reset timezone state when TZ env var changes

When the TZ env var is modified change fish's internal timezone state.

Fixes #3181.

src/env.cpp

@@ -13,6 +13,7 @@
 #endif
 #include <sys/stat.h>
 #include <sys/types.h>
+#include <time.h>
 #include <unistd.h>
 #include <wchar.h>
 #include <wctype.h>
@@ -159,6 +160,24 @@ static mode_t get_umask() {
     return res;
 }
 
+/// Check if the specified variable is a locale variable.
+static bool var_is_timezone(const wcstring &key) { return key == L"TZ"; }
+
+/// Properly sets all locale information.
+static void handle_timezone(const wchar_t *env_var_name) {
+    debug(2, L"handle_timezone() called in response to '%ls' changing", env_var_name);
+    const env_var_t val = env_get_string(env_var_name, ENV_EXPORT);
+    const std::string &value = wcs2string(val);
+    const std::string &name = wcs2string(env_var_name);
+    debug(2, L"timezone var %s='%s'", name.c_str(), value.c_str());
+    if (val.empty()) {
+        unsetenv(name.c_str());
+    } else {
+        setenv(name.c_str(), value.c_str(), 1);
+    }
+    tzset();
+}
+
 /// Check if the specified variable is a locale variable.
 static bool var_is_locale(const wcstring &key) {
     for (size_t i = 0; locale_variable[i]; i++) {
@@ -234,6 +253,8 @@ static void react_to_variable_change(const wcstring &key) {
         handle_locale(key.c_str());
     } else if (var_is_curses(key)) {
         handle_curses(key.c_str());
+    } else if (var_is_timezone(key)) {
+        handle_timezone(key.c_str());
     } else if (key == L"fish_term256" || key == L"fish_term24bit") {
         update_fish_color_support();
         reader_react_to_color_change();

src/fish_tests.cpp

@@ -3780,6 +3780,42 @@ static void test_string(void) {
     }
 }
 
+/// Helper for test_timezone_env_vars().
+long return_timezone_hour(time_t tstamp, const wchar_t *timezone) {
+    struct tm ltime;
+    char ltime_str[3];
+    char *str_ptr;
+    int n;
+
+    env_set(L"TZ", timezone, ENV_EXPORT);
+    localtime_r(&tstamp, &ltime);
+    n = strftime(ltime_str, 3, "%H", &ltime);
+    if (n != 2) {
+        err(L"strftime() returned %d, expected 2", n);
+        return 0;
+    }
+    return strtol(ltime_str, &str_ptr, 10);
+}
+
+/// Verify that setting special env vars have the expected effect on the current shell process.
+static void test_timezone_env_vars(void) {
+    // Confirm changing the timezone affects fish's idea of the local time.
+    time_t tstamp = time(NULL);
+
+    long first_tstamp = return_timezone_hour(tstamp, L"UTC-1");
+    long second_tstamp = return_timezone_hour(tstamp, L"UTC-2");
+    long delta = second_tstamp - first_tstamp;
+    if (delta != 1 && delta != -23) {
+        err(L"expected a one hour timezone delta got %ld", delta);
+    }
+}
+
+/// Verify that setting special env vars have the expected effect on the current shell process.
+static void test_env_vars(void) {
+    test_timezone_env_vars();
+    // TODO: Add tests for the locale and ncurses vars.
+}
+
 /// Main test.
 int main(int argc, char **argv) {
     // Look for the file tests/test.fish. We expect to run in a directory containing that file.
@@ -3869,6 +3905,7 @@ int main(int argc, char **argv) {
     if (should_test_function("history_races")) history_tests_t::test_history_races();
     if (should_test_function("history_formats")) history_tests_t::test_history_formats();
     if (should_test_function("string")) test_string();
+    if (should_test_function("env_vars")) test_env_vars();
     // history_tests_t::test_history_speed();
 
     say(L"Encountered %d errors in low-level tests", err_count);