[TypeSpec Validation] verify folder structure (#25712)

* folder structure

* typespec folder depth limit

* main.tsp and client.tsp

* fix windows separator issue

eng/tools/TypeSpecValidation/src/rules/folder-structure.ts

@@ -1,6 +1,8 @@
 import { globby } from "globby";
+import path from "path";
 import { Rule } from "../rule.js";
 import { RuleResult } from "../rule-result.js";
+import { checkFileExists } from "../utils.js";
 
 export class FolderStructureRule implements Rule {
   readonly name = "FolderStructure";
@@ -18,6 +20,57 @@ export class FolderStructureRule implements Rule {
       }
     });
 
+    // Verify top level folder is lower case
+    let folderStruct = folder.split("/");
+    if (folderStruct[1].match(/[A-Z]/g)) {
+      success = false;
+      errorOutput += `Invalid folder name. Folders under specification/ must be lower case.\n`;
+    }
+
+    let packageFolder = folderStruct[folderStruct.length - 1];
+
+    // Verify package folder is at most 3 levels deep
+    if (folderStruct.length > 4) {
+      success = false;
+      errorOutput += `Please limit TypeSpec folder depth to 3 levels or less`;
+    }
+
+    // Verify second level folder is capitalized after each '.'
+    if (
+      /(^|\. *)([a-z])/g.test(packageFolder) &&
+      !["data-plane", "resource-manager"].includes(packageFolder)
+    ) {
+      success = false;
+      errorOutput += `Invalid folder name. Folders under specification/${folderStruct[1]} must be capitalized after each '.'\n`;
+    }
+
+    // Verify 'Shared' follows 'Management'
+    if (packageFolder.includes("Management") && packageFolder.includes("Shared")) {
+      if (!packageFolder.includes("Management.Shared")) {
+        success = false;
+        errorOutput += `Invalid folder name. For management libraries with a shared component, 'Shared' should follow 'Management'.`;
+      }
+    }
+
+    // Verify tspconfig, main.tsp, examples/
+    let containsMinStruct =
+      (await checkFileExists(path.join(folder, "main.tsp"))) ||
+      (await checkFileExists(path.join(folder, "client.tsp")));
+
+    if (await checkFileExists(path.join(folder, "main.tsp"))) {
+      containsMinStruct =
+        containsMinStruct && (await checkFileExists(path.join(folder, "examples")));
+    }
+
+    if (!packageFolder.includes("Shared")) {
+      containsMinStruct =
+        containsMinStruct && (await checkFileExists(path.join(folder, "tspconfig.yaml")));
+    }
+    if (!containsMinStruct) {
+      success = false;
+      errorOutput += `Invalid folder structure. Package must contain main.tsp or client.tsp, tspconfig.yaml, and examples folder if there's main.tsp.`;
+    }
+
     return {
       success: success,
       stdOutput: stdOutput,