fix: Allow absolute paths in indexHtmlFile (#28324)

* fix: allow absolute paths in indexHtmlFile

* Update CHANGELOG.md

* Updated readme

---------

Co-authored-by: Ryan Manuel <ryanm@cypress.io>
Co-authored-by: Jennifer Shehane <jennifer@cypress.io>
Co-authored-by: Jordan <jordan@jpdesigning.com>

cli/CHANGELOG.md

@@ -10,6 +10,7 @@ _Released 11/21/2023 (PENDING)_
 
 **Bugfixes:**
 
+- We now allow absolute paths when setting `component.indexHtmlFile` in the Cypress config. Fixes [#27750](https://github.com/cypress-io/cypress/issues/27750).
 - Fixed an issue where dynamic intercept aliases now show with alias name instead of "no alias" in driver. Addresses [#24653](https://github.com/cypress-io/cypress/issues/24653)
 - Fixed an issue where [aliasing individual requests](https://docs.cypress.io/api/commands/intercept#Aliasing-individual-requests) with `cy.intercept()` led to an error when retrieving all of the aliases with `cy.get(@alias.all)` . Addresses [#25448](https://github.com/cypress-io/cypress/issues/25448)
 - The URL of the application under test and command error "Learn more" links now open externally instead of in the Cypress-launched browser. Fixes [#24572](https://github.com/cypress-io/cypress/issues/24572).

npm/webpack-dev-server/src/makeDefaultWebpackConfig.ts

@@ -81,7 +81,7 @@ export function makeCypressWebpackConfig (
     },
     plugins: [
       new (HtmlWebpackPlugin as typeof import('html-webpack-plugin-5'))({
-        template: indexHtmlFile ? path.join(projectRoot, indexHtmlFile) : undefined,
+        template: indexHtmlFile ? path.isAbsolute(indexHtmlFile) ? indexHtmlFile : path.join(projectRoot, indexHtmlFile) : undefined,
         // Angular generates all of it's scripts with <script type="module">. Live-reloading breaks without this option.
         // We need to manually set the base here to `/__cypress/src/` so that static assets load with our proxy
         ...(framework === 'angular' ? { scriptLoading: 'module', base: '/__cypress/src/' } : {}),