fix(gatsby): handle case of removing trailing slash in inc builds (#29953)

* add test case

* add one more edge case to tests

* add more assertions

* fix(gatsby): [incremental builds] handle case of page path changing during or between builds that wouldn't result in change of artifact filenames

this is to cover for cases like `gatsby-plugin-remove-trailing-slashes` that change page path during the build or
case when page path might be created from some cms content and trailing slash being added or removed there

* make normalizePagePath terser

* initial setup for calcDirtyHtmlFiles unit tests

* flesh out tests

Author: pieh

integration-tests/artifacts/__tests__/index.js

@@ -369,7 +369,12 @@ describe(`First run (baseline)`, () => {
     })
   })
 
-  const expectedPages = [`stale-pages/stable`, `stale-pages/only-in-first`]
+  const expectedPages = [
+    `stale-pages/stable`,
+    `stale-pages/only-in-first`,
+    `page-that-will-have-trailing-slash-removed`,
+    `/stale-pages/sometimes-i-have-trailing-slash-sometimes-i-dont`,
+  ]
   const unexpectedPages = [`stale-pages/only-not-in-first`]
 
   describe(`html files`, () => {
@@ -460,6 +465,7 @@ describe(`Second run (different pages created, data changed)`, () => {
     `/page-query-dynamic-2/`,
     `/static-query-result-tracking/should-invalidate/`,
     `/page-query-template-change/`,
+    `/stale-pages/sometimes-i-have-trailing-slash-sometimes-i-dont/`,
   ]
 
   const expectedPagesToRemainFromPreviousBuild = [
@@ -468,6 +474,7 @@ describe(`Second run (different pages created, data changed)`, () => {
     `/page-query-changing-but-not-invalidating-html/`,
     `/static-query-result-tracking/stable/`,
     `/static-query-result-tracking/rerun-query-but-dont-recreate-html/`,
+    `/page-that-will-have-trailing-slash-removed`,
   ]
 
   const expectedPages = [
@@ -542,6 +549,8 @@ describe(`Third run (js change, all pages are recreated)`, () => {
   const expectedPages = [
     `/stale-pages/only-not-in-first`,
     `/page-query-dynamic-3/`,
+    `/page-that-will-have-trailing-slash-removed`,
+    `/stale-pages/sometimes-i-have-trailing-slash-sometimes-i-dont`,
   ]
 
   const unexpectedPages = [

integration-tests/artifacts/gatsby-node.js

@@ -31,6 +31,7 @@ exports.onPreInit = ({ emitter }) => {
 }
 
 let previouslyCreatedNodes = new Map()
+let didRemoveTrailingSlashForTestedPage = false
 
 exports.sourceNodes = ({
   actions,
@@ -145,6 +146,12 @@ exports.createPages = async ({ actions, graphql }) => {
     createPageHelper(`only-not-in-first`)
   }
 
+  createPageHelper(
+    `sometimes-i-have-trailing-slash-sometimes-i-dont${
+      runNumber % 2 === 0 ? `/` : ``
+    }`
+  )
+
   const { data } = await graphql(`
     {
       allDepPageQuery {
@@ -181,6 +188,13 @@ exports.onPreBuild = () => {
 let counter = 1
 exports.onPostBuild = async ({ graphql }) => {
   console.log(`[test] onPostBuild`)
+
+  if (!didRemoveTrailingSlashForTestedPage) {
+    throw new Error(
+      `Test setup failed - didn't remove trailing slash for /pages-that-will-have-trailing-slash-removed/ page`
+    )
+  }
+
   const { data } = await graphql(`
     {
       allSitePage(filter: { path: { ne: "/dev-404-page/" } }) {
@@ -206,3 +220,15 @@ exports.onPostBuild = async ({ graphql }) => {
     }
   )
 }
+
+// simulating "gatsby-plugin-remove-trailing-slashes" scenario
+exports.onCreatePage = ({ page, actions }) => {
+  if (page.path === `/page-that-will-have-trailing-slash-removed/`) {
+    actions.deletePage(page)
+    actions.createPage({
+      ...page,
+      path: `/page-that-will-have-trailing-slash-removed`,
+    })
+    didRemoveTrailingSlashForTestedPage = true
+  }
+}

integration-tests/artifacts/src/pages/page-that-will-have-trailing-slash-removed.js

@@ -0,0 +1,5 @@
+import * as React from "react"
+
+export default function NoTrailingSlashPage({ path, pathname }) {
+  return <div>I don't have trailing slash</div>
+}