fix(openapi3): emit @encode decorator for anyOf/oneOf with unixtime format

.chronus/changes/fix-anyof-unixtime-decorator-2025-12-09-16-54-20.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/openapi3"
+---
+
+Import OpenAPI schemas with anyOf/oneOf containing unixtime format correctly emits `@encode(DateTimeKnownEncoding.unixTimestamp, integer)` decorator for nullable utcDateTime properties

packages/openapi3/src/cli/actions/convert/utils/decorators.ts

@@ -172,8 +172,35 @@ export function getDecoratorsForSchema(
     : schema.type;
 
   // Handle unixtime format with @encode decorator
-  if (schema.format === "unixtime") {
-    decorators.push(...getUnixtimeSchemaDecorators(effectiveType));
+  // Check both direct format and format from anyOf/oneOf members
+  let formatToUse = schema.format;
+  let typeForFormat = effectiveType;
+
+  // If format is not directly on the schema, check anyOf/oneOf members for unixtime format
+  if (!formatToUse) {
+    const unionMembers = schema.anyOf || schema.oneOf;
+    if (unionMembers) {
+      for (const member of unionMembers) {
+        if ("$ref" in member) continue;
+        // Check if this is a non-null member with unixtime format
+        if (member.format === "unixtime" && member.type !== "null") {
+          formatToUse = member.format;
+          // Extract effective type from member (handle type arrays)
+          const memberType = Array.isArray(member.type)
+            ? member.type.find((t) => t !== "null")
+            : member.type;
+          // Only use if we found a valid type
+          if (memberType) {
+            typeForFormat = memberType;
+          }
+          break;
+        }
+      }
+    }
+  }
+
+  if (formatToUse === "unixtime") {
+    decorators.push(...getUnixtimeSchemaDecorators(typeForFormat));
   }
 
   switch (effectiveType) {

packages/openapi3/test/tsp-openapi3/convert-openapi3-doc.test.ts

@@ -407,4 +407,91 @@ describe("unixtime format conversion", () => {
       "Expected 'created?: string' but got: " + tsp,
     );
   });
+
+  it("should convert anyOf with integer unixtime and null to utcDateTime | null with @encode decorator", async () => {
+    const tsp = await convertOpenAPI3Document({
+      openapi: "3.1.0",
+      info: {
+        title: "Test Service",
+        version: "0.0.0",
+      },
+      paths: {},
+      components: {
+        schemas: {
+          Foo: {
+            type: "object",
+            properties: {
+              finished_at: {
+                anyOf: [
+                  {
+                    type: "integer",
+                    format: "unixtime",
+                  },
+                  {
+                    type: "null",
+                  },
+                ],
+              },
+            },
+          },
+        },
+      },
+    });
+
+    // Should contain "@encode(DateTimeKnownEncoding.unixTimestamp, integer)" and "finished_at?: utcDateTime | null"
+    strictEqual(
+      tsp.includes("@encode(DateTimeKnownEncoding.unixTimestamp, integer)"),
+      true,
+      "Expected '@encode(DateTimeKnownEncoding.unixTimestamp, integer)' but got: " + tsp,
+    );
+    strictEqual(
+      tsp.includes("finished_at?: utcDateTime | null"),
+      true,
+      "Expected 'finished_at?: utcDateTime | null' but got: " + tsp,
+    );
+  });
+
+  it("should convert oneOf with integer unixtime and null to utcDateTime | null with @encode decorator", async () => {
+    const tsp = await convertOpenAPI3Document({
+      openapi: "3.1.0",
+      info: {
+        title: "Test Service",
+        version: "0.0.0",
+      },
+      paths: {},
+      components: {
+        schemas: {
+          Foo: {
+            type: "object",
+            properties: {
+              started_at: {
+                oneOf: [
+                  {
+                    type: "integer",
+                    format: "unixtime",
+                  },
+                  {
+                    type: "null",
+                  },
+                ],
+              },
+            },
+          },
+        },
+      },
+    });
+
+    // Should contain "@encode(DateTimeKnownEncoding.unixTimestamp, integer)" and "@oneOf" and "started_at?: utcDateTime | null"
+    strictEqual(
+      tsp.includes("@encode(DateTimeKnownEncoding.unixTimestamp, integer)"),
+      true,
+      "Expected '@encode(DateTimeKnownEncoding.unixTimestamp, integer)' but got: " + tsp,
+    );
+    strictEqual(tsp.includes("@oneOf"), true, "Expected '@oneOf' but got: " + tsp);
+    strictEqual(
+      tsp.includes("started_at?: utcDateTime | null"),
+      true,
+      "Expected 'started_at?: utcDateTime | null' but got: " + tsp,
+    );
+  });
 });