Merge branch 'mg/detached-head-report'

"git branch" on a detached HEAD always said "(detached from xyz)",
even when "git status" would report "detached at xyz".  The HEAD is
actually at xyz and haven't been moved since it was detached in
such a case, but the user cannot read what the current value of
HEAD is when "detached from" is used.

* mg/detached-head-report:
  branch: name detached HEAD analogous to status
  wt-status: refactor detached HEAD analysis

builtin/branch.c

@@ -589,9 +589,16 @@ static char *get_head_description(void)
 	else if (state.bisect_in_progress)
 		strbuf_addf(&desc, _("(no branch, bisect started on %s)"),
 			    state.branch);
-	else if (state.detached_from)
-		strbuf_addf(&desc, _("(detached from %s)"),
-			    state.detached_from);
+	else if (state.detached_from) {
+		/* TRANSLATORS: make sure these match _("HEAD detached at ")
+		   and _("HEAD detached from ") in wt-status.c */
+		if (state.detached_at)
+			strbuf_addf(&desc, _("(HEAD detached at %s)"),
+				state.detached_from);
+		else
+			strbuf_addf(&desc, _("(HEAD detached from %s)"),
+				state.detached_from);
+	}
 	else
 		strbuf_addstr(&desc, _("(no branch)"));
 	free(state.branch);

t/t3203-branch-output.sh

@@ -96,7 +96,7 @@ test_expect_success 'git branch -v pattern does not show branch summaries' '
 
 test_expect_success 'git branch shows detached HEAD properly' '
 	cat >expect <<EOF &&
-* (detached from $(git rev-parse --short HEAD^0))
+* (HEAD detached at $(git rev-parse --short HEAD^0))
   branch-one
   branch-two
   master
@@ -106,4 +106,41 @@ EOF
 	test_i18ncmp expect actual
 '
 
+test_expect_success 'git branch shows detached HEAD properly after moving' '
+	cat >expect <<EOF &&
+* (HEAD detached from $(git rev-parse --short HEAD))
+  branch-one
+  branch-two
+  master
+EOF
+	git reset --hard HEAD^1 &&
+	git branch >actual &&
+	test_i18ncmp expect actual
+'
+
+test_expect_success 'git branch shows detached HEAD properly from tag' '
+	cat >expect <<EOF &&
+* (HEAD detached at fromtag)
+  branch-one
+  branch-two
+  master
+EOF
+	git tag fromtag master &&
+	git checkout fromtag &&
+	git branch >actual &&
+	test_i18ncmp expect actual
+'
+
+test_expect_success 'git branch shows detached HEAD properly after moving from tag' '
+	cat >expect <<EOF &&
+* (HEAD detached from fromtag)
+  branch-one
+  branch-two
+  master
+EOF
+	git reset --hard HEAD^1 &&
+	git branch >actual &&
+	test_i18ncmp expect actual
+'
+
 test_done

wt-status.c

@@ -1242,6 +1242,8 @@ static void wt_status_get_detached_from(struct wt_status_state *state)
 		state->detached_from =
 			xstrdup(find_unique_abbrev(cb.nsha1, DEFAULT_ABBREV));
 	hashcpy(state->detached_sha1, cb.nsha1);
+	state->detached_at = !get_sha1("HEAD", sha1) &&
+			     !hashcmp(sha1, state->detached_sha1);
 
 	free(ref);
 	strbuf_release(&cb.buf);
@@ -1330,10 +1332,8 @@ void wt_status_print(struct wt_status *s)
 				on_what = _("rebase in progress; onto ");
 				branch_name = state.onto;
 			} else if (state.detached_from) {
-				unsigned char sha1[20];
 				branch_name = state.detached_from;
-				if (!get_sha1("HEAD", sha1) &&
-				    !hashcmp(sha1, state.detached_sha1))
+				if (state.detached_at)
 					on_what = _("HEAD detached at ");
 				else
 					on_what = _("HEAD detached from ");

wt-status.h

@@ -84,6 +84,7 @@ struct wt_status_state {
 	int cherry_pick_in_progress;
 	int bisect_in_progress;
 	int revert_in_progress;
+	int detached_at;
 	char *branch;
 	char *onto;
 	char *detached_from;