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

3 files changed, 51 insertions, 0 deletions

diff --git a/errors/doc.go b/errors/doc.go
new file mode 100644
index 00000000..32afcd10
--- /dev/null
+++ b/errors/doc.go
@@ -0,0 +1,2 @@
+// Package errors defines error types shared across furgit.
+package errors
diff --git a/errors/missing.go b/errors/missing.go
new file mode 100644
index 00000000..3ca27583
--- /dev/null
+++ b/errors/missing.go
@@ -0,0 +1,18 @@
+package errors
+
+import (
+	"fmt"
+
+	"codeberg.org/lindenii/furgit/objectid"
+)
+
+// ObjectMissingError indicates that a referenced object is absent from the
+// repository object store.
+type ObjectMissingError struct {
+	OID objectid.ObjectID
+}
+
+// Error implements error.
+func (e *ObjectMissingError) Error() string {
+	return fmt.Sprintf("missing object %s", e.OID)
+}
diff --git a/errors/type.go b/errors/type.go
new file mode 100644
index 00000000..82ca993a
--- /dev/null
+++ b/errors/type.go
@@ -0,0 +1,31 @@
+package errors
+
+import (
+	"fmt"
+
+	"codeberg.org/lindenii/furgit/objectid"
+	"codeberg.org/lindenii/furgit/objecttype"
+)
+
+// ObjectTypeError indicates that a referenced object has a different type than
+// what the operation expected.
+type ObjectTypeError struct {
+	OID  objectid.ObjectID
+	Got  objecttype.Type
+	Want objecttype.Type
+}
+
+// Error implements error.
+func (e *ObjectTypeError) Error() string {
+	gotName, gotOK := objecttype.Name(e.Got)
+	if !gotOK {
+		gotName = fmt.Sprintf("type(%d)", e.Got)
+	}
+
+	wantName, wantOK := objecttype.Name(e.Want)
+	if !wantOK {
+		wantName = fmt.Sprintf("type(%d)", e.Want)
+	}
+
+	return fmt.Sprintf("object %s has type %s, want %s", e.OID, gotName, wantName)
+}