feat: always use root signature parameter names

In languages such as Python (<3.8) and Ruby, positional parameters can
be referred to using their names, making these names part of the
function signature. In order to avoid enforing parameter name
consistency on the TypeScript source, the `jsii` compiler will always
use the root declaration's parameter names when emitting the `.jsii`
assembly file.

Related #2927

packages/jsii/lib/validator.ts

@@ -461,6 +461,10 @@ function _defaultValidations(): ValidationFunction[] {
             ),
           );
         }
+        // Standardize to the root method's argument signature, because in
+        // Python and Ruby, positional parameters can also be referred to by
+        // name, which makes their names be a part of the function's signature.
+        actParam.name = expParam.name;
       }
     }
 

packages/jsii/test/compat.test.ts

@@ -0,0 +1,107 @@
+import { sourceToAssemblyHelper } from '../lib';
+
+////////////////////////////////////////////////////////////////////////////////
+// In Python and Ruby, positional parameters can be referred to by name, making
+// them part of a function's signature. Always using the root implementation
+// parameter names makes no difference in the undelying runtime, as JS
+// positional arguments are... positional, but it reduces friction for Python
+// and Ruby developers.
+test('overriding methods use the overriden parameter names', async () => {
+  const assembly = await sourceToAssemblyHelper(`
+    export abstract class AbstractClass {
+      public abstract method(param: number): void;
+    }
+
+    export class ConcreteClass extends AbstractClass {
+      private constructor() { super(); }
+
+      public method(_arg: number): void {
+        // Nothing to do...
+      }
+    }
+  `);
+
+  expect(assembly.types!['testpkg.AbstractClass']).toEqual({
+    abstract: true,
+    assembly: 'testpkg',
+    fqn: 'testpkg.AbstractClass',
+    kind: 'class',
+    methods: [
+      {
+        abstract: true,
+        locationInModule: { filename: 'index.ts', line: 3 },
+        name: 'method',
+        parameters: [{ name: 'param', type: { primitive: 'number' } }],
+      },
+    ],
+    initializer: {},
+    locationInModule: { filename: 'index.ts', line: 2 },
+    name: 'AbstractClass',
+  });
+
+  expect(assembly.types!['testpkg.ConcreteClass']).toEqual({
+    assembly: 'testpkg',
+    base: 'testpkg.AbstractClass',
+    fqn: 'testpkg.ConcreteClass',
+    kind: 'class',
+    methods: [
+      {
+        locationInModule: { filename: 'index.ts', line: 9 },
+        name: 'method',
+        overrides: 'testpkg.AbstractClass',
+        parameters: [{ name: 'param', type: { primitive: 'number' } }],
+      },
+    ],
+    locationInModule: { filename: 'index.ts', line: 6 },
+    name: 'ConcreteClass',
+  });
+});
+
+test('implementing methods use the interface parameter names', async () => {
+  const assembly = await sourceToAssemblyHelper(`
+    export interface IInterface {
+      method(param: number): void;
+    }
+
+    export class ConcreteClass implements IInterface {
+      private constructor() {}
+
+      public method(_arg: number): void {
+        // Nothing to do...
+      }
+    }
+  `);
+
+  expect(assembly.types!['testpkg.IInterface']).toEqual({
+    assembly: 'testpkg',
+    fqn: 'testpkg.IInterface',
+    kind: 'interface',
+    methods: [
+      {
+        abstract: true,
+        locationInModule: { filename: 'index.ts', line: 3 },
+        name: 'method',
+        parameters: [{ name: 'param', type: { primitive: 'number' } }],
+      },
+    ],
+    locationInModule: { filename: 'index.ts', line: 2 },
+    name: 'IInterface',
+  });
+
+  expect(assembly.types!['testpkg.ConcreteClass']).toEqual({
+    assembly: 'testpkg',
+    interfaces: ['testpkg.IInterface'],
+    fqn: 'testpkg.ConcreteClass',
+    kind: 'class',
+    methods: [
+      {
+        locationInModule: { filename: 'index.ts', line: 9 },
+        name: 'method',
+        overrides: 'testpkg.IInterface',
+        parameters: [{ name: 'param', type: { primitive: 'number' } }],
+      },
+    ],
+    locationInModule: { filename: 'index.ts', line: 6 },
+    name: 'ConcreteClass',
+  });
+});