Fix discriminated union property access to use camelCase property names

packages/typespec-ts/src/modular/serialization/buildDeserializerFunction.ts

@@ -165,7 +165,7 @@ function buildPolymorphicDeserializer(
   });
 
   statements.push(`
-      switch (item.${type.discriminatorProperty.name}) {
+      switch (item.${normalizeName(type.discriminatorProperty.name, NameType.Property)}) {
        ${cases.join("\n")}
         default:
           return item;
@@ -232,7 +232,7 @@ function buildDiscriminatedUnionDeserializer(
     `);
   }
   output.push(`
-    switch (item.${type.discriminatorProperty?.name}) {
+    switch (item.${type.discriminatorProperty ? normalizeName(type.discriminatorProperty.name, NameType.Property) : "unknown"}) {
      ${cases.join("\n")}
       default:
         return ${baseDeserializerName}(item);

packages/typespec-ts/src/modular/serialization/buildSerializerFunction.ts

@@ -172,7 +172,7 @@ function buildPolymorphicSerializer(
   });
 
   statements.push(`
-      switch (item.${type.discriminatorProperty.name}) {
+      switch (item.${normalizeName(type.discriminatorProperty.name, NameType.Property)}) {
        ${cases.join("\n")}
         default:
           return item;
@@ -239,7 +239,7 @@ function buildDiscriminatedUnionSerializer(
     `);
   }
   output.push(`
-    switch (item.${type.discriminatorProperty?.name}) {
+    switch (item.${type.discriminatorProperty ? normalizeName(type.discriminatorProperty.name, NameType.Property) : "unknown"}) {
      ${cases.join("\n")}
       default:
         return ${baseSerializerName}(item);

packages/typespec-ts/test/modularUnit/scenarios/models/deserialization/discriminatedUnion.md

@@ -267,4 +267,228 @@ export function discountTypeProductSkuDeserializer(
     skuId: item["skuId"],
   };
 }
+```
+
+# Should correctly handle PascalCase discriminator property names
+
+Verify that discriminated union serializers correctly use camelCase property names when accessing discriminator properties in TypeScript interfaces, even when the TypeSpec property name is PascalCase.
+
+## TypeSpec
+
+This is tsp definition.
+
+```tsp
+@doc("Document type")
+union DocumentType {
+  string,
+  Request: "Request",
+  RemoteDependency: "RemoteDependency",
+  Exception: "Exception",
+  Event: "Event",
+  Trace: "Trace",
+  Unknown: "Unknown",
+}
+
+@discriminator("DocumentType")
+model DocumentIngress {
+  DocumentType: DocumentType;
+  DocumentStreamIds?: string[];
+  Properties?: string[];
+}
+
+model Request extends DocumentIngress {
+  DocumentType: DocumentType.Request;
+  Name?: string;
+  Url?: string;
+}
+
+model Exception extends DocumentIngress {
+  DocumentType: DocumentType.Exception;
+  ExceptionType?: string;
+  ExceptionMessage?: string;
+}
+
+@route("/documents")
+interface DocumentService {
+  op processDocument(@body body: DocumentIngress): DocumentIngress;
+}
+```
+
+Should ignore the warning `@azure-tools/typespec-ts/property-name-normalized`:
+
+```yaml
+mustEmptyDiagnostic: false
+```
+
+## Provide generated models and its serializer
+
+Generated Models.
+
+```ts models
+/** model interface DocumentIngress */
+export interface DocumentIngress {
+  documentType: DocumentType;
+  documentStreamIds?: string[];
+  properties?: string[];
+}
+
+export function documentIngressSerializer(item: DocumentIngress): any {
+  return {
+    DocumentType: item["documentType"],
+    DocumentStreamIds: !item["documentStreamIds"]
+      ? item["documentStreamIds"]
+      : item["documentStreamIds"].map((p: any) => {
+          return p;
+        }),
+    Properties: !item["properties"]
+      ? item["properties"]
+      : item["properties"].map((p: any) => {
+          return p;
+        }),
+  };
+}
+
+export function documentIngressDeserializer(item: any): DocumentIngress {
+  return {
+    documentType: item["DocumentType"],
+    documentStreamIds: !item["DocumentStreamIds"]
+      ? item["DocumentStreamIds"]
+      : item["DocumentStreamIds"].map((p: any) => {
+          return p;
+        }),
+    properties: !item["Properties"]
+      ? item["Properties"]
+      : item["Properties"].map((p: any) => {
+          return p;
+        }),
+  };
+}
+
+/** Alias for DocumentIngressUnion */
+export type DocumentIngressUnion = Request | Exception | DocumentIngress;
+
+export function documentIngressUnionSerializer(
+  item: DocumentIngressUnion,
+): any {
+  switch (item.documentType) {
+    case "Request":
+      return requestSerializer(item as Request);
+
+    case "Exception":
+      return exceptionSerializer(item as Exception);
+
+    default:
+      return documentIngressSerializer(item);
+  }
+}
+
+export function documentIngressUnionDeserializer(
+  item: any,
+): DocumentIngressUnion {
+  switch (item.documentType) {
+    case "Request":
+      return requestDeserializer(item as Request);
+
+    case "Exception":
+      return exceptionDeserializer(item as Exception);
+
+    default:
+      return documentIngressDeserializer(item);
+  }
+}
+
+/** Document type */
+export type DocumentType =
+  | "Request"
+  | "RemoteDependency"
+  | "Exception"
+  | "Event"
+  | "Trace"
+  | "Unknown";
+
+/** model interface Request */
+export interface Request extends DocumentIngress {
+  documentType: "Request";
+  name?: string;
+  url?: string;
+}
+
+export function requestSerializer(item: Request): any {
+  return {
+    DocumentType: item["documentType"],
+    DocumentStreamIds: !item["documentStreamIds"]
+      ? item["documentStreamIds"]
+      : item["documentStreamIds"].map((p: any) => {
+          return p;
+        }),
+    Properties: !item["properties"]
+      ? item["properties"]
+      : item["properties"].map((p: any) => {
+          return p;
+        }),
+    Name: item["name"],
+    Url: item["url"],
+  };
+}
+
+export function requestDeserializer(item: any): Request {
+  return {
+    documentType: item["DocumentType"],
+    documentStreamIds: !item["DocumentStreamIds"]
+      ? item["DocumentStreamIds"]
+      : item["DocumentStreamIds"].map((p: any) => {
+          return p;
+        }),
+    properties: !item["Properties"]
+      ? item["Properties"]
+      : item["Properties"].map((p: any) => {
+          return p;
+        }),
+    name: item["Name"],
+    url: item["Url"],
+  };
+}
+
+/** model interface Exception */
+export interface Exception extends DocumentIngress {
+  documentType: "Exception";
+  exceptionType?: string;
+  exceptionMessage?: string;
+}
+
+export function exceptionSerializer(item: Exception): any {
+  return {
+    DocumentType: item["documentType"],
+    DocumentStreamIds: !item["documentStreamIds"]
+      ? item["documentStreamIds"]
+      : item["documentStreamIds"].map((p: any) => {
+          return p;
+        }),
+    Properties: !item["properties"]
+      ? item["properties"]
+      : item["properties"].map((p: any) => {
+          return p;
+        }),
+    ExceptionType: item["exceptionType"],
+    ExceptionMessage: item["exceptionMessage"],
+  };
+}
+
+export function exceptionDeserializer(item: any): Exception {
+  return {
+    documentType: item["DocumentType"],
+    documentStreamIds: !item["DocumentStreamIds"]
+      ? item["DocumentStreamIds"]
+      : item["DocumentStreamIds"].map((p: any) => {
+          return p;
+        }),
+    properties: !item["Properties"]
+      ? item["Properties"]
+      : item["Properties"].map((p: any) => {
+          return p;
+        }),
+    exceptionType: item["ExceptionType"],
+    exceptionMessage: item["ExceptionMessage"],
+  };
+}
 ```