archive: optionally add "virtual" files

With the `--add-virtual-file=<path>:<content>` option, `git archive` now
supports use cases where relatively trivial files need to be added that
do not exist on disk.

This will allow us to generate `.zip` files with generated content,
without having to add said content to the object database and without
having to write it out to disk.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
[jc: tweaked <path> handling]
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-archive.txt

@@ -51,7 +51,7 @@ OPTIONS
 --prefix=<prefix>/::
 	Prepend <prefix>/ to paths in the archive.  Can be repeated; its
 	rightmost value is used for all tracked files.  See below which
-	value gets used by `--add-file`.
+	value gets used by `--add-file` and `--add-virtual-file`.
 
 -o <file>::
 --output=<file>::
@@ -63,6 +63,17 @@ OPTIONS
 	concatenating the value of the last `--prefix` option (if any)
 	before this `--add-file` and the basename of <file>.
 
+--add-virtual-file=<path>:<content>::
+	Add the specified contents to the archive.  Can be repeated to add
+	multiple files.  The path of the file in the archive is built
+	by concatenating the value of the last `--prefix` option (if any)
+	before this `--add-virtual-file` and `<path>`.
++
+The `<path>` cannot contain any colon, the file mode is limited to
+a regular file, and the option may be subject to platform-dependent
+command-line limits. For non-trivial cases, write an untracked file
+and use `--add-file` instead.
+
 --worktree-attributes::
 	Look for attributes in .gitattributes files in the working tree
 	as well (see <<ATTRIBUTES>>).

archive.c

@@ -263,6 +263,7 @@ static int queue_or_write_archive_entry(const struct object_id *oid,
 struct extra_file_info {
 	char *base;
 	struct stat stat;
+	void *content;
 };
 
 int write_archive_entries(struct archiver_args *args,
@@ -331,19 +332,27 @@ int write_archive_entries(struct archiver_args *args,
 
 		put_be64(fake_oid.hash, i + 1);
 
-		strbuf_reset(&path_in_archive);
-		if (info->base)
-			strbuf_addstr(&path_in_archive, info->base);
-		strbuf_addstr(&path_in_archive, basename(path));
-
-		strbuf_reset(&content);
-		if (strbuf_read_file(&content, path, info->stat.st_size) < 0)
-			err = error_errno(_("cannot read '%s'"), path);
-		else
-			err = write_entry(args, &fake_oid, path_in_archive.buf,
-					  path_in_archive.len,
+		if (!info->content) {
+			strbuf_reset(&path_in_archive);
+			if (info->base)
+				strbuf_addstr(&path_in_archive, info->base);
+			strbuf_addstr(&path_in_archive, basename(path));
+
+			strbuf_reset(&content);
+			if (strbuf_read_file(&content, path, info->stat.st_size) < 0)
+				err = error_errno(_("cannot read '%s'"), path);
+			else
+				err = write_entry(args, &fake_oid, path_in_archive.buf,
+						  path_in_archive.len,
+						  canon_mode(info->stat.st_mode),
+						  content.buf, content.len);
+		} else {
+			err = write_entry(args, &fake_oid,
+					  path, strlen(path),
 					  canon_mode(info->stat.st_mode),
-					  content.buf, content.len);
+					  info->content, info->stat.st_size);
+		}
+
 		if (err)
 			break;
 	}
@@ -493,6 +502,7 @@ static void extra_file_info_clear(void *util, const char *str)
 {
 	struct extra_file_info *info = util;
 	free(info->base);
+	free(info->content);
 	free(info);
 }
 
@@ -514,14 +524,40 @@ static int add_file_cb(const struct option *opt, const char *arg, int unset)
 	if (!arg)
 		return -1;
 
-	path = prefix_filename(args->prefix, arg);
-	item = string_list_append_nodup(&args->extra_files, path);
-	item->util = info = xmalloc(sizeof(*info));
+	info = xmalloc(sizeof(*info));
 	info->base = xstrdup_or_null(base);
-	if (stat(path, &info->stat))
-		die(_("File not found: %s"), path);
-	if (!S_ISREG(info->stat.st_mode))
-		die(_("Not a regular file: %s"), path);
+
+	if (!strcmp(opt->long_name, "add-file")) {
+		path = prefix_filename(args->prefix, arg);
+		if (stat(path, &info->stat))
+			die(_("File not found: %s"), path);
+		if (!S_ISREG(info->stat.st_mode))
+			die(_("Not a regular file: %s"), path);
+		info->content = NULL; /* read the file later */
+	} else if (!strcmp(opt->long_name, "add-virtual-file")) {
+		const char *colon = strchr(arg, ':');
+		char *p;
+
+		if (!colon)
+			die(_("missing colon: '%s'"), arg);
+
+		p = xstrndup(arg, colon - arg);
+		if (!args->prefix)
+			path = p;
+		else {
+			path = prefix_filename(args->prefix, p);
+			free(p);
+		}
+		memset(&info->stat, 0, sizeof(info->stat));
+		info->stat.st_mode = S_IFREG | 0644;
+		info->content = xstrdup(colon + 1);
+		info->stat.st_size = strlen(info->content);
+	} else {
+		BUG("add_file_cb() called for %s", opt->long_name);
+	}
+	item = string_list_append_nodup(&args->extra_files, path);
+	item->util = info;
+
 	return 0;
 }
 
@@ -554,6 +590,9 @@ static int parse_archive_args(int argc, const char **argv,
 		{ OPTION_CALLBACK, 0, "add-file", args, N_("file"),
 		  N_("add untracked file to archive"), 0, add_file_cb,
 		  (intptr_t)&base },
+		{ OPTION_CALLBACK, 0, "add-virtual-file", args,
+		  N_("path:content"), N_("add untracked file to archive"), 0,
+		  add_file_cb, (intptr_t)&base },
 		OPT_STRING('o', "output", &output, N_("file"),
 			N_("write the archive to this file")),
 		OPT_BOOL(0, "worktree-attributes", &worktree_attributes,

t/t5003-archive-zip.sh

@@ -206,6 +206,18 @@ test_expect_success 'git archive --format=zip --add-file' '
 check_zip with_untracked
 check_added with_untracked untracked untracked
 
+test_expect_success UNZIP 'git archive --format=zip --add-virtual-file' '
+	git archive --format=zip >with_file_with_content.zip \
+		--add-virtual-file=hello:world $EMPTY_TREE &&
+	test_when_finished "rm -rf tmp-unpack" &&
+	mkdir tmp-unpack && (
+		cd tmp-unpack &&
+		"$GIT_UNZIP" ../with_file_with_content.zip &&
+		test_path_is_file hello &&
+		test world = $(cat hello)
+	)
+'
+
 test_expect_success 'git archive --format=zip --add-file twice' '
 	echo untracked >untracked &&
 	git archive --format=zip --prefix=one/ --add-file=untracked \