approxidate_careful() reports errorneous date string

For a long time, the time based reflog syntax (e.g. master@{yesterday})
didn't complain when the "human readable" timestamp was misspelled, as
the underlying mechanism tried to be as lenient as possible.  The funny
thing was that parsing of "@{now}" even relied on the fact that anything
not recognized by the machinery returned the current timestamp.

Introduce approxidate_careful() that takes an optional pointer to an
integer, that gets assigned 1 when the input does not make sense as a
timestamp.

As I am too lazy to fix all the callers that use approxidate(), most of
the callers do not take advantage of the error checking, but convert the
code to parse reflog to use it as a demonstration.

Tests are mostly from Jeff King.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

4 files changed, 86 insertions, 10 deletions

diff --git a/cache.h b/cache.h
index b90f671f7..0f163dbbe 100644
--- a/cache.h
+++ b/cache.h
@@ -740,7 +740,8 @@ const char *show_date_relative(unsigned long time, int tz,
 			       size_t timebuf_size);
 int parse_date(const char *date, char *buf, int bufsize);
 void datestamp(char *buf, int bufsize);
-unsigned long approxidate(const char *);
+#define approxidate(s) approxidate_careful((s), NULL)
+unsigned long approxidate_careful(const char *, int *);
 unsigned long approxidate_relative(const char *date, const struct timeval *now);
 enum date_mode parse_date_format(const char *format);
 
diff --git a/date.c b/date.c
index 5d05ef61c..17385a9b6 100644
--- a/date.c
+++ b/date.c
@@ -696,6 +696,11 @@ static unsigned long update_tm(struct tm *tm, struct tm *now, unsigned long sec)
 	return n;
 }
 
+static void date_now(struct tm *tm, struct tm *now, int *num)
+{
+	update_tm(tm, now, 0);
+}
+
 static void date_yesterday(struct tm *tm, struct tm *now, int *num)
 {
 	update_tm(tm, now, 24*60*60);
@@ -770,6 +775,7 @@ static const struct special {
 	{ "PM", date_pm },
 	{ "AM", date_am },
 	{ "never", date_never },
+	{ "now", date_now },
 	{ NULL }
 };
 
@@ -790,7 +796,7 @@ static const struct typelen {
 	{ NULL }
 };
 
-static const char *approxidate_alpha(const char *date, struct tm *tm, struct tm *now, int *num)
+static const char *approxidate_alpha(const char *date, struct tm *tm, struct tm *now, int *num, int *touched)
 {
 	const struct typelen *tl;
 	const struct special *s;
@@ -804,6 +810,7 @@ static const char *approxidate_alpha(const char *date, struct tm *tm, struct tm
 		int match = match_string(date, month_names[i]);
 		if (match >= 3) {
 			tm->tm_mon = i;
+			*touched = 1;
 			return end;
 		}
 	}
@@ -812,6 +819,7 @@ static const char *approxidate_alpha(const char *date, struct tm *tm, struct tm
 		int len = strlen(s->name);
 		if (match_string(date, s->name) == len) {
 			s->fn(tm, now, num);
+			*touched = 1;
 			return end;
 		}
 	}
@@ -821,11 +829,14 @@ static const char *approxidate_alpha(const char *date, struct tm *tm, struct tm
 			int len = strlen(number_name[i]);
 			if (match_string(date, number_name[i]) == len) {
 				*num = i;
+				*touched = 1;
 				return end;
 			}
 		}
-		if (match_string(date, "last") == 4)
+		if (match_string(date, "last") == 4) {
 			*num = 1;
+			*touched = 1;
+		}
 		return end;
 	}
 
@@ -835,6 +846,7 @@ static const char *approxidate_alpha(const char *date, struct tm *tm, struct tm
 		if (match_string(date, tl->type) >= len-1) {
 			update_tm(tm, now, tl->length * *num);
 			*num = 0;
+			*touched = 1;
 			return end;
 		}
 		tl++;
@@ -852,6 +864,7 @@ static const char *approxidate_alpha(const char *date, struct tm *tm, struct tm
 			diff += 7*n;
 
 			update_tm(tm, now, diff * 24 * 60 * 60);
+			*touched = 1;
 			return end;
 		}
 	}
@@ -866,6 +879,7 @@ static const char *approxidate_alpha(const char *date, struct tm *tm, struct tm
 			tm->tm_year--;
 		}
 		tm->tm_mon = n;
+		*touched = 1;
 		return end;
 	}
 
@@ -873,6 +887,7 @@ static const char *approxidate_alpha(const char *date, struct tm *tm, struct tm
 		update_tm(tm, now, 0); /* fill in date fields if needed */
 		tm->tm_year -= *num;
 		*num = 0;
+		*touched = 1;
 		return end;
 	}
 
@@ -929,9 +944,12 @@ static void pending_number(struct tm *tm, int *num)
 	}
 }
 
-static unsigned long approxidate_str(const char *date, const struct timeval *tv)
+static unsigned long approxidate_str(const char *date,
+				     const struct timeval *tv,
+				     int *error_ret)
 {
 	int number = 0;
+	int touched = 0;
 	struct tm tm, now;
 	time_t time_sec;
 
@@ -951,33 +969,42 @@ static unsigned long approxidate_str(const char *date, const struct timeval *tv)
 		if (isdigit(c)) {
 			pending_number(&tm, &number);
 			date = approxidate_digit(date-1, &tm, &number);
+			touched = 1;
 			continue;
 		}
 		if (isalpha(c))
-			date = approxidate_alpha(date-1, &tm, &now, &number);
+			date = approxidate_alpha(date-1, &tm, &now, &number, &touched);
 	}
 	pending_number(&tm, &number);
+	if (!touched)
+		*error_ret = 1;
 	return update_tm(&tm, &now, 0);
 }
 
 unsigned long approxidate_relative(const char *date, const struct timeval *tv)
 {
 	char buffer[50];
+	int errors = 0;
 
 	if (parse_date(date, buffer, sizeof(buffer)) > 0)
 		return strtoul(buffer, NULL, 0);
 
-	return approxidate_str(date, tv);
+	return approxidate_str(date, tv, &errors);
 }
 
-unsigned long approxidate(const char *date)
+unsigned long approxidate_careful(const char *date, int *error_ret)
 {
 	struct timeval tv;
 	char buffer[50];
+	int dummy = 0;
+	if (!error_ret)
+		error_ret = &dummy;
 
-	if (parse_date(date, buffer, sizeof(buffer)) > 0)
+	if (parse_date(date, buffer, sizeof(buffer)) > 0) {
+		*error_ret = 0;
 		return strtoul(buffer, NULL, 0);
+	}
 
 	gettimeofday(&tv, NULL);
-	return approxidate_str(date, &tv);
+	return approxidate_str(date, &tv, error_ret);
 }
diff --git a/sha1_name.c b/sha1_name.c
index 44bb62d27..f4a74fe99 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -395,8 +395,11 @@ static int get_sha1_basic(const char *str, int len, unsigned char *sha1)
 		} else if (0 <= nth)
 			at_time = 0;
 		else {
+			int errors = 0;
 			char *tmp = xstrndup(str + at + 2, reflog_len);
-			at_time = approxidate(tmp);
+			at_time = approxidate_careful(tmp, &errors);
+			if (errors)
+				die("Bogus timestamp '%s'", tmp);
 			free(tmp);
 		}
 		if (read_ref_at(real_ref, at_time, nth, sha1, NULL,
diff --git a/t/t0101-at-syntax.sh b/t/t0101-at-syntax.sh
new file mode 100755
index 000000000..ccabc37a1
--- /dev/null
+++ b/t/t0101-at-syntax.sh
@@ -0,0 +1,45 @@
+#!/bin/sh
+
+test_description='various @{whatever} syntax tests'
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit one &&
+	test_commit two
+'
+
+check_at() {
+	echo "$2" >expect &&
+	git log -1 --format=%s "$1" >actual &&
+	test_cmp expect actual
+}
+
+test_expect_success '@{0} shows current' '
+	check_at @{0} two
+'
+
+test_expect_success '@{1} shows old' '
+	check_at @{1} one
+'
+
+test_expect_success '@{now} shows current' '
+	check_at @{now} two
+'
+
+test_expect_success '@{30.years.ago} shows old' '
+	check_at @{30.years.ago} one
+'
+
+test_expect_success 'silly approxidates work' '
+	check_at @{3.hot.dogs.and.30.years.ago} one
+'
+
+test_expect_success 'notice misspelled upstream' '
+	test_must_fail git log -1 --format=%s @{usptream}
+'
+
+test_expect_success 'complain about total nonsense' '
+	test_must_fail git log -1 --format=%s @{utter.bogosity}
+'
+
+test_done