Add check before executing nix commands

Author: ofalvai

toolprovider/mise/install.go

@@ -26,35 +26,29 @@ func installRequest(toolRequest provider.ToolRequest, useNix bool) provider.Tool
 }
 
 func canBeInstalledWithNix(tool provider.ToolRequest, execEnv execenv.ExecEnv) bool {
+	// Force switch for integration testing. No fallback to regular install when this is active. This makes failures explicit.
+	forceNix := os.Getenv("BITRISE_TOOLSETUP_FAST_INSTALL_FORCE") == "1"
+	if forceNix {
+		return true
+	}
+
 	if !nixpkgs.ShouldUseBackend(tool) {
 		return false
 	}
 
-	// Force switch for integration testing. No fallback to regular install when this is active. This makes failures explicit.
-	forceNix := os.Getenv("BITRISE_TOOLSETUP_FAST_INSTALL_FORCE") == "1"
-
 	_, err := execEnv.RunMisePlugin("install", nixpkgs.PluginName, nixpkgs.PluginGitURL)
 	if err != nil {
-		if forceNix {
-			return true
-		}
 		log.Warnf("Error while installing nixpkgs plugin (%s). Falling back to core plugin installation.", nixpkgs.PluginGitURL, err)
 		return false
 	}
 
 	nameWithBackend := provider.ToolID(fmt.Sprintf("nixpkgs:%s", tool.ToolName))
 	available, err := versionExists(execEnv, nameWithBackend, tool.UnparsedVersion)
 	if err != nil {
-		if forceNix {
-			return true
-		}
 		log.Warnf("Error while checking nixpkgs index for %s@%s: %v. Falling back to core plugin installation.", tool.ToolName, tool.UnparsedVersion, err)
 		return false
 	}
 	if !available {
-		if forceNix {
-			return true
-		}
 		log.Warnf("%s@%s not found in nixpkgs index, doing a source build. This may take some time...", tool.ToolName, tool.UnparsedVersion)
 		return false
 	}

toolprovider/mise/nixpkgs/nixpkgs.go

@@ -2,6 +2,7 @@ package nixpkgs
 
 import (
 	"os"
+	"os/exec"
 	"strings"
 
 	"github.com/bitrise-io/bitrise/v2/log"
@@ -13,19 +14,39 @@ const (
 	PluginName   = "nixpkgs"
 )
 
-// TODO: check if Nix works at all
-
 func ShouldUseBackend(request provider.ToolRequest) bool {
 	if request.ToolName != "ruby" {
 		log.Debugf("[TOOLPROVIDER] The mise-nixpkgs backend is only enabled for Ruby for now. Using core plugin to install %s", request.ToolName)
 		return false
 	}
 
 	value, ok := os.LookupEnv("BITRISE_TOOLSETUP_FAST_INSTALL")
-	if ok && strings.TrimSpace(value) == "1" {
-		log.Debugf("[TOOLPROVIDER] Using nixpkgs backend for %s as BITRISE_TOOLSETUP_FAST_INSTALL is set", request.ToolName)
-		return true
+	if !ok || strings.TrimSpace(value) != "1" {
+		log.Debugf("[TOOLPROVIDER] Using core mise plugin for %s", request.ToolName)
+		return false
+	}
+
+	if !isNixAvailable() {
+		log.Debugf("[TOOLPROVIDER] Nix is not available on the system, cannot use nixpkgs backend for %s", request.ToolName)
+		return false
+	}
+
+	log.Debugf("[TOOLPROVIDER] Using nixpkgs backend for %s as BITRISE_TOOLSETUP_FAST_INSTALL is set", request.ToolName)
+	return true
+}
+
+func isNixAvailable() bool {
+	_, err := exec.LookPath("nix")
+	if err != nil {
+		return false
 	}
-	log.Debugf("[TOOLPROVIDER] Using core plugin for %s", request.ToolName)
-	return false
+
+	cmd := exec.Command("nix", "--version")
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		log.Debugf("[TOOLPROVIDER] Exec nix --version: %s, output:\n%s", err, out)
+		return false
+	}
+
+	return true
 }