Extended transform support

CHANGELOG.md

@@ -41,6 +41,9 @@ postcssImport({
 })
 ```
 
+- Changed: support promise in `transform` option and `undefined` result will be skipped
+([#147](https://github.com/postcss/postcss-import/pull/147))
+
 # 7.1.3 - 2015-11-05
 
 - Fixed: ensure node 0.12 compatibility, round 2

README.md

@@ -109,7 +109,8 @@ _Note: nested `@import` will additionally benefit of the relative dirname of imp
 Type: `Function`  
 Default: `null`
 
-A function to transform the content of imported files. Take one argument (file content) & should return the modified content.
+A function to transform the content of imported files. Take one argument (file content) and should return the modified content or promise with it.
+`undefined` result will be skipped.
 
 #### `plugins`
 

index.js

@@ -284,10 +284,15 @@ function loadImportContent(
 
   return Promise.resolve(options.load(filename, options))
   .then(function(content) {
-    if (typeof options.transform === "function") {
-      content = options.transform(content, filename)
+    if (typeof options.transform !== "function") {
+      return content
     }
-
+    return Promise.resolve(options.transform(content, filename, options))
+    .then(function(transformed) {
+      return typeof transformed === "string" ? transformed : content
+    })
+  })
+  .then(function(content) {
     if (content.trim() === "") {
       result.warn(filename + " is empty", { node: atRule })
       return

package.json

@@ -24,7 +24,6 @@
   },
   "devDependencies": {
     "ava": "^0.8.0",
-    "css-whitespace": "^1.1.1",
     "eslint": "^1.1.0",
     "postcss-scss": "^0.1.3"
   },

test/fixtures/transform-content.css

@@ -0,0 +1 @@
+@import "foo"

test/fixtures/transform-content.expected.css

@@ -0,0 +1 @@
+transformed-content {}

test/fixtures/transform-undefined.css

@@ -0,0 +1 @@
+@import "foo"

test/fixtures/transform-undefined.expected.css

@@ -0,0 +1 @@
+foo{}

test/import.js

@@ -31,12 +31,6 @@ test("should import stylsheets relatively", t => {
   return compareFixtures(t, "relative")
 })
 
-test("should support transform", t => {
-  return compareFixtures(t, "transform", {
-    transform: require("css-whitespace"),
-  })
-})
-
 test("should work without a specified path", t => {
   return compareFixtures(t, "cwd")
 })

test/transform.js

@@ -0,0 +1,26 @@
+import test from "ava"
+import compareFixtures from "./lib/compare-fixtures"
+
+test.serial("should accept content", t => {
+  return compareFixtures(t, "transform-content", {
+    transform: () => "transformed-content {}",
+  })
+})
+
+test.serial("should accept promised content", t => {
+  return compareFixtures(t, "transform-content", {
+    transform: () => Promise.resolve("transformed-content {}"),
+  })
+})
+
+test.serial("should ignore returned undefined", t => {
+  return compareFixtures(t, "transform-undefined", {
+    transform: () => undefined,
+  })
+})
+
+test.serial("should ignore promised undefined", t => {
+  return compareFixtures(t, "transform-undefined", {
+    transform: () => Promise.resolve(undefined),
+  })
+})