[PATCH v2 7/8] alias_lookup(): optionally return top-level directory

[Johannes Schindelin <johannes.schindelin@gmx.de>]

When an alias expands to a shell command, and when we are inside a
regular worktree's subdirectory (i.e. not inside the .git/ directory nor
in a worktree initialized via `git worktree add`), and only then, the
current working directory is switched to the top-level directory of the
worktree before running the expanded alias.

While this behavior is somewhat confusing, it is well-established and
needs to be preserved, even with the upcoming change to use the early
config machinery to expand aliases.

That means that alias_lookup() needs to determine the working directory
to switch to, in case the alias turns out to expand to a shall command.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 alias.c        | 33 +++++++++++++++++++++++++--------
 builtin/help.c |  2 +-
 cache.h        |  2 +-
 git.c          |  2 +-
 4 files changed, 28 insertions(+), 11 deletions(-)

diff --git a/alias.c b/alias.c
index 3b90397a99d..b7c4a4f0217 100644
--- a/alias.c
+++ b/alias.c
@@ -1,14 +1,31 @@
 #include "cache.h"
 
-char *alias_lookup(const char *alias)
+struct config_alias_data
 {
-	char *v = NULL;
-	struct strbuf key = STRBUF_INIT;
-	strbuf_addf(&key, "alias.%s", alias);
-	if (git_config_key_is_valid(key.buf))
-		git_config_get_string(key.buf, &v);
-	strbuf_release(&key);
-	return v;
+	struct strbuf key;
+	char *v;
+};
+
+static int config_alias_cb(const char *key, const char *value, void *d)
+{
+	struct config_alias_data *data = d;
+
+	if (!strcmp(key, data->key.buf))
+		return git_config_string((const char **)&data->v, key, value);
+
+	return 0;
+}
+
+char *alias_lookup(const char *alias, struct strbuf *cdup_dir)
+{
+	struct config_alias_data data = { STRBUF_INIT, NULL };
+
+	strbuf_addf(&data.key, "alias.%s", alias);
+	if (git_config_key_is_valid(data.key.buf))
+		read_early_config(config_alias_cb, &data, cdup_dir);
+	strbuf_release(&data.key);
+
+	return data.v;
 }
 
 #define SPLIT_CMDLINE_BAD_ENDING 1
diff --git a/builtin/help.c b/builtin/help.c
index 49f7a07f85d..6f208ff1ab3 100644
--- a/builtin/help.c
+++ b/builtin/help.c
@@ -435,7 +435,7 @@ static const char *check_git_cmd(const char* cmd)
 	if (is_git_command(cmd))
 		return cmd;
 
-	alias = alias_lookup(cmd);
+	alias = alias_lookup(cmd, NULL);
 	if (alias) {
 		printf_ln(_("`git %s' is aliased to `%s'"), cmd, alias);
 		free(alias);
diff --git a/cache.h b/cache.h
index f769ef1779c..65f2e5bf04c 100644
--- a/cache.h
+++ b/cache.h
@@ -2189,7 +2189,7 @@ extern int ws_blank_line(const char *line, int len, unsigned ws_rule);
 /* ls-files */
 void overlay_tree_on_cache(const char *tree_name, const char *prefix);
 
-char *alias_lookup(const char *alias);
+char *alias_lookup(const char *alias, struct strbuf *cdup_dir);
 int split_cmdline(char *cmdline, const char ***argv);
 /* Takes a negative value returned by split_cmdline */
 const char *split_cmdline_strerror(int cmdline_errno);
diff --git a/git.c b/git.c
index 8ff44f081d4..4163beaead4 100644
--- a/git.c
+++ b/git.c
@@ -256,7 +256,7 @@ static int handle_alias(int *argcp, const char ***argv)
 	setup_git_directory_gently(&unused_nongit);
 
 	alias_command = (*argv)[0];
-	alias_string = alias_lookup(alias_command);
+	alias_string = alias_lookup(alias_command, NULL);
 	if (alias_string) {
 		if (alias_string[0] == '!') {
 			struct child_process child = CHILD_PROCESS_INIT;
-- 
2.13.0.windows.1.460.g13f583bedb5