Fix timezone extraction to work in all locales

Followup to #21585

Author: sbc100

.circleci/config.yml

@@ -918,7 +918,9 @@ jobs:
           python: "$EMSDK_PYTHON"
       - run-tests:
           title: "crossplatform tests"
-          test_targets: "--crossplatform-only"
+          # Skipping test_strftime_zZ_gb_locale since this test forces the
+          # locale to one that is not necessarily available on macOS.
+          test_targets: "--crossplatform-only skip:other.test_strftime_zZ_gb_locale"
       - upload-test-results
 
   test-mac-arm64:
@@ -940,7 +942,9 @@ jobs:
       # are currently missing arm64 macos binaries.
       - run-tests:
           title: "crossplatform tests"
-          test_targets: "--crossplatform-only"
+          # Skipping test_strftime_zZ_gb_locale since this test forces the
+          # locale to one that is not necessarily available on macOS.
+          test_targets: "--crossplatform-only skip:other.test_strftime_zZ_gb_locale"
       - upload-test-results
 
 workflows:

src/library.js

@@ -649,10 +649,12 @@ addToLibrary({
 
     {{{ makeSetValue('daylight', '0', 'Number(winterOffset != summerOffset)', 'i32') }}};
 
-    var extractZone = (date) => date.toLocaleTimeString(undefined, {timeZoneName:'short'}).split(' ')[2];
+    var extractZone = (date) => date.toLocaleTimeString(undefined, {hour12:false, timeZoneName:'short'}).split(' ')[1];
     var winterName = extractZone(winter);
     var summerName = extractZone(summer);
 #if ASSERTIONS
+    assert(winterName);
+    assert(summerName);
     assert(lengthBytesUTF8(winterName) <= {{{ cDefs.TZNAME_MAX }}}, `timezone name truncated to fit in TZNAME_MAX (${winterName})`);
     assert(lengthBytesUTF8(summerName) <= {{{ cDefs.TZNAME_MAX }}}, `timezone name truncated to fit in TZNAME_MAX (${summerName})`);
 #endif

test/common.py

@@ -365,6 +365,25 @@ def modified(self, *args, **kwargs):
   return decorated
 
 
+# Decorator version of env_modify
+def also_with_env_modify(name, updates):
+
+  def decorated(f):
+    @wraps(f)
+    def metafunc(self, modified, *args, **kwargs):
+      if modified:
+        with env_modify(updates):
+          return f(self, *args, **kwargs)
+      else:
+        return f(self, *args, **kwargs)
+
+    metafunc._parameterize = {'': (False,),
+                              name: (True,)}
+    return metafunc
+
+  return decorated
+
+
 def also_with_minimal_runtime(f):
   assert callable(f)
 

test/test_other.py

@@ -34,7 +34,8 @@
 from common import env_modify, no_mac, no_windows, only_windows, requires_native_clang, with_env_modify
 from common import create_file, parameterized, NON_ZERO, node_pthreads, TEST_ROOT, test_file
 from common import compiler_for, EMBUILDER, requires_v8, requires_node, requires_wasm64, requires_node_canary
-from common import requires_wasm_eh, crossplatform, with_both_eh_sjlj, with_both_sjlj, also_with_standalone_wasm
+from common import requires_wasm_eh, crossplatform, with_both_eh_sjlj, with_both_sjlj
+from common import also_with_standalone_wasm, also_with_env_modify
 from common import also_with_minimal_runtime, also_with_wasm_bigint, also_with_wasm64, flaky
 from common import EMTEST_BUILD_VERBOSE, PYTHON, WEBIDL_BINDER
 from common import requires_network
@@ -5717,6 +5718,8 @@ def test_only_force_stdlibs_2(self):
       self.run_process([EMXX, 'src.cpp', '-sDISABLE_EXCEPTION_CATCHING=0'])
     self.assertContained('Caught exception: std::exception', self.run_js('a.out.js'))
 
+  @crossplatform
+  @also_with_env_modify('gb_locale', {'LC_ALL': 'en_GB'})
   def test_strftime_zZ(self):
     create_file('src.c', r'''
 #include <errno.h>