fix: handle undefined and null as stats value (#302)

In certain cases depending on the inputFileSystem `stats` doesn't throw, but returns a falsey value such as `undefined` and `null`. In this case an error from globby will be thrown `Patterns must be a string or an array of strings`

src/preProcessPattern.js

@@ -59,21 +59,29 @@ export default function preProcessPattern(globalRef, pattern) {
 
     debug(`determined '${pattern.from}' to be read from '${pattern.absoluteFrom}'`);
 
-    return stat(inputFileSystem, pattern.absoluteFrom)
-    .catch(() => {
+    const noStatsHandler = () => {
         // If from doesn't appear to be a glob, then log a warning
         if (isGlob(pattern.from) || pattern.from.indexOf('*') !== -1) {
             pattern.fromType = 'glob';
             pattern.glob = escape(pattern.context, pattern.from);
         } else {
             const msg = `unable to locate '${pattern.from}' at '${pattern.absoluteFrom}'`;
-            warning(msg);
-            compilation.errors.push(`[copy-webpack-plugin] ${msg}`);
+            const warningMsg = `[copy-webpack-plugin] ${msg}`;
+            // only display the same message once
+            if (compilation.errors.indexOf(warningMsg) === -1) {
+                warning(msg);
+                compilation.errors.push(warningMsg);
+            }
+
             pattern.fromType = 'nonexistent';
         }
-    })
+    };
+
+    return stat(inputFileSystem, pattern.absoluteFrom)
+    .catch(() => noStatsHandler())
     .then((stat) => {
         if (!stat) {
+            noStatsHandler();
             return pattern;
         }
 

tests/index.js

@@ -56,6 +56,15 @@ class MockCompiler {
     }
 }
 
+
+class MockCompilerNoStat extends MockCompiler {
+    constructor (options = {}) {
+        super(options);
+
+        this.inputFileSystem.stat = (file, cb) => cb(undefined, undefined);
+    }
+}
+
 describe('apply function', () => {
     // Ideally we pass in patterns and confirm the resulting assets
     const run = (opts) => {
@@ -621,6 +630,23 @@ describe('apply function', () => {
             .catch(done);
         });
 
+        it('warns when file not found and stats is undefined', (done) => {
+            runEmit({
+                compiler: new MockCompilerNoStat(),
+                expectedAssetKeys: [],
+                expectedErrors: [
+                    `[copy-webpack-plugin] unable to locate 'nonexistent.txt' at '${HELPER_DIR}${path.sep}nonexistent.txt'`
+                ],
+                patterns: [{
+                    from: 'nonexistent.txt',
+                    to: '.',
+                    toType: 'dir'
+                }]
+            })
+            .then(done)
+            .catch(done);
+        });
+
         it('warns when tranform failed', (done) => {
             runEmit({
                 expectedAssetKeys: [],