feat: allow covariant overrides in classes (backport #2324)

src/assembler.ts

@@ -226,7 +226,7 @@ export class Assembler implements Emitter {
       jsiiVersion,
       bin: this.projectInfo.bin,
       fingerprint: '<TBD>',
-      usedFeatures: this.usedFeatures.size > 0 ? Array.from(this.usedFeatures) : undefined,
+      usedFeatures: _assemblyFeatures(this.usedFeatures), // might be appended later
     };
 
     if (this.deprecatedRemover) {
@@ -249,6 +249,15 @@ export class Assembler implements Emitter {
 
     const validator = new Validator(this.projectInfo, assembly);
     const validationResult = validator.emit();
+
+    // Inject detected features
+    if (validationResult.usedFeatures) {
+      for (const item of validationResult.usedFeatures) {
+        this.usedFeatures.add(item);
+      }
+      assembly.usedFeatures = _assemblyFeatures(this.usedFeatures);
+    }
+
     if (!validationResult.emitSkipped) {
       const zipped = writeAssembly(this.projectInfo.projectRoot, _fingerprint(assembly), {
         compress: this.compressAssembly ?? false,
@@ -269,6 +278,10 @@ export class Assembler implements Emitter {
       this._afterEmit();
     }
 
+    function _assemblyFeatures(usedFeatures: Set<spec.JsiiFeature>): spec.JsiiFeature[] | undefined {
+      return usedFeatures.size > 0 ? Array.from(usedFeatures).sort() : undefined;
+    }
+
     function _loadReadme(this: Assembler) {
       // Search for `README.md` in a case-insensitive way
       const fileName = fs

src/helpers.ts

@@ -28,7 +28,7 @@ export type MultipleSourceFiles = {
 /**
  * Assembly features supported by this compiler
  */
-export const ASSEMBLY_FEATURES_SUPPORTED: spec.JsiiFeature[] = ['intersection-types'];
+export const ASSEMBLY_FEATURES_SUPPORTED: spec.JsiiFeature[] = ['intersection-types', 'class-covariant-overrides'];
 
 /**
  * Compile a piece of source and return the JSII assembly for it