Re-throw errors from PostCSS nodes (#18373)

Fixes #18370

---------

Co-authored-by: Robin Malfait <malfait.robin@gmail.com>

CHANGELOG.md

@@ -23,6 +23,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Do not migrate `variant = 'outline'` during upgrades ([#18922](https://github.com/tailwindlabs/tailwindcss/pull/18922))
 - Show Lightning CSS warnings (if any) when optimizing/minifying ([#18918](https://github.com/tailwindlabs/tailwindcss/pull/18918))
 - Use `default` export condition for `@tailwindcss/vite` ([#18948](https://github.com/tailwindlabs/tailwindcss/pull/18948))
+- Re-throw errors from PostCSS nodes ([#18373](https://github.com/tailwindlabs/tailwindcss/pull/18373))
 
 ## [4.1.13] - 2025-09-03
 

integrations/postcss/index.test.ts

@@ -1,5 +1,5 @@
 import path from 'node:path'
-import { candidate, css, html, js, json, retryAssertion, test, ts, yaml } from '../utils'
+import { candidate, css, html, js, json, test, ts, yaml } from '../utils'
 
 test(
   'production build (string)',
@@ -662,23 +662,56 @@ test(
       `,
       'src/index.css': css` @import './tailwind.css'; `,
       'src/tailwind.css': css`
-        @reference 'tailwindcss/does-not-exist';
+        @reference 'tailwindcss/theme';
         @import 'tailwindcss/utilities';
       `,
     },
   },
   async ({ fs, expect, spawn }) => {
+    // 1. Start the watcher
+    //
+    // It must have valid CSS for the initial build
     let process = await spawn('pnpm postcss src/index.css --output dist/out.css --watch --verbose')
 
+    await process.onStderr((message) => message.includes('Waiting for file changes...'))
+
+    expect(await fs.dumpFiles('dist/*.css')).toMatchInlineSnapshot(`
+      "
+      --- dist/out.css ---
+      .underline {
+        text-decoration-line: underline;
+      }
+      "
+    `)
+
+    // 2. Cause an error
+    await fs.write(
+      'src/tailwind.css',
+      css`
+        @reference 'tailwindcss/does-not-exist';
+        @import 'tailwindcss/utilities';
+      `,
+    )
+
+    // 2.5 Write to a content file
+    await fs.write('src/index.html', html`
+      <div class="flex underline"></div>
+    `)
+
     await process.onStderr((message) =>
       message.includes('does-not-exist is not exported from package'),
     )
 
-    await retryAssertion(async () => expect(await fs.read('dist/out.css')).toEqual(''))
+    expect(await fs.dumpFiles('dist/*.css')).toMatchInlineSnapshot(`
+      "
+      --- dist/out.css ---
+      .underline {
+        text-decoration-line: underline;
+      }
+      "
+    `)
 
-    await process.onStderr((message) => message.includes('Waiting for file changes...'))
-
-    // Fix the CSS file
+    // 3. Fix the CSS file
     await fs.write(
       'src/tailwind.css',
       css`
@@ -686,11 +719,15 @@ test(
         @import 'tailwindcss/utilities';
       `,
     )
-    await process.onStderr((message) => message.includes('Finished'))
+
+    await process.onStderr((message) => message.includes('Waiting for file changes...'))
 
     expect(await fs.dumpFiles('dist/*.css')).toMatchInlineSnapshot(`
       "
       --- dist/out.css ---
+      .flex {
+        display: flex;
+      }
       .underline {
         text-decoration-line: underline;
       }
@@ -705,11 +742,22 @@ test(
         @import 'tailwindcss/utilities';
       `,
     )
+
     await process.onStderr((message) =>
       message.includes('does-not-exist is not exported from package'),
     )
 
-    await retryAssertion(async () => expect(await fs.read('dist/out.css')).toEqual(''))
+    expect(await fs.dumpFiles('dist/*.css')).toMatchInlineSnapshot(`
+      "
+      --- dist/out.css ---
+      .flex {
+        display: flex;
+      }
+      .underline {
+        text-decoration-line: underline;
+      }
+      "
+    `)
   },
 )
 

packages/@tailwindcss-postcss/src/ast.test.ts

@@ -84,7 +84,7 @@ it('should convert a Tailwind CSS AST into a PostCSS AST', () => {
   `
 
   let ast = parse(input)
-  let transformedAst = cssAstToPostCssAst(ast)
+  let transformedAst = cssAstToPostCssAst(postcss, ast)
 
   expect(transformedAst.toString()).toMatchInlineSnapshot(`
     "@charset "UTF-8";

packages/@tailwindcss-postcss/src/ast.ts

@@ -1,10 +1,4 @@
-import postcss, {
-  Input,
-  type ChildNode as PostCssChildNode,
-  type Container as PostCssContainerNode,
-  type Root as PostCssRoot,
-  type Source as PostcssSource,
-} from 'postcss'
+import type * as postcss from 'postcss'
 import { atRule, comment, decl, rule, type AstNode } from '../../tailwindcss/src/ast'
 import { createLineTable, type LineTable } from '../../tailwindcss/src/source-maps/line-table'
 import type { Source, SourceLocation } from '../../tailwindcss/src/source-maps/source'
@@ -12,9 +6,13 @@ import { DefaultMap } from '../../tailwindcss/src/utils/default-map'
 
 const EXCLAMATION_MARK = 0x21
 
-export function cssAstToPostCssAst(ast: AstNode[], source: PostcssSource | undefined): PostCssRoot {
-  let inputMap = new DefaultMap<Source, Input>((src) => {
-    return new Input(src.code, {
+export function cssAstToPostCssAst(
+  postcss: postcss.Postcss,
+  ast: AstNode[],
+  source?: postcss.Source,
+): postcss.Root {
+  let inputMap = new DefaultMap<Source, postcss.Input>((src) => {
+    return new postcss.Input(src.code, {
       map: source?.input.map,
       from: src.file ?? undefined,
     })
@@ -25,7 +23,7 @@ export function cssAstToPostCssAst(ast: AstNode[], source: PostcssSource | undef
   let root = postcss.root()
   root.source = source
 
-  function toSource(loc: SourceLocation | undefined): PostcssSource | undefined {
+  function toSource(loc: SourceLocation | undefined): postcss.Source | undefined {
     // Use the fallback if this node has no location info in the AST
     if (!loc) return
     if (!loc[0]) return
@@ -49,7 +47,7 @@ export function cssAstToPostCssAst(ast: AstNode[], source: PostcssSource | undef
     }
   }
 
-  function updateSource(astNode: PostCssChildNode, loc: SourceLocation | undefined) {
+  function updateSource(astNode: postcss.ChildNode, loc: SourceLocation | undefined) {
     let source = toSource(loc)
 
     // The `source` property on PostCSS nodes must be defined if present because
@@ -63,7 +61,7 @@ export function cssAstToPostCssAst(ast: AstNode[], source: PostcssSource | undef
     }
   }
 
-  function transform(node: AstNode, parent: PostCssContainerNode) {
+  function transform(node: AstNode, parent: postcss.Container) {
     // Declaration
     if (node.kind === 'declaration') {
       let astNode = postcss.decl({
@@ -125,13 +123,13 @@ export function cssAstToPostCssAst(ast: AstNode[], source: PostcssSource | undef
   return root
 }
 
-export function postCssAstToCssAst(root: PostCssRoot): AstNode[] {
-  let inputMap = new DefaultMap<Input, Source>((input) => ({
+export function postCssAstToCssAst(root: postcss.Root): AstNode[] {
+  let inputMap = new DefaultMap<postcss.Input, Source>((input) => ({
     file: input.file ?? input.id ?? null,
     code: input.css,
   }))
 
-  function toSource(node: PostCssChildNode): SourceLocation | undefined {
+  function toSource(node: postcss.ChildNode): SourceLocation | undefined {
     let source = node.source
     if (!source) return
 
@@ -144,7 +142,7 @@ export function postCssAstToCssAst(root: PostCssRoot): AstNode[] {
   }
 
   function transform(
-    node: PostCssChildNode,
+    node: postcss.ChildNode,
     parent: Extract<AstNode, { nodes: AstNode[] }>['nodes'],
   ) {
     // Declaration

packages/@tailwindcss-postcss/src/index.test.ts

@@ -391,7 +391,7 @@ describe('concurrent builds', () => {
       let ast = postcss.parse(input)
       for (let runner of (plugin as any).plugins) {
         if (runner.Once) {
-          await runner.Once(ast, { result: { opts: { from }, messages: [] } })
+          await runner.Once(ast, { postcss, result: { opts: { from }, messages: [] } })
         }
       }
       return ast.toString()

packages/@tailwindcss-postcss/src/index.ts

@@ -11,7 +11,7 @@ import { clearRequireCache } from '@tailwindcss/node/require-cache'
 import { Scanner } from '@tailwindcss/oxide'
 import fs from 'node:fs'
 import path, { relative } from 'node:path'
-import postcss, { type AcceptedPlugin, type PluginCreator } from 'postcss'
+import type { AcceptedPlugin, PluginCreator, Postcss, Root } from 'postcss'
 import { toCss, type AstNode } from '../../tailwindcss/src/ast'
 import { cssAstToPostCssAst, postCssAstToCssAst } from './ast'
 import fixRelativePathsPlugin from './postcss-fix-relative-paths'
@@ -23,13 +23,13 @@ interface CacheEntry {
   compiler: null | ReturnType<typeof compileAst>
   scanner: null | Scanner
   tailwindCssAst: AstNode[]
-  cachedPostCssAst: postcss.Root
-  optimizedPostCssAst: postcss.Root
+  cachedPostCssAst: Root
+  optimizedPostCssAst: Root
   fullRebuildPaths: string[]
 }
 const cache = new QuickLRU<string, CacheEntry>({ maxSize: 50 })
 
-function getContextFromCache(inputFile: string, opts: PluginOptions): CacheEntry {
+function getContextFromCache(postcss: Postcss, inputFile: string, opts: PluginOptions): CacheEntry {
   let key = `${inputFile}:${opts.base ?? ''}:${JSON.stringify(opts.optimize)}`
   if (cache.has(key)) return cache.get(key)!
   let entry = {
@@ -83,7 +83,7 @@ function tailwindcss(opts: PluginOptions = {}): AcceptedPlugin {
 
       {
         postcssPlugin: 'tailwindcss',
-        async Once(root, { result }) {
+        async Once(root, { result, postcss }) {
           using I = new Instrumentation()
 
           let inputFile = result.opts.from ?? ''
@@ -114,7 +114,7 @@ function tailwindcss(opts: PluginOptions = {}): AcceptedPlugin {
             DEBUG && I.end('Quick bail check')
           }
 
-          let context = getContextFromCache(inputFile, opts)
+          let context = getContextFromCache(postcss, inputFile, opts)
           let inputBasePath = path.dirname(path.resolve(inputFile))
 
           // Whether this is the first build or not, if it is, then we can
@@ -310,7 +310,7 @@ function tailwindcss(opts: PluginOptions = {}): AcceptedPlugin {
               } else {
                 // Convert our AST to a PostCSS AST
                 DEBUG && I.start('Transform Tailwind CSS AST into PostCSS AST')
-                context.cachedPostCssAst = cssAstToPostCssAst(tailwindCssAst, root.source)
+                context.cachedPostCssAst = cssAstToPostCssAst(postcss, tailwindCssAst, root.source)
                 DEBUG && I.end('Transform Tailwind CSS AST into PostCSS AST')
               }
             }
@@ -349,7 +349,12 @@ function tailwindcss(opts: PluginOptions = {}): AcceptedPlugin {
             // We found that throwing the error will cause PostCSS to no longer watch for changes
             // in some situations so we instead log the error and continue with an empty stylesheet.
             console.error(error)
-            root.removeAll()
+
+            if (error && typeof error === 'object' && 'message' in error) {
+              throw root.error(`${error.message}`)
+            }
+
+            throw root.error(`${error}`)
           }
         },
       },