Be explicit about setlocale() scope

We use the following locale-variables via locale-aware C functions
(to look them up, grep for "libc::$function_name"):

- LC_CTYPE:    wcwidth
- LC_MESSAGES: strerror, strerror 
- LC_NUMERIC:  localeconv/localeconv_l, snprintf (only in tests)
- LC_TIME:     strftime

Additionally, we interpret LC_MESSAGES in our own code.

As of today, the PCRE2 library does not seem to use LC_MESSAGES
(their error messages are English-only); and I don't think it uses
LC_CTYPE unless we use "pcre2_maketables()".

Let's make it more obvious which locale categories are actually used
by setting those instead of LC_ALL.

This means that instead of logging the return value of «
setlocale(LC_ALL, "") » (which is an opaque binary string on Linux),
we can log the actual per-category locales that are in effect.
This means that there's no longer really a reason to hardcode a log
for the LC_MESSAGES locale. We're not logging at early startup but
we will log if any locale var had been set at startup.

src/bin/fish.rs

@@ -408,7 +408,9 @@ fn throwing_main() -> i32 {
     threads::init();
 
     // Safety: single-threaded.
-    unsafe { set_libc_locales() };
+    unsafe {
+        set_libc_locales(/*log_ok=*/ false)
+    };
 
     fish::wutil::gettext::initialize_gettext();
 

src/builtins/fish_indent.rs

@@ -890,7 +890,9 @@ fn throwing_main() -> i32 {
     let mut streams = IoStreams::new(&mut out, &mut err, &io_chain);
     streams.stdin_fd = STDIN_FILENO;
     // Safety: single-threaded.
-    unsafe { set_libc_locales() };
+    unsafe {
+        set_libc_locales(/*log_ok=*/ false)
+    };
     crate::wutil::gettext::initialize_gettext();
     env_init(None, true, false);
 

src/env_dispatch.rs

@@ -17,10 +17,7 @@
 use crate::wchar::prelude::*;
 use crate::wutil::fish_wcstoi;
 use crate::{function, terminal};
-use std::borrow::Cow;
 use std::collections::HashMap;
-use std::ffi::{CStr, CString};
-use std::ptr;
 use std::sync::atomic::{AtomicBool, Ordering};
 
 /// List of all locale environment variable names that might trigger (re)initializing of the locale
@@ -502,16 +499,6 @@ pub fn read_terminfo_database(vars: &EnvStack) {
 fn init_locale(vars: &EnvStack) {
     let _guard = crate::locale::LOCALE_LOCK.lock().unwrap();
 
-    let old_msg_locale: CString = {
-        let old = unsafe { libc::setlocale(libc::LC_MESSAGES, ptr::null()) };
-        assert_ne!(old, ptr::null_mut());
-        // We have to make a copy because the subsequent setlocale() call to change the locale will
-        // invalidate the pointer from this setlocale() call.
-
-        // safety: `old` is not a null-pointer, and should be a reference to the currently set locale
-        unsafe { CStr::from_ptr(old.cast()) }.to_owned()
-    };
-
     for var_name in LOCALE_VARIABLES {
         let var = vars
             .getf_unless_empty(var_name, EnvMode::EXPORT)
@@ -525,40 +512,15 @@ fn init_locale(vars: &EnvStack) {
         }
     }
 
-    let user_locale = {
-        // Safety: we hold the locale lock.
-        let loc = unsafe { set_libc_locales() };
-        if loc.is_none() {
-            FLOG!(env_locale, "user has an invalid locale configured");
-        }
-        loc
-    };
+    // Safety: we hold the locale lock.
+    if !unsafe {
+        set_libc_locales(/*log_ok=*/ true)
+    } {
+        FLOG!(env_locale, "user has an invalid locale configured");
+    }
 
     // Update cached locale information.
     crate::common::fish_setlocale();
-    FLOG!(
-        env_locale,
-        "init_locale() setlocale():",
-        user_locale
-            .map(CStr::to_string_lossy)
-            .unwrap_or(Cow::Borrowed("(null)"))
-    );
-
-    let new_msg_loc_ptr = unsafe { libc::setlocale(libc::LC_MESSAGES, std::ptr::null()) };
-    // should never fail
-    assert_ne!(new_msg_loc_ptr, ptr::null_mut());
-    // safety: we just asserted it is not a null-pointer.
-    let new_msg_locale = unsafe { CStr::from_ptr(new_msg_loc_ptr) };
-    FLOG!(
-        env_locale,
-        "Old LC_MESSAGES locale:",
-        old_msg_locale.to_string_lossy()
-    );
-    FLOG!(
-        env_locale,
-        "New LC_MESSAGES locale:",
-        new_msg_locale.to_string_lossy()
-    );
 
     #[cfg(feature = "localize-messages")]
     crate::wutil::gettext::update_locale_from_env(vars);

src/locale.rs

@@ -8,10 +8,35 @@
 /// # Safety
 /// Call this either before starting any locale-using thread, or while holding a lock on the
 /// above mutex.
-pub unsafe fn set_libc_locales() -> Option<&'static CStr> {
-    let opaque_locale_str = setlocale(libc::LC_ALL, Some(c""));
-    setlocale(libc::LC_CTYPE, Some(c"C.UTF-8"));
-    opaque_locale_str
+pub unsafe fn set_libc_locales(log_ok: bool) -> bool {
+    let mut ok = true;
+    let mut set = |category_name, category, value| {
+        let locale_string = setlocale(category, Some(value));
+        if log_ok {
+            crate::flog::FLOG!(
+                env_locale,
+                match locale_string {
+                    Some(locale_string) => {
+                        format!("Set {category_name} to {}", locale_string.to_string_lossy())
+                    }
+                    None => {
+                        format!("Failed to set {category_name}",)
+                    }
+                },
+            );
+        }
+        ok &= locale_string.is_some();
+    };
+    let from_environment = c"";
+    // For wcwidth(3p)
+    set("LC_CTYPE", libc::LC_CTYPE, c"C.UTF-8");
+    // For strerror(3p) and strsignal(3p)
+    set("LC_MESSAGES", libc::LC_MESSAGES, from_environment);
+    // For builtin printf
+    set("LC_NUMERIC", libc::LC_NUMERIC, from_environment);
+    // For "history --show-time"
+    set("LC_TIME", libc::LC_TIME, from_environment);
+    ok
 }
 
 fn setlocale(category: libc::c_int, locale: Option<&CStr>) -> Option<&'static CStr> {

src/tests/prelude.rs

@@ -27,7 +27,9 @@ pub fn test_init() -> impl ScopeGuarding<Target = ()> {
         std::fs::create_dir_all(&test_dir).unwrap();
         set_current_dir(&test_dir).unwrap();
         // Safety: all tests that access locale should go through the enclosing function.
-        unsafe { set_libc_locales() };
+        unsafe {
+            set_libc_locales(/*log_ok=*/ false)
+        };
         topic_monitor_init();
         crate::threads::init();
         proc_init();