Fix: Validating cross namespace (microsoft#4304)

.chronus/changes/fix-versioning-cross-ns-ref-2024-7-29-18-19-44.md

@@ -0,0 +1,6 @@
+---
+changeKind: internal
+packages:
+  - "@typespec/versioning"
+---
+

packages/versioning/src/validate.ts

@@ -605,7 +605,17 @@ function validateTargetVersionCompatible(
 ) {
   const sourceAvailability = resolveAvailabilityForStack(program, source);
   const [sourceNamespace] = getVersions(program, sourceAvailability.type);
-
+  // If we cannot get source availability check if there is some different versioning across the stack which would mean we verify across namespace and is causing issues.
+  if (sourceAvailability.map === undefined) {
+    const sources = Array.isArray(source) ? source : [source];
+    const baseNs = getVersions(program, sources[0]);
+    for (const type of sources) {
+      const ns = getVersions(program, type);
+      if (ns !== baseNs) {
+        return undefined;
+      }
+    }
+  }
   const targetAvailability = resolveAvailabilityForStack(program, target);
   const [targetNamespace] = getVersions(program, targetAvailability.type);
   if (!targetAvailability.map || !targetNamespace) return;

packages/versioning/test/versioned-dependencies.test.ts

@@ -551,6 +551,32 @@ describe("versioning: dependencies", () => {
     runner = await createVersioningTestRunner();
   });
 
+  it("cross namespace operation", async () => {
+    const diagnostics = await runner.diagnose(`
+      @versioned(Versions)
+      namespace Service {
+        enum Versions {
+          v1,
+          v2,
+        }
+
+        @added(Versions.v2)
+        op test(purpose: FilePurpose): void;
+
+        @added(Versions.v2)
+        model FilePurpose {
+          a: string;
+        }
+      }
+
+      @useDependency(Service.Versions.v2)
+      namespace Client {
+        op testClient is Service.test;
+      }
+    `);
+    expectDiagnosticEmpty(diagnostics);
+  });
+
   it("use model defined in non versioned library spreading properties", async () => {
     const { MyService, Test } = (await runner.compile(`
       namespace NonVersionedLib {