commit: allow partial commits with relative paths

In order to do partial commits, git-commit overlays a tree on the
cache and checks pathspecs against the result. Currently, the
overlaying is done using "prefix" which prevents relative pathspecs
with ".." and absolute pathspec from matching when they refer to
files not under "prefix" and absent from the index, but still in
the tree (i.e.  files staged for removal).

The point of providing a prefix at all is performance optimization.
If we say there is no common prefix for the files of interest, then
we have to read the entire tree into the index.

But even if we cannot use the working directory as a prefix, we can
still figure out if there is a common prefix for all given paths,
and use that instead. The pathspec_prefix() routine from ls-files.c
does exactly that.

Any use of global variables is removed from pathspec_prefix() so
that it can be called from commit.c.

Reported-by: Reuben Thomas <rrt@sc3d.org>
Analyzed-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Clemens Buchacher <drizzd@aon.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/commit.c

@@ -256,8 +256,10 @@ static int list_paths(struct string_list *list, const char *with_tree,
 		;
 	m = xcalloc(1, i);
 
-	if (with_tree)
+	if (with_tree) {
-		overlay_tree_on_cache(with_tree, prefix);
+		const char *max_prefix = pathspec_prefix(prefix, pattern);
+		overlay_tree_on_cache(with_tree, max_prefix);
+	}
 
 	for (i = 0; i < active_nr; i++) {
 		struct cache_entry *ce = active_cache[i];

builtin/ls-files.c

@@ -276,41 +276,6 @@ static void prune_cache(const char *prefix)
 	active_nr = last;
 }
 
-static const char *pathspec_prefix(const char *prefix)
-{
-	const char **p, *n, *prev;
-	unsigned long max;
-
-	if (!pathspec) {
-		max_prefix_len = prefix ? strlen(prefix) : 0;
-		return prefix;
-	}
-
-	prev = NULL;
-	max = PATH_MAX;
-	for (p = pathspec; (n = *p) != NULL; p++) {
-		int i, len = 0;
-		for (i = 0; i < max; i++) {
-			char c = n[i];
-			if (prev && prev[i] != c)
-				break;
-			if (!c || c == '*' || c == '?')
-				break;
-			if (c == '/')
-				len = i+1;
-		}
-		prev = n;
-		if (len < max) {
-			max = len;
-			if (!max)
-				break;
-		}
-	}
-
-	max_prefix_len = max;
-	return max ? xmemdupz(prev, max) : NULL;
-}
-
 static void strip_trailing_slash_from_submodules(void)
 {
 	const char **p;
@@ -576,7 +541,8 @@ int cmd_ls_files(int argc, const char **argv, const char *cmd_prefix)
 		strip_trailing_slash_from_submodules();
 
 	/* Find common prefix for all pathspec's */
-	max_prefix = pathspec_prefix(prefix);
+	max_prefix = pathspec_prefix(prefix, pathspec);
+	max_prefix_len = max_prefix ? strlen(max_prefix) : 0;
 
 	/* Treat unmatching pathspec elements as errors */
 	if (pathspec && error_unmatch) {

cache.h

@@ -426,6 +426,7 @@ extern void set_git_work_tree(const char *tree);
 #define ALTERNATE_DB_ENVIRONMENT "GIT_ALTERNATE_OBJECT_DIRECTORIES"
 
 extern const char **get_pathspec(const char *prefix, const char **pathspec);
+extern const char *pathspec_prefix(const char *prefix, const char **pathspec);
 extern void setup_work_tree(void);
 extern const char *setup_git_directory_gently(int *);
 extern const char *setup_git_directory(void);

setup.c

@@ -264,6 +264,38 @@ const char **get_pathspec(const char *prefix, const char **pathspec)
 	return pathspec;
 }
 
+const char *pathspec_prefix(const char *prefix, const char **pathspec)
+{
+	const char **p, *n, *prev;
+	unsigned long max;
+
+	if (!pathspec)
+		return prefix ? xmemdupz(prefix, strlen(prefix)) : NULL;
+
+	prev = NULL;
+	max = PATH_MAX;
+	for (p = pathspec; (n = *p) != NULL; p++) {
+		int i, len = 0;
+		for (i = 0; i < max; i++) {
+			char c = n[i];
+			if (prev && prev[i] != c)
+				break;
+			if (!c || c == '*' || c == '?')
+				break;
+			if (c == '/')
+				len = i+1;
+		}
+		prev = n;
+		if (len < max) {
+			max = len;
+			if (!max)
+				break;
+		}
+	}
+
+	return max ? xmemdupz(prev, max) : NULL;
+}
+
 /*
  * Test if it looks like we're at a git directory.
  * We want to see: