From 8feeada50cf3f783fe3c8113d5da51ad8c0b3014 Mon Sep 17 00:00:00 2001
From: LE Manh Cuong <cuong.manhle.vn@gmail.com>
Date: Wed, 30 Jan 2019 12:38:15 +0700
Subject: [PATCH] time: fix misleading error with the leading zero format

When the leading zero format is used, we currently don't handle the
month and year properly.

For the month, we were reporting an out of range error when getnum
returns zero of its own, as it also returns the month 0. That's
confusing, so only check the range when getnum returns a nil error.

For the year, we don't restore the value when parsing error occurs. For
example, with the incorrect input "111-01", "01" will be used to report
an error. So restore the value when an error occurs fix the problem.

Fixes #29918
Fixes #29916

Change-Id: I3145f8c46813a0457766b7c302482e6b56f94ed6
Reviewed-on: https://go-review.googlesource.com/c/go/+/160338
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
---
 src/time/format.go      |  7 +++++--
 src/time/format_test.go | 46 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+), 2 deletions(-)

diff --git a/src/time/format.go b/src/time/format.go
index d8e295f696e..b531cb47604 100644
--- a/src/time/format.go
+++ b/src/time/format.go
@@ -865,9 +865,12 @@ func parse(layout, value string, defaultLocation, local *Location) (Time, error)
 				err = errBad
 				break
 			}
+			hold := value
 			p, value = value[0:2], value[2:]
 			year, err = atoi(p)
-			if year >= 69 { // Unix time starts Dec 31 1969 in some time zones
+			if err != nil {
+				value = hold
+			} else if year >= 69 { // Unix time starts Dec 31 1969 in some time zones
 				year += 1900
 			} else {
 				year += 2000
@@ -887,7 +890,7 @@ func parse(layout, value string, defaultLocation, local *Location) (Time, error)
 			month++
 		case stdNumMonth, stdZeroMonth:
 			month, value, err = getnum(value, std == stdZeroMonth)
-			if month <= 0 || 12 < month {
+			if err == nil && (month <= 0 || 12 < month) {
 				rangeErrString = "month"
 			}
 		case stdWeekDay:
diff --git a/src/time/format_test.go b/src/time/format_test.go
index 516099266c8..c08ff87d100 100644
--- a/src/time/format_test.go
+++ b/src/time/format_test.go
@@ -710,3 +710,49 @@ func TestUnderscoreTwoThousand(t *testing.T) {
 		t.Errorf("Incorrect minute, got %d", m)
 	}
 }
+
+// Issue 29918, 29916
+func TestStd0xParseError(t *testing.T) {
+	tests := []struct {
+		format, value, valueElemPrefix string
+	}{
+		{"01 MST", "0 MST", "0"},
+		{"01 MST", "1 MST", "1"},
+		{RFC850, "Thursday, 04-Feb-1 21:00:57 PST", "1"},
+	}
+	for _, tt := range tests {
+		_, err := Parse(tt.format, tt.value)
+		if err == nil {
+			t.Errorf("Parse(%q, %q) did not fail as expected", tt.format, tt.value)
+		} else if perr, ok := err.(*ParseError); !ok {
+			t.Errorf("Parse(%q, %q) returned error type %T, expected ParseError", tt.format, tt.value, perr)
+		} else if !strings.Contains(perr.Error(), "cannot parse") || !strings.HasPrefix(perr.ValueElem, tt.valueElemPrefix) {
+			t.Errorf("Parse(%q, %q) returned wrong parsing error message: %v", tt.format, tt.value, perr)
+		}
+	}
+}
+
+var monthOutOfRangeTests = []struct {
+	value string
+	ok    bool
+}{
+	{"00-01", false},
+	{"13-01", false},
+	{"01-01", true},
+}
+
+func TestParseMonthOutOfRange(t *testing.T) {
+	for _, test := range monthOutOfRangeTests {
+		_, err := Parse("01-02", test.value)
+		switch {
+		case !test.ok && err != nil:
+			if !strings.Contains(err.Error(), "month out of range") {
+				t.Errorf("%q: expected 'month' error, got %v", test.value, err)
+			}
+		case test.ok && err != nil:
+			t.Errorf("%q: unexpected error: %v", test.value, err)
+		case !test.ok && err == nil:
+			t.Errorf("%q: expected 'month' error, got none", test.value)
+		}
+	}
+}