feat: Remove node-sass from peerDependencies (#533)

- Only require("node-sass") on runtime when loader has been called
- Based on feedback from #533 and facebook/create-react-app#4195

BREAKING CHANGE: The sass-loader throws an error at runtime now and refuses to compile if the peer dependency is wrong. This could break applications where npm's peer dependency warning was just ignored.

Author: Timer

.nycrc

@@ -7,8 +7,8 @@
         "lib/**/*.js"
     ],
     "lines": 97,
-    "statements": 91,
+    "statements": 97,
     "functions": 100,
-    "branches": 89,
+    "branches": 91,
     "check-coverage": true
 }

lib/loader.js

@@ -1,6 +1,5 @@
 "use strict";
 
-const sass = require("node-sass");
 const path = require("path");
 const async = require("neo-async");
 const formatSassError = require("./formatSassError");
@@ -12,7 +11,7 @@ const pify = require("pify");
 // fs tasks when running the custom importer code.
 // This can be removed as soon as node-sass implements a fix for this.
 const threadPoolSize = process.env.UV_THREADPOOL_SIZE || 4;
-const asyncSassJobQueue = async.queue(sass.render, threadPoolSize - 1);
+let asyncSassJobQueue = null;
 
 /**
  * The sass-loader makes node-sass available to webpack modules.
@@ -21,6 +20,28 @@ const asyncSassJobQueue = async.queue(sass.render, threadPoolSize - 1);
  * @param {string} content
  */
 function sassLoader(content) {
+    if (asyncSassJobQueue === null) {
+        let sass;
+        let sassVersion;
+
+        try {
+            sass = require("node-sass");
+            sassVersion = /^(\d+)/.exec(require("node-sass/package.json").version).pop();
+        } catch (e) {
+            throw new Error(
+                "`sass-loader` requires `node-sass` >=4. Please install a compatible version."
+            );
+        }
+
+        if (Number(sassVersion) < 4) {
+            throw new Error(
+                "The installed version of `node-sass` is not compatible (expected: >= 4, actual: " + sassVersion + ")."
+            );
+        }
+
+        asyncSassJobQueue = async.queue(sass.render, threadPoolSize - 1);
+    }
+
     const callback = this.async();
     const isSync = typeof callback !== "function";
     const self = this;

package-lock.json

@@ -40,6 +40,7 @@
     "eslint-plugin-jsdoc": "^2.4.0",
     "file-loader": "^0.11.2",
     "mocha": "^3.0.2",
+    "mock-require": "^3.0.1",
     "node-sass": "^4.5.0",
     "nyc": "^11.0.2",
     "raw-loader": "^0.5.1",
@@ -54,7 +55,6 @@
     "node": ">= 6.9.0 || >= 8.9.0"
   },
   "peerDependencies": {
-    "node-sass": "^4.0.0",
     "webpack": "^3.0.0 || ^4.0.0"
   },
   "keywords": [

package.json

@@ -11,6 +11,7 @@ const customFunctions = require("./tools/customFunctions.js");
 const pathToSassLoader = require.resolve("../lib/loader.js");
 const testLoader = require("./tools/testLoader");
 const sassLoader = require(pathToSassLoader);
+const mockRequire = require("mock-require");
 
 const CR = /\r/g;
 const syntaxStyles = ["scss", "sass"];
@@ -256,6 +257,40 @@ describe("sass-loader", () => {
                 done();
             });
         });
+        it("should output a message when `node-sass` is missing", (done) => {
+            mockRequire.reRequire(pathToSassLoader);
+            const module = require("module");
+            const originalResolve = module._resolveFilename;
+
+            module._resolveFilename = function (filename) {
+                if (!filename.match(/node-sass/)) {
+                    return originalResolve.apply(this, arguments);
+                }
+                const err = new Error();
+
+                err.code = "MODULE_NOT_FOUND";
+                throw err;
+            };
+            runWebpack({
+                entry: pathToSassLoader + "!" + pathToErrorFile
+            }, (err) => {
+                module._resolveFilename = originalResolve;
+                mockRequire.reRequire("node-sass");
+                err.message.should.match(/Please install a compatible version/);
+                done();
+            });
+        });
+        it("should output a message when `node-sass` is an incompatible version", (done) => {
+            mockRequire.reRequire(pathToSassLoader);
+            mockRequire("node-sass/package.json", { version: "3.0.0" });
+            runWebpack({
+                entry: pathToSassLoader + "!" + pathToErrorFile
+            }, (err) => {
+                mockRequire.stop("node-sass");
+                err.message.should.match(/The installed version of `node-sass` is not compatible/);
+                done();
+            });
+        });
     });
 });