
 
 	line := strings.TrimSpace(string(content))
 
 	prefix := "gitdir: "
 	if !strings.HasPrefix(line, prefix) {
-		t.Fatalf("%q file does not begin with %q", gitPath, prefix)
+		t.Fatalf("%q file does not begin with %q", filepath.Join(worktreeRoot, ".git"), prefix)
 	}
 
 	gitdirRel := strings.TrimSpace(line[len(prefix):])
 	if gitdirRel == "" {
-		t.Fatalf("%q contains empty gitdir path", gitPath)
+		t.Fatalf("%q contains empty gitdir path", filepath.Join(worktreeRoot, ".git"))
 	}
 
 	gitdirPath := gitdirRel
@@ -78,42 +92,54 @@ func TestRepositoryDepthFirstEnumerationCurrentWorktree(t *testing.T) {
 		gitdirPath = filepath.Join(worktreeRoot, gitdirPath)
 	}
 
-	commondirPath := filepath.Join(gitdirPath, "commondir")
+	gitRoot, err := os.OpenRoot(gitdirPath)
+	if err != nil {
+		t.Fatalf("os.OpenRoot(%q): %v", gitdirPath, err)
+	}
+
+	defer func() { _ = gitRoot.Close() }()
 
-	commondirContent, err := os.ReadFile(commondirPath) //#nosec G304
+	commondirContent, err := gitRoot.ReadFile("commondir")
 	if err != nil {
-		t.Fatalf("read %q: %v", commondirPath, err)
+		t.Fatalf("read %q: %v", filepath.Join(gitdirPath, "commondir"), err)
 	}
 
 	repoPath := strings.TrimSpace(string(commondirContent))
 	if repoPath == "" {
-		t.Fatalf("%q contains empty repo path", commondirPath)
+		t.Fatalf("%q contains empty repo path", filepath.Join(gitdirPath, "commondir"))
 	}
 
 	if filepath.IsAbs(repoPath) {
-		walkRepositoryFromHead(t, repoPath)
+		repoRoot, err := os.OpenRoot(repoPath)
+		if err != nil {
+			t.Fatalf("os.OpenRoot(%q): %v", repoPath, err)
+		}
+
+		defer func() { _ = repoRoot.Close() }()
+
+		walkRepositoryFromRoot(t, repoRoot, repoPath)
 
 		return
 	}
 
 	repoPath = filepath.Join(gitdirPath, repoPath)
 
-	walkRepositoryFromHead(t, repoPath)
-}
-
-func walkRepositoryFromHead(t *testing.T, repoPath string) {
-	t.Helper()
-
-	root, err := os.OpenRoot(repoPath)
+	repoRoot, err := os.OpenRoot(repoPath)
 	if err != nil {
 		t.Fatalf("os.OpenRoot(%q): %v", repoPath, err)
 	}
 
-	defer func() { _ = root.Close() }()
+	defer func() { _ = repoRoot.Close() }()
+
+	walkRepositoryFromRoot(t, repoRoot, repoPath)
+}
+
+func walkRepositoryFromRoot(t *testing.T, root *os.Root, label string) {
+	t.Helper()
 
 	repo, err := repository.Open(root)
 	if err != nil {
-		t.Fatalf("repository.Open(root for %q): %v", repoPath, err)
+		t.Fatalf("repository.Open(root for %q): %v", label, err)
 	}
 
 	defer func() { _ = repo.Close() }()
@@ -129,7 +155,7 @@ func walkRepositoryFromHead(t *testing.T, repoPath string) {
 	}
 
 	if objectsRead <= 0 {
-		t.Fatalf("no objects were enumerated from HEAD (%s)", fmt.Sprintf("%q", repoPath))
+		t.Fatalf("no objects were enumerated from HEAD (%s)", fmt.Sprintf("%q", label))
 	}
 }
 
diff --git a/repository/write_loose_test.go b/repository/write_loose_test.go
index 6cd9b8a1..6b0a8572 100644
--- a/repository/write_loose_test.go
+++ b/repository/write_loose_test.go
@@ -2,13 +2,11 @@ package repository_test
 
 import (
 	"bytes"
-	"os"
 	"testing"
 
 	"codeberg.org/lindenii/furgit/internal/testgit"
 	"codeberg.org/lindenii/furgit/objectid"
 	"codeberg.org/lindenii/furgit/objecttype"
-	"codeberg.org/lindenii/furgit/repository"
 )
 
 func TestWriteLooseBytesContent(t *testing.T) {
@@ -21,19 +19,7 @@ func TestWriteLooseBytesContent(t *testing.T) {
 			RefFormat:    "files",
 		})
 
-		root, err := os.OpenRoot(repoHarness.Dir())
-		if err != nil {
-			t.Fatalf("os.OpenRoot: %v", err)
-		}
-
-		defer func() { _ = root.Close() }()
-
-		repo, err := repository.Open(root)
-		if err != nil {
-			t.Fatalf("repository.Open: %v", err)
-		}
-
-		defer func() { _ = repo.Close() }()
+		repo := repoHarness.OpenRepository(t)
 
 		content := []byte("write-loose-bytes-content\n")
 
@@ -72,19 +58,7 @@ func TestWriteLooseReaderContent(t *testing.T) {
 			RefFormat:    "files",
 		})
 
-		root, err := os.OpenRoot(repoHarness.Dir())
-		if err != nil {
-			t.Fatalf("os.OpenRoot: %v", err)
-		}
-
-		defer func() { _ = root.Close() }()
-
-		repo, err := repository.Open(root)
-		if err != nil {
-			t.Fatalf("repository.Open: %v", err)
-		}
-
-		defer func() { _ = repo.Close() }()
+		repo := repoHarness.OpenRepository(t)
 
 		content := []byte("write-loose-reader-content\n")
 
@@ -111,19 +85,7 @@ func TestWriteLooseFull(t *testing.T) {
 		})
 		_, _, commitID := repoHarness.MakeCommit(t, "write-loose-full")
 
-		root, err := os.OpenRoot(repoHarness.Dir())
-		if err != nil {
-			t.Fatalf("os.OpenRoot: %v", err)
-		}
-
-		defer func() { _ = root.Close() }()
-
-		repo, err := repository.Open(root)
-		if err != nil {
-			t.Fatalf("repository.Open: %v", err)
-		}
-
-		defer func() { _ = repo.Close() }()
+		repo := repoHarness.OpenRepository(t)
 
 		raw, err := repo.Objects().ReadBytesFull(commitID)
 		if err != nil {