Bug 1491159 - More complete handling of TZ environment variable when initializing ICU timezone. r=anba

This improves on the changes in bug 1484829 by handling the absolute
filename form of TZ environment variables both with and without an
initial ':' character, and by improving comments about relative and
absolute paths.  (Note that relative paths without the ':' are just
Olson time zone names.)

Note that the only test that failed without the patch was:
  setTimeZone("/usr/share/zoneinfo/America/Chicago");
  assertEq(timeZoneName(), "Central Daylight Time");
and it reported
  Error: Assertion failed: got "GMT-06:00", expected "Central Daylight Time"
which seems to be a sign that ICU gets some information out of that time
zone identifier (i.e., it reported the correct standard-time GMT
offset), but not everything.

Differential Revision: https://phabricator.services.mozilla.com/D5827

--HG--
rename : js/src/tests/non262/Date/time-zone-etc_localetime.js => js/src/tests/non262/Date/time-zone-path.js
extra : moz-landing-system : lando

js/src/tests/non262/Date/time-zone-path.js

@@ -0,0 +1,30 @@
+// |reftest| skip-if(xulRuntime.OS=="WINNT"||!xulRuntime.shell)
+
+assertEq(/^(PST|PDT)$/.test(getTimeZone()), true,
+         "The default time zone is set to PST8PDT for all jstests (when run in the shell)");
+
+function timeZoneName() {
+    var dtf = new Intl.DateTimeFormat("en-US", {timeZoneName: "long"});
+    return dtf.formatToParts(Date.UTC(2017, 2, 31, 12, 0, 0)).filter(x => x.type === "timeZoneName")[0].value;
+}
+
+setTimeZone("Europe/Paris");
+assertEq(timeZoneName(), "Central European Summer Time");
+
+setTimeZone(":Europe/Helsinki");
+assertEq(timeZoneName(), "Eastern European Summer Time");
+
+setTimeZone("::Europe/London"); // two colons, invalid
+assertEq(timeZoneName(), "Coordinated Universal Time");
+
+setTimeZone("/this-part-is-ignored/zoneinfo/America/Chicago");
+assertEq(timeZoneName(), "Central Daylight Time");
+
+setTimeZone(":/this-part-is-ignored/zoneinfo/America/Phoenix");
+assertEq(timeZoneName(), "Mountain Standard Time");
+
+setTimeZone("::/this-part-is-ignored/zoneinfo/America/Los_Angeles"); // two colons, invalid
+assertEq(timeZoneName(), "Coordinated Universal Time");
+
+if (typeof reportCompare === "function")
+    reportCompare(true, true);

js/src/vm/DateTime.cpp

@@ -626,13 +626,17 @@ IsOlsonCompatibleWindowsTimeZoneId(const char* tz)
 }
 #elif ENABLE_INTL_API && defined(ICU_TZ_HAS_RECREATE_DEFAULT)
 static inline const char*
-TZContainsPath(const char* tzVar)
+TZContainsAbsolutePath(const char* tzVar)
 {
-    // A TZ beginning with a colon is expected to be followed by a path --
-    // typically an absolute path (often /etc/localtime), but alternatively a
-    // path relative to /usr/share/zoneinfo/.
-    // NB: We currently only support absolute paths.
-    return tzVar[0] == ':' && tzVar[1] == '/' ? tzVar + 1 : nullptr;
+    // A TZ environment variable may be an absolute path. The path
+    // format of TZ may begin with a colon. (ICU handles relative paths.)
+    if (tzVar[0] == ':' && tzVar[1] == '/') {
+        return tzVar + 1;
+    }
+    if (tzVar[0] == '/') {
+        return tzVar;
+    }
+    return nullptr;
 }
 
 /**
@@ -777,10 +781,13 @@ js::ResyncICUDefaultTimeZone()
                 // TODO: Handle invalid time zone identifiers (bug 342068).
             }
 #else
-            // Handle links (starting with ':') manually because ICU currently
-            // doesn't support the TZ filespec format.
+            // The TZ environment variable allows both absolute and
+            // relative paths, optionally beginning with a colon (':').
+            // (Relative paths, without the colon, are just Olson time
+            // zone names.)  We need to handle absolute paths ourselves,
+            // including handling that they might be symlinks.
             // <https://unicode-org.atlassian.net/browse/ICU-13694>
-            if (const char* tzlink = TZContainsPath(tz))
+            if (const char* tzlink = TZContainsAbsolutePath(tz))
                 tzid.setTo(ReadTimeZoneLink(tzlink));
 #endif /* defined(XP_WIN) */