From 4c391df7442e9c5139c007d07fdcf39a5619d0e5 Mon Sep 17 00:00:00 2001
From: Timothee Guerin <tiguerin@microsoft.com>
Date: Tue, 12 Mar 2024 15:50:23 -0700
Subject: [PATCH 1/3] Fix: OpenAPI3 emitter produce format: binary when
 multipart part is union with bytes

---
 packages/openapi3/src/schema-emitter.ts  | 13 ++++++++--
 packages/openapi3/test/multipart.test.ts | 31 ++++++++++++++++++++++++
 2 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/packages/openapi3/src/schema-emitter.ts b/packages/openapi3/src/schema-emitter.ts
index 5b579c6dee..32cc4f4d09 100644
--- a/packages/openapi3/src/schema-emitter.ts
+++ b/packages/openapi3/src/schema-emitter.ts
@@ -339,7 +339,8 @@ export class OpenAPI3SchemaEmitter extends TypeEmitter<
     }
 
     const refSchema = this.emitter.emitTypeReference(prop.type, {
-      referenceContext: isMultipart ? { contentType: "application/json" } : {},
+      referenceContext:
+        prop.type.kind !== "Union" && isMultipart ? { contentType: "application/json" } : {},
     });
 
     if (refSchema.kind !== "code") {
@@ -471,6 +472,7 @@ export class OpenAPI3SchemaEmitter extends TypeEmitter<
     const schemaMembers: { schema: any; type: Type | null }[] = [];
     let nullable = false;
     const discriminator = getDiscriminator(program, union);
+    const isMultipart = this.#getContentType().startsWith("multipart/");
 
     for (const variant of variants) {
       if (isNullType(variant.type)) {
@@ -478,6 +480,11 @@ export class OpenAPI3SchemaEmitter extends TypeEmitter<
         continue;
       }
 
+      if (isMultipart && this.#isBytesKeptRaw(variant.type)) {
+        schemaMembers.push({ schema: { type: "string", format: "binary" }, type: variant.type });
+        continue;
+      }
+
       if (isLiteralType(variant.type)) {
         if (!literalVariantEnumByType[variant.type.kind]) {
           const enumSchema = this.emitter.emitTypeReference(variant.type);
@@ -491,7 +498,9 @@ export class OpenAPI3SchemaEmitter extends TypeEmitter<
           literalVariantEnumByType[variant.type.kind].enum.push(variant.type.value);
         }
       } else {
-        const enumSchema = this.emitter.emitTypeReference(variant.type);
+        const enumSchema = this.emitter.emitTypeReference(variant.type, {
+          referenceContext: isMultipart ? { contentType: "application/json" } : {},
+        });
         compilerAssert(enumSchema.kind === "code", "Unexpected enum schema. Should be kind: code");
         schemaMembers.push({ schema: enumSchema.value, type: variant.type });
       }
diff --git a/packages/openapi3/test/multipart.test.ts b/packages/openapi3/test/multipart.test.ts
index ef50856d44..43707d3441 100644
--- a/packages/openapi3/test/multipart.test.ts
+++ b/packages/openapi3/test/multipart.test.ts
@@ -39,6 +39,37 @@ describe("typespec-autorest: multipart", () => {
     });
   });
 
+  it("part of type union `bytes | {content: bytes}` produce `type: string, format: binary`", async () => {
+    const res = await openApiFor(
+      `
+      op upload(@header contentType: "multipart/form-data", profileImage: bytes | {content: bytes}): void;
+      `
+    );
+    const op = res.paths["/"].post;
+    deepStrictEqual(op.requestBody.content["multipart/form-data"], {
+      schema: {
+        type: "object",
+        properties: {
+          profileImage: {
+            anyOf: [
+              {
+                format: "binary",
+                type: "string",
+              },
+              {
+                type: "object",
+                properties: {
+                  content: { type: "string" },
+                },
+              },
+            ],
+          },
+        },
+        required: ["profileImage"],
+      },
+    });
+  });
+
   it("part of type `bytes[]` produce `type: array, items: {type: string, format: binary}`", async () => {
     const res = await openApiFor(
       `

From efdb51a0a4a17c1d2c1377750277c17040a6d762 Mon Sep 17 00:00:00 2001
From: Timothee Guerin <tiguerin@microsoft.com>
Date: Tue, 12 Mar 2024 15:51:08 -0700
Subject: [PATCH 2/3] Fix test

---
 packages/openapi3/test/multipart.test.ts | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/packages/openapi3/test/multipart.test.ts b/packages/openapi3/test/multipart.test.ts
index 43707d3441..7317d1e7b8 100644
--- a/packages/openapi3/test/multipart.test.ts
+++ b/packages/openapi3/test/multipart.test.ts
@@ -53,14 +53,15 @@ describe("typespec-autorest: multipart", () => {
           profileImage: {
             anyOf: [
               {
-                format: "binary",
                 type: "string",
+                format: "binary",
               },
               {
                 type: "object",
                 properties: {
-                  content: { type: "string" },
+                  content: { type: "string", format: "byte" },
                 },
+                required: ["content"],
               },
             ],
           },

From 5fa4f582c96c4fee12f3e5b44ebfcfbc5a24e8f8 Mon Sep 17 00:00:00 2001
From: Timothee Guerin <timothee.guerin@outlook.com>
Date: Tue, 12 Mar 2024 15:53:26 -0700
Subject: [PATCH 3/3] Create
 fix-openapi3-multipart-union-bytes-2024-2-12-22-52-55.md

---
 ...x-openapi3-multipart-union-bytes-2024-2-12-22-52-55.md | 8 ++++++++
 1 file changed, 8 insertions(+)
 create mode 100644 .chronus/changes/fix-openapi3-multipart-union-bytes-2024-2-12-22-52-55.md

diff --git a/.chronus/changes/fix-openapi3-multipart-union-bytes-2024-2-12-22-52-55.md b/.chronus/changes/fix-openapi3-multipart-union-bytes-2024-2-12-22-52-55.md
new file mode 100644
index 0000000000..f5328e7012
--- /dev/null
+++ b/.chronus/changes/fix-openapi3-multipart-union-bytes-2024-2-12-22-52-55.md
@@ -0,0 +1,8 @@
+---
+# Change versionKind to one of: internal, fix, dependencies, feature, deprecation, breaking
+changeKind: fix
+packages:
+  - "@typespec/openapi3"
+---
+
+Fix: OpenAPI3 not marking part of bytes or something else as `format: binary`