start: use nixGL if Hyprland is nix but not NixOS (#12845)

---------

Co-authored-by: Mihai Fufezan <mihai@fufexan.net>

start/src/helpers/Nix.cpp

@@ -0,0 +1,110 @@
+#include "Nix.hpp"
+
+#include "Logger.hpp"
+#include "../core/State.hpp"
+
+#include <filesystem>
+#include <algorithm>
+#include <hyprutils/string/VarList2.hpp>
+#include <hyprutils/string/String.hpp>
+#include <hyprutils/os/Process.hpp>
+#include <hyprutils/os/File.hpp>
+
+#include <glaze/glaze.hpp>
+
+using namespace Hyprutils::String;
+using namespace Hyprutils::OS;
+
+using namespace Hyprutils::File;
+
+static std::optional<std::string> getFromEtcOsRelease(const std::string_view& sv) {
+    static std::string content = "";
+    static bool        once    = true;
+
+    if (once) {
+        once = false;
+
+        auto read = readFileAsString("/etc/os-release");
+        content   = read.value_or("");
+    }
+
+    static CVarList2 vars(std::move(content), 0, '\n', true);
+
+    for (const auto& v : vars) {
+        if (v.starts_with(sv) && v.contains('=')) {
+            // found
+            auto value = trim(v.substr(v.find('=') + 1));
+
+            if (value.back() == value.front() && value.back() == '"')
+                value = value.substr(1, value.size() - 2);
+
+            return std::string{value};
+        }
+    }
+
+    return std::nullopt;
+}
+
+static bool executableExistsInPath(const std::string& exe) {
+    const char* PATHENV = std::getenv("PATH");
+    if (!PATHENV)
+        return false;
+
+    CVarList2       paths(PATHENV, 0, ':', true);
+    std::error_code ec;
+
+    for (const auto& PATH : paths) {
+        std::filesystem::path candidate = std::filesystem::path(PATH) / exe;
+        if (!std::filesystem::exists(candidate, ec) || ec)
+            continue;
+        if (!std::filesystem::is_regular_file(candidate, ec) || ec)
+            continue;
+        auto perms = std::filesystem::status(candidate, ec).permissions();
+        if (ec)
+            continue;
+        if ((perms & std::filesystem::perms::others_exec) != std::filesystem::perms::none)
+            return true;
+    }
+
+    return false;
+}
+
+std::expected<void, std::string> Nix::nixEnvironmentOk() {
+    if (!shouldUseNixGL())
+        return {};
+
+    if (!executableExistsInPath("nixGL"))
+        return std::unexpected(
+            "Hyprland was installed using Nix, but you're not on NixOS. This requires nixGL to be installed as well.\nYou can install nixGL by running \"nix profile install "
+            "github:guibou/nixGL --impure\" in your terminal.");
+
+    return {};
+}
+
+bool Nix::shouldUseNixGL() {
+    if (g_state->noNixGl)
+        return false;
+
+    // check if installed hyprland is nix'd
+    CProcess proc("Hyprland", {"--version-json"});
+    if (!proc.runSync()) {
+        g_logger->log(Hyprutils::CLI::LOG_ERR, "failed to obtain hyprland version string");
+        return false;
+    }
+
+    auto json = glz::read_json<glz::generic>(proc.stdOut());
+    if (!json) {
+        g_logger->log(Hyprutils::CLI::LOG_ERR, "failed to obtain hyprland version string (bad json)");
+        return false;
+    }
+
+    const auto FLAGS  = (*json)["flags"].get_array();
+    const bool IS_NIX = std::ranges::any_of(FLAGS, [](const auto& e) { return e.get_string() == std::string_view{"nix"}; });
+
+    if (IS_NIX) {
+        const auto NAME = getFromEtcOsRelease("NAME");
+        return !NAME || *NAME != "NixOS";
+    }
+
+    return false;
+}

start/src/helpers/Nix.hpp

@@ -0,0 +1,9 @@
+#pragma once
+
+#include <expected>
+#include <string>
+
+namespace Nix {
+    std::expected<void, std::string> nixEnvironmentOk();
+    bool                             shouldUseNixGL();
+};