Don't always derefence ref

how_to/Change_32.md

@@ -0,0 +1,8 @@
+- data: Create Refvalue container
+
+To make working with symbolic refs easier, we will create a `Refvalue` container
+to represent the value of a ref. `Refvalue` will have a property symbolic that
+will say whether it's a symbolic or a direct ref.
+
+This change is just refactoring, we will wrap every OID that is written or read
+from a ref in a `RefValue`.

how_to/Change_33.md

@@ -0,0 +1,17 @@
+data: Dereference refs when reading and writing
+
+Now we'll dereference symbolic refs not only when reading them but also when
+writing them.
+
+We'll implement a helper function called `_get_ref_internal` which will return
+the path and the value of the last ref pointed by a symbolic ref. In simple words:
+
+- When given a non-symbolic ref, `_get_ref_internal` will return the ref name
+and value.
+- When given a symbolic ref, `_get_ref_internal` will dereference the ref
+recursively, and then return the name of the last (non-symbolic) ref that points
+to an OID, plus its value.
+
+Now `update_ref` will use `_get_ref_internal` to know which ref it needs to update.
+
+Additionally, we'll use `_get_ref_internal` in `get_ref`.

how_to/Change_34.md

@@ -0,0 +1,15 @@
+- data: Don't always dereference refs (for `ugit k`)
+
+Actually, it's not always desirable to dereference a ref all the way. Sometimes
+we would like to know at which ref a symbolic ref points, rather than the final
+OID. Or we would like to update a ref directly, rather then updating the last
+ref in the chain.
+
+One such usecase is `ugit k`. When visualizing refs it would be nice to see
+which ref points to which ref. We will see another usecase soon.
+
+To accomodate this, we will add a `deref` option to `get_ref`, `iter_refs` and
+`update_ref`. If they will be called with `deref=False`, they will work on the
+raw value of a ref and not dereference any symbolic refs.
+
+Then we will update `k` to use `deref=False`.

ugit/base.py

@@ -84,7 +84,7 @@ def read_tree(tree_oid):
 def commit(message):
     commit = f"tree {write_tree()}\n"
 
-    HEAD = data.get_ref("HEAD")
+    HEAD = data.get_ref("HEAD").value
     if HEAD:
         commit += f"parent {HEAD}\n"
 
@@ -93,23 +93,23 @@ def commit(message):
 
     oid = data.hash_object(commit.encode(), "commit")
 
-    data.update_ref("HEAD", oid)
+    data.update_ref("HEAD", data.RefValue(symbolic=False, value=oid))
 
     return oid
 
 
 def create_tag(name, oid):
-    data.update_ref(f"refs/tags/{name}", oid)
+    data.update_ref(f"refs/tags/{name}", data.RefValue(symbolic=False, value=oid))
 
 
 def checkout(oid):
     commit = get_commit(oid)
     read_tree(commit.tree)
-    data.update_ref("HEAD", oid)
+    data.update_ref("HEAD", data.RefValue(symbolic=False, value=oid))
 
 
 def create_branch(name, oid):
-    data.update_ref(f"refs/heads/{name}", oid)
+    data.update_ref(f"refs/heads/{name}", data.RefValue(symbolic=False, value=oid))
 
 
 Commit = namedtuple("Commit", ["tree", "parent", "message"])
@@ -161,8 +161,8 @@ def get_oid(name):
         f"refs/heads/{name}",
     ]
     for ref in refs_to_try:
-        if data.get_ref(ref):
+        if data.get_ref(ref, deref=False).value:
-            return data.get_ref(ref)
+            return data.get_ref(ref).value
 
     # Name is SHA1
     is_hex = all(c in string.hexdigits for c in name)

ugit/cli.py

@@ -121,10 +121,11 @@ def k(args):
     dot = "digraph commits {\n"
 
     oids = set()
-    for refname, ref in data.iter_refs():
+    for refname, ref in data.iter_refs(deref=False):
         dot += f"'{refname}' [shape=note]\n"
-        dot += f"'{refname}' -> '{ref}'\n"
+        dot += f"'{refname}' -> '{ref.value}'\n"
-        oids.add(ref)
+        if not ref.symbolic:
+            oids.add(ref.value)
 
     for oid in base.iter_commits_and_parents(oids):
         commit = base.get_commit(oid)

ugit/data.py

@@ -3,6 +3,8 @@ from pathlib import Path, PurePath
 import hashlib
 import os
 
+from collections import namedtuple
+
 GIT_DIR = ".ugit"
 
 
@@ -11,24 +13,35 @@ def init():
     Path.mkdir(f"{GIT_DIR}/objects")
 
 
-def update_ref(ref, oid):
+RefValue = namedtuple("RefValue", ["symbolic", "value"])
+
+
+def update_ref(ref, value, deref=True):
+    assert not value.symbolic
+    ref = _get_ref_internal(ref, deref)[0]
     ref_path = f"{GIT_DIR}/{ref}"
     Path.mkdir(ref_path, exist_ok=True)
     with open(ref_path, "w") as f:
-        f.write(oid)
+        f.write(value.value)
 
 
 def get_ref(ref):
+    return _get_ref_internal(ref)[1]
+
+
+def _get_ref_internal(ref):
     ref_path = f"{GIT_DIR}/{ref}"
     value = None
     if Path.is_file(ref_path):
         with open(ref_path) as f:
             value = f.read().strip()
 
-    if value and value.startswith("ref:"):
+    symbolic = bool(value) and value.startswith("ref")
-        return get_ref(value.split(":", 1)[1].strip())
+    if symbolic:
+        value = value.split(":", 1)[1].strip()
+        return _get_ref_internal(value)
 
-    return value
+    return ref, RefValue(symbolic=False, value=value)
 
 
 def iter_refs():