feat: protect --impure behind feature flag

Author: imfede

internal/boxcli/featureflag/impure_print_dev_env.go

@@ -0,0 +1,12 @@
+// Copyright 2024 Jetify Inc. and contributors. All rights reserved.
+// Use of this source code is governed by the license in the LICENSE file.
+
+package featureflag
+
+// ImpurePrintDevEnv controls whether the `devbox print-dev-env` command
+// will be called with the `--impure` flag.
+// Using the `--impure` flag will have two consequences:
+//  1. All environment variables will be passed to nix, this will enable
+//     the usage of flakes that rely on environment variables.
+//  2. It will disable nix caching, making the command slower.
+var ImpurePrintDevEnv = disable("IMPURE_PRINT_DEV_ENV")

internal/nix/nix.go

@@ -20,6 +20,7 @@ import (
 	"time"
 
 	"github.com/pkg/errors"
+	"go.jetpack.io/devbox/internal/boxcli/featureflag"
 	"go.jetpack.io/devbox/internal/boxcli/usererr"
 	"go.jetpack.io/devbox/internal/redact"
 	"golang.org/x/mod/semver"
@@ -74,7 +75,11 @@ func (*Nix) PrintDevEnv(ctx context.Context, args *PrintDevEnvArgs) (*PrintDevEn
 	}
 
 	if len(data) == 0 {
-		cmd := command("print-dev-env", "--json", "--impure",
+		optionalImpureFlag := ""
+		if featureflag.ImpurePrintDevEnv.Enabled() {
+			optionalImpureFlag = "--impure"
+		}
+		cmd := command("print-dev-env", "--json", optionalImpureFlag,
 			"path:"+flakeDirResolved,
 		)
 		slog.Debug("running print-dev-env cmd", "cmd", cmd)