From 8e3240a16a2acf25b7783e9fcc3e038bd0360d7b Mon Sep 17 00:00:00 2001
From: Travis Prescott <tjprescott@users.noreply.github.com>
Date: Wed, 20 Sep 2023 09:43:26 -0700
Subject: [PATCH] OpenAPI3 - Fix CSV format representation (#2446)

Fixes #2234.
---
 .../openapi3-FixCsvFormat_2023-09-19-21-04.json        | 10 ++++++++++
 packages/openapi3/src/openapi.ts                       |  7 ++++++-
 packages/openapi3/test/parameters.test.ts              |  3 ++-
 3 files changed, 18 insertions(+), 2 deletions(-)
 create mode 100644 common/changes/@typespec/openapi3/openapi3-FixCsvFormat_2023-09-19-21-04.json

diff --git a/common/changes/@typespec/openapi3/openapi3-FixCsvFormat_2023-09-19-21-04.json b/common/changes/@typespec/openapi3/openapi3-FixCsvFormat_2023-09-19-21-04.json
new file mode 100644
index 0000000000..cdcd568687
--- /dev/null
+++ b/common/changes/@typespec/openapi3/openapi3-FixCsvFormat_2023-09-19-21-04.json
@@ -0,0 +1,10 @@
+{
+  "changes": [
+    {
+      "packageName": "@typespec/openapi3",
+      "comment": "Fix issue with CSV format representation.",
+      "type": "none"
+    }
+  ],
+  "packageName": "@typespec/openapi3"
+}
\ No newline at end of file
diff --git a/packages/openapi3/src/openapi.ts b/packages/openapi3/src/openapi.ts
index ac109efeec..cefb96bced 100644
--- a/packages/openapi3/src/openapi.ts
+++ b/packages/openapi3/src/openapi.ts
@@ -1162,7 +1162,12 @@ function createOAPIEmitter(program: Program, options: ResolvedOpenAPI3EmitterOpt
     ph.in = parameter.type;
     if (parameter.type === "query" || parameter.type === "header") {
       if (parameter.format === "csv" || parameter.format === "simple") {
-        ph.style = "simple";
+        if (parameter.type === "query") {
+          ph.style = "form";
+          ph.explode = false;
+        } else {
+          ph.style = "simple";
+        }
       } else if (parameter.format === "multi" || parameter.format === "form") {
         if (parameter.type === "header") {
           reportDiagnostic(program, {
diff --git a/packages/openapi3/test/parameters.test.ts b/packages/openapi3/test/parameters.test.ts
index 70c7eb7ce7..80b8c6e315 100644
--- a/packages/openapi3/test/parameters.test.ts
+++ b/packages/openapi3/test/parameters.test.ts
@@ -54,7 +54,8 @@ describe("openapi3: parameters", () => {
     deepStrictEqual(params[1], {
       in: "query",
       name: "$csv",
-      style: "simple",
+      style: "form",
+      explode: false,
       schema: {
         type: "array",
         items: {