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

---------

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

5 files changed, 147 insertions, 2 deletions

diff --git a/start/src/core/Instance.cpp b/start/src/core/Instance.cpp
index ec56cc75..2f5007bd 100644
--- a/start/src/core/Instance.cpp
+++ b/start/src/core/Instance.cpp
@@ -1,6 +1,7 @@
 #include "Instance.hpp"
 #include "State.hpp"
 #include "../helpers/Logger.hpp"
+#include "../helpers/Nix.hpp"
 
 #include <cstdlib>
 #include <cstring>
@@ -54,7 +55,12 @@ void CHyprlandInstance::runHyprlandThread(bool safeMode) {
         procctl(P_PID, getpid(), PROC_PDEATHSIG_CTL, &sig);
 #endif
 
-        execvp(g_state->customPath.value_or("Hyprland").c_str(), args.data());
+        if (Nix::shouldUseNixGL()) {
+            argsStd.insert(argsStd.begin(), g_state->customPath.value_or("Hyprland"));
+            args.insert(args.begin(), strdup(argsStd.front().c_str()));
+            execvp("nixGL", args.data());
+        } else
+            execvp(g_state->customPath.value_or("Hyprland").c_str(), args.data());
 
         g_logger->log(Hyprutils::CLI::LOG_ERR, "fork(): execvp failed: {}", strerror(errno));
         std::fflush(stdout);
diff --git a/start/src/core/State.hpp b/start/src/core/State.hpp
index 6cf73a96..d00a1757 100644
--- a/start/src/core/State.hpp
+++ b/start/src/core/State.hpp
@@ -8,6 +8,7 @@
 struct SState {
     std::span<const char*>     rawArgvNoBinPath;
     std::optional<std::string> customPath;
+    bool                       noNixGl = false;
 };
 
 inline UP<SState> g_state = makeUnique<SState>();
\ No newline at end of file
diff --git a/start/src/helpers/Nix.cpp b/start/src/helpers/Nix.cpp
new file mode 100644
index 00000000..07cd2a4a
--- /dev/null
+++ b/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;
+}
diff --git a/start/src/helpers/Nix.hpp b/start/src/helpers/Nix.hpp
new file mode 100644
index 00000000..edc01b19
--- /dev/null
+++ b/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();
+};
\ No newline at end of file
diff --git a/start/src/main.cpp b/start/src/main.cpp
index 74de393c..e73fcfa5 100644
--- a/start/src/main.cpp
+++ b/start/src/main.cpp
@@ -3,6 +3,7 @@
 #include <print>
 
 #include "helpers/Logger.hpp"
+#include "helpers/Nix.hpp"
 #include "core/State.hpp"
 #include "core/Instance.hpp"
 
@@ -16,7 +17,12 @@ using namespace Hyprutils::CLI;
     }
 
 constexpr const char* HELP_INFO = R"#(start-hyprland - A binary to properly start Hyprland via a watchdog process.
-Any arguments after -- are passed to Hyprland. For Hyprland help, run start-hyprland -- --help or Hyprland --help)#";
+Any arguments after -- are passed to Hyprland. For Hyprland help, run start-hyprland -- --help or Hyprland --help
+
+Additional arguments for start-hyprland:
+ --path [path]       -> Override Hyprland path
+ --no-nixgl          -> Force disable nixGL
+)#";
 
 //
 static void onSignal(int sig) {
@@ -69,6 +75,10 @@ int main(int argc, const char** argv, const char** envp) {
             g_state->customPath = argv[++i];
             continue;
         }
+        if (arg == "--no-nixgl") {
+            g_state->noNixGl = true;
+            continue;
+        }
     }
 
     if (startArgv != -1)
@@ -77,6 +87,15 @@ int main(int argc, const char** argv, const char** envp) {
     if (!g_state->rawArgvNoBinPath.empty())
         g_logger->log(Hyprutils::CLI::LOG_WARN, "Arguments after -- are passed to Hyprland");
 
+    // check if our environment is OK
+    if (const auto RET = Nix::nixEnvironmentOk(); !RET) {
+        g_logger->log(Hyprutils::CLI::LOG_ERR, "Nix environment check failed:\n{}", RET.error());
+        return 1;
+    }
+
+    if (Nix::shouldUseNixGL())
+        g_logger->log(Hyprutils::CLI::LOG_DEBUG, "Hyprland was compiled with Nix - will use nixGL");
+
     bool safeMode = false;
     while (true) {
         g_instance     = makeUnique<CHyprlandInstance>();