[PATCH v5 1/2] checkout: improve message for ambiguous remote branch name

["Yoichi NAKAYAMA via GitGitGadget" <gitgitgadget@gmail.com>]

From: Yoichi NAKAYAMA <yoichi.nakayama@gmail.com>

When the user runs 'git checkout bar-topic' command that does not
exactly say which remote they want to work with, and there is no local
branch named bar-topic, we try to guess which remote by passing
bar-topic then create a new branch named bar-topic which tracks the
remote branch.

If multiple remotes have a branch named bar-topic, we cannot determine
a single specific remote. Therefore, we provide information that the
user can utilize to resolve the issue.

To make the advice more feasible, we will provide matched remote names
for the specified branch name.

To achive that, we add an optional feature to the
`unique_tracking_name()` function that allows the matched remote name
to be exposed to the caller.

Signed-off-by: Yoichi NAKAYAMA <yoichi.nakayama@gmail.com>
---
 builtin/checkout.c | 75 +++++++++++++++++++++++++++-------------------
 builtin/worktree.c |  4 +--
 checkout.c         | 14 +++++++--
 checkout.h         |  5 +++-
 4 files changed, 63 insertions(+), 35 deletions(-)

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 55e3a89a85..a2749352e6 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1343,13 +1343,51 @@ enum checkout_command {
 	CHECKOUT_RESTORE = 3,
 };
 
+static void be_explicit(const char *branch,
+			enum checkout_command which_command,
+			const struct string_list *matched_remote_names)
+{
+	const char *cmdname;
+	struct string_list_item *item;
+
+	switch (which_command) {
+	case CHECKOUT_CHECKOUT:
+		cmdname = "checkout";
+		break;
+	case CHECKOUT_SWITCH:
+		cmdname = "switch";
+		break;
+	default:
+		BUG("command <%d> should not reach parse_remote_branch",
+		     which_command);
+		break;
+	}
+
+	advise(_("Branches with the same name appears in multiple remotes:"));
+	for_each_string_list_item(item, matched_remote_names) {
+		advise(_("  %s"), item->string);
+	}
+	advise(_("If you meant to check out a remote tracking branch on <remote>,\n"
+		 "you can do so by fully qualifying the name with the --track option:\n"
+		 "\n"
+		 "    git %s --track <remote>/%s\n"
+		 "\n"
+		 "If you'd like to always have checkouts of an ambiguous name prefer\n"
+		 "one remote, e.g. the 'origin' remote, consider setting\n"
+		 "checkout.defaultRemote=origin in your config."),
+	       cmdname, branch);
+}
+
 static char *parse_remote_branch(const char *arg,
 				 struct object_id *rev,
 				 int could_be_checkout_paths,
 				 enum checkout_command which_command)
 {
 	int num_matches = 0;
-	char *remote = unique_tracking_name(arg, rev, &num_matches);
+	struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+	char *remote = unique_tracking_name(arg, rev, &num_matches,
+					    &matched_remote_names);
 
 	if (remote && could_be_checkout_paths) {
 		die(_("'%s' could be both a local file and a tracking branch.\n"
@@ -1358,37 +1396,14 @@ static char *parse_remote_branch(const char *arg,
 	}
 
 	if (!remote && num_matches > 1) {
-	    if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME)) {
-		    const char *cmdname;
-
-		    switch (which_command) {
-		    case CHECKOUT_CHECKOUT:
-			    cmdname = "checkout";
-			    break;
-		    case CHECKOUT_SWITCH:
-			    cmdname = "switch";
-			    break;
-		    default:
-			    BUG("command <%d> should not reach parse_remote_branch",
-				which_command);
-			    break;
-		    }
-
-		    advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
-			     "you can do so by fully qualifying the name with the --track option:\n"
-			     "\n"
-			     "    git %s --track origin/<name>\n"
-			     "\n"
-			     "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
-			     "one remote, e.g. the 'origin' remote, consider setting\n"
-			     "checkout.defaultRemote=origin in your config."),
-			   cmdname);
-	    }
-
-	    die(_("'%s' matched multiple (%d) remote tracking branches"),
-		arg, num_matches);
+		if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+			be_explicit(arg, which_command, &matched_remote_names);
+		die(_("'%s' matched multiple (%d) remote tracking branches"),
+		    arg, num_matches);
 	}
 
+	string_list_clear(&matched_remote_names, 0);
+
 	return remote;
 }
 
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 654d27c3e1..22c8e5e131 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -782,7 +782,7 @@ static char *dwim_branch(const char *path, char **new_branch)
 	*new_branch = branchname;
 	if (guess_remote) {
 		struct object_id oid;
-		char *remote = unique_tracking_name(*new_branch, &oid, NULL);
+		char *remote = unique_tracking_name(*new_branch, &oid, NULL, NULL);
 		return remote;
 	}
 	return NULL;
@@ -904,7 +904,7 @@ static int add(int ac, const char **av, const char *prefix,
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL);
+			remote = unique_tracking_name(branch, &oid, NULL, NULL);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
diff --git a/checkout.c b/checkout.c
index 1588b116ee..2806b783ec 100644
--- a/checkout.c
+++ b/checkout.c
@@ -8,6 +8,7 @@
 #include "checkout.h"
 #include "config.h"
 #include "strbuf.h"
+#include "string-list.h"
 
 struct tracking_name_data {
 	/* const */ char *src_ref;
@@ -17,6 +18,7 @@ struct tracking_name_data {
 	const char *default_remote;
 	char *default_dst_ref;
 	struct object_id *default_dst_oid;
+	struct string_list **remote_names;
 };
 
 #define TRACKING_NAME_DATA_INIT { 0 }
@@ -39,6 +41,8 @@ static int check_tracking_name(struct remote *remote, void *cb_data)
 		oidcpy(dst, cb->dst_oid);
 		cb->default_dst_oid = dst;
 	}
+	if (cb->remote_names)
+		string_list_append(*cb->remote_names, remote->name);
 	if (cb->dst_ref) {
 		free(query.dst);
 		return 0;
@@ -48,14 +52,20 @@ static int check_tracking_name(struct remote *remote, void *cb_data)
 }
 
 char *unique_tracking_name(const char *name, struct object_id *oid,
-			   int *dwim_remotes_matched)
+			   int *dwim_remotes_matched,
+			   struct string_list *dwim_remote_names)
 {
 	struct tracking_name_data cb_data = TRACKING_NAME_DATA_INIT;
 	const char *default_remote = NULL;
-	if (!repo_config_get_string_tmp(the_repository, "checkout.defaultremote", &default_remote))
+
+	if (!repo_config_get_string_tmp(the_repository,
+					"checkout.defaultremote",
+					&default_remote))
 		cb_data.default_remote = default_remote;
 	cb_data.src_ref = xstrfmt("refs/heads/%s", name);
 	cb_data.dst_oid = oid;
+	if (dwim_remote_names)
+		cb_data.remote_names = &dwim_remote_names;
 	for_each_remote(check_tracking_name, &cb_data);
 	if (dwim_remotes_matched)
 		*dwim_remotes_matched = cb_data.num_matches;
diff --git a/checkout.h b/checkout.h
index 55920e7aeb..0b185a0fc9 100644
--- a/checkout.h
+++ b/checkout.h
@@ -3,6 +3,8 @@
 
 #include "hash.h"
 
+struct string_list;
+
 /*
  * Check if the branch name uniquely matches a branch name on a remote
  * tracking branch.  Return the name of the remote if such a branch
@@ -10,6 +12,7 @@
  */
 char *unique_tracking_name(const char *name,
 			   struct object_id *oid,
-			   int *dwim_remotes_matched);
+			   int *dwim_remotes_matched,
+			   struct string_list *dwim_remote_names);
 
 #endif /* CHECKOUT_H */
-- 
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