Merge branch 'jt/interpret-branch-name-fallback'

"git status" has trouble showing where it came from by interpreting
reflog entries that recordcertain events, e.g. "checkout @{u}", and
gives a hard/fatal error.  Even though it inherently is impossible
to give a correct answer because the reflog entries lose some
information (e.g. "@{u}" does not record what branch the user was
on hence which branch 'the upstream' needs to be computed, and even
if the record were available, the relationship between branches may
have changed), at least hide the error to allow "status" show its
output.

* jt/interpret-branch-name-fallback:
  wt-status: tolerate dangling marks
  refs: move dwim_ref() to header file
  sha1-name: replace unsigned int with option struct

20 files changed, 98 insertions, 53 deletions

diff --git a/archive.c b/archive.c
index fb39706120..0de6048bfc 100644
--- a/archive.c
+++ b/archive.c
@@ -397,10 +397,10 @@ static void parse_treeish_arg(const char **argv,
 		const char *colon = strchrnul(name, ':');
 		int refnamelen = colon - name;
 
-		if (!dwim_ref(name, refnamelen, &oid, &ref))
+		if (!dwim_ref(name, refnamelen, &oid, &ref, 0))
 			die(_("no such ref: %.*s"), refnamelen, name);
 	} else {
-		dwim_ref(name, strlen(name), &oid, &ref);
+		dwim_ref(name, strlen(name), &oid, &ref, 0);
 	}
 
 	if (get_oid(name, &oid))
diff --git a/branch.c b/branch.c
index 7095f78058..9c9dae1eae 100644
--- a/branch.c
+++ b/branch.c
@@ -281,7 +281,7 @@ void create_branch(struct repository *r,
 		die(_("Not a valid object name: '%s'."), start_name);
 	}
 
-	switch (dwim_ref(start_name, strlen(start_name), &oid, &real_ref)) {
+	switch (dwim_ref(start_name, strlen(start_name), &oid, &real_ref, 0)) {
 	case 0:
 		/* Not branching from any existing branch */
 		if (explicit_tracking)
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 6ec82097a2..0951f8fee5 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -651,7 +651,7 @@ static void setup_branch_path(struct branch_info *branch)
 	 * If this is a ref, resolve it; otherwise, look up the OID for our
 	 * expression.  Failure here is okay.
 	 */
-	if (!dwim_ref(branch->name, strlen(branch->name), &branch->oid, &branch->refname))
+	if (!dwim_ref(branch->name, strlen(branch->name), &branch->oid, &branch->refname, 0))
 		repo_get_oid_committish(the_repository, branch->name, &branch->oid);
 
 	strbuf_branchname(&buf, branch->name, INTERPRET_BRANCH_LOCAL);
@@ -1345,7 +1345,7 @@ static void die_expecting_a_branch(const struct branch_info *branch_info)
 	struct object_id oid;
 	char *to_free;
 
-	if (dwim_ref(branch_info->name, strlen(branch_info->name), &oid, &to_free) == 1) {
+	if (dwim_ref(branch_info->name, strlen(branch_info->name), &oid, &to_free, 0) == 1) {
 		const char *ref = to_free;
 
 		if (skip_prefix(ref, "refs/tags/", &ref))
diff --git a/builtin/fast-export.c b/builtin/fast-export.c
index 9f37895d4c..1b8fca3ee0 100644
--- a/builtin/fast-export.c
+++ b/builtin/fast-export.c
@@ -943,7 +943,7 @@ static void get_tags_and_duplicates(struct rev_cmdline_info *info)
 		if (e->flags & UNINTERESTING)
 			continue;
 
-		if (dwim_ref(e->name, strlen(e->name), &oid, &full_name) != 1)
+		if (dwim_ref(e->name, strlen(e->name), &oid, &full_name, 0) != 1)
 			continue;
 
 		if (refspecs.nr) {
diff --git a/builtin/log.c b/builtin/log.c
index b58f8da09e..4ec7f57cf4 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -1061,7 +1061,7 @@ static char *find_branch_name(struct rev_info *rev)
 		return NULL;
 	ref = rev->cmdline.rev[positive].name;
 	tip_oid = &rev->cmdline.rev[positive].item->oid;
-	if (dwim_ref(ref, strlen(ref), &branch_oid, &full_ref) &&
+	if (dwim_ref(ref, strlen(ref), &branch_oid, &full_ref, 0) &&
 	    skip_prefix(full_ref, "refs/heads/", &v) &&
 	    oideq(tip_oid, &branch_oid))
 		branch = xstrdup(v);
diff --git a/builtin/merge.c b/builtin/merge.c
index b9a89ba858..032a8f5434 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -500,7 +500,7 @@ static void merge_name(const char *remote, struct strbuf *msg)
 	if (!remote_head)
 		die(_("'%s' does not point to a commit"), remote);
 
-	if (dwim_ref(remote, strlen(remote), &branch_head, &found_ref) > 0) {
+	if (dwim_ref(remote, strlen(remote), &branch_head, &found_ref, 0) > 0) {
 		if (starts_with(found_ref, "refs/heads/")) {
 			strbuf_addf(msg, "%s\t\tbranch '%s' of .\n",
 				    oid_to_hex(&branch_head), remote);
diff --git a/builtin/reset.c b/builtin/reset.c
index 8ae69d6f2b..c635b062c3 100644
--- a/builtin/reset.c
+++ b/builtin/reset.c
@@ -423,7 +423,7 @@ int cmd_reset(int argc, const char **argv, const char *prefix)
 			char *ref = NULL;
 			int err;
 
-			dwim_ref(rev, strlen(rev), &dummy, &ref);
+			dwim_ref(rev, strlen(rev), &dummy, &ref, 0);
 			if (ref && !starts_with(ref, "refs/"))
 				ref = NULL;
 
diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
index 669dd2fd6f..ed200c8af1 100644
--- a/builtin/rev-parse.c
+++ b/builtin/rev-parse.c
@@ -136,7 +136,7 @@ static void show_rev(int type, const struct object_id *oid, const char *name)
 			struct object_id discard;
 			char *full;
 
-			switch (dwim_ref(name, strlen(name), &discard, &full)) {
+			switch (dwim_ref(name, strlen(name), &discard, &full, 0)) {
 			case 0:
 				/*
 				 * Not found -- not a ref.  We could
diff --git a/builtin/show-branch.c b/builtin/show-branch.c
index 7eae5f3801..d6d2dabeca 100644
--- a/builtin/show-branch.c
+++ b/builtin/show-branch.c
@@ -741,7 +741,7 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 			die(Q_("only %d entry can be shown at one time.",
 			       "only %d entries can be shown at one time.",
 			       MAX_REVS), MAX_REVS);
-		if (!dwim_ref(*av, strlen(*av), &oid, &ref))
+		if (!dwim_ref(*av, strlen(*av), &oid, &ref, 0))
 			die(_("no such ref %s"), *av);
 
 		/* Has the base been specified? */
diff --git a/builtin/stash.c b/builtin/stash.c
index 4bdfaf8397..3f811f3050 100644
--- a/builtin/stash.c
+++ b/builtin/stash.c
@@ -185,7 +185,7 @@ static int get_stash_info(struct stash_info *info, int argc, const char **argv)
 	end_of_rev = strchrnul(revision, '@');
 	strbuf_add(&symbolic, revision, end_of_rev - revision);
 
-	ret = dwim_ref(symbolic.buf, symbolic.len, &dummy, &expanded_ref);
+	ret = dwim_ref(symbolic.buf, symbolic.len, &dummy, &expanded_ref, 0);
 	strbuf_release(&symbolic);
 	switch (ret) {
 	case 0: /* Not found, but valid ref */
diff --git a/bundle.c b/bundle.c
index 995a940dfd..cb0e5931ac 100644
--- a/bundle.c
+++ b/bundle.c
@@ -403,7 +403,7 @@ static int write_bundle_refs(int bundle_fd, struct rev_info *revs)
 
 		if (e->item->flags & UNINTERESTING)
 			continue;
-		if (dwim_ref(e->name, strlen(e->name), &oid, &ref) != 1)
+		if (dwim_ref(e->name, strlen(e->name), &oid, &ref, 0) != 1)
 			goto skip_write_ref;
 		if (read_ref_full(e->name, RESOLVE_REF_READING, &oid, &flag))
 			flag = 0;
diff --git a/cache.h b/cache.h
index 4cad61ffa4..cee8aa5dc3 100644
--- a/cache.h
+++ b/cache.h
@@ -1557,21 +1557,32 @@ int parse_oid_hex_any(const char *hex, struct object_id *oid, const char **end);
  *
  * If the input was ok but there are not N branch switches in the
  * reflog, it returns 0.
- *
- * If "allowed" is non-zero, it is a treated as a bitfield of allowable
- * expansions: local branches ("refs/heads/"), remote branches
- * ("refs/remotes/"), or "HEAD". If no "allowed" bits are set, any expansion is
- * allowed, even ones to refs outside of those namespaces.
  */
 #define INTERPRET_BRANCH_LOCAL (1<<0)
 #define INTERPRET_BRANCH_REMOTE (1<<1)
 #define INTERPRET_BRANCH_HEAD (1<<2)
+struct interpret_branch_name_options {
+	/*
+	 * If "allowed" is non-zero, it is a treated as a bitfield of allowable
+	 * expansions: local branches ("refs/heads/"), remote branches
+	 * ("refs/remotes/"), or "HEAD". If no "allowed" bits are set, any expansion is
+	 * 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,
 			       struct strbuf *buf,
-			       unsigned allowed);
-#define interpret_branch_name(str, len, buf, allowed) \
-	repo_interpret_branch_name(the_repository, str, len, buf, allowed)
+			       const struct interpret_branch_name_options *options);
+#define interpret_branch_name(str, len, buf, options) \
+	repo_interpret_branch_name(the_repository, str, len, buf, options)
 
 int validate_headref(const char *ref);
 
diff --git a/commit.c b/commit.c
index bc741e78ad..f53429c0ac 100644
--- a/commit.c
+++ b/commit.c
@@ -921,7 +921,7 @@ struct commit *get_fork_point(const char *refname, struct commit *commit)
 	struct commit *ret = NULL;
 	char *full_refname;
 
-	switch (dwim_ref(refname, strlen(refname), &oid, &full_refname)) {
+	switch (dwim_ref(refname, strlen(refname), &oid, &full_refname, 0)) {
 	case 0:
 		die("No such ref: '%s'", refname);
 	case 1:
diff --git a/refs.c b/refs.c
index 156fdcd459..8374dfefa6 100644
--- a/refs.c
+++ b/refs.c
@@ -598,10 +598,14 @@ 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;
-	int ret = repo_interpret_branch_name(r, *string, *len, &buf, 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) {
 		size_t size;
@@ -614,19 +618,15 @@ 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;
 }
 
-int dwim_ref(const char *str, int len, struct object_id *oid, char **ref)
-{
-	return repo_dwim_ref(the_repository, str, len, oid, ref);
-}
-
 int expand_ref(struct repository *repo, const char *str, int len,
 	       struct object_id *oid, char **ref)
 {
@@ -665,7 +665,7 @@ 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 04bd25019f..6695518156 100644
--- a/refs.h
+++ b/refs.h
@@ -1,6 +1,8 @@
 #ifndef REFS_H
 #define REFS_H
 
+#include "cache.h"
+
 struct object_id;
 struct ref_store;
 struct repository;
@@ -151,9 +153,15 @@ 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);
+static inline int dwim_ref(const char *str, int len, struct object_id *oid,
+			   char **ref, int nonfatal_dangling_mark)
+{
+	return repo_dwim_ref(the_repository, str, len, oid, ref,
+			     nonfatal_dangling_mark);
+}
 int dwim_log(const char *str, int len, struct object_id *oid, char **ref);
 
 /*
diff --git a/remote.c b/remote.c
index c5ed74f91c..420150837b 100644
--- a/remote.c
+++ b/remote.c
@@ -1558,7 +1558,7 @@ static void set_merge(struct branch *ret)
 		    strcmp(ret->remote_name, "."))
 			continue;
 		if (dwim_ref(ret->merge_name[i], strlen(ret->merge_name[i]),
-			     &oid, &ref) == 1)
+			     &oid, &ref, 0) == 1)
 			ret->merge[i]->dst = ref;
 		else
 			ret->merge[i]->dst = xstrdup(ret->merge_name[i]);
diff --git a/revision.c b/revision.c
index 0d67b842fd..1239023f93 100644
--- a/revision.c
+++ b/revision.c
@@ -315,13 +315,14 @@ static void add_pending_object_with_path(struct rev_info *revs,
 					 const char *name, unsigned mode,
 					 const char *path)
 {
+	struct interpret_branch_name_options options = { 0 };
 	if (!obj)
 		return;
 	if (revs->no_walk && (obj->flags & UNINTERESTING))
 		revs->no_walk = 0;
 	if (revs->reflog_info && obj->type == OBJ_COMMIT) {
 		struct strbuf buf = STRBUF_INIT;
-		int len = interpret_branch_name(name, 0, &buf, 0);
+		int len = interpret_branch_name(name, 0, &buf, &options);
 
 		if (0 < len && name[len] && buf.len)
 			strbuf_addstr(&buf, name + len);
diff --git a/sha1-name.c b/sha1-name.c
index 0b8cb5247a..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;
@@ -1427,9 +1427,12 @@ static int reinterpret(struct repository *r,
 	struct strbuf tmp = STRBUF_INIT;
 	int used = buf->len;
 	int ret;
+	struct interpret_branch_name_options options = {
+		.allowed = allowed
+	};
 
 	strbuf_add(buf, name + len, namelen - len);
-	ret = repo_interpret_branch_name(r, buf->buf, buf->len, &tmp, allowed);
+	ret = repo_interpret_branch_name(r, buf->buf, buf->len, &tmp, &options);
 	/* that data was not interpreted, remove our cruft */
 	if (ret < 0) {
 		strbuf_setlen(buf, used);
@@ -1471,7 +1474,7 @@ static int interpret_branch_mark(struct repository *r,
 				 int (*get_mark)(const char *, int),
 				 const char *(*get_data)(struct branch *,
 							 struct strbuf *),
-				 unsigned allowed)
+				 const struct interpret_branch_name_options *options)
 {
 	int len;
 	struct branch *branch;
@@ -1493,10 +1496,16 @@ 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, allowed))
+	if (!branch_interpret_allowed(value, options->allowed))
 		return -1;
 
 	set_shortened_ref(r, buf, value);
@@ -1506,7 +1515,7 @@ static int interpret_branch_mark(struct repository *r,
 int repo_interpret_branch_name(struct repository *r,
 			       const char *name, int namelen,
 			       struct strbuf *buf,
-			       unsigned allowed)
+			       const struct interpret_branch_name_options *options)
 {
 	char *at;
 	const char *start;
@@ -1515,7 +1524,7 @@ int repo_interpret_branch_name(struct repository *r,
 	if (!namelen)
 		namelen = strlen(name);
 
-	if (!allowed || (allowed & INTERPRET_BRANCH_LOCAL)) {
+	if (!options->allowed || (options->allowed & INTERPRET_BRANCH_LOCAL)) {
 		len = interpret_nth_prior_checkout(r, name, namelen, buf);
 		if (!len) {
 			return len; /* syntax Ok, not enough switches */
@@ -1523,7 +1532,8 @@ int repo_interpret_branch_name(struct repository *r,
 			if (len == namelen)
 				return len; /* consumed all */
 			else
-				return reinterpret(r, name, namelen, len, buf, allowed);
+				return reinterpret(r, name, namelen, len, buf,
+						   options->allowed);
 		}
 	}
 
@@ -1531,22 +1541,22 @@ int repo_interpret_branch_name(struct repository *r,
 	     (at = memchr(start, '@', namelen - (start - name)));
 	     start = at + 1) {
 
-		if (!allowed || (allowed & INTERPRET_BRANCH_HEAD)) {
+		if (!options->allowed || (options->allowed & INTERPRET_BRANCH_HEAD)) {
 			len = interpret_empty_at(name, namelen, at - name, buf);
 			if (len > 0)
 				return reinterpret(r, name, namelen, len, buf,
-						   allowed);
+						   options->allowed);
 		}
 
 		len = interpret_branch_mark(r, name, namelen, at - name, buf,
 					    upstream_mark, branch_get_upstream,
-					    allowed);
+					    options);
 		if (len > 0)
 			return len;
 
 		len = interpret_branch_mark(r, name, namelen, at - name, buf,
 					    push_mark, branch_get_push,
-					    allowed);
+					    options);
 		if (len > 0)
 			return len;
 	}
@@ -1557,7 +1567,10 @@ int repo_interpret_branch_name(struct repository *r,
 void strbuf_branchname(struct strbuf *sb, const char *name, unsigned allowed)
 {
 	int len = strlen(name);
-	int used = interpret_branch_name(name, len, sb, allowed);
+	struct interpret_branch_name_options options = {
+		.allowed = allowed
+	};
+	int used = interpret_branch_name(name, len, sb, &options);
 
 	if (used < 0)
 		used = 0;
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 bb0f9120de..d9872d543b 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 (dwim_ref(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 */