Add holo-dev-server to the dev shell when --holo is passed

We add a --holo flag to the example subcommand.
When this flag is passed, we add holo-nixpkgs as a flake input and we
add holo-dev-server to the dev shell's packages.

run_test.sh

@@ -148,3 +148,40 @@ set -e
 npm i
 npm t 
 "
+
+rm -rf /tmp/holo-flake
+cd /tmp
+
+hc-scaffold web-app holo-flake --template vue
+cd holo-flake
+
+nix develop --command bash -c "
+set -e
+# Check if holo-dev-server is in the path
+if command -v holo-dev-server >/dev/null 2>&1; then
+  echo 'holo-dev-server is available in the PATH while it shouldn\'t'
+  exit 1
+else
+  echo 'holo-dev-server is NOT available in the PATH'
+fi
+"
+
+rm -rf /tmp/holo-flake
+cd /tmp
+
+hc-scaffold web-app holo-flake --template vue --holo
+cd holo-flake
+
+nix develop --accept-flake-config --command bash -c "
+set -e
+# Check if holo-dev-server is in the path
+if command -v holo-dev-server >/dev/null 2>&1; then
+  echo 'holo-dev-server is available in the PATH'
+else
+  echo 'holo-dev-server is NOT available in the PATH'
+  exit 1
+fi
+"
+
+rm -rf /tmp/holo-flake
+cd /tmp

src/cli.rs

@@ -216,6 +216,9 @@ pub enum HcScaffold {
         /// The template to scaffold the example for
         /// Must be an option from the built-in templates: "vanilla", "vue", "lit", "svelte"
         template: Option<String>,
+
+        #[structopt(long = "holo", hidden = true)]
+        holo_enabled: bool,
     },
 }
 
@@ -702,7 +705,11 @@ Collection "{}" scaffolded!
                     println!("{}", i);
                 }
             }
-            HcScaffold::Example { example, template } => {
+            HcScaffold::Example {
+                example,
+                template,
+                holo_enabled,
+            } => {
                 let example = match example {
                     Some(e) => e,
                     None => choose_example()?,
@@ -736,7 +743,7 @@ Collection "{}" scaffolded!
                             &template_file_tree,
                             template_name.clone(),
                             false,
-                            false,
+                            holo_enabled,
                         )?;
 
                         file_tree
@@ -750,7 +757,7 @@ Collection "{}" scaffolded!
                             &template_file_tree,
                             template_name.clone(),
                             false,
-                            false,
+                            holo_enabled,
                         )?;
 
                         // scaffold dna hello_world

src/scaffold/app/nix.rs

@@ -9,12 +9,49 @@ use crate::error::{ScaffoldError, ScaffoldResult};
 use crate::file_tree::*;
 use crate::versions::holochain_nix_version;
 
-pub fn flake_nix() -> FileTree {
+pub fn flake_nix(holo_enabled: bool) -> FileTree {
     let holochain_nix_version = holochain_nix_version();
+
+    let holo_nix_config = holo_enabled
+        .then_some(
+            r#"
+  nixConfig = {
+    extra-substituters = [
+      "https://cache.holo.host"
+    ];
+    extra-trusted-public-keys = [
+      "cache.holo.host-1:lNXIXtJgS9Iuw4Cu6X0HINLu9sTfcjEntnrgwMQIMcE="
+      "cache.holo.host-2:ZJCkX3AUYZ8soxTLfTb60g+F3MkWD7hkH9y8CgqwhDQ="
+    ];
+  };"#,
+        )
+        .unwrap_or("");
+
+    let holo_inputs = holo_enabled
+        .then_some(
+            r#"
+    holo-nixpkgs = {
+      # Take the latest version from the Holo-Host develop branch
+      url = "https://hydra.holo.host/job/holo-nixpkgs/develop/holo-nixpkgs/latest/download";
+      inputs = {
+        versions.follows = "holochain-flake/versions";
+        holochain.follows = "holochain-flake";
+        flake-compat.follows = "holochain-flake/flake-compat";
+      };
+    };"#,
+        )
+        .unwrap_or("");
+
+    let holo_packages = holo_enabled
+        .then_some("inputs'.holo-nixpkgs.legacyPackages.holo-dev-server")
+        .unwrap_or("");
+
     file!(format!(
         r#"{{
   description = "Template for Holochain app development";
 
+  {holo_nix_config}
+
   inputs = {{
     versions.url  = "github:holochain/holochain?dir=versions/{holochain_nix_version}";
 
@@ -23,6 +60,7 @@ pub fn flake_nix() -> FileTree {
 
     nixpkgs.follows = "holochain-flake/nixpkgs";
     flake-parts.follows = "holochain-flake/flake-parts";
+    {holo_inputs}
   }};
 
   outputs = inputs:
@@ -43,6 +81,7 @@ pub fn flake_nix() -> FileTree {
               inputsFrom = [ inputs'.holochain-flake.devShells.holonix ];
               packages = [
                 pkgs.nodejs-18_x
+                {holo_packages}
                 # more packages go here
               ];
             }};

src/scaffold/web_app.rs

@@ -41,7 +41,7 @@ fn web_app_skeleton(
         app_file_tree
             .dir_content_mut()
             .ok_or(ScaffoldError::PathNotFound(PathBuf::new()))?
-            .insert(OsString::from("flake.nix"), flake_nix());
+            .insert(OsString::from("flake.nix"), flake_nix(holo_enabled));
     }
     if scaffold_template {
         app_file_tree