Add warning about enabling plugins in presets

lib/svgo.test.js

@@ -66,6 +66,38 @@ test('allow to disable and customize plugins in preset', () => {
   `);
 });
 
+test('warn when user tries enable plugins in preset', () => {
+  const svg = `
+    <svg viewBox="0 0 120 120"></svg>
+  `;
+  const warn = jest.spyOn(console, 'warn');
+  optimize(svg, {
+    plugins: [
+      {
+        name: 'preset-default',
+        params: {
+          overrides: {
+            cleanupListOfValues: true,
+          },
+        },
+      },
+    ],
+    js2svg: { pretty: true, indent: 2 },
+  });
+  expect(warn)
+    .toBeCalledWith(`You are trying to enable cleanupListOfValues which is not part of preset.
+Try to put it before or after preset, for example
+
+plugins: [
+  {
+    name: 'preset-default',
+  },
+  'cleanupListOfValues'
+]
+`);
+  warn.mockRestore();
+});
+
 describe('allow to configure EOL', () => {
   test('should respect EOL set to LF', () => {
     const svg = `

lib/svgo/plugins.js

@@ -86,6 +86,22 @@ const createPreset = ({ name, plugins }) => {
       if (floatPrecision != null) {
         globalOverrides.floatPrecision = floatPrecision;
       }
+      if (overrides) {
+        for (const [pluginName, override] of Object.entries(overrides)) {
+          if (override === true) {
+            console.warn(
+              `You are trying to enable ${pluginName} which is not part of preset.\n` +
+                `Try to put it before or after preset, for example\n\n` +
+                `plugins: [\n` +
+                `  {\n` +
+                `    name: 'preset-default',\n` +
+                `  },\n` +
+                `  'cleanupListOfValues'\n` +
+                `]\n`
+            );
+          }
+        }
+      }
       return invokePlugins(ast, info, plugins, overrides, globalOverrides);
     },
   };