Merge branch 'tr/previous-branch'

* tr/previous-branch:
  t1505: remove debugging cruft
  Simplify parsing branch switching events in reflog
  Introduce for_each_recent_reflog_ent().
  interpret_nth_last_branch(): plug small memleak
  Fix reflog parsing for a malformed branch switching entry
  Fix parsing of @{-1}@{1}
  interpret_nth_last_branch(): avoid traversing the reflog twice
  checkout: implement "-" abbreviation, add docs and tests
  sha1_name: support @{-N} syntax in get_sha1()
  sha1_name: tweak @{-N} lookup
  checkout: implement "@{-N}" shortcut name for N-th last branch

Conflicts:
	sha1_name.c

Documentation/git-checkout.txt

@@ -133,6 +133,10 @@ the conflicted merge in the specified paths.
 +
 When this parameter names a non-branch (but still a valid commit object),
 your HEAD becomes 'detached'.
++
+As a special case, the "`@\{-N\}`" syntax for the N-th last branch
+checks out the branch (instead of detaching).  You may also specify
+"`-`" which is synonymous with "`@\{-1\}`".
 
 
 Detached HEAD

Documentation/git-rev-parse.txt

@@ -212,6 +212,9 @@ when you run 'git-merge'.
   reflog of the current branch. For example, if you are on the
   branch 'blabla', then '@\{1\}' means the same as 'blabla@\{1\}'.
 
+* The special construct '@\{-<n>\}' means the <n>th branch checked out
+  before the current one.
+
 * A suffix '{caret}' to a revision parameter means the first parent of
   that commit object.  '{caret}<n>' means the <n>th parent (i.e.
   'rev{caret}'

builtin-checkout.c

@@ -351,8 +351,16 @@ struct branch_info {
 static void setup_branch_path(struct branch_info *branch)
 {
 	struct strbuf buf = STRBUF_INIT;
-	strbuf_addstr(&buf, "refs/heads/");
-	strbuf_addstr(&buf, branch->name);
+	int ret;
+
+	if ((ret = interpret_nth_last_branch(branch->name, &buf))
+	    && ret == strlen(branch->name)) {
+		branch->name = xstrdup(buf.buf);
+		strbuf_splice(&buf, 0, 0, "refs/heads/", 11);
+	} else {
+		strbuf_addstr(&buf, "refs/heads/");
+		strbuf_addstr(&buf, branch->name);
+	}
 	branch->path = strbuf_detach(&buf, NULL);
 }
 
@@ -661,6 +669,9 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		arg = argv[0];
 		has_dash_dash = (argc > 1) && !strcmp(argv[1], "--");
 
+		if (!strcmp(arg, "-"))
+			arg = "@{-1}";
+
 		if (get_sha1(arg, rev)) {
 			if (has_dash_dash)          /* case (1) */
 				die("invalid reference: %s", arg);

cache.h

@@ -667,6 +667,7 @@ extern int read_ref(const char *filename, unsigned char *sha1);
 extern const char *resolve_ref(const char *path, unsigned char *sha1, int, int *);
 extern int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref);
 extern int dwim_log(const char *str, int len, unsigned char *sha1, char **ref);
+extern int interpret_nth_last_branch(const char *str, struct strbuf *);
 
 extern int refname_match(const char *abbrev_name, const char *full_name, const char **rules);
 extern const char *ref_rev_parse_rules[];

refs.c

@@ -1453,7 +1453,7 @@ int read_ref_at(const char *ref, unsigned long at_time, int cnt, unsigned char *
 	return 1;
 }
 
-int for_each_reflog_ent(const char *ref, each_reflog_ent_fn fn, void *cb_data)
+int for_each_recent_reflog_ent(const char *ref, each_reflog_ent_fn fn, long ofs, void *cb_data)
 {
 	const char *logfile;
 	FILE *logfp;
@@ -1464,6 +1464,16 @@ int for_each_reflog_ent(const char *ref, each_reflog_ent_fn fn, void *cb_data)
 	logfp = fopen(logfile, "r");
 	if (!logfp)
 		return -1;
+
+	if (ofs) {
+		struct stat statbuf;
+		if (fstat(fileno(logfp), &statbuf) ||
+		    statbuf.st_size < ofs ||
+		    fseek(logfp, -ofs, SEEK_END) ||
+		    fgets(buf, sizeof(buf), logfp))
+			return -1;
+	}
+
 	while (fgets(buf, sizeof(buf), logfp)) {
 		unsigned char osha1[20], nsha1[20];
 		char *email_end, *message;
@@ -1497,6 +1507,11 @@ int for_each_reflog_ent(const char *ref, each_reflog_ent_fn fn, void *cb_data)
 	return ret;
 }
 
+int for_each_reflog_ent(const char *ref, each_reflog_ent_fn fn, void *cb_data)
+{
+	return for_each_recent_reflog_ent(ref, fn, 0, cb_data);
+}
+
 static int do_for_each_reflog(const char *base, each_ref_fn fn, void *cb_data)
 {
 	DIR *dir = opendir(git_path("logs/%s", base));

refs.h

@@ -60,6 +60,7 @@ extern int read_ref_at(const char *ref, unsigned long at_time, int cnt, unsigned
 /* iterate over reflog entries */
 typedef int each_reflog_ent_fn(unsigned char *osha1, unsigned char *nsha1, const char *, unsigned long, int, const char *, void *);
 int for_each_reflog_ent(const char *ref, each_reflog_ent_fn fn, void *cb_data);
+int for_each_recent_reflog_ent(const char *ref, each_reflog_ent_fn fn, long, void *cb_data);
 
 /*
  * Calls the specified function for each reflog file until it returns nonzero,

sha1_name.c

@@ -238,8 +238,28 @@ static int ambiguous_path(const char *path, int len)
 	return slash;
 }
 
+/*
+ * *string and *len will only be substituted, and *string returned (for
+ * later free()ing) if the string passed in is of the form @{-<n>}.
+ */
+static char *substitute_nth_last_branch(const char **string, int *len)
+{
+	struct strbuf buf = STRBUF_INIT;
+	int ret = interpret_nth_last_branch(*string, &buf);
+
+	if (ret == *len) {
+		size_t size;
+		*string = strbuf_detach(&buf, &size);
+		*len = size;
+		return (char *)*string;
+	}
+
+	return NULL;
+}
+
 int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref)
 {
+	char *last_branch = substitute_nth_last_branch(&str, &len);
 	const char **p, *r;
 	int refs_found = 0;
 
@@ -259,11 +279,13 @@ int dwim_ref(const char *str, int len, unsigned char *sha1, char **ref)
 				break;
 		}
 	}
+	free(last_branch);
 	return refs_found;
 }
 
 int dwim_log(const char *str, int len, unsigned char *sha1, char **log)
 {
+	char *last_branch = substitute_nth_last_branch(&str, &len);
 	const char **p;
 	int logs_found = 0;
 
@@ -294,9 +316,12 @@ int dwim_log(const char *str, int len, unsigned char *sha1, char **log)
 		if (!warn_ambiguous_refs)
 			break;
 	}
+	free(last_branch);
 	return logs_found;
 }
 
+static int get_sha1_1(const char *name, int len, unsigned char *sha1);
+
 static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 {
 	static const char *warning = "warning: refname '%.*s' is ambiguous.\n";
@@ -307,10 +332,10 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 	if (len == 40 && !get_sha1_hex(str, sha1))
 		return 0;
 
-	/* basic@{time or number} format to query ref-log */
+	/* basic@{time or number or -number} format to query ref-log */
 	reflog_len = at = 0;
 	if (len && str[len-1] == '}') {
-		for (at = 0; at < len - 1; at++) {
+		for (at = len-2; at >= 0; at--) {
 			if (str[at] == '@' && str[at+1] == '{') {
 				reflog_len = (len-1) - (at+2);
 				len = at;
@@ -324,6 +349,16 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 		return -1;
 
 	if (!len && reflog_len) {
+		struct strbuf buf = STRBUF_INIT;
+		int ret;
+		/* try the @{-N} syntax for n-th checkout */
+		ret = interpret_nth_last_branch(str+at, &buf);
+		if (ret > 0) {
+			/* substitute this branch name and restart */
+			return get_sha1_1(buf.buf, buf.len, sha1);
+		} else if (ret == 0) {
+			return -1;
+		}
 		/* allow "@{...}" to mean the current branch reflog */
 		refs_found = dwim_ref("HEAD", 4, sha1, &real_ref);
 	} else if (reflog_len)
@@ -379,8 +414,6 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 	return 0;
 }
 
-static int get_sha1_1(const char *name, int len, unsigned char *sha1);
-
 static int get_parent(const char *name, int len,
 		      unsigned char *result, int idx)
 {
@@ -674,6 +707,92 @@ static int get_sha1_oneline(const char *prefix, unsigned char *sha1)
 	return retval;
 }
 
+struct grab_nth_branch_switch_cbdata {
+	long cnt, alloc;
+	struct strbuf *buf;
+};
+
+static int grab_nth_branch_switch(unsigned char *osha1, unsigned char *nsha1,
+				  const char *email, unsigned long timestamp, int tz,
+				  const char *message, void *cb_data)
+{
+	struct grab_nth_branch_switch_cbdata *cb = cb_data;
+	const char *match = NULL, *target = NULL;
+	size_t len;
+	int nth;
+
+	if (!prefixcmp(message, "checkout: moving from ")) {
+		match = message + strlen("checkout: moving from ");
+		target = strstr(match, " to ");
+	}
+
+	if (!match || !target)
+		return 0;
+
+	len = target - match;
+	nth = cb->cnt++ % cb->alloc;
+	strbuf_reset(&cb->buf[nth]);
+	strbuf_add(&cb->buf[nth], match, len);
+	return 0;
+}
+
+/*
+ * This reads "@{-N}" syntax, finds the name of the Nth previous
+ * branch we were on, and places the name of the branch in the given
+ * buf and returns the number of characters parsed if successful.
+ *
+ * If the input is not of the accepted format, it returns a negative
+ * number to signal an error.
+ *
+ * If the input was ok but there are not N branch switches in the
+ * reflog, it returns 0.
+ */
+int interpret_nth_last_branch(const char *name, struct strbuf *buf)
+{
+	long nth;
+	int i, retval;
+	struct grab_nth_branch_switch_cbdata cb;
+	const char *brace;
+	char *num_end;
+
+	if (name[0] != '@' || name[1] != '{' || name[2] != '-')
+		return -1;
+	brace = strchr(name, '}');
+	if (!brace)
+		return -1;
+	nth = strtol(name+3, &num_end, 10);
+	if (num_end != brace)
+		return -1;
+	if (nth <= 0)
+		return -1;
+	cb.alloc = nth;
+	cb.buf = xmalloc(nth * sizeof(struct strbuf));
+	for (i = 0; i < nth; i++)
+		strbuf_init(&cb.buf[i], 20);
+	cb.cnt = 0;
+	retval = 0;
+	for_each_recent_reflog_ent("HEAD", grab_nth_branch_switch, 40960, &cb);
+	if (cb.cnt < nth) {
+		cb.cnt = 0;
+		for (i = 0; i < nth; i++)
+			strbuf_release(&cb.buf[i]);
+		for_each_reflog_ent("HEAD", grab_nth_branch_switch, &cb);
+	}
+	if (cb.cnt < nth)
+		goto release_return;
+	i = cb.cnt % nth;
+	strbuf_reset(buf);
+	strbuf_add(buf, cb.buf[i].buf, cb.buf[i].len);
+	retval = brace-name+1;
+
+release_return:
+	for (i = 0; i < nth; i++)
+		strbuf_release(&cb.buf[i]);
+	free(cb.buf);
+
+	return retval;
+}
+
 /*
  * This is like "get_sha1_basic()", except it allows "sha1 expressions",
  * notably "xyz^" for "parent of xyz"

t/t1505-rev-parse-last.sh

@@ -0,0 +1,69 @@
+#!/bin/sh
+
+test_description='test @{-N} syntax'
+
+. ./test-lib.sh
+
+
+make_commit () {
+	echo "$1" > "$1" &&
+	git add "$1" &&
+	git commit -m "$1"
+}
+
+
+test_expect_success 'setup' '
+
+	make_commit 1 &&
+	git branch side &&
+	make_commit 2 &&
+	make_commit 3 &&
+	git checkout side &&
+	make_commit 4 &&
+	git merge master &&
+	git checkout master
+
+'
+
+# 1 -- 2 -- 3 master
+#  \         \
+#   \         \
+#    --- 4 --- 5 side
+#
+# and 'side' should be the last branch
+
+test_rev_equivalent () {
+
+	git rev-parse "$1" > expect &&
+	git rev-parse "$2" > output &&
+	test_cmp expect output
+
+}
+
+test_expect_success '@{-1} works' '
+	test_rev_equivalent side @{-1}
+'
+
+test_expect_success '@{-1}~2 works' '
+	test_rev_equivalent side~2 @{-1}~2
+'
+
+test_expect_success '@{-1}^2 works' '
+	test_rev_equivalent side^2 @{-1}^2
+'
+
+test_expect_success '@{-1}@{1} works' '
+	test_rev_equivalent side@{1} @{-1}@{1}
+'
+
+test_expect_success '@{-2} works' '
+	test_rev_equivalent master @{-2}
+'
+
+test_expect_success '@{-3} fails' '
+	test_must_fail git rev-parse @{-3}
+'
+
+test_done
+
+

t/t2012-checkout-last.sh

@@ -0,0 +1,94 @@
+#!/bin/sh
+
+test_description='checkout can switch to last branch'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	echo hello >world &&
+	git add world &&
+	git commit -m initial &&
+	git branch other &&
+	echo "hello again" >>world &&
+	git add world &&
+	git commit -m second
+'
+
+test_expect_success '"checkout -" does not work initially' '
+	test_must_fail git checkout -
+'
+
+test_expect_success 'first branch switch' '
+	git checkout other
+'
+
+test_expect_success '"checkout -" switches back' '
+	git checkout - &&
+	test "z$(git symbolic-ref HEAD)" = "zrefs/heads/master"
+'
+
+test_expect_success '"checkout -" switches forth' '
+	git checkout - &&
+	test "z$(git symbolic-ref HEAD)" = "zrefs/heads/other"
+'
+
+test_expect_success 'detach HEAD' '
+	git checkout $(git rev-parse HEAD)
+'
+
+test_expect_success '"checkout -" attaches again' '
+	git checkout - &&
+	test "z$(git symbolic-ref HEAD)" = "zrefs/heads/other"
+'
+
+test_expect_success '"checkout -" detaches again' '
+	git checkout - &&
+	test "z$(git rev-parse HEAD)" = "z$(git rev-parse other)" &&
+	test_must_fail git symbolic-ref HEAD
+'
+
+test_expect_success 'more switches' '
+	for i in 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
+	do
+		git checkout -b branch$i
+	done
+'
+
+more_switches () {
+	for i in 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1
+	do
+		git checkout branch$i
+	done
+}
+
+test_expect_success 'switch to the last' '
+	more_switches &&
+	git checkout @{-1} &&
+	test "z$(git symbolic-ref HEAD)" = "zrefs/heads/branch2"
+'
+
+test_expect_success 'switch to second from the last' '
+	more_switches &&
+	git checkout @{-2} &&
+	test "z$(git symbolic-ref HEAD)" = "zrefs/heads/branch3"
+'
+
+test_expect_success 'switch to third from the last' '
+	more_switches &&
+	git checkout @{-3} &&
+	test "z$(git symbolic-ref HEAD)" = "zrefs/heads/branch4"
+'
+
+test_expect_success 'switch to fourth from the last' '
+	more_switches &&
+	git checkout @{-4} &&
+	test "z$(git symbolic-ref HEAD)" = "zrefs/heads/branch5"
+'
+
+test_expect_success 'switch to twelfth from the last' '
+	more_switches &&
+	git checkout @{-12} &&
+	test "z$(git symbolic-ref HEAD)" = "zrefs/heads/branch13"
+'
+
+test_done