Create an optional whitelist parameter

README.md

@@ -56,4 +56,6 @@ export default [
 
 #### Options
 
-- none, yet
+- whitelist: an array or Set of SPDX license identifiers that are allowed in the
+  list. If provided and a non-whitelisted dependency is encountered, the transform
+  will reject.

index.js

@@ -48,6 +48,14 @@ function equalityMap() {
   };
 }
 
+function flattenLicense(root) {
+  if (root.left) {
+    return [...flattenLicense(root.left), ...flattenLicense(root.right)];
+  } else if (root.license) {
+    return [root.license];
+  }
+}
+
 function arrayToSentence(arr) {
   const separator = ", ";
   const lastSeparator = " and ";
@@ -102,9 +110,10 @@ function groupByAuthor(modules) {
   }));
 }
 
-module.exports = (options = {}) => {
+module.exports = ({ whitelist } = {}) => {
   const cache = new Map();
   const dependencies = new Map();
+  const whitelistSet = new Set(whitelist);
   const cwd = process.cwd();
 
   return {
@@ -160,6 +169,15 @@ module.exports = (options = {}) => {
           continue;
         }
         let parsedLicense = licenseObjects(parseSPDX(dependency.license));
+        if (whitelist) {
+          for (let license of flattenLicense(parsedLicense)) {
+            if (!whitelistSet.has(license)) {
+              throw new Error(
+                `Non-whitelisted license detected in ${name}: ${license}`
+              );
+            }
+          }
+        }
 
         let existing = licenseGroups.get(parsedLicense);
         licenseGroups.set(
@@ -179,3 +197,5 @@ module.exports = (options = {}) => {
     }
   };
 };
+
+module.exports.flattenLicense = flattenLicense;

test/test.js

@@ -5,6 +5,31 @@ const commonjs = require("rollup-plugin-commonjs");
 const nodeResolve = require("rollup-plugin-node-resolve");
 const credits = require("../");
 
+test("flattenLicense", t => {
+  t.deepEqual(
+    credits.flattenLicense({
+      left: { license: "LGPL-2.1" },
+      conjunction: "or",
+      right: {
+        left: { license: "BSD-3-Clause" },
+        conjunction: "and",
+        right: { license: "MIT" }
+      }
+    }),
+    ["LGPL-2.1", "BSD-3-Clause", "MIT"]
+  );
+  t.deepEqual(
+    credits.flattenLicense({
+      left: { license: "BSD-3-Clause" },
+      conjunction: "and",
+      right: { license: "MIT" }
+    }),
+    ["BSD-3-Clause", "MIT"]
+  );
+  t.deepEqual(credits.flattenLicense({ license: "LGPL-2.1" }), ["LGPL-2.1"]);
+  t.end();
+});
+
 test("rollup-plugin-credits", t => {
   t.ok("required");
 
@@ -64,3 +89,31 @@ test("rollup-plugin-credits", t => {
     t.end();
   });
 });
+
+test("rollup-plugin-credits whitelist", t => {
+  const rollupConfig = {
+    input: path.join(__dirname, "example.js"),
+    output: {
+      format: "es"
+    },
+    plugins: [
+      nodeResolve(),
+      commonjs(),
+      credits({ debug: true, whitelist: ["MIT"] })
+    ]
+  };
+
+  rollup.rollup(rollupConfig).then(async bundle => {
+    try {
+      const { code, map } = await bundle.generate({ format: "es" });
+      t.fail();
+    } catch (e) {
+      t.ok(
+        e.message.includes("Non-whitelisted license detected in inherits: ISC"),
+        "Got infringment"
+      );
+    }
+
+    t.end();
+  });
+});