Split up tree diff functions into tree-diff.c library

This makes the tree diff functionality independent of the "git-diff-tree"
program, by splitting the core functionality up into a library file.

This will be needed for when we teach git-rev-list to only follow a
specified set of pathnames, rather than the global revision history.

Most of it is a fairly straightforward code move, but it also involves
some calling convention cleanup, and moving some of the static variables
from diff-tree.c into the options structure.

The actual tree change callback routines also become paramterized by the
diff_options structure, allowing the library functionality to do something
else than just show the diff on stdout.

Right now the only user of this functionality remains git-diff-tree
itself.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

1 files changed, 270 insertions, 0 deletions

diff --git a/tree-diff.c b/tree-diff.c
new file mode 100644
index 0000000000..0ef06a9e36
--- /dev/null
+++ b/tree-diff.c
@@ -0,0 +1,270 @@
+/*
+ * Helper functions for tree diff generation
+ */
+#include "cache.h"
+#include "diff.h"
+
+// What paths are we interested in?
+static int nr_paths = 0;
+static const char **paths = NULL;
+static int *pathlens = NULL;
+
+static void update_tree_entry(struct tree_desc *desc)
+{
+	void *buf = desc->buf;
+	unsigned long size = desc->size;
+	int len = strlen(buf) + 1 + 20;
+
+	if (size < len)
+		die("corrupt tree file");
+	desc->buf = buf + len;
+	desc->size = size - len;
+}
+
+static const unsigned char *extract(struct tree_desc *desc, const char **pathp, unsigned int *modep)
+{
+	void *tree = desc->buf;
+	unsigned long size = desc->size;
+	int len = strlen(tree)+1;
+	const unsigned char *sha1 = tree + len;
+	const char *path = strchr(tree, ' ');
+	unsigned int mode;
+
+	if (!path || size < len + 20 || sscanf(tree, "%o", &mode) != 1)
+		die("corrupt tree file");
+	*pathp = path+1;
+	*modep = DIFF_FILE_CANON_MODE(mode);
+	return sha1;
+}
+
+static char *malloc_base(const char *base, const char *path, int pathlen)
+{
+	int baselen = strlen(base);
+	char *newbase = xmalloc(baselen + pathlen + 2);
+	memcpy(newbase, base, baselen);
+	memcpy(newbase + baselen, path, pathlen);
+	memcpy(newbase + baselen + pathlen, "/", 2);
+	return newbase;
+}
+
+static int show_entry(struct diff_options *opt, const char *prefix, struct tree_desc *desc, const char *base);
+
+static int compare_tree_entry(struct tree_desc *t1, struct tree_desc *t2, const char *base, struct diff_options *opt)
+{
+	unsigned mode1, mode2;
+	const char *path1, *path2;
+	const unsigned char *sha1, *sha2;
+	int cmp, pathlen1, pathlen2;
+
+	sha1 = extract(t1, &path1, &mode1);
+	sha2 = extract(t2, &path2, &mode2);
+
+	pathlen1 = strlen(path1);
+	pathlen2 = strlen(path2);
+	cmp = base_name_compare(path1, pathlen1, mode1, path2, pathlen2, mode2);
+	if (cmp < 0) {
+		show_entry(opt, "-", t1, base);
+		return -1;
+	}
+	if (cmp > 0) {
+		show_entry(opt, "+", t2, base);
+		return 1;
+	}
+	if (!opt->find_copies_harder &&
+	    !memcmp(sha1, sha2, 20) && mode1 == mode2)
+		return 0;
+
+	/*
+	 * If the filemode has changed to/from a directory from/to a regular
+	 * file, we need to consider it a remove and an add.
+	 */
+	if (S_ISDIR(mode1) != S_ISDIR(mode2)) {
+		show_entry(opt, "-", t1, base);
+		show_entry(opt, "+", t2, base);
+		return 0;
+	}
+
+	if (opt->recursive && S_ISDIR(mode1)) {
+		int retval;
+		char *newbase = malloc_base(base, path1, pathlen1);
+		if (opt->tree_in_recursive)
+			opt->change(opt, mode1, mode2,
+				    sha1, sha2, base, path1);
+		retval = diff_tree_sha1(sha1, sha2, newbase, opt);
+		free(newbase);
+		return retval;
+	}
+
+	opt->change(opt, mode1, mode2, sha1, sha2, base, path1);
+	return 0;
+}
+
+static int interesting(struct tree_desc *desc, const char *base)
+{
+	const char *path;
+	unsigned mode;
+	int i;
+	int baselen, pathlen;
+
+	if (!nr_paths)
+		return 1;
+
+	(void)extract(desc, &path, &mode);
+
+	pathlen = strlen(path);
+	baselen = strlen(base);
+
+	for (i=0; i < nr_paths; i++) {
+		const char *match = paths[i];
+		int matchlen = pathlens[i];
+
+		if (baselen >= matchlen) {
+			/* If it doesn't match, move along... */
+			if (strncmp(base, match, matchlen))
+				continue;
+
+			/* The base is a subdirectory of a path which was specified. */
+			return 1;
+		}
+
+		/* Does the base match? */
+		if (strncmp(base, match, baselen))
+			continue;
+
+		match += baselen;
+		matchlen -= baselen;
+
+		if (pathlen > matchlen)
+			continue;
+
+		if (matchlen > pathlen) {
+			if (match[pathlen] != '/')
+				continue;
+			if (!S_ISDIR(mode))
+				continue;
+		}
+
+		if (strncmp(path, match, pathlen))
+			continue;
+
+		return 1;
+	}
+	return 0; /* No matches */
+}
+
+/* A whole sub-tree went away or appeared */
+static void show_tree(struct diff_options *opt, const char *prefix, struct tree_desc *desc, const char *base)
+{
+	while (desc->size) {
+		if (interesting(desc, base))
+			show_entry(opt, prefix, desc, base);
+		update_tree_entry(desc);
+	}
+}
+
+/* A file entry went away or appeared */
+static int show_entry(struct diff_options *opt, const char *prefix, struct tree_desc *desc, const char *base)
+{
+	unsigned mode;
+	const char *path;
+	const unsigned char *sha1 = extract(desc, &path, &mode);
+
+	if (opt->recursive && S_ISDIR(mode)) {
+		char type[20];
+		char *newbase = malloc_base(base, path, strlen(path));
+		struct tree_desc inner;
+		void *tree;
+
+		tree = read_sha1_file(sha1, type, &inner.size);
+		if (!tree || strcmp(type, "tree"))
+			die("corrupt tree sha %s", sha1_to_hex(sha1));
+
+		inner.buf = tree;
+		show_tree(opt, prefix, &inner, newbase);
+
+		free(tree);
+		free(newbase);
+		return 0;
+	}
+
+	opt->add_remove(opt, prefix[0], mode, sha1, base, path);
+	return 0;
+}
+
+int diff_tree(struct tree_desc *t1, struct tree_desc *t2, const char *base, struct diff_options *opt)
+{
+	while (t1->size | t2->size) {
+		if (nr_paths && t1->size && !interesting(t1, base)) {
+			update_tree_entry(t1);
+			continue;
+		}
+		if (nr_paths && t2->size && !interesting(t2, base)) {
+			update_tree_entry(t2);
+			continue;
+		}
+		if (!t1->size) {
+			show_entry(opt, "+", t2, base);
+			update_tree_entry(t2);
+			continue;
+		}
+		if (!t2->size) {
+			show_entry(opt, "-", t1, base);
+			update_tree_entry(t1);
+			continue;
+		}
+		switch (compare_tree_entry(t1, t2, base, opt)) {
+		case -1:
+			update_tree_entry(t1);
+			continue;
+		case 0:
+			update_tree_entry(t1);
+			/* Fallthrough */
+		case 1:
+			update_tree_entry(t2);
+			continue;
+		}
+		die("git-diff-tree: internal error");
+	}
+	return 0;
+}
+
+int diff_tree_sha1(const unsigned char *old, const unsigned char *new, const char *base, struct diff_options *opt)
+{
+	void *tree1, *tree2;
+	struct tree_desc t1, t2;
+	int retval;
+
+	tree1 = read_object_with_reference(old, "tree", &t1.size, NULL);
+	if (!tree1)
+		die("unable to read source tree (%s)", sha1_to_hex(old));
+	tree2 = read_object_with_reference(new, "tree", &t2.size, NULL);
+	if (!tree2)
+		die("unable to read destination tree (%s)", sha1_to_hex(new));
+	t1.buf = tree1;
+	t2.buf = tree2;
+	retval = diff_tree(&t1, &t2, base, opt);
+	free(tree1);
+	free(tree2);
+	return retval;
+}
+
+static int count_paths(const char **paths)
+{
+	int i = 0;
+	while (*paths++)
+		i++;
+	return i;
+}
+
+void diff_tree_setup_paths(const char **p)
+{
+	if (p) {
+		int i;
+
+		paths = p;
+		nr_paths = count_paths(paths);
+		pathlens = xmalloc(nr_paths * sizeof(int));
+		for (i=0; i<nr_paths; i++)
+			pathlens[i] = strlen(paths[i]);
+	}
+}