[PATCH v2 2/2] wt-status: tolerate dangling marks

[Jonathan Tan <jonathantanmy@google.com>]

When a user checks out the upstream branch of HEAD, the upstream branch
not being a local branch, and then runs "git status", like this:

  git clone $URL client
  cd client
  git checkout @{u}
  git status

no status is printed, but instead an error message:

  fatal: HEAD does not point to a branch

(This error message when running "git branch" persists even after
checking out other things - it only stops after checking out a branch.)

This is because "git status" reads the reflog when determining the "HEAD
detached" message, and thus attempts to DWIM "@{u}", but that doesn't
work because HEAD no longer points to a branch.

Therefore, when calculating the status of a worktree, tolerate dangling
marks. This is done by adding an additional parameter to
repo_dwim_ref().

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
---
 cache.h           |  7 +++++++
 refs.c            | 16 ++++++++++------
 refs.h            |  3 ++-
 sha1-name.c       | 16 +++++++++++-----
 t/t7508-status.sh | 12 ++++++++++++
 wt-status.c       |  2 +-
 6 files changed, 43 insertions(+), 13 deletions(-)

diff --git a/cache.h b/cache.h
index 4f16a57ba4..cee8aa5dc3 100644
--- a/cache.h
+++ b/cache.h
@@ -1569,6 +1569,13 @@ struct interpret_branch_name_options {
 	 * allowed, even ones to refs outside of those namespaces.
 	 */
 	unsigned allowed;
+
+	/*
+	 * If ^{upstream} or ^{push} (or equivalent) is requested, and the
+	 * branch in question does not have such a reference, return -1 instead
+	 * of die()-ing.
+	 */
+	unsigned nonfatal_dangling_mark : 1;
 };
 int repo_interpret_branch_name(struct repository *r,
 			       const char *str, int len,
diff --git a/refs.c b/refs.c
index cf09cd039f..b6f1a2f452 100644
--- a/refs.c
+++ b/refs.c
@@ -598,10 +598,13 @@ const char *git_default_branch_name(void)
  * to name a branch.
  */
 static char *substitute_branch_name(struct repository *r,
-				    const char **string, int *len)
+				    const char **string, int *len,
+				    int nonfatal_dangling_mark)
 {
 	struct strbuf buf = STRBUF_INIT;
-	struct interpret_branch_name_options options = { 0 } ;
+	struct interpret_branch_name_options options = {
+		.nonfatal_dangling_mark = nonfatal_dangling_mark
+	};
 	int ret = repo_interpret_branch_name(r, *string, *len, &buf, &options);
 
 	if (ret == *len) {
@@ -615,9 +618,10 @@ static char *substitute_branch_name(struct repository *r,
 }
 
 int repo_dwim_ref(struct repository *r, const char *str, int len,
-		  struct object_id *oid, char **ref)
+		  struct object_id *oid, char **ref, int nonfatal_dangling_mark)
 {
-	char *last_branch = substitute_branch_name(r, &str, &len);
+	char *last_branch = substitute_branch_name(r, &str, &len,
+						   nonfatal_dangling_mark);
 	int   refs_found  = expand_ref(r, str, len, oid, ref);
 	free(last_branch);
 	return refs_found;
@@ -625,7 +629,7 @@ int repo_dwim_ref(struct repository *r, const char *str, int len,
 
 int dwim_ref(const char *str, int len, struct object_id *oid, char **ref)
 {
-	return repo_dwim_ref(the_repository, str, len, oid, ref);
+	return repo_dwim_ref(the_repository, str, len, oid, ref, 0);
 }
 
 int expand_ref(struct repository *repo, const char *str, int len,
@@ -666,7 +670,7 @@ int repo_dwim_log(struct repository *r, const char *str, int len,
 		  struct object_id *oid, char **log)
 {
 	struct ref_store *refs = get_main_ref_store(r);
-	char *last_branch = substitute_branch_name(r, &str, &len);
+	char *last_branch = substitute_branch_name(r, &str, &len, 0);
 	const char **p;
 	int logs_found = 0;
 	struct strbuf path = STRBUF_INIT;
diff --git a/refs.h b/refs.h
index 29e28124cd..b94a7fd4f7 100644
--- a/refs.h
+++ b/refs.h
@@ -149,7 +149,8 @@ struct strvec;
 void expand_ref_prefix(struct strvec *prefixes, const char *prefix);
 
 int expand_ref(struct repository *r, const char *str, int len, struct object_id *oid, char **ref);
-int repo_dwim_ref(struct repository *r, const char *str, int len, struct object_id *oid, char **ref);
+int repo_dwim_ref(struct repository *r, const char *str, int len,
+		  struct object_id *oid, char **ref, int nonfatal_dangling_mark);
 int repo_dwim_log(struct repository *r, const char *str, int len, struct object_id *oid, char **ref);
 int dwim_ref(const char *str, int len, struct object_id *oid, char **ref);
 int dwim_log(const char *str, int len, struct object_id *oid, char **ref);
diff --git a/sha1-name.c b/sha1-name.c
index a7a9de66c4..0b23b86ceb 100644
--- a/sha1-name.c
+++ b/sha1-name.c
@@ -809,7 +809,7 @@ static int get_oid_basic(struct repository *r, const char *str, int len,
 
 	if (len == r->hash_algo->hexsz && !get_oid_hex(str, oid)) {
 		if (warn_ambiguous_refs && warn_on_object_refname_ambiguity) {
-			refs_found = repo_dwim_ref(r, str, len, &tmp_oid, &real_ref);
+			refs_found = repo_dwim_ref(r, str, len, &tmp_oid, &real_ref, 0);
 			if (refs_found > 0) {
 				warning(warn_msg, len, str);
 				if (advice_object_name_warning)
@@ -860,11 +860,11 @@ static int get_oid_basic(struct repository *r, const char *str, int len,
 
 	if (!len && reflog_len)
 		/* allow "@{...}" to mean the current branch reflog */
-		refs_found = repo_dwim_ref(r, "HEAD", 4, oid, &real_ref);
+		refs_found = repo_dwim_ref(r, "HEAD", 4, oid, &real_ref, 0);
 	else if (reflog_len)
 		refs_found = repo_dwim_log(r, str, len, oid, &real_ref);
 	else
-		refs_found = repo_dwim_ref(r, str, len, oid, &real_ref);
+		refs_found = repo_dwim_ref(r, str, len, oid, &real_ref, 0);
 
 	if (!refs_found)
 		return -1;
@@ -1496,8 +1496,14 @@ static int interpret_branch_mark(struct repository *r,
 		branch = branch_get(NULL);
 
 	value = get_data(branch, &err);
-	if (!value)
-		die("%s", err.buf);
+	if (!value) {
+		if (options->nonfatal_dangling_mark) {
+			strbuf_release(&err);
+			return -1;
+		} else {
+			die("%s", err.buf);
+		}
+	}
 
 	if (!branch_interpret_allowed(value, options->allowed))
 		return -1;
diff --git a/t/t7508-status.sh b/t/t7508-status.sh
index e81759319f..45e1f6ff68 100755
--- a/t/t7508-status.sh
+++ b/t/t7508-status.sh
@@ -846,6 +846,18 @@ test_expect_success 'status refreshes the index' '
 	test_cmp expect output
 '
 
+test_expect_success 'status shows detached HEAD properly after checking out non-local upstream branch' '
+	test_when_finished rm -rf upstream downstream actual &&
+
+	test_create_repo upstream &&
+	test_commit -C upstream foo &&
+
+	git clone upstream downstream &&
+	git -C downstream checkout @{u} &&
+	git -C downstream status >actual &&
+	test_i18ngrep "HEAD detached at [0-9a-f]\\+" actual
+'
+
 test_expect_success 'setup status submodule summary' '
 	test_create_repo sm && (
 		cd sm &&
diff --git a/wt-status.c b/wt-status.c
index 7ce58b8aae..ae16faf40d 100644
--- a/wt-status.c
+++ b/wt-status.c
@@ -1569,7 +1569,7 @@ static void wt_status_get_detached_from(struct repository *r,
 		return;
 	}
 
-	if (dwim_ref(cb.buf.buf, cb.buf.len, &oid, &ref) == 1 &&
+	if (repo_dwim_ref(the_repository, cb.buf.buf, cb.buf.len, &oid, &ref, 1) == 1 &&
 	    /* sha1 is a commit? match without further lookup */
 	    (oideq(&cb.noid, &oid) ||
 	     /* perhaps sha1 is a tag, try to dereference to a commit */
-- 
2.28.0.402.g5ffc5be6b7-goog