Rework Vite plugin to support lightningcss pre processor and fast rebuilds (#14269)

Fixes #14205
Fixes #14106

This PR reworks the Vite extension in order to supprt `lightningcss` as
the pre-processor, enable faster rebuilds, and adds support for `vite
build --watch` mode. To make this change possible, we've done two major
changes to the extension that have caused the other changes.

## 1. Tailwind CSS is a preprocessor

We now run all of our modifications in `enforce: 'pre'`. This means that
Tailwind CSS now gets the untransformed CSS files rather than the one
already going through postcss or lightningcss. We do this because
Tailwind CSS _is_ a preprocessor at the same level as those tools and we
do sometimes use the language in ways that [creates problems when it's
the input for other
bundlers](#14269).

The correct solution here is to make Tailwind not depend on any other
transformations. The main reason we were not using the `enforce: 'pre'`
phase in Vite before was becuase we relied on the `@import` flattening
of postcss so we now have to do this manually. `@import` flattening is
now a concern that every Tailwind V4 client has to deal with so this
might actually be something we want to inline into tailwindcss in the
future.

## 2. A Vite config can have multiple Tailwind roots 

This is something that we have not made very explicit in the previous
iteration of the Vite plugin but we have to support multiple Tailwind
roots in a single Vite workspace. A Tailwind root is a CSS file that is
used to configure Tailwind. Technically, any CSS file can be the input
for `tailwindcss` but you have to add certain rules (e.g. `@import
"tailwindcss";`) to make the compiler do something.

A workspace can have multiple of these rules (e.g. by having different
Tailwind configures for different sub-pages). With the addition of
[support for `@source`
rules](#14078) and [JS
config files](#14239),
Tailwind roots become more complex and can have a custom list of
_dependencies_ (that is other JavaScript modules the compiler includes
as part of these new rules). In order to _only rebuild the roots we need
to_, we have to make this separation very clear.

---------

Co-authored-by: Jordan Pittman <jordan@cryptica.me>
Co-authored-by: Adam Wathan <4323180+adamwathan@users.noreply.github.com>

Author: 3 people

CHANGELOG.md

@@ -23,6 +23,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add new standalone builds of Tailwind CSS v4 ([#14270](https://github.com/tailwindlabs/tailwindcss/pull/14270))
 - Support JavaScript configuration files using `@config` ([#14239](https://github.com/tailwindlabs/tailwindcss/pull/14239))
 - Support plugin options in `@plugin` ([#14264](https://github.com/tailwindlabs/tailwindcss/pull/14264))
+- Add support for using the Vite extension with `css.transformer` set to `lightningcss` ([#14269](https://github.com/tailwindlabs/tailwindcss/pull/14269))
 
 ### Fixed
 
@@ -32,6 +33,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fix fallback values when using the CSS `theme()` function ([#14262](https://github.com/tailwindlabs/tailwindcss/pull/14262))
 - Fix support for declaration fallbacks in plugins ([#14265](https://github.com/tailwindlabs/tailwindcss/pull/14265))
 - Support bare values when using `tailwindcss/defaultTheme` ([#14257](https://github.com/tailwindlabs/tailwindcss/pull/14257))
+- Correctly update builds when using the Vite extension with `build --watch` ([#14269](https://github.com/tailwindlabs/tailwindcss/pull/14269))
 
 ### Changed
 

integrations/utils.ts

@@ -1,7 +1,7 @@
 import dedent from 'dedent'
 import fastGlob from 'fast-glob'
 import killPort from 'kill-port'
-import { execSync, spawn } from 'node:child_process'
+import { exec, spawn } from 'node:child_process'
 import fs from 'node:fs/promises'
 import net from 'node:net'
 import { homedir, platform, tmpdir } from 'node:os'
@@ -89,11 +89,23 @@ export function test(
             console.log(`> cd ${relative}`)
           }
           if (debug) console.log(`> ${command}`)
-          return execSync(command, {
-            cwd,
-            stdio: 'pipe',
-            ...childProcessOptions,
-          }).toString()
+          return new Promise((resolve, reject) => {
+            exec(
+              command,
+              {
+                cwd,
+                ...childProcessOptions,
+              },
+              (error, stdout, stderr) => {
+                if (error) {
+                  console.error(stderr)
+                  reject(error)
+                } else {
+                  resolve(stdout.toString())
+                }
+              },
+            )
+          })
         },
         async spawn(command: string, childProcessOptions: ChildProcessOptions = {}) {
           let resolveDisposal: (() => void) | undefined