Add --hide-unchanged option to hide unchanged SVGs

lib/svgo/coa.js

@@ -78,6 +78,10 @@ export default function makeProgram(program) {
       '-q, --quiet',
       'Only output error messages, not regular status messages',
     )
+    .option(
+      '-h, --hide-unchanged',
+      'Hide Unchanged/Unoptimized files in the output (only show Optimized files)',
+    )
     .option('--show-plugins', 'Show available plugins and exit')
     // used by picocolors internally
     .option('--no-color', 'Output plain text without color')
@@ -166,6 +170,11 @@ async function action(args, opts, command) {
     config.quiet = opts.quiet;
   }
 
+  // --hide-unchanged
+  if (opts.hideUnchanged) {
+    config.hideUnchanged = opts.hideUnchanged;
+  }
+
   // --recursive
   if (opts.recursive) {
     config.recursive = opts.recursive;
@@ -414,6 +423,9 @@ function processSVGData(config, info, data, output, input) {
 
   return writeOutput(input, output, result.data).then(
     function () {
+      if (config.hideUnchanged && prevFileSize === resultFileSize) {
+        return;
+      }
       if (!config.quiet && output != '-') {
         if (input) {
           console.log(`\n${path.basename(input)}:`);

test/coa/_index.test.js

@@ -12,7 +12,7 @@ const svgFiles = [
   path.resolve(__dirname, 'testSvg/test.svg'),
   path.resolve(__dirname, 'testSvg/test.1.svg'),
 ];
-const tempFolder = 'temp';
+const tempFolder = 'temp/';
 
 /**
  * @param {ReadonlyArray<string>} args
@@ -140,5 +140,52 @@ describe('coa', function () {
         ]),
       ).rejects.toThrow(/No SVG files have been found/);
     });
+
+    it('Should not show output when svg remains unchanged (--hide-unchanged is set)', async () => {
+      let output = '';
+      const original = console.log;
+      console.log = function (...args) {
+        output += args.join(' ') + '\n';
+      };
+      try {
+        await expect(
+          runProgram([
+            '--folder',
+            path.resolve(__dirname, 'testFolderUnchangedSvg'),
+            '--hide-unchanged',
+            '--output',
+            tempFolder,
+          ]),
+        ).resolves.toBeDefined();
+
+        expect(output).not.toContain('unchanged.svg');
+      } finally {
+        console.log = original;
+      }
+    });
+
+    it('Should show output when svg gets optimized (--hide-unchanged is set)', async () => {
+      let output = '';
+      const original = console.log;
+      console.log = function (...args) {
+        output += args.join(' ') + '\n';
+      };
+      try {
+        await expect(
+          runProgram([
+            '--folder',
+            path.resolve(__dirname, 'testFolderUnchangedSvg'),
+            '--hide-unchanged',
+            '--output',
+            tempFolder,
+          ]),
+        ).resolves.toBeDefined();
+
+        expect(output).toContain('optimizable.svg');
+        expect(output).not.toContain('unchanged.svg');
+      } finally {
+        console.log = original;
+      }
+    });
   });
 });