fix: improve some Terser & Webpack error reporting

- show result with error info from Terser if needed
- show informative message instead of an internal error
  in case there is no code for Webpack to process
  (temporary workaround solution)

ref: #21

src/index.js

@@ -77,14 +77,18 @@ export const sizeSnapshot = (options?: Options = {}): Plugin => {
 
       const outputName = chunk.fileName;
 
-      // Improvement with better error handling was proposed in
+      // Cleaner error reporting was discussed in
       // brodybits/rollup-plugin-size-snapshot#17
       // but a reproduction is needed to add a test case, see
       // https://github.com/brodybits/rollup-plugin-size-snapshot/issues/19
-      const minified = minify(source).code;
-      if (!minified) {
+      const minifyResult = minify(source);
+      const minified = minifyResult.code;
+      if (!minified && minified !== "") {
+        // TODO needs test case with a reproduction, see
+        // https://github.com/brodybits/rollup-plugin-size-snapshot/issues/19
         throw new Error(
-          "INTERNAL ERROR - terser error - see https://github.com/brodybits/rollup-plugin-size-snapshot/issues/19"
+          "INTERNAL ERROR - terser error - see https://github.com/brodybits/rollup-plugin-size-snapshot/issues/19 " +
+            JSON.stringify(minifyResult)
         );
       }
 

src/treeshakeWithWebpack.js

@@ -38,6 +38,11 @@ export const treeshakeWithWebpack = (code: string): Promise<Output> => {
     ],
   });
 
+  // TEMPORARY WORKAROUND SOLUTION:
+  if (code === "") {
+    return Promise.reject(new Error("no minified code for Webpack to process"));
+  }
+
   inputFS.writeFileSync(`/${inputName}`, `import {} from '/${bundleName}'`);
   inputFS.writeFileSync(`/${bundleName}`, code);
 

tests/index.test.js

@@ -445,5 +445,5 @@ test("reproduce failure for esm with comments only ref: brodybits/rollup-plugin-
       plugins: [sizeSnapshot({ snapshotPath })],
       output: { file: path.resolve("fixtures/output.js"), format: "esm" },
     });
-  }).rejects.toThrow(/INTERNAL ERROR - terser error/); // was "No content" in v0.13.2
+  }).rejects.toThrow(/no minified code for Webpack to process/);
 });