feat(@angular-devkit/build-optimizer): remove constructor __param

Author: filipesilva

packages/angular_devkit/build_optimizer/src/transforms/scrub-file.ts

@@ -410,6 +410,7 @@ function pickDecorateNodesToRemove(
 
   // Only remove constructor parameter metadata on non-whitelisted classes.
   if (platformWhitelist.indexOf(classId.text) === -1) {
+    // Remove __metadata calls of type 'design:paramtypes'.
     const metadataCalls = elements.filter((el) => {
       if (!isTslibHelper(el, '__metadata', tslibImports, checker)) {
         return false;
@@ -427,7 +428,21 @@ function pickDecorateNodesToRemove(
 
       return true;
     });
-    ngDecoratorCalls.push(...metadataCalls);
+    // Remove all __param calls.
+    const paramCalls = elements.filter((el) => {
+      if (!isTslibHelper(el, '__param', tslibImports, checker)) {
+        return false;
+      }
+      if (el.arguments.length != 2) {
+        return false;
+      }
+      if (el.arguments[0].kind !== ts.SyntaxKind.NumericLiteral) {
+        return false;
+      }
+
+      return true;
+    });
+    ngDecoratorCalls.push(...metadataCalls, ...paramCalls);
   }
 
   // If all decorators are metadata decorators then return the whole `Class = __decorate([...])'`

packages/angular_devkit/build_optimizer/src/transforms/scrub-file_spec.ts

@@ -422,6 +422,38 @@ describe('scrub-file', () => {
     });
   });
 
+  describe('__param', () => {
+    it('removes all constructor parameters and their type metadata', () => {
+      const output = tags.stripIndent`
+        var MyClass = /** @class */ (function () {
+            function MyClass(myParam) {
+                this.myProp = 'foo';
+            }
+            MyClass = __decorate([
+                myDecorator()
+            ], MyClass);
+            return MyClass;
+        }());
+      `;
+      const input = tags.stripIndent`
+        var MyClass = /** @class */ (function () {
+            function MyClass(myParam) {
+                this.myProp = 'foo';
+            }
+            MyClass = __decorate([
+                myDecorator(),
+                __param(0, myDecorator()),
+                __metadata("design:paramtypes", [Number])
+            ], MyClass);
+            return MyClass;
+        }());
+      `;
+
+      expect(testScrubFile(input)).toBeTruthy();
+      expect(tags.oneLine`${transform(input)}`).toEqual(tags.oneLine`${output}`);
+    });
+  });
+
   describe('propDecorators', () => {
     it('removes top-level Angular propDecorators', () => {
       const output = tags.stripIndent`