From 97cc3553d4b474a49f913d1ab089f8740a518841 Mon Sep 17 00:00:00 2001
From: Ben Surgison <ben.surgison@digital.cabinet-office.gov.uk>
Date: Fri, 20 Oct 2023 11:06:59 +0100
Subject: [PATCH] Delay adding filters and functions until last

---
 CHANGELOG.md                |  1 +
 lib/filters/api.js          |  3 +-
 lib/filters/core-filters.js | 10 ++++---
 server.js                   | 58 ++++++++++++++++++-------------------
 4 files changed, 38 insertions(+), 34 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 307f75d747..698621ee9c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,7 @@
 
 ### Fixes
 
+- [#2362: Delay adding filters and functions until last](https://github.com/alphagov/govuk-prototype-kit/pull/2362)
 - [#2364: Fix plugin update detection](https://github.com/alphagov/govuk-prototype-kit/pull/2364)
 
 ## 13.13.5
diff --git a/lib/filters/api.js b/lib/filters/api.js
index 4570e33418..f1565299fd 100644
--- a/lib/filters/api.js
+++ b/lib/filters/api.js
@@ -56,5 +56,6 @@ module.exports = {
     addFilter,
     getFilter
   },
-  setEnvironment
+  setEnvironment,
+  runWhenEnvIsAvailable
 }
diff --git a/lib/filters/core-filters.js b/lib/filters/core-filters.js
index ce55f0c479..7dacb78091 100644
--- a/lib/filters/core-filters.js
+++ b/lib/filters/core-filters.js
@@ -1,8 +1,7 @@
 
 // local dependencies
-const { addFilter, getFilter } = require('../../').views
-
-const nunjucksSafe = getFilter('safe')
+const { runWhenEnvIsAvailable, external } = require('./api')
+const { addFilter, getFilter } = external
 
 /**
  * Logs an object in the template to the console in the browser.
@@ -11,4 +10,7 @@ const nunjucksSafe = getFilter('safe')
  * @example {{ "hello world" | log }}
  * @example {{ "hello world" | log | safe }}  [for environments with autoescaping turned on]
  */
-addFilter('log', a => nunjucksSafe('<script>console.log(' + JSON.stringify(a, null, '\t') + ');</script>'))
+runWhenEnvIsAvailable(() => {
+  const nunjucksSafe = getFilter('safe')
+  addFilter('log', a => nunjucksSafe('<script>console.log(' + JSON.stringify(a, null, '\t') + ');</script>'))
+})
diff --git a/server.js b/server.js
index b801d1a0c5..f211ef8048 100644
--- a/server.js
+++ b/server.js
@@ -31,6 +31,19 @@ routesApi.setApp(app)
 // Set up configuration variables
 const releaseVersion = packageJson.version
 
+// Find GOV.UK Frontend (via project, internal package fallback)
+const govukFrontend = govukFrontendPaths([projectDir, packageDir])
+
+// Find GOV.UK Frontend (via internal package, project fallback)
+const govukFrontendInternal = govukFrontendPaths([packageDir, projectDir])
+
+// Finds GOV.UK Frontend via `getAppViews()` only if installed
+// but uses the internal package as a backup if uninstalled
+const nunjucksAppEnv = getNunjucksAppEnv(
+  plugins.getAppViews([appViewsDir, finalBackupNunjucksDir]),
+  govukFrontendInternal
+)
+
 // Force HTTPS on production. Do this before using basicAuth to avoid
 // asking for username/password twice (for `http`, then `https`).
 const isSecure = (config.isProduction && config.useHttps)
@@ -39,12 +52,6 @@ if (isSecure) {
   app.set('trust proxy', 1) // needed for secure cookies on heroku
 }
 
-// Find GOV.UK Frontend (via project, internal package fallback)
-const govukFrontend = govukFrontendPaths([projectDir, packageDir])
-
-// Find GOV.UK Frontend (via internal package, project fallback)
-const govukFrontendInternal = govukFrontendPaths([packageDir, projectDir])
-
 // Add variables that are available in all views
 app.locals.asset_path = '/public/'
 app.locals.useAutoStoreData = config.useAutoStoreData
@@ -90,23 +97,6 @@ if (config.isDevelopment) {
   nunjucksConfig.watch = true
 }
 
-nunjucksConfig.express = app
-
-// Finds GOV.UK Frontend via `getAppViews()` only if installed
-// but uses the internal package as a backup if uninstalled
-const nunjucksAppEnv = getNunjucksAppEnv(
-  plugins.getAppViews([appViewsDir, finalBackupNunjucksDir]),
-  govukFrontendInternal
-)
-
-expressNunjucks(nunjucksAppEnv, app)
-
-// Add Nunjucks filters
-utils.addNunjucksFilters(nunjucksAppEnv)
-
-// Add Nunjucks functions
-utils.addNunjucksFunctions(nunjucksAppEnv)
-
 // Set views engine
 app.set('view engine', 'njk')
 
@@ -120,12 +110,6 @@ app.use(bodyParser.urlencoded({
   extended: true
 }))
 
-// Automatically store all data users enter
-if (config.useAutoStoreData) {
-  app.use(sessionUtils.autoStoreData)
-  sessionUtils.addCheckedFunction(nunjucksAppEnv)
-}
-
 // Prevent search indexing
 app.use((req, res, next) => {
   // Setting headers stops pages being indexed even if indexed pages link to them.
@@ -133,6 +117,12 @@ app.use((req, res, next) => {
   next()
 })
 
+// Automatically store all data users enter
+if (config.useAutoStoreData) {
+  app.use(sessionUtils.autoStoreData)
+  sessionUtils.addCheckedFunction(nunjucksAppEnv)
+}
+
 require('./lib/manage-prototype-routes.js')
 require('./lib/plugins/plugins-routes.js')
 const { getErrorModel } = require('./lib/utils/errorModel')
@@ -217,4 +207,14 @@ app.use((err, req, res, next) => {
 
 app.close = stopWatchingNunjucks
 
+nunjucksConfig.express = app
+
+expressNunjucks(nunjucksAppEnv, app)
+
+// Add Nunjucks filters
+utils.addNunjucksFilters(nunjucksAppEnv)
+
+// Add Nunjucks functions
+utils.addNunjucksFunctions(nunjucksAppEnv)
+
 module.exports = app