[TypeSpec Validation] exclude trailing slash when calculating folder depth (#26626)

* trailing slash tsv folder rule

* Update eng/tools/typespec-validation/src/rules/folder-structure.ts

Author: ckairen

eng/tools/typespec-validation/src/rules/folder-structure.ts

@@ -31,8 +31,8 @@ export class FolderStructureRule implements Rule {
       }
     });
 
-    // Verify top level folder is lower case
-    let folderStruct = relativePath.split("/");
+    // Verify top level folder is lower case and remove empty entries when splitting by slash
+    let folderStruct = relativePath.split("/").filter(Boolean);
     if (folderStruct[1].match(/[A-Z]/g)) {
       success = false;
       errorOutput += `Invalid folder name. Folders under specification/ must be lower case.\n`;

eng/tools/typespec-validation/test/folder-structure.test.ts

@@ -28,6 +28,22 @@ describe("folder-structure", function () {
     assert(result.errorOutput.includes("must be lower case"));
   });
 
+  it("should succeed if package folder has trailing slash", async function () {
+    let host = new TsvTestHost();
+    host.globby = async () => {
+      return ["/foo/bar/tspconfig.yaml"];
+    };
+    host.normalizePath = () => {
+      return "/gitroot";
+    };
+
+    const result = await new FolderStructureRule().execute(
+      host,
+      "/gitroot/specification/foo/Foo/Foo/",
+    );
+    assert(result.success);
+  });
+
   it("should fail if package folder is more than 3 levels deep", async function () {
     let host = new TsvTestHost();
     host.globby = async () => {