Fix required eTag conditional headers in Python

.chronus/changes/fix-required-etag-header-2026-09-14.md

@@ -0,0 +1,8 @@
+---
+changeKind: fix
+packages:
+  - "@typespec/http-client-python"
+---
+
+Generate required `If-Match` headers as direct `if_match` parameters instead of
+the optional `etag` and `match_condition` convenience API.

packages/http-client-python/emitter/src/http.ts

@@ -206,7 +206,11 @@ function isEtagType(type: SdkType): boolean {
   );
 }
 
-function getEtagRole(parameter: SdkHeaderParameter): string | undefined {
+export function getEtagRole(parameter: SdkHeaderParameter): string | undefined {
+  // The etag/match_condition convenience API can omit or redirect the wire
+  // header, so it is only valid when the TypeSpec header itself is optional.
+  if (!parameter.optional) return undefined;
+
   const name = parameter.name.toLowerCase();
   const wire = parameter.serializedName.toLowerCase();
   // Standard If-Match / If-None-Match headers work with any type

packages/http-client-python/emitter/test/http.test.ts

@@ -0,0 +1,19 @@
+import type { SdkHeaderParameter } from "@azure-tools/typespec-client-generator-core";
+import { strictEqual } from "assert";
+import { describe, it } from "vitest";
+import { getEtagRole } from "../src/http.js";
+
+function createHeaderParameter(optional: boolean): SdkHeaderParameter {
+  return {
+    name: "ifMatch",
+    serializedName: "If-Match",
+    optional,
+  } as SdkHeaderParameter;
+}
+
+describe("typespec-python: HTTP parameters", () => {
+  it("only promotes optional If-Match headers to the conditional convenience API", () => {
+    strictEqual(getEtagRole(createHeaderParameter(true)), "ifMatch");
+    strictEqual(getEtagRole(createHeaderParameter(false)), undefined);
+  });
+});

packages/http-client-python/tests/mock_api/azure/asynctests/test_azure_special_headers_conditional_request_async.py

@@ -21,6 +21,11 @@ async def test_post_if_match(client: ConditionalRequestClient):
     await client.post_if_match(etag="valid", match_condition=MatchConditions.IfNotModified)
 
 
+@pytest.mark.asyncio
+async def test_post_required_if_match(client: ConditionalRequestClient):
+    await client.post_required_if_match(if_match='"required"')
+
+
 @pytest.mark.asyncio
 async def test_post_if_none_match(client: ConditionalRequestClient):
     await client.post_if_none_match(etag="invalid", match_condition=MatchConditions.IfModified)

packages/http-client-python/tests/mock_api/azure/test_azure_special_headers_conditional_request.py

@@ -19,6 +19,10 @@ def test_post_if_match(client: ConditionalRequestClient):
     client.post_if_match(etag="valid", match_condition=MatchConditions.IfNotModified)
 
 
+def test_post_required_if_match(client: ConditionalRequestClient):
+    client.post_required_if_match(if_match='"required"')
+
+
 def test_post_if_none_match(client: ConditionalRequestClient):
     client.post_if_none_match(etag="invalid", match_condition=MatchConditions.IfModified)