Re: [PATCH] merge-base

Re: [PATCH] merge-base

[Linus Torvalds]

On Wed, 13 Apr 2005, Daniel Barkalow wrote:
>
> I wrote a pretty dumb program that will find some common ancestor for a
> pair of commits. It finds the one which is closest to one of the commits
> by number of generations. This is, at least, not strictly worse than any
> other common ancestor, at least (like picking the original release would
> be).
> 
> It wouldn't be too hard to do this much with rev-tree, but should be
> easier to extend.

I agree. But I did the silly "common revision tracking" part slightly
differently and in particular I already made fsck and rev-tree use the 
same exact code.

Also, I don't see why you did the "common parent" thing as part of the
"library", since that really does seem to be a very specific to this 
problem, and neither fsck nor rev-tree really wants it. 

Also, the date parsing really is a separate issue from the revision 
tracking (fsck does not want date parsing, but rev-tool does), so I think 
you might want to do for date parsing what I just did for the revision.h 
thing? No point in tying them together.

So could I ask you to re-factor it and base it on my current tree? Make 
the "merge-base" program have that common parent thing in it, and factor 
out the common date parsing into "parse-date.c" or something?

		Linus

Re: [PATCH] merge-base

[Daniel Barkalow]

On Wed, 13 Apr 2005, Linus Torvalds wrote:

> I agree. But I did the silly "common revision tracking" part slightly
> differently and in particular I already made fsck and rev-tree use the 
> same exact code.

I think I only saw a cut-and-paste version, and I didn't want to follow
that pattern.

> Also, I don't see why you did the "common parent" thing as part of the
> "library", since that really does seem to be a very specific to this 
> problem, and neither fsck nor rev-tree really wants it. 

That was just silly; on the other hand, I think I'll eventually want to
have a "support-for-merging" library file, so that people can write
alternative merging programs which call library functions to pick out
history details. But that obviously shouldn't be the same file that
rev-tree and fsck share, and I'll probably do that by pulling main() out
of the program later.

> Also, the date parsing really is a separate issue from the revision 
> tracking (fsck does not want date parsing, but rev-tool does), so I think 
> you might want to do for date parsing what I just did for the revision.h 
> thing? No point in tying them together.

I think there is some value in having a library file that completely
parses "commit"-tagged files. Having the date field in struct revision
without the code to parse it in the file that defines the struct seems
poor to me.

> So could I ask you to re-factor it and base it on my current tree? Make 
> the "merge-base" program have that common parent thing in it, and factor 
> out the common date parsing into "parse-date.c" or something?

I'm not actually using the date in merge-base, either, so I'll just leave
that alone for now (merge-base is based on generations, not time,
currently).

	-Daniel
*This .sig left intentionally blank*

[PATCH] merge-base-rebased

[Daniel Barkalow]

Add a dumb-but-improvable program to find a not-too-bad commit to do a
three-way-merge of two commits.

Signed-Off-By: Daniel Barkalow <barkalow@iabervon.org>

Index: Makefile
===================================================================
--- 1756b578489f93999ded68ae347bef7d6063101c/Makefile  (mode:100644 sha1:b39b4ea37586693dd707d1d0750a9b580350ec50)
+++ b07fe1a7e0836e7d906c16c4f63b2e42b4a5193a/Makefile  (mode:100644 sha1:a2d920a36c1124fb0a031ae43fdd3a8106529c8f)
@@ -14,7 +14,7 @@
 
 PROG=   update-cache show-diff init-db write-tree read-tree commit-tree \
 	cat-file fsck-cache checkout-cache diff-tree rev-tree show-files \
-	check-files ls-tree merge-tree
+	check-files ls-tree merge-tree merge-base
 
 all: $(PROG)
 
@@ -67,6 +67,9 @@
 merge-tree: merge-tree.o read-cache.o
 	$(CC) $(CFLAGS) -o merge-tree merge-tree.o read-cache.o $(LIBS)
 
+merge-base: merge-base.o read-cache.o
+	$(CC) $(CFLAGS) -o merge-base merge-base.o read-cache.o $(LIBS)
+
 read-cache.o: cache.h
 show-diff.o: cache.h
 
Index: merge-base.c
===================================================================
--- /dev/null  (tree:1756b578489f93999ded68ae347bef7d6063101c)
+++ b07fe1a7e0836e7d906c16c4f63b2e42b4a5193a/merge-base.c  (mode:100644 sha1:a3e885ef8e2ae761d76c3217002467d19bf75a8d)
@@ -0,0 +1,132 @@
+#include <stdlib.h>
+#include "cache.h"
+#include "revision.h"
+
+static int parse_commit(struct revision *rev)
+{
+	if (!(rev->flags & SEEN)) {
+		void *buffer, *bufptr;
+		unsigned long size;
+		char type[20];
+		unsigned char parent[20];
+
+		rev->flags |= SEEN;
+		buffer = bufptr = read_sha1_file(rev->sha1, type, &size);
+		if (!buffer || strcmp(type, "commit"))
+			return -1;
+		bufptr += 46; /* "tree " + "hex sha1" + "\n" */
+		while (!memcmp(bufptr, "parent ", 7) && 
+		       !get_sha1_hex(bufptr+7, parent)) {
+			add_relationship(rev, parent);
+			bufptr += 48;   /* "parent " + "hex sha1" + "\n" */
+		}
+		//rev->date = parse_commit_date(bufptr);
+		free(buffer);
+	}
+	return 0;
+}
+
+struct revision *common_ancestor(struct revision *rev1, struct revision *rev2)
+{
+	struct parent *parent;
+
+	struct parent *rev1list = malloc(sizeof(struct parent));
+	struct parent *rev2list = malloc(sizeof(struct parent));
+        
+	struct parent *posn, *temp;
+
+	rev1list->parent = rev1;
+	rev1list->next = NULL;
+
+	rev2list->parent = rev2;
+	rev2list->next = NULL;
+
+	while (rev1list || rev2list) {
+		posn = rev1list;
+		rev1list = NULL;
+		while (posn) {
+			parse_commit(posn->parent);
+			if (posn->parent->flags & 0x0001) {
+				/*
+				printf("1 already seen %s %x\n",
+				       sha1_to_hex(posn->parent->sha1),
+				       posn->parent->flags);
+				*/
+                                // do nothing
+			} else if (posn->parent->flags & 0x0002) {
+                                // XXXX free lists
+				return posn->parent;
+			} else {
+				/*
+				printf("1 based on %s\n",
+				       sha1_to_hex(posn->parent->sha1));
+				*/
+				posn->parent->flags |= 0x0001;
+
+				parent = posn->parent->parent;
+				while (parent) {
+					temp = malloc(sizeof(struct parent));
+					temp->next = rev1list;
+					temp->parent = parent->parent;
+					rev1list = temp;
+					parent = parent->next;
+				}
+			}
+			posn = posn->next;
+		}
+		posn = rev2list;
+		rev2list = NULL;
+		while (posn) {
+			parse_commit(posn->parent);
+			if (posn->parent->flags & 0x0002) {
+				/*
+				printf("2 already seen %s\n",
+				       sha1_to_hex(posn->parent->sha1));
+				*/
+                                // do nothing
+			} else if (posn->parent->flags & 0x0001) {
+                                // XXXX free lists
+				return posn->parent;
+			} else {
+				/*
+				printf("2 based on %s\n",
+				       sha1_to_hex(posn->parent->sha1));
+				*/
+				posn->parent->flags |= 0x0002;
+
+				parent = posn->parent->parent;
+				while (parent) {
+					temp = malloc(sizeof(struct parent));
+					temp->next = rev2list;
+					temp->parent = parent->parent;
+					rev2list = temp;
+					parent = parent->next;
+				}
+			}
+			posn = posn->next;
+		}
+	}
+	return NULL;
+}
+
+int main(int argc, char **argv)
+{
+	struct revision *rev1, *rev2, *ret;
+	unsigned char rev1key[20], rev2key[20];
+	if (argc != 3 ||
+	    get_sha1_hex(argv[1], rev1key) ||
+	    get_sha1_hex(argv[2], rev2key)) {
+		usage("mergebase <commit-id> <commit-id>");
+	}
+	rev1 = lookup_rev(rev1key);
+	rev2 = lookup_rev(rev2key);
+	ret = common_ancestor(rev1, rev2);
+	if (ret) {
+		printf("%s\n", sha1_to_hex(ret->sha1));
+		return 0;
+	} else {
+		printf("Sorry.\n");
+		return 1;
+	}
+	
+}