Work around Boost.Process invalid locale bug/crash

This should not be causing any issues, but it seems like some people
skip the locale setup step in the Arch installation guide and then end
up with a distro without any locales, with invalid locales, or with a
non-generated locale. glibc and libstd++ fall back to the C locale when
this happens, but Boost.Process triggers one of the edge cases where
this doesn't happen. https://github.com/boostorg/process/pull/179 fixes
this in Boost.Process, but it will be a while until this is in every
distro's copy of Boost.

https://svn.boost.org/trac10/changeset/72855

CHANGELOG.md

@@ -43,6 +43,10 @@ Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Fixed
 
+- Worked around a [bug](https://svn.boost.org/trac10/changeset/72855) in
+  Boost.Process that would cause yabridge to crash with
+  `locale::facet::_S_create_c_locale name not valid` when (part of) the current
+  locale is invalid.
 - Fixed _New Sonic Arts' Vice_ plugin freezing when loading the plugin. This
   happened because the plugin tried to spawn new threads and perform drawing
   calls when changing the sample rate or block size from the audio thread. We're

src/plugin/utils.cpp

@@ -16,6 +16,8 @@
 
 #include "utils.h"
 
+#include <iostream>
+
 #include <unistd.h>
 #include <boost/dll/runtime_symbol_info.hpp>
 #include <boost/process/io.hpp>
@@ -369,6 +371,31 @@ boost::filesystem::path generate_group_endpoint(
 }
 
 std::vector<boost::filesystem::path> get_augmented_search_path() {
+    // HACK: `std::locale("")` would return the current locale, but this
+    //       overload is implementation specific, and libstdc++ returns an error
+    //       when this happens and one of the locale variables (or `LANG`) is
+    //       set to a locale that doesn't exist. Because of that, you should use
+    //       the default constructor instead which does fall back gracefully
+    //       when using an invalid locale. Boost.Process sadly doesn't seem to
+    //       do this, so some intervention is required. We can remove this once
+    //       the PR linked below is merged into Boost proper and included in
+    //       most distro's copy of Boost (which will probably take a while):
+    //
+    //       https://svn.boost.org/trac10/changeset/72855
+    //
+    //       https://github.com/boostorg/process/pull/179
+    try {
+        std::locale("");
+    } catch (const std::runtime_error&) {
+        // We normally avoid modifying the current process' environment and
+        // instead use `boost::process::environment` to only modify the
+        // environment of launched child processes, but in this case we do need
+        // to fix this
+        // TODO: We don't have access to the logger here, so we can't inform the
+        //       user that their locale is broken when this happens
+        setenv("LC_ALL", "C", true);  // NOLINT(concurrency-mt-unsafe)
+    }
+
     std::vector<boost::filesystem::path> search_path =
         boost::this_process::path();