[tcgc] add linter for empty client names (Azure#1066)

fixes Azure#647

---------

Co-authored-by: iscai-msft <isabellavcai@gmail.com>
Co-authored-by: catalinaperalta <catalinaperaltah@hotmail.com>

.chronus/changes/whitespace_client_name-2024-5-24-14-18-45.md

@@ -0,0 +1,7 @@
+---
+changeKind: fix
+packages:
+  - "@azure-tools/typespec-client-generator-core"
+---
+
+Add linter for empty `@clientName` values

packages/typespec-client-generator-core/src/decorators.ts

@@ -977,7 +977,13 @@ export function $clientName(
       }
     }
   }
-
+  if (value.trim() === "") {
+    reportDiagnostic(context.program, {
+      code: "empty-client-name",
+      format: {},
+      target: entity,
+    });
+  }
   setScopedDecoratorData(context, $clientName, clientNameKey, entity, value, scope);
 }
 

packages/typespec-client-generator-core/src/lib.ts

@@ -147,6 +147,12 @@ export const $lib = createTypeSpecLibrary({
         default: paramMessage`Can not find name for your emitter, please check your emitter name.`,
       },
     },
+    "empty-client-name": {
+      severity: "warning",
+      messages: {
+        default: `Cannot pass an empty value to the @clientName decorator`,
+      },
+    },
   },
 });
 

packages/typespec-client-generator-core/test/decorators.test.ts

@@ -2684,6 +2684,22 @@ describe("typespec-client-generator-core: decorators", () => {
         "body"
       );
     });
+    it("empty client name", async () => {
+      const diagnostics = await runner.diagnose(`
+        @service({})
+        namespace MyService;
+        
+        @clientName(" ")
+        model Test {
+          id: string;
+          prop: string;
+        }
+      `);
+
+      expectDiagnostics(diagnostics, {
+        code: "@azure-tools/typespec-client-generator-core/empty-client-name",
+      });
+    });
   });
 
   describe("versioning projection", () => {