Fix: OpenAPI3 params are explode: true by default

.chronus/changes/fix-openapi-explode-query-false-2024-7-13-16-6-10.md

@@ -0,0 +1,8 @@
+---
+# Change versionKind to one of: internal, fix, dependencies, feature, deprecation, breaking
+changeKind: fix
+packages:
+  - "@typespec/openapi3"
+---
+
+Fix: query params are `explode: true` by default in OpenAPI 3.0

.github/workflows/consistency.yml

@@ -24,13 +24,13 @@ jobs:
 
       - uses: ./.github/actions/setup
 
-      - run: git pull --force --no-tags origin main:main
-        name: Get main ref
+      - run: git pull --force --no-tags origin ${{ github.event.pull_request.base.ref }}:${{ github.event.pull_request.base.ref }}
+        name: Get ${{ github.event.pull_request.base.ref }} ref for ${{ github.ref}}, evt ${{ github.event_name }}
 
       - run: pnpm install
         name: Install dependencies
 
-      - run: npx chronus verify
+      - run: npx chronus verify --since ${{ github.event.pull_request.base.ref }}
         name: Check changelog
         if: |
           !startsWith(github.head_ref, 'publish/') &&

packages/openapi3/src/openapi.ts

@@ -1456,18 +1456,20 @@ function createOAPIEmitter(
   function getQueryParameterAttributes(parameter: HttpOperationParameter & { type: "query" }) {
     const attributes: { style?: string; explode?: boolean } = {};
 
-    if (parameter.explode) {
-      attributes.explode = true;
+    if (parameter.explode !== true) {
+      // For query parameters(style: form) the default is explode: true https://spec.openapis.org/oas/v3.0.2#fixed-fields-9
+      attributes.explode = false;
     }
 
     switch (parameter.format) {
       case "ssv":
         return { style: "spaceDelimited", explode: false };
       case "pipes":
         return { style: "pipeDelimited", explode: false };
-      case undefined:
       case "csv":
       case "simple":
+        return { explode: false };
+      case undefined:
       case "multi":
       case "form":
         return attributes;

packages/openapi3/test/metadata.test.ts

@@ -661,6 +661,7 @@ describe("openapi3: metadata", () => {
         "Parameters.q": {
           name: "q",
           in: "query",
+          explode: false,
           required: true,
           schema: { type: "string" },
         },
@@ -717,6 +718,7 @@ describe("openapi3: metadata", () => {
               name: "q",
               in: "query",
               required: true,
+              explode: false,
               schema: { type: "string" },
             },
             {

packages/openapi3/test/parameters.test.ts

@@ -31,18 +31,32 @@ describe("query parameters", () => {
     strictEqual(param.name, "$select");
   });
 
-  describe("set explode: true", () => {
+  describe("doesn't set explode if explode: true (Openapi3.0 inverse default)", () => {
     it("with option", async () => {
       const param = await getQueryParam(`op test(@query(#{explode: true}) myParam: string): void;`);
+      expect(param).not.toHaveProperty("explode");
+    });
+
+    it("with uri template", async () => {
+      const param = await getQueryParam(`@route("{?myParam*}") op test(myParam: string): void;`);
+      expect(param).not.toHaveProperty("explode");
+    });
+  });
+
+  describe("set explode: false if explode is not set", () => {
+    it("with option", async () => {
+      const param = await getQueryParam(
+        `op test(@query(#{explode: false}) myParam: string): void;`
+      );
       expect(param).toMatchObject({
-        explode: true,
+        explode: false,
       });
     });
 
     it("with uri template", async () => {
-      const param = await getQueryParam(`@route("{?myParam*}") op test(myParam: string): void;`);
+      const param = await getQueryParam(`@route("{?myParam}") op test(myParam: string): void;`);
       expect(param).toMatchObject({
-        explode: true,
+        explode: false,
       });
     });
   });
@@ -66,7 +80,6 @@ describe("query parameters", () => {
       in: "query",
       name: "$multi",
       required: true,
-      explode: true,
       schema: {
         type: "array",
         items: {
@@ -77,6 +90,7 @@ describe("query parameters", () => {
     deepStrictEqual(params[1], {
       in: "query",
       name: "$csv",
+      explode: false,
       schema: {
         type: "array",
         items: {
@@ -134,6 +148,7 @@ describe("query parameters", () => {
     deepStrictEqual(res.paths["/"].get.parameters[0], {
       in: "query",
       name: "id",
+      explode: false,
       required: true,
       schema: {
         type: "string",

packages/openapi3/test/shared-routes.test.ts

@@ -70,6 +70,7 @@ describe("openapi3: shared routes", () => {
       {
         in: "query",
         name: "resourceGroup",
+        explode: false,
         required: false,
         schema: {
           type: "string",
@@ -78,6 +79,7 @@ describe("openapi3: shared routes", () => {
       {
         in: "query",
         name: "foo",
+        explode: false,
         required: true,
         schema: {
           type: "string",
@@ -86,6 +88,7 @@ describe("openapi3: shared routes", () => {
       {
         in: "query",
         name: "subscription",
+        explode: false,
         required: false,
         schema: {
           type: "string",
@@ -130,6 +133,7 @@ describe("openapi3: shared routes", () => {
       {
         in: "query",
         name: "filter",
+        explode: false,
         required: true,
         schema: {
           type: "string",
@@ -176,6 +180,7 @@ describe("openapi3: shared routes", () => {
         name: "filter",
         in: "query",
         required: false,
+        explode: false,
         schema: {
           type: "string",
           enum: ["resourceGroup"],