Rewrite composes rules inside @imported stylesheets

index.js

@@ -160,7 +160,7 @@ function parseStyles(result, styles, options, state, media) {
           if (stmt.children) {
             stmt.children.forEach((child, index) => {
               if (child.type === "import") imports.push(child)
-              else bundle.push(child)
+              else bundle.push(rewriteComposes(child, path.dirname(stmt.uri)))
               // For better output
               if (index === 0) child.parent = stmt
             })
@@ -174,6 +174,21 @@ function parseStyles(result, styles, options, state, media) {
     })
 }
 
+function rewriteComposes(stmt, dirname) {
+  if (stmt.nodes) {
+    stmt.nodes.forEach(child => {
+      rewriteComposes(child, dirname)
+    })
+  }
+  if (stmt.type === "decl" && stmt.prop === "composes") {
+    stmt.value = stmt.value.replace(
+      /(from\s*["'])(\.\.?\/[^'"]*)/,
+      (m, m1, m2) => m1 + path.normalize(dirname+'/'+m2)
+    )
+  }
+  return stmt
+}
+
 function resolveImportId(result, stmt, options, state) {
   const atRule = stmt.node
   let sourceFile

test/fixtures/composes-second.css

@@ -0,0 +1 @@
+.a {}

test/fixtures/imports/composes-first.css

@@ -0,0 +1 @@
+.a { composes: a from '../composes-second.css'; }

test/import.js

@@ -1,5 +1,5 @@
 // builtin tooling
-import { readFileSync } from "fs"
+import { existsSync, readFileSync } from "fs"
 import path from "path"
 
 // external tooling
@@ -98,3 +98,16 @@ test("should work with no styles without throwing an error", t => {
       t.is(result.warnings().length, 0)
     })
 })
+
+test("should rewrite relative paths in `composes` inside @imported stylesheet", t => {
+  return postcss()
+    .use(atImport())
+    .process("@import 'test/fixtures/imports/composes-first.css';", {
+      from: undefined,
+    })
+    .then(result => {
+      const path = (/from '(.*)'/.exec(result.css) || [])[1]
+      t.is(existsSync(path), true)
+      t.is(result.warnings().length, 0)
+    })
+})