dashboard: decouple prettier-svelte from dashboard source

f255345a1ad29e923b0f22d0f5d13c815d1f697d · 2026-01-23 12:47:43 +0000 · Jake Hillion

The prettier-svelte formatter depended on the full dashboard build
(dashboardFull), causing the devshell to rebuild whenever any dashboard
source file changed.

Created a deps-only dream2nix derivation (deps.nix) that uses a stub
source containing only package.json, package-lock.json, and minimal
files for vite to succeed. Updated prettier-svelte to use this
derivation instead of dashboardFull.

The stub source is constant unless lockfiles change, so prettier-svelte
and the devshell no longer rebuild when dashboard source files are
modified.

Test plan:
- nix flake check passed
- nix fmt successfully formatted svelte files

Files touched

M dashboard/parts.nix

Diff

commit f255345a1ad29e923b0f22d0f5d13c815d1f697d
Author: Jake Hillion <jake@hillion.co.uk>
Date:   Fri Jan 23 12:47:43 2026 +0000

    dashboard: decouple prettier-svelte from dashboard source
    
    The prettier-svelte formatter depended on the full dashboard build
    (dashboardFull), causing the devshell to rebuild whenever any dashboard
    source file changed.
    
    Created a deps-only dream2nix derivation (deps.nix) that uses a stub
    source containing only package.json, package-lock.json, and minimal
    files for vite to succeed. Updated prettier-svelte to use this
    derivation instead of dashboardFull.
    
    The stub source is constant unless lockfiles change, so prettier-svelte
    and the devshell no longer rebuild when dashboard source files are
    modified.
    
    Test plan:
    - nix flake check passed
    - nix fmt successfully formatted svelte files
---
 dashboard/parts.nix | 46 +++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 43 insertions(+), 3 deletions(-)

diff --git a/dashboard/parts.nix b/dashboard/parts.nix
index 487078d5..8edcc6b7 100644
--- a/dashboard/parts.nix
+++ b/dashboard/parts.nix
@@ -3,6 +3,45 @@
   perSystem =
     { pkgs, lib, ... }:
     let
+      # Stub source with lockfiles and minimal files for build to succeed
+      # This allows prettier-svelte to avoid rebuilding when dashboard source changes
+      dashboardStubSrc = pkgs.runCommand "dashboard-stub-src" { } ''
+        mkdir -p $out
+        cp ${inputs.self}/dashboard/package.json $out/
+        cp ${inputs.self}/dashboard/package-lock.json $out/
+        # Minimal files so vite build succeeds (produces empty output)
+        echo '<!DOCTYPE html><html><head></head><body></body></html>' > $out/index.html
+        mkdir -p $out/src
+        touch $out/src/app.html
+      '';
+
+      # Deps-only build using stub source (for prettier-svelte)
+      # Only rebuilds when package.json or package-lock.json change
+      dashboardDeps = inputs.dream2nix.lib.evalModules {
+        packageSets.nixpkgs = pkgs;
+        modules = [
+          ./dashboard.nix
+          {
+            paths.projectRoot = inputs.self;
+            paths.projectRootFile = "flake.nix";
+            paths.package = inputs.self + "/dashboard";
+          }
+          {
+            deps.dashboardSrc = lib.mkForce dashboardStubSrc;
+          }
+          # Override build phases to skip the actual build - just need node_modules
+          {
+            mkDerivation = {
+              buildPhase = lib.mkForce "true";
+              installPhase = lib.mkForce ''
+                runHook preInstall
+                runHook postInstall
+              '';
+            };
+          }
+        ];
+      };
+
       # Filter source to only include dashboard directory
       dashboardSrc = lib.cleanSourceWith {
         src = inputs.self;
@@ -42,11 +81,12 @@
       '';
 
       # Prettier with svelte plugin for treefmt
+      # Uses dashboardDeps instead of dashboardFull to avoid rebuilding on source changes
       packages.prettier-svelte = pkgs.writeShellScriptBin "prettier-svelte" ''
-        export NODE_PATH="${dashboardFull}/lib/node_modules/exo-dashboard/node_modules"
+        export NODE_PATH="${dashboardDeps}/lib/node_modules/exo-dashboard/node_modules"
         exec ${pkgs.nodejs}/bin/node \
-          ${dashboardFull}/lib/node_modules/exo-dashboard/node_modules/prettier/bin/prettier.cjs \
-          --plugin "${dashboardFull}/lib/node_modules/exo-dashboard/node_modules/prettier-plugin-svelte/plugin.js" \
+          ${dashboardDeps}/lib/node_modules/exo-dashboard/node_modules/prettier/bin/prettier.cjs \
+          --plugin "${dashboardDeps}/lib/node_modules/exo-dashboard/node_modules/prettier-plugin-svelte/plugin.js" \
           "$@"
       '';
     };

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