Ensure changes to the input CSS file result in a full rebuild (#14744)

Fixes #14726

I think we broke this when we changed core so that it can handle
`@import "…"` in CSS.

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Allow spaces spaces around operators in attribute selector variants ([#14703](https://github.com/tailwindlabs/tailwindcss/pull/14703))
 - Ensure color opacity modifiers work with OKLCH colors ([#14741](https://github.com/tailwindlabs/tailwindcss/pull/14741))
+- Ensure changes to the input CSS file result in a full rebuild ([#14744](https://github.com/tailwindlabs/tailwindcss/pull/14744))
 - _Upgrade (experimental)_: Migrate `flex-grow` to `grow` and `flex-shrink` to `shrink` ([#14721](https://github.com/tailwindlabs/tailwindcss/pull/14721))
 - _Upgrade (experimental)_: Minify arbitrary values when printing candidates ([#14720](https://github.com/tailwindlabs/tailwindcss/pull/14720))
 - _Upgrade (experimental)_: Ensure legacy theme values ending in `1` (like `theme(spacing.1)`) are correctly migrated to custom properties ([#14724](https://github.com/tailwindlabs/tailwindcss/pull/14724))

integrations/cli/index.test.ts

@@ -210,6 +210,23 @@ describe.each([
           }
         `,
       ])
+
+      await fs.write(
+        'project-a/src/index.css',
+        css`
+          @import 'tailwindcss/utilities';
+          @theme {
+            --color-*: initial;
+          }
+        `,
+      )
+
+      await fs.expectFileToContain('project-a/dist/out.css', [
+        css`
+          :root {
+          }
+        `,
+      ])
     },
   )
 

packages/@tailwindcss-cli/src/commands/build/index.ts

@@ -122,11 +122,12 @@ export async function handle(args: Result<ReturnType<typeof options>>) {
     env.DEBUG && console.timeEnd('[@tailwindcss/cli] Write output')
   }
 
-  let inputBasePath =
-    args['--input'] && args['--input'] !== '-'
-      ? path.dirname(path.resolve(args['--input']))
-      : process.cwd()
-  let fullRebuildPaths: string[] = []
+  let inputFilePath =
+    args['--input'] && args['--input'] !== '-' ? path.resolve(args['--input']) : null
+
+  let inputBasePath = inputFilePath ? path.dirname(inputFilePath) : process.cwd()
+
+  let fullRebuildPaths: string[] = inputFilePath ? [inputFilePath] : []
 
   async function createCompiler(css: string) {
     env.DEBUG && console.time('[@tailwindcss/cli] Setup compiler')
@@ -201,7 +202,7 @@ export async function handle(args: Result<ReturnType<typeof options>>) {
                   @import 'tailwindcss';
                 `
             clearRequireCache(resolvedFullRebuildPaths)
-            fullRebuildPaths = []
+            fullRebuildPaths = inputFilePath ? [inputFilePath] : []
 
             // Create a new compiler, given the new `input`
             compiler = await createCompiler(input)