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[PATCH 4/7] add object_as_type helper for casting objects

From
Jeff King <peff@peff.net>
Date
Jul 11, 2014, 08:48 UTC
Message-ID
<20140711084823.GD5625@sigill.intra.peff.net>
In-Reply-To
<20140711084141.GA5521@sigill.intra.peff.net>

When we call lookup_commit, lookup_tree, etc, the logic goes something like:

  1. Look for an existing object struct. If we don't have
     one, allocate and return a new one.
  2. Double check that any object we have is the expected
     type (and complain and return NULL otherwise).
  3. Convert an object with type OBJ_NONE (from a prior
     call to lookup_unknown_object) to the expected type.

We can encapsulate steps 2 and 3 in a helper function which checks whether we have the expected object type, converts OBJ_NONE as appropriate, and returns the object.

Not only does this shorten the code, but it also provides one central location for converting OBJ_NONE objects into objects of other types. Future patches will use that to enforce type-specific invariants.

Since this is a refactoring, we would want it to behave exactly as the current code. It takes a little reasoning to see that this is the case:

  - for lookup_{commit,tree,etc} functions, we are just
    pulling steps 2 and 3 into a function that does the same
    thing.
  - for the call in peel_object, we currently only do step 3
    (but we want to consolidate it with the others, as
    mentioned above). However, step 2 is a noop here, as the
    surrounding conditional makes sure we have OBJ_NONE
    (which we want to keep to avoid an extraneous call to
    sha1_object_info).
  - for the call in lookup_commit_reference_gently, we are
    currently doing step 2 but not step 3. However, step 3
    is a noop here. The object we got will have just come
    from deref_tag, which must have figured out the type for
    each object in order to know when to stop peeling.
    Therefore the type will never be OBJ_NONE.
Signed-off-by: Jeff King <peff@peff.net>
---
 blob.c   |  9 +--------
 commit.c | 19 ++-----------------
 object.c | 17 +++++++++++++++++
 object.h |  2 ++
 refs.c   |  3 +--
 tag.c    |  9 +--------
 tree.c   |  9 +--------
 7 files changed, 25 insertions(+), 43 deletions(-)
diff --git a/blob.c b/blob.c
index 5720a38..1fcb8e4 100644
--- a/blob.c
+++ b/blob.c
@@ -8,14 +8,7 @@ struct blob *lookup_blob(const unsigned char *sha1)
 	struct object *obj = lookup_object(sha1);
 	if (!obj)
 		return create_object(sha1, alloc_blob_node());
-	if (!obj->type)
-		obj->type = OBJ_BLOB;
-	if (obj->type != OBJ_BLOB) {
-		error("Object %s is a %s, not a blob",
-		      sha1_to_hex(sha1), typename(obj->type));
-		return NULL;
-	}
-	return (struct blob *) obj;
+	return object_as_type(obj, OBJ_BLOB, 0);
 }
 
 int parse_blob_buffer(struct blob *item, void *buffer, unsigned long size)
diff --git a/commit.c b/commit.c
index 21ed310..dd638de 100644
--- a/commit.c
+++ b/commit.c
@@ -18,19 +18,6 @@ int save_commit_buffer = 1;
 
 const char *commit_type = "commit";
 
-static struct commit *check_commit(struct object *obj,
-				   const unsigned char *sha1,
-				   int quiet)
-{
-	if (obj->type != OBJ_COMMIT) {
-		if (!quiet)
-			error("Object %s is a %s, not a commit",
-			      sha1_to_hex(sha1), typename(obj->type));
-		return NULL;
-	}
-	return (struct commit *) obj;
-}
-
 struct commit *lookup_commit_reference_gently(const unsigned char *sha1,
 					      int quiet)
 {
@@ -38,7 +25,7 @@ struct commit *lookup_commit_reference_gently(const unsigned char *sha1,
 
 	if (!obj)
 		return NULL;
-	return check_commit(obj, sha1, quiet);
+	return object_as_type(obj, OBJ_COMMIT, quiet);
 }
 
 struct commit *lookup_commit_reference(const unsigned char *sha1)
@@ -65,9 +52,7 @@ struct commit *lookup_commit(const unsigned char *sha1)
 		struct commit *c = alloc_commit_node();
 		return create_object(sha1, c);
 	}
-	if (!obj->type)
-		obj->type = OBJ_COMMIT;
-	return check_commit(obj, sha1, 0);
+	return object_as_type(obj, OBJ_COMMIT, 0);
 }
 
 struct commit *lookup_commit_reference_by_name(const char *name)
diff --git a/object.c b/object.c
index 472aa8d..b2319f6 100644
--- a/object.c
+++ b/object.c
@@ -158,6 +158,23 @@ void *create_object(const unsigned char *sha1, void *o)
 	return obj;
 }
 
+void *object_as_type(struct object *obj, enum object_type type, int quiet)
+{
+	if (obj->type == type)
+		return obj;
+	else if (obj->type == OBJ_NONE) {
+		obj->type = type;
+		return obj;
+	}
+	else {
+		if (!quiet)
+			error("object %s is a %s, not a %s",
+			      sha1_to_hex(obj->sha1),
+			      typename(obj->type), typename(type));
+		return NULL;
+	}
+}
+
 struct object *lookup_unknown_object(const unsigned char *sha1)
 {
 	struct object *obj = lookup_object(sha1);
diff --git a/object.h b/object.h
index 8020ace..5e8d8ee 100644
--- a/object.h
+++ b/object.h
@@ -81,6 +81,8 @@ struct object *lookup_object(const unsigned char *sha1);
 
 extern void *create_object(const unsigned char *sha1, void *obj);
 
+void *object_as_type(struct object *obj, enum object_type type, int quiet);
+
 /*
  * Returns the object, having parsed it to find out what it is.
  *
diff --git a/refs.c b/refs.c
index 20e2bf1..5a18e2d 100644
--- a/refs.c
+++ b/refs.c
@@ -1729,9 +1729,8 @@ static enum peel_status peel_object(const unsigned char *name, unsigned char *sh
 
 	if (o->type == OBJ_NONE) {
 		int type = sha1_object_info(name, NULL);
-		if (type < 0)
+		if (type < 0 || !object_as_type(o, type, 0))
 			return PEEL_INVALID;
-		o->type = type;
 	}
 
 	if (o->type != OBJ_TAG)
diff --git a/tag.c b/tag.c
index 79552c7..82d841b 100644
--- a/tag.c
+++ b/tag.c
@@ -41,14 +41,7 @@ struct tag *lookup_tag(const unsigned char *sha1)
 	struct object *obj = lookup_object(sha1);
 	if (!obj)
 		return create_object(sha1, alloc_tag_node());
-	if (!obj->type)
-		obj->type = OBJ_TAG;
-	if (obj->type != OBJ_TAG) {
-		error("Object %s is a %s, not a tag",
-		      sha1_to_hex(sha1), typename(obj->type));
-		return NULL;
-	}
-	return (struct tag *) obj;
+	return object_as_type(obj, OBJ_TAG, 0);
 }
 
 static unsigned long parse_tag_date(const char *buf, const char *tail)
diff --git a/tree.c b/tree.c
index ed66575..bb02c1c 100644
--- a/tree.c
+++ b/tree.c
@@ -184,14 +184,7 @@ struct tree *lookup_tree(const unsigned char *sha1)
 	struct object *obj = lookup_object(sha1);
 	if (!obj)
 		return create_object(sha1, alloc_tree_node());
-	if (!obj->type)
-		obj->type = OBJ_TREE;
-	if (obj->type != OBJ_TREE) {
-		error("Object %s is a %s, not a tree",
-		      sha1_to_hex(sha1), typename(obj->type));
-		return NULL;
-	}
-	return (struct tree *) obj;
+	return object_as_type(obj, OBJ_TREE, 0);
 }
 
 int parse_tree_buffer(struct tree *item, void *buffer, unsigned long size)

-- 
2.0.0.566.gfe3e6b2
Previous: Jeff KingNext: Ramsay Jones
Message 29 of 35 in “alloc.c: remove the redundant commit_count variable”
  1. 2/2 alloc.c: remove the redundant commit_count variableRamsay Jones, Jul 10, 2014
  2. Jeff KingJul 11, 2014
  3. Ramsay JonesJul 11, 2014
  4. Jeff KingJul 11, 2014
  5. Ramsay JonesJul 11, 2014
  6. 0/7 ensure index is set for all OBJ_COMMIT objects variableJeff King, Jul 11, 2014
  7. 1/7 alloc.c: remove the alloc_raw_commit_node() functionJeff King, Jul 11, 2014
  8. 2/7 move setting of object->type to alloc_* functionsJeff King, Jul 11, 2014
  9. Ramsay JonesJul 12, 2014
  10. Jeff KingJul 12, 2014
  11. Jeff KingJul 13, 2014
  12. 1/8 alloc.c: remove the alloc_raw_commit_node() functionJeff King, Jul 13, 2014
  13. Junio C HamanoJul 15, 2014
  14. 2/8 alloc: write out allocator definitionsJeff King, Jul 13, 2014
  15. Junio C HamanoJul 15, 2014
  16. 3/8 move setting of object->type to alloc_* functionsJeff King, Jul 13, 2014
  17. Junio C HamanoJul 15, 2014
  18. 4/8 parse_object_buffer: do not set object typeJeff King, Jul 13, 2014
  19. 5/8 add object_as_type helper for casting objectsJeff King, Jul 13, 2014
  20. 6/8 alloc: factor out commit indexJeff King, Jul 13, 2014
  21. 7/8 object_as_type: set commit indexJeff King, Jul 13, 2014
  22. 8/8 diff-tree: avoid lookup_unknown_objectJeff King, Jul 13, 2014
  23. Ramsay JonesJul 13, 2014
  24. Jeff KingJul 14, 2014
  25. Ramsay JonesJul 14, 2014
  26. Ramsay JonesJul 12, 2014
  27. Jeff KingJul 12, 2014
  28. 3/7 parse_object_buffer: do not set object typeJeff King, Jul 11, 2014
  29. 4/7 add object_as_type helper for casting objectsJeff King, Jul 11, 2014
  30. Ramsay JonesJul 11, 2014
  31. Jeff KingJul 11, 2014
  32. 5/7 alloc: factor out commit indexJeff King, Jul 11, 2014
  33. 6/7 object_as_type: set commit indexJeff King, Jul 11, 2014
  34. 7/7 diff-tree: avoid lookup_unknown_objectJeff King, Jul 11, 2014
  35. Ramsay JonesJul 11, 2014

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