Add --option CLI flag for overriding configuration options.

It requires to specify the infered Nix type:

--option languages.redis.enable:bool true

This is usefor for temporary changing the configuration, like testing a
matrix of options.

Author: domenkozar

devenv/src/cli.rs

@@ -144,6 +144,15 @@ pub struct GlobalOptions {
         help = "Override inputs in devenv.yaml."
     )]
     pub override_input: Vec<String>,
+
+    #[arg(
+        long,
+        global = true,
+        num_args = 2,
+        value_delimiter = ' ',
+        help = "Override configuration options with typed values, e.g. --option languages.rust.version:string beta"
+    )]
+    pub option: Vec<String>,
 }
 
 impl Default for GlobalOptions {
@@ -165,6 +174,7 @@ impl Default for GlobalOptions {
             nix_debugger: false,
             nix_option: vec![],
             override_input: vec![],
+            option: vec![],
         }
     }
 }

devenv/src/devenv.rs

@@ -886,6 +886,52 @@ impl Devenv {
         fs::create_dir_all(&self.devenv_runtime)
             .unwrap_or_else(|_| panic!("Failed to create {}", self.devenv_runtime.display()));
 
+        // Create cli-options.nix if there are CLI options
+        if !self.global_options.option.is_empty() {
+            let mut cli_options = String::from("{\n");
+
+            const SUPPORTED_TYPES: &[&str] = &["string", "int", "float", "bool", "path"];
+
+            for chunk in self.global_options.option.chunks_exact(2) {
+                // Parse the path and type from the first value
+                let key_parts: Vec<&str> = chunk[0].split(':').collect();
+                if key_parts.len() < 2 {
+                    panic!("Invalid option format: '{}'. Must include type, e.g. 'languages.rust.version:string'. Supported types: {}", 
+                           chunk[0], SUPPORTED_TYPES.join(", "));
+                }
+
+                let path = key_parts[0];
+                let type_name = key_parts[1];
+
+                // Format value based on type
+                let value = match type_name {
+                    "string" => format!("\"{}\"", &chunk[1]),
+                    "int" => chunk[1].clone(),
+                    "float" => chunk[1].clone(),
+                    "bool" => chunk[1].clone(), // true/false will work directly in Nix
+                    "path" => format!("./{}", &chunk[1]), // relative path
+                    _ => panic!(
+                        "Unsupported type: '{}'. Supported types: {}",
+                        type_name,
+                        SUPPORTED_TYPES.join(", ")
+                    ),
+                };
+
+                cli_options.push_str(&format!("  {} = {};\n", path, value));
+            }
+
+            cli_options.push_str("}\n");
+
+            fs::write(self.devenv_dotfile.join("cli-options.nix"), cli_options)
+                .expect("Failed to write cli-options.nix");
+        } else {
+            // Remove the file if it exists but there are no CLI options
+            let cli_options_path = self.devenv_dotfile.join("cli-options.nix");
+            if cli_options_path.exists() {
+                fs::remove_file(&cli_options_path).expect("Failed to remove cli-options.nix");
+            }
+        }
+
         // create flake.devenv.nix
         let vars = indoc::formatdoc!(
             "version = \"{}\";

devenv/src/flake.tmpl.nix

@@ -91,6 +91,7 @@
               ./devenv.nix
               (devenv.devenv or { })
               (if builtins.pathExists ./devenv.local.nix then ./devenv.local.nix else { })
+              (if builtins.pathExists (devenv_dotfile + "/cli-options.nix") then import (devenv_dotfile + "/cli-options.nix") else { })
             ];
           };
           config = project.config;

tests/cli-options/.test.sh

@@ -0,0 +1,53 @@
+#!/usr/bin/env bash
+set -eu -o pipefail
+
+# Test CLI options feature
+cd "$(dirname "$0")"
+
+# Test basic string and bool types
+OUTPUT=$(devenv --option languages.rust.version:string beta --option services.redis.enable:bool true info)
+
+# Check for expected RUST_VERSION
+echo "$OUTPUT" | grep -E "RUST_VERSION:.*beta" || {
+  echo "ERROR: Expected CLI option override for RUST_VERSION to be 'beta'"
+  exit 1
+}
+
+# Check for expected REDIS_ENABLED
+echo "$OUTPUT" | grep -E "REDIS_ENABLED:.*true" || {
+  echo "ERROR: Expected CLI option override for REDIS_ENABLED to be 'true'"
+  exit 1
+}
+
+# Test int type 
+OUTPUT=$(devenv --option env.TEST_INT:int 42 info)
+echo "$OUTPUT" | grep -E "TEST_INT:.*42" || {
+  echo "ERROR: Expected CLI option override for TEST_INT to be '42'"
+  exit 1
+}
+
+# Test float type
+OUTPUT=$(devenv --option env.TEST_FLOAT:float 3.14 info)
+echo "$OUTPUT" | grep -E "TEST_FLOAT:.*3.14" || {
+  echo "ERROR: Expected CLI option override for TEST_FLOAT to be '3.14'"
+  exit 1
+}
+
+# Test path type
+OUTPUT=$(devenv --option env.TEST_PATH:path somepath info)
+echo "$OUTPUT" | grep -E "TEST_PATH:.*/somepath" || {
+  echo "ERROR: Expected CLI option override for TEST_PATH to include 'somepath'"
+  exit 1
+}
+
+# Test invalid type (should fail)
+if devenv --option languages.rust.version:invalid value info &> /dev/null; then
+  echo "ERROR: Expected CLI option with invalid type to fail"
+  exit 1
+fi
+
+# Test missing type (should fail)
+if devenv --option languages.rust.version value info &> /dev/null; then
+  echo "ERROR: Expected CLI option without type specification to fail"
+  exit 1
+fi

tests/cli-options/devenv.nix

@@ -0,0 +1,22 @@
+{ pkgs, lib, config, ... }:
+
+{
+  # Default language - will be overridden by CLI option
+  languages.rust.enable = lib.mkDefault true;
+  languages.rust.version = "stable";
+
+  # Default services - will be overridden by CLI option
+  services.redis.enable = lib.mkDefault false;
+
+  # Environment variables to expose configuration values
+  env = {
+    # Base config from the original test
+    RUST_VERSION = config.languages.rust.version;
+    REDIS_ENABLED = builtins.toString config.services.redis.enable;
+
+    # For testing different value types
+    TEST_INT = lib.mkDefault "0";
+    TEST_FLOAT = lib.mkDefault "0.0";
+    TEST_PATH = lib.mkDefault "";
+  };
+}

tests/cli-options/devenv.yaml

@@ -0,0 +1,6 @@
+inputs:
+  fenix:
+    url: github:nix-community/fenix
+    inputs:
+      nixpkgs:
+        follows: nixpkgs