time: avoid creating a parse error from the next chunk of the value

When it reports a parse error, it uses the "value" variable as the
value element of the parse error. Previously, in some of the cases,
the "value" variable is always updated to the next chunk of the value
to be parsed (even if an earlier chunk is invalid). The reported
parse error is confusing in this case.

This CL addresses this issue by holding the original value, and when
it fails to parse the time, use it to create the parse error.

Fixes #56730.

Change-Id: I445b1d8a1b910208d0608b2186881746adb550e0
GitHub-Last-Rev: 67b1102b5e9b345beb2ddcc529a8e608e5afc865
GitHub-Pull-Request: golang/go#56754
Reviewed-on: https://go-review.googlesource.com/c/go/+/450936
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Joedian Reid <joedian@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>

1 files changed, 14 insertions, 8 deletions

diff --git a/src/time/format_test.go b/src/time/format_test.go
index b1d85f510b..8a26eaa35b 100644
--- a/src/time/format_test.go
+++ b/src/time/format_test.go
@@ -620,13 +620,13 @@ type ParseErrorTest struct {
 }
 
 var parseErrorTests = []ParseErrorTest{
-	{ANSIC, "Feb  4 21:00:60 2010", "cannot parse"}, // cannot parse Feb as Mon
-	{ANSIC, "Thu Feb  4 21:00:57 @2010", "cannot parse"},
+	{ANSIC, "Feb  4 21:00:60 2010", `cannot parse "Feb  4 21:00:60 2010" as "Mon"`},
+	{ANSIC, "Thu Feb  4 21:00:57 @2010", `cannot parse "@2010" as "2006"`},
 	{ANSIC, "Thu Feb  4 21:00:60 2010", "second out of range"},
 	{ANSIC, "Thu Feb  4 21:61:57 2010", "minute out of range"},
 	{ANSIC, "Thu Feb  4 24:00:60 2010", "hour out of range"},
-	{"Mon Jan _2 15:04:05.000 2006", "Thu Feb  4 23:00:59x01 2010", "cannot parse"},
-	{"Mon Jan _2 15:04:05.000 2006", "Thu Feb  4 23:00:59.xxx 2010", "cannot parse"},
+	{"Mon Jan _2 15:04:05.000 2006", "Thu Feb  4 23:00:59x01 2010", `cannot parse "x01 2010" as ".000"`},
+	{"Mon Jan _2 15:04:05.000 2006", "Thu Feb  4 23:00:59.xxx 2010", `cannot parse ".xxx 2010" as ".000"`},
 	{"Mon Jan _2 15:04:05.000 2006", "Thu Feb  4 23:00:59.-123 2010", "fractional second out of range"},
 	// issue 4502. StampNano requires exactly 9 digits of precision.
 	{StampNano, "Dec  7 11:22:01.000000", `cannot parse ".000000" as ".000000000"`},
@@ -641,8 +641,8 @@ var parseErrorTests = []ParseErrorTest{
 	// issue 54569
 	{RFC3339, "0000-01-01T00:00:.0+00:00", `parsing time "0000-01-01T00:00:.0+00:00" as "2006-01-02T15:04:05Z07:00": cannot parse ".0+00:00" as "05"`},
 	// issue 21113
-	{"_2 Jan 06 15:04 MST", "4 --- 00 00:00 GMT", "cannot parse"},
-	{"_2 January 06 15:04 MST", "4 --- 00 00:00 GMT", "cannot parse"},
+	{"_2 Jan 06 15:04 MST", "4 --- 00 00:00 GMT", `cannot parse "--- 00 00:00 GMT" as "Jan"`},
+	{"_2 January 06 15:04 MST", "4 --- 00 00:00 GMT", `cannot parse "--- 00 00:00 GMT" as "January"`},
 
 	// invalid or mismatched day-of-year
 	{"Jan _2 002 2006", "Feb  4 034 2006", "day-of-year does not match day"},
@@ -653,8 +653,14 @@ var parseErrorTests = []ParseErrorTest{
 	{RFC3339, "\"", `parsing time "\"" as "2006-01-02T15:04:05Z07:00": cannot parse "\"" as "2006"`},
 
 	// issue 54570
-	{RFC3339, "0000-01-01T00:00:00+00:+0", `parsing time "0000-01-01T00:00:00+00:+0" as "2006-01-02T15:04:05Z07:00": cannot parse "" as "Z07:00"`},
-	{RFC3339, "0000-01-01T00:00:00+-0:00", `parsing time "0000-01-01T00:00:00+-0:00" as "2006-01-02T15:04:05Z07:00": cannot parse "" as "Z07:00"`},
+	{RFC3339, "0000-01-01T00:00:00+00:+0", `parsing time "0000-01-01T00:00:00+00:+0" as "2006-01-02T15:04:05Z07:00": cannot parse "+00:+0" as "Z07:00"`},
+	{RFC3339, "0000-01-01T00:00:00+-0:00", `parsing time "0000-01-01T00:00:00+-0:00" as "2006-01-02T15:04:05Z07:00": cannot parse "+-0:00" as "Z07:00"`},
+
+	// issue 56730
+	{"2006-01-02", "22-10-25", `parsing time "22-10-25" as "2006-01-02": cannot parse "22-10-25" as "2006"`},
+	{"06-01-02", "a2-10-25", `parsing time "a2-10-25" as "06-01-02": cannot parse "a2-10-25" as "06"`},
+	{"03:04PM", "12:03pM", `parsing time "12:03pM" as "03:04PM": cannot parse "pM" as "PM"`},
+	{"03:04pm", "12:03pM", `parsing time "12:03pM" as "03:04pm": cannot parse "pM" as "pm"`},
 }
 
 func TestParseErrors(t *testing.T) {