[PATCH v4 2/2] diff: generate pretty filenames in prep_temp_blob()

[David Aguilar <davvid@gmail.com>]

Naturally, prep_temp_blob() did not care about filenames.
As a result, scripts that used GIT_EXTERNAL_DIFF or textconv
ended up with filenames such as ".diff_XXXXXX".

This modifies prep_temp_blob() to generate user-friendly
filenames when creating temporary files.

Diffing "name.ext" now generates "XXXXXX_name.ext".

Signed-off-by: David Aguilar <davvid@gmail.com>
Tested-by: Johannes Sixt <j6t@kdbg.org> (Windows)
---

This includes Peff's suggestion to make this the
default behavior.

Peff mentioned that: "Switching to user-friendly
temp filenames for textconv was on my todo list".

This patch accomplishes exactly that for both
textconv and GIT_EXTERNAL_DIFF.

 cache.h                  |    2 ++
 diff.c                   |   19 ++++++++++++++++++-
 path.c                   |   16 ++++++++++++++++
 t/t4020-diff-external.sh |    9 +++++++++
 4 files changed, 45 insertions(+), 1 deletions(-)

diff --git a/cache.h b/cache.h
index b8503ad..871c984 100644
--- a/cache.h
+++ b/cache.h
@@ -614,6 +614,8 @@ extern int is_empty_blob_sha1(const unsigned char *sha1);
 
 int git_mkstemp(char *path, size_t n, const char *template);
 
+int git_mkstemps(char *path, size_t n, const char *template, int suffix_len);
+
 /*
  * NOTE NOTE NOTE!!
  *
diff --git a/diff.c b/diff.c
index dcfbcb0..85503ce 100644
--- a/diff.c
+++ b/diff.c
@@ -1964,8 +1964,24 @@ static void prep_temp_blob(const char *path, struct diff_tempfile *temp,
 {
 	int fd;
 	struct strbuf buf = STRBUF_INIT;
+	struct strbuf template = STRBUF_INIT;
+	char *basename = ((char*)path) + strlen(path) - 1;
+
+	/* Windows lacks basename() */
+	while(*basename && basename > path) {
+		basename--;
+		if (is_dir_sep(*basename)) {
+			basename++;
+			break;
+		}
+	}
+
+	/* Generate "XXXXXX_basename.ext" */
+	strbuf_addstr(&template, "XXXXXX_");
+	strbuf_addstr(&template, basename);
 
-	fd = git_mkstemp(temp->tmp_path, PATH_MAX, ".diff_XXXXXX");
+	fd = git_mkstemps(temp->tmp_path, PATH_MAX, template.buf,
+			strlen(basename) + 1);
 	if (fd < 0)
 		die("unable to create temp-file: %s", strerror(errno));
 	if (convert_to_working_tree(path,
@@ -1981,6 +1997,7 @@ static void prep_temp_blob(const char *path, struct diff_tempfile *temp,
 	temp->hex[40] = 0;
 	sprintf(temp->mode, "%06o", mode);
 	strbuf_release(&buf);
+	strbuf_release(&template);
 }
 
 static struct diff_tempfile *prepare_temp_file(const char *name,
diff --git a/path.c b/path.c
index 8a0a674..047fdb0 100644
--- a/path.c
+++ b/path.c
@@ -139,6 +139,22 @@ int git_mkstemp(char *path, size_t len, const char *template)
 	return mkstemp(path);
 }
 
+/* git_mkstemps() - create tmp file with suffix honoring TMPDIR variable. */
+int git_mkstemps(char *path, size_t len, const char *template, int suffix_len)
+{
+	const char *tmp;
+	size_t n;
+
+	tmp = getenv("TMPDIR");
+	if (!tmp)
+		tmp = "/tmp";
+	n = snprintf(path, len, "%s/%s", tmp, template);
+	if (len <= n) {
+		errno = ENAMETOOLONG;
+		return -1;
+	}
+	return mkstemps(path, suffix_len);
+}
 
 int validate_headref(const char *path)
 {
diff --git a/t/t4020-diff-external.sh b/t/t4020-diff-external.sh
index 0720001..4ea42e0 100755
--- a/t/t4020-diff-external.sh
+++ b/t/t4020-diff-external.sh
@@ -136,6 +136,15 @@ test_expect_success 'GIT_EXTERNAL_DIFF with more than one changed files' '
 	GIT_EXTERNAL_DIFF=echo git diff
 '
 
+test_expect_success 'GIT_EXTERNAL_DIFF generates pretty paths' '
+	touch file.ext &&
+	git add file.ext &&
+	echo with extension > file.ext &&
+	GIT_EXTERNAL_DIFF=echo git diff file.ext | grep ......_file\.ext &&
+	git update-index --force-remove file.ext &&
+	rm file.ext
+'
+
 echo "#!$SHELL_PATH" >fake-diff.sh
 cat >> fake-diff.sh <<\EOF
 cat $2 >> crlfed.txt
-- 
1.6.1.3