From 0849aa8f2099e92018be9a14ca23037daa1f16eb Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Tue, 11 Jul 2023 11:50:12 -0700
Subject: [PATCH] validate locale prior to setting, fallback to en_US.UTF-8

Fixes #201

I don't fully understand locales, but it appears that the locale
returned from NSLocale can be "valid" in general but invalid according
to libc's locale API. If you attempt to `setlocale` with this bad
locale, it defaults everything to "C", which ends up breaking a lot of
things.

This commit validates the locale, and if it is invalid, we default to
"en_US.UTF-8" so things tend to work. This behavior can be overridden
using standard environment variables (LANG, LC_ALL, etc.).

This also doesn't touch env vars so further subprocesses from the shell
see original locale env vars.
---
 src/os/locale.zig | 33 ++++++++++++++++++++++++++++++---
 1 file changed, 30 insertions(+), 3 deletions(-)

diff --git a/src/os/locale.zig b/src/os/locale.zig
index 21de12387..ebc347b7c 100644
--- a/src/os/locale.zig
+++ b/src/os/locale.zig
@@ -25,12 +25,35 @@ pub fn ensureLocale() void {
         }
     }
 
+    // If we have a locale set in the env, we verify it is valid. If it isn't
+    // valid, then we set it to a default value of en_US.UTF-8. We don't touch
+    // the existing LANG value in the env so that child processes can use it,
+    // though.
+    const locale: []const u8 = locale: {
+        // If we don't have lang set, we use "" and let the default happen.
+        const lang = std.os.getenv("LANG") orelse break :locale "";
+
+        // If the locale is valid, we also use "" because LANG is already set.
+        if (localeIsValid(lang)) break :locale "";
+
+        log.info("LANG is not valid according to libc, will use en_US.UTF-8", .{});
+        break :locale "en_US.UTF-8";
+    };
+
     // Set the locale
-    if (setlocale(LC_ALL, "")) |locale| {
-        log.debug("setlocale result={s}", .{locale});
+    if (setlocale(LC_ALL, locale.ptr)) |v| {
+        log.debug("setlocale result={s}", .{v});
     } else log.warn("setlocale failed, locale may be incorrect", .{});
 }
 
+/// Returns true if the given locale is valid according to libc. This value
+/// can be `en_US` or `en_US.utf-8` style of formatting.
+fn localeIsValid(locale: []const u8) bool {
+    const v = newlocale(LC_ALL_MASK, locale.ptr, null) orelse return false;
+    defer freelocale(v);
+    return true;
+}
+
 /// This sets the LANG environment variable based on the macOS system
 /// preferences selected locale settings.
 fn setLangFromCocoa() void {
@@ -87,5 +110,9 @@ fn setLangFromCocoa() void {
 }
 
 const LC_ALL: c_int = 6; // from locale.h
-extern "c" fn setlocale(category: c_int, locale: ?[*]const u8) ?[*:0]u8;
+const LC_ALL_MASK: c_int = 0x7fffffff; // from locale.h
+const locale_t = ?*anyopaque;
 extern "c" fn setenv(name: ?[*]const u8, value: ?[*]const u8, overwrite: c_int) c_int;
+extern "c" fn setlocale(category: c_int, locale: ?[*]const u8) ?[*:0]u8;
+extern "c" fn newlocale(category: c_int, locale: ?[*]const u8, base: locale_t) locale_t;
+extern "c" fn freelocale(v: locale_t) void;