lib: set locale per cli or env

Author: Uzlopak

doc/api/cli.md

@@ -1138,6 +1138,19 @@ surface on other platforms, but the performance impact may be severe.
 This flag is inherited from V8 and is subject to change upstream. It may
 disappear in a non-semver-major release.
 
+### `--locale`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+Set the default locale used by ICU (`Intl` object). It expects a string
+representing the language version as defined in [RFC 5646][] (also known as
+BCP 47). (Overrides `LOCALE`.)
+
+Examples of valid language codes include "en", "en-US", "fr", "fr-FR", "es-ES",
+etc.
+
 ### `--max-http-header-size=size`
 
 <!-- YAML
@@ -2197,6 +2210,15 @@ and `NODE_DISABLE_COLORS` environment variables are ignored.
 
 Any other value will result in colorized output being disabled.
 
+### `LOCALE=value`
+
+The `LOCALE` environment variable is used to set the default locale used by
+ICU (`Intl` object). It expects a string representing the language version as
+defined in [RFC 5646][] (also known as BCP 47).
+
+Examples of valid language codes include "en", "en-US", "fr", "fr-FR", "es-ES",
+etc.
+
 ### `NO_COLOR=<any>`
 
 [`NO_COLOR`][]  is an alias for `NODE_DISABLE_COLORS`. The value of the

src/node.cc

@@ -949,6 +949,15 @@ static ExitCode InitializeNodeWithArgsInternal(
   }
 # endif
 
+  std::string locale;
+  if (credentials::SafeGetenv("LOCALE", &locale) && !locale.empty()) {
+    i18n::SetDefaultLocale(locale.c_str());
+  }
+
+  if (!per_process::cli_options->locale.empty()) {
+    i18n::SetDefaultLocale(per_process::cli_options->locale.c_str());
+  }
+
 #endif  // defined(NODE_HAVE_I18N_SUPPORT)
 
   // We should set node_is_initialized here instead of in node::Start,

src/node_env_var.cc

@@ -100,6 +100,28 @@ void DateTimeConfigurationChangeNotification(
   }
 }
 
+template <typename T>
+void LocaleConfigurationChangeNotification(
+    Isolate* isolate,
+    const T& key,
+    const char* val = nullptr) {
+  if (
+    key.length() == 6 &&
+    key[0] == 'L' &&
+    key[1] == 'O' &&
+    key[2] == 'C' &&
+    key[3] == 'A' &&
+    key[4] == 'L' &&
+    key[5] == 'E'
+  ) {
+
+# if defined(NODE_HAVE_I18N_SUPPORT)
+    i18n::SetDefaultLocale(val);
+# endif
+    isolate->LocaleConfigurationChangeNotification();
+  }
+}
+
 Maybe<std::string> RealEnvStore::Get(const char* key) const {
   Mutex::ScopedLock lock(per_process::env_var_mutex);
 
@@ -148,6 +170,7 @@ void RealEnvStore::Set(Isolate* isolate,
 #endif
   uv_os_setenv(*key, *val);
   DateTimeConfigurationChangeNotification(isolate, key, *val);
+  LocaleConfigurationChangeNotification(isolate, key, *val);
 }
 
 int32_t RealEnvStore::Query(const char* key) const {
@@ -182,6 +205,7 @@ void RealEnvStore::Delete(Isolate* isolate, Local<String> property) {
 
   node::Utf8Value key(isolate, property);
   uv_os_unsetenv(*key);
+  LocaleConfigurationChangeNotification(isolate, key);
   DateTimeConfigurationChangeNotification(isolate, key);
 }
 

src/node_i18n.cc

@@ -61,6 +61,7 @@
 #include <unicode/ucnv.h>
 #include <unicode/udata.h>
 #include <unicode/uidna.h>
+#include <unicode/uloc.h>
 #include <unicode/ulocdata.h>
 #include <unicode/urename.h>
 #include <unicode/ustring.h>
@@ -601,6 +602,22 @@ void SetDefaultTimeZone(const char* tzid) {
   CHECK(U_SUCCESS(status));
 }
 
+void SetDefaultLocale(const char* localeid) {
+  UErrorCode status = U_ZERO_ERROR;
+
+  if (localeid != nullptr) {
+    size_t localelen = strlen(localeid) + 1;
+    MaybeStackBuffer<UChar, 256> id(localelen);
+    u_charsToUChars(localeid, id.out(), localelen);
+    // This is threadsafe:
+    uloc_setDefault(localeid, &status);
+    CHECK(U_SUCCESS(status));
+  } else {
+    uloc_setDefault(localeid, &status);
+    CHECK(U_SUCCESS(status));
+  }
+}
+
 int32_t ToUnicode(MaybeStackBuffer<char>* buf,
                   const char* input,
                   size_t length) {

src/node_i18n.h

@@ -42,6 +42,8 @@ bool InitializeICUDirectory(const std::string& path, std::string* error);
 
 void SetDefaultTimeZone(const char* tzid);
 
+void SetDefaultLocale(const char* localid);
+
 enum class idna_mode {
   // Default mode for maximum compatibility.
   kDefault,

src/node_options.cc

@@ -934,6 +934,11 @@ PerProcessOptionsParser::PerProcessOptionsParser(
             ,
             &PerProcessOptions::icu_data_dir,
             kAllowedInEnvvar);
+
+  AddOption("--locale",
+            "Set the locale of the node instance",
+            &PerProcessOptions::locale,
+            kAllowedInEnvvar);
 #endif
 
 #if HAVE_OPENSSL

src/node_options.h

@@ -271,6 +271,7 @@ class PerProcessOptions : public Options {
 
 #ifdef NODE_HAVE_I18N_SUPPORT
   std::string icu_data_dir;
+  std::string locale;
 #endif
 
   // Per-process because they affect singleton OpenSSL shared library state,

test/parallel/test-process-env-locale.js

@@ -0,0 +1,21 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+
+if (!common.hasIntl)
+  common.skip('Intl not present.');
+
+if (!common.isMainThread)
+  common.skip('process.env.LOCALE is not intercepted in Workers');
+
+process.env.LOCALE = 'de-DE-custom';
+assert.strictEqual(
+  new Intl.NumberFormat().resolvedOptions().locale,
+  'de-DE-custom',
+);
+
+delete process.env.LOCALE;
+assert.notStrictEqual(
+  new Intl.NumberFormat().resolvedOptions().locale,
+  'de-DE-custom',
+);