config: prompt user for flakes

src/action/base/create_group.rs

@@ -37,7 +37,7 @@ impl CreateGroup {
             },
         }
 
-        // Ensure group does not exists
+        // Ensure group does not exist
         if let Some(group) = Group::from_name(name.as_str())
             .map_err(|e| ActionErrorKind::GettingGroupId(name.clone(), e))
             .map_err(Self::error)?

src/action/base/create_or_merge_nix_config.rs

@@ -17,7 +17,7 @@ use crate::action::{
 
 /// The `nix.conf` configuration names that are safe to merge.
 // FIXME(@cole-h): make configurable by downstream users?
-const MERGEABLE_CONF_NAMES: &[&str] = &["experimental-features"];
+const MERGEABLE_CONF_NAMES: &[&str] = &["experimental-features", "substituters", "trusted-public-keys"];
 const NIX_CONF_MODE: u32 = 0o664;
 const NIX_CONF_COMMENT_CHAR: char = '#';
 

src/action/common/configure_nix.rs

@@ -46,6 +46,7 @@ impl ConfigureNix {
             settings.proxy.clone(),
             settings.ssl_cert_file.clone(),
             settings.extra_conf.clone(),
+            settings.enable_flakes,
             settings.force,
         )
         .await

src/action/common/place_nix_configuration.rs

@@ -30,6 +30,7 @@ impl PlaceNixConfiguration {
         proxy: Option<Url>,
         ssl_cert_file: Option<PathBuf>,
         extra_conf: Vec<UrlOrPathOrString>,
+        enable_flakes: bool,
         force: bool,
     ) -> Result<StatefulAction<Self>, ActionError> {
         let mut extra_conf_text = vec![];
@@ -91,7 +92,13 @@ impl PlaceNixConfiguration {
         let settings = nix_config.settings_mut();
 
         settings.insert("build-users-group".to_string(), nix_build_group_name);
-        let experimental_features = ["nix-command", "flakes", "repl-flake"];
+        let mut experimental_features = vec!["nix-command"];
+
+        // Enable flakes if desired.
+        if enable_flakes {
+            experimental_features.push("flakes");
+        }
+
         match settings.entry("experimental-features".to_string()) {
             Entry::Occupied(mut slot) => {
                 let slot_mut = slot.get_mut();
@@ -125,10 +132,24 @@ impl PlaceNixConfiguration {
                 ssl_cert_file_canonical.display().to_string(),
             );
         }
+
+        // Set up our substituters.
         settings.insert(
-            "extra-nix-path".to_string(),
-            "nixpkgs=flake:nixpkgs".to_string(),
+            "substituters".to_string(),
+            "https://cache.nixos.org https://cache.lix.systems".to_string(),
         );
+        settings.insert(
+            "trusted-public-keys".to_string(),
+            "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY= cache.lix.systems:aBnZUw8zA7H35Cz2RyKFVs3H4PlGTLawyY5KRbvJR8o=".to_string()
+        );
+
+        if enable_flakes {
+            settings.insert(
+                "extra-nix-path".to_string(),
+                "nixpkgs=flake:nixpkgs".to_string(),
+            );
+        }
+
         let create_directory = CreateDirectory::plan(NIX_CONF_FOLDER, None, None, 0o0755, force)
             .await
             .map_err(Self::error)?;

src/cli/interaction.rs

@@ -16,6 +16,7 @@ pub enum PromptChoice {
 // The below method was adopted from Rustup at https://github.com/rust-lang/rustup/blob/3331f34c01474bf216c99a1b1706725708833de1/src/cli/term2.rs#L37
 pub(crate) async fn prompt(
     question: impl AsRef<str>,
+    prompt_text: impl AsRef<str>,
     default: PromptChoice,
     currently_explaining: bool,
 ) -> eyre::Result<PromptChoice> {
@@ -29,7 +30,7 @@ pub(crate) async fn prompt(
         {are_you_sure} ({yes}/{no}{maybe_explain}): \
     ",
         question = question.as_ref(),
-        are_you_sure = "Proceed?".bold(),
+        are_you_sure = prompt_text.as_ref().bold(),
         no = if default == PromptChoice::No {
             "[N]o"
         } else {

src/cli/mod.rs

@@ -92,7 +92,7 @@ pub fn ensure_root() -> eyre::Result<()> {
     if !is_root() {
         eprintln!(
             "{}",
-            "`nix-installer` needs to run as `root`, attempting to escalate now via `sudo`..."
+            "`lix-installer` needs to run as `root`, attempting to escalate now via `sudo`..."
                 .yellow()
                 .dimmed()
         );

src/cli/subcommand/install.rs

@@ -170,7 +170,39 @@ impl CommandExecute for Install {
                 serde_json::from_str(&install_plan_string)?
             },
             (None, None) => {
-                let builtin_planner = BuiltinPlanner::from_common_settings(settings.clone())
+                let mut settings_to_apply = settings.clone();
+
+                if !no_confirm {
+                    // Say hello.
+                    let mut term = term.expect("Internal consistency: term should have been None checked already!");
+                    let hello_message = format!("{}{}", "\n\nWelcome to the Lix installer!".bold(), " Just a couple of quick questions.\n\n");
+
+                    term.write_all(hello_message.as_bytes())?;
+                    term.flush()?;
+
+                    // Ask about flakes.
+                    match interaction::prompt(
+                        "Flakes are an experimental feature, but widely used in the community.\nYou can change this later in `/etc/nix/nix.conf`.",
+                        "Enable flakes?",
+                        PromptChoice::Yes,
+                        true,
+                    )
+                    .await?
+                    {
+                        PromptChoice::Yes => settings_to_apply.enable_flakes = true,
+                        PromptChoice::Explain => panic!("This prompt has no explanation."),
+                        PromptChoice::No => settings_to_apply.enable_flakes = false,
+                    }
+
+                    // Notify the user about the nix command.
+                    let nixcmd_message = format!("{}{}{}{}{}",
+                        "\nQUICK NOTE:".bold().yellow(), " we've enabled the experimental", " nix ".bold(), "command for you!\n",
+                        "Be aware that commands starting with `nix ` such as `nix build` may change syntax.\n\n".green());
+                    term.write_all(nixcmd_message.as_bytes())?;
+                    term.flush()?;
+                }
+
+                let builtin_planner = BuiltinPlanner::from_common_settings(settings_to_apply)
                     .await
                     .map_err(|e| eyre::eyre!(e))?;
 
@@ -236,6 +268,7 @@ impl CommandExecute for Install {
                         .describe_install(currently_explaining)
                         .await
                         .map_err(|e| eyre!(e))?,
+                    "Proceed?",
                     PromptChoice::Yes,
                     currently_explaining,
                 )
@@ -276,6 +309,7 @@ impl CommandExecute for Install {
                                 .describe_uninstall(currently_explaining)
                                 .await
                                 .map_err(|e| eyre!(e))?,
+                            "Proceed?",
                             PromptChoice::Yes,
                             currently_explaining,
                         )

src/cli/subcommand/uninstall.rs

@@ -169,6 +169,7 @@ impl CommandExecute for Uninstall {
                     plan.describe_uninstall(currently_explaining)
                         .await
                         .map_err(|e| eyre!(e))?,
+                    "Proceed?",
                     PromptChoice::Yes,
                     currently_explaining,
                 )

src/settings.rs

@@ -203,6 +203,20 @@ pub struct CommonSettings {
         )
     )]
     pub force: bool,
+
+    /// If `nix-installer` should enable flakes.
+    #[cfg_attr(
+        feature = "cli",
+        clap(
+            long,
+            action(ArgAction::SetFalse),
+            default_value = "true",
+            global = true,
+            env = "NIX_INSTALLER_ENABLE_FLAKES"
+        )
+    )]
+    pub enable_flakes: bool,
+
 }
 
 impl CommonSettings {
@@ -270,6 +284,7 @@ impl CommonSettings {
             proxy: Default::default(),
             extra_conf: Default::default(),
             force: false,
+            enable_flakes: true,
             ssl_cert_file: Default::default(),
         })
     }
@@ -287,6 +302,7 @@ impl CommonSettings {
             proxy,
             extra_conf,
             force,
+            enable_flakes,
             ssl_cert_file,
         } = self;
         let mut map = HashMap::default();
@@ -322,6 +338,7 @@ impl CommonSettings {
         map.insert("proxy".into(), serde_json::to_value(proxy)?);
         map.insert("ssl_cert_file".into(), serde_json::to_value(ssl_cert_file)?);
         map.insert("extra_conf".into(), serde_json::to_value(extra_conf)?);
+        map.insert("enable_flakes".into(), serde_json::to_value(enable_flakes)?);
         map.insert("force".into(), serde_json::to_value(force)?);
         Ok(map)
     }