libgo patch committed: make time test more robust

[Ian Lance Taylor]

This patch to libgo backports a change from Go tip to make the time
test ParseInLocation more robust.  This lets the test pass on systems
that have updated their timezone database to 2017a or later.  This
fixes GCC PR 80302.  Bootstrapped and ran Go time test on
x86_64-pc-linux-gnu.  Committed to mainline.

Ian
-------------- next part --------------
Index: libgo/go/time/format_test.go
===================================================================
--- libgo/go/time/format_test.go	(revision 245745)
+++ libgo/go/time/format_test.go	(working copy)
@@ -245,27 +245,45 @@ func TestParseDayOutOfRange(t *testing.T
 	}
 }
 
+// TestParseInLocation checks that the Parse and ParseInLocation
+// functions do not get confused by the fact that AST (Arabia Standard
+// Time) and AST (Atlantic Standard Time) are different time zones,
+// even though they have the same abbreviation.
+//
+// ICANN has been slowly phasing out invented abbreviation in favor of
+// numeric time zones (for example, the Asia/Baghdad time zone
+// abbreviation got changed from AST to +03 in the 2017a tzdata
+// release); but we still want to make sure that the time package does
+// not get confused on systems with slightly older tzdata packages.
 func TestParseInLocation(t *testing.T) {
-	// Check that Parse (and ParseInLocation) understand that
-	// Feb 01 AST (Arabia Standard Time) and Feb 01 AST (Atlantic Standard Time)
-	// are in different time zones even though both are called AST
 
 	baghdad, err := LoadLocation("Asia/Baghdad")
 	if err != nil {
 		t.Fatal(err)
 	}
 
-	t1, err := ParseInLocation("Jan 02 2006 MST", "Feb 01 2013 AST", baghdad)
+	var t1, t2 Time
+
+	t1, err = ParseInLocation("Jan 02 2006 MST", "Feb 01 2013 AST", baghdad)
 	if err != nil {
 		t.Fatal(err)
 	}
-	t2 := Date(2013, February, 1, 00, 00, 00, 0, baghdad)
-	if t1 != t2 {
-		t.Fatalf("ParseInLocation(Feb 01 2013 AST, Baghdad) = %v, want %v", t1, t2)
-	}
+
 	_, offset := t1.Zone()
-	if offset != 3*60*60 {
-		t.Fatalf("ParseInLocation(Feb 01 2013 AST, Baghdad).Zone = _, %d, want _, %d", offset, 3*60*60)
+
+	// A zero offset means that ParseInLocation did not recognize the
+	// 'AST' abbreviation as matching the current location (Baghdad,
+	// where we'd expect a +03 hrs offset); likely because we're using
+	// a recent tzdata release (2017a or newer).
+	// If it happens, skip the Baghdad test.
+	if offset != 0 {
+		t2 = Date(2013, February, 1, 00, 00, 00, 0, baghdad)
+		if t1 != t2 {
+			t.Fatalf("ParseInLocation(Feb 01 2013 AST, Baghdad) = %v, want %v", t1, t2)
+		}
+		if offset != 3*60*60 {
+			t.Fatalf("ParseInLocation(Feb 01 2013 AST, Baghdad).Zone = _, %d, want _, %d", offset, 3*60*60)
+		}
 	}
 
 	blancSablon, err := LoadLocation("America/Blanc-Sablon")
@@ -273,6 +291,9 @@ func TestParseInLocation(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	// In this case 'AST' means 'Atlantic Standard Time', and we
+	// expect the abbreviation to correctly match the american
+	// location.
 	t1, err = ParseInLocation("Jan 02 2006 MST", "Feb 01 2013 AST", blancSablon)
 	if err != nil {
 		t.Fatal(err)