fix(rosetta): gets confused by type unions (#3156)

Rosetta gets confused by type unions when it's trying to derive
the type of a struct.

This bites CDK as we're generating examples for L1s, and they all have
unions with `IResolvable` in all their properties.

If we can match a struct, let's do so.



---

By submitting this pull request, I confirm that my contribution is made under the terms of the [Apache 2.0 license].

[Apache 2.0 license]: https://www.apache.org/licenses/LICENSE-2.0

packages/jsii-rosetta/lib/jsii/jsii-types.ts

@@ -61,7 +61,10 @@ export function determineJsiiType(typeChecker: ts.TypeChecker, type: ts.Type): J
   }
 
   if (type.isUnion() || type.isIntersection()) {
-    return { kind: 'error', message: 'Type unions or intersections are not supported in examples' };
+    return {
+      kind: 'error',
+      message: `Type unions or intersections are not supported in examples, got: ${typeChecker.typeToString(type)}`,
+    };
   }
   return { kind: 'unknown' };
 }
@@ -94,10 +97,15 @@ export function analyzeObjectLiteral(
     return isDeclaredCall ? { kind: 'map' } : { kind: 'unknown' };
   }
 
-  const structType = analyzeStructType(type);
-  if (structType) {
-    return { kind: structType, type };
+  // If the type is a union between a struct and something else, return the first possible struct
+  const structCandidates = type.isUnion() ? type.types : [type];
+  for (const candidate of structCandidates) {
+    const structType = analyzeStructType(candidate);
+    if (structType) {
+      return { kind: structType, type: candidate };
+    }
   }
+
   return { kind: 'map' };
 }
 

packages/jsii-rosetta/test/translations/structs/infer_struct_from_union.cs

@@ -0,0 +1,6 @@
+Takes(new MyProps {
+    Struct = new SomeStruct {
+        Enabled = false,
+        Option = "option"
+    }
+});

packages/jsii-rosetta/test/translations/structs/infer_struct_from_union.java

@@ -0,0 +1,6 @@
+takes(MyProps.builder()
+        .struct(SomeStruct.builder()
+                .enabled(false)
+                .option("option")
+                .build())
+        .build());

packages/jsii-rosetta/test/translations/structs/infer_struct_from_union.py

@@ -0,0 +1,6 @@
+takes(
+    struct=SomeStruct(
+        enabled=False,
+        option="option"
+    )
+)

packages/jsii-rosetta/test/translations/structs/infer_struct_from_union.ts

@@ -0,0 +1,29 @@
+/// !hide
+/// fake-from-jsii
+interface IResolvable {
+  resolve(): any;
+}
+
+/// fake-from-jsii
+interface SomeStruct {
+  readonly enabled: boolean | IResolvable;
+  readonly option?: string | IResolvable;
+}
+
+/// fake-from-jsii
+interface MyProps {
+  readonly struct?: IResolvable | SomeStruct;
+}
+
+function takes(props: MyProps) {
+}
+/// !show
+
+takes({
+  struct: {
+    enabled: false,
+    option: 'option',
+  },
+});
+
+