fix: locate Terraform entrypoint file (#16753)

Fixes: https://github.com/coder/coder/issues/16360

site/src/pages/TemplateVersionEditorPage/TemplateVersionEditorPage.test.tsx

@@ -22,9 +22,12 @@ import {
 	waitForLoaderToBeRemoved,
 } from "testHelpers/renderHelpers";
 import { server } from "testHelpers/server";
+import type { FileTree } from "utils/filetree";
 import type { MonacoEditorProps } from "./MonacoEditor";
 import { Language } from "./PublishTemplateVersionDialog";
-import TemplateVersionEditorPage from "./TemplateVersionEditorPage";
+import TemplateVersionEditorPage, {
+	findEntrypointFile,
+} from "./TemplateVersionEditorPage";
 
 const { API } = apiModule;
 
@@ -409,3 +412,127 @@ function renderEditorPage(queryClient: QueryClient) {
 		</AppProviders>,
 	);
 }
+
+describe("Find entrypoint", () => {
+	it("empty tree", () => {
+		const ft: FileTree = {};
+		const mainFile = findEntrypointFile(ft);
+		expect(mainFile).toBeUndefined();
+	});
+	it("flat structure, main.tf in root", () => {
+		const ft: FileTree = {
+			"aaa.tf": "hello",
+			"bbb.tf": "world",
+			"main.tf": "foobar",
+			"nnn.tf": "foobaz",
+		};
+
+		const mainFile = findEntrypointFile(ft);
+		expect(mainFile).toBe("main.tf");
+	});
+	it("flat structure, no main.tf", () => {
+		const ft: FileTree = {
+			"aaa.tf": "hello",
+			"bbb.tf": "world",
+			"ccc.tf": "foobaz",
+			"nnn.tf": "foobaz",
+		};
+
+		const mainFile = findEntrypointFile(ft);
+		expect(mainFile).toBe("nnn.tf");
+	});
+	it("with dirs, single main.tf", () => {
+		const ft: FileTree = {
+			"aaa-dir": {
+				"aaa.tf": "hello",
+				"bbb.tf": "world",
+			},
+			"bbb-dir": {
+				"aaa.tf": "hello",
+				"bbb.tf": "world",
+			},
+			"main.tf": "foobar",
+			"nnn.tf": "foobaz",
+		};
+
+		const mainFile = findEntrypointFile(ft);
+		expect(mainFile).toBe("main.tf");
+	});
+	it("with dirs, multiple main.tf's", () => {
+		const ft: FileTree = {
+			"aaa-dir": {
+				"aaa.tf": "hello",
+				"bbb.tf": "world",
+				"main.tf": "foobar",
+			},
+			"bbb-dir": {
+				"aaa.tf": "hello",
+				"bbb.tf": "world",
+				"main.tf": "foobar",
+			},
+			"ccc-dir": {
+				"aaa.tf": "hello",
+				"bbb.tf": "world",
+			},
+			"main.tf": "foobar",
+			"nnn.tf": "foobaz",
+			"zzz-dir": {
+				"aaa.tf": "hello",
+				"bbb.tf": "world",
+				"main.tf": "foobar",
+			},
+		};
+
+		const mainFile = findEntrypointFile(ft);
+		expect(mainFile).toBe("main.tf");
+	});
+	it("with dirs, multiple main.tf, no main.tf in root", () => {
+		const ft: FileTree = {
+			"aaa-dir": {
+				"aaa.tf": "hello",
+				"bbb.tf": "world",
+				"main.tf": "foobar",
+			},
+			"bbb-dir": {
+				"aaa.tf": "hello",
+				"bbb.tf": "world",
+				"main.tf": "foobar",
+			},
+			"ccc-dir": {
+				"aaa.tf": "hello",
+				"bbb.tf": "world",
+			},
+			"nnn.tf": "foobaz",
+			"zzz-dir": {
+				"aaa.tf": "hello",
+				"bbb.tf": "world",
+				"main.tf": "foobar",
+			},
+		};
+
+		const mainFile = findEntrypointFile(ft);
+		expect(mainFile).toBe("aaa-dir/main.tf");
+	});
+	it("with dirs, multiple main.tf, unordered file tree", () => {
+		const ft: FileTree = {
+			"ccc-dir": {
+				"aaa.tf": "hello",
+				"bbb.tf": "world",
+				"main.tf": "foobar",
+			},
+			"aaa-dir": {
+				"aaa.tf": "hello",
+				"bbb.tf": "world",
+				"main.tf": "foobar",
+			},
+			"zzz-dir": {
+				"aaa.tf": "hello",
+				"bbb.tf": "world",
+				"main.tf": "foobar",
+			},
+		};
+
+		const mainFile = findEntrypointFile(ft);
+		expect(mainFile).toBe("aaa-dir/main.tf");
+	});
+});

site/src/pages/TemplateVersionEditorPage/TemplateVersionEditorPage.tsx

@@ -90,7 +90,7 @@ export const TemplateVersionEditorPage: FC = () => {
 	// File navigation
 	// It can be undefined when a selected file is deleted
 	const activePath: string | undefined =
-		searchParams.get("path") ?? findInitialFile(fileTree ?? {});
+		searchParams.get("path") ?? findEntrypointFile(fileTree ?? {});
 	const onActivePathChange = (path: string | undefined) => {
 		if (path) {
 			searchParams.set("path", path);
@@ -357,10 +357,33 @@ const publishVersion = async (options: {
 	return Promise.all(publishActions);
 };
 
-const findInitialFile = (fileTree: FileTree): string | undefined => {
+const defaultMainTerraformFile = "main.tf";
+
+// findEntrypointFile function locates the entrypoint file to open in the Editor.
+// It browses the filetree following these steps:
+// 1. If "main.tf" exists in root, return it.
+// 2. Traverse through sub-directories.
+// 3. If "main.tf" exists in a sub-directory, skip further browsing, and return the path.
+// 4. If "main.tf" was not found, return the last reviewed "".tf" file.
+export const findEntrypointFile = (fileTree: FileTree): string | undefined => {
 	let initialFile: string | undefined;
 
-	traverse(fileTree, (content, filename, path) => {
+	if (Object.keys(fileTree).find((key) => key === defaultMainTerraformFile)) {
+		return defaultMainTerraformFile;
+	}
+
+	let skip = false;
+	traverse(fileTree, (_, filename, path) => {
+		if (skip) {
+			return;
+		}
+
+		if (filename === defaultMainTerraformFile) {
+			initialFile = path;
+			skip = true;
+			return;
+		}
+
 		if (filename.endsWith(".tf")) {
 			initialFile = path;
 		}

site/src/utils/filetree.test.ts

@@ -122,6 +122,6 @@ test("traverse() go trough all the file tree files", () => {
 	traverse(fileTree, (_content, _filename, fullPath) => {
 		filePaths.push(fullPath);
 	});
-	const expectedFilePaths = ["main.tf", "images", "images/java.Dockerfile"];
+	const expectedFilePaths = ["images", "images/java.Dockerfile", "main.tf"];
 	expect(filePaths).toEqual(expectedFilePaths);
 });

site/src/utils/filetree.ts

@@ -96,7 +96,9 @@ export const traverse = (
 	) => void,
 	parent?: string,
 ) => {
-	for (const [filename, content] of Object.entries(fileTree)) {
+	for (const [filename, content] of Object.entries(fileTree).sort(([a], [b]) =>
+		a.localeCompare(b),
+	)) {
 		const fullPath = parent ? `${parent}/${filename}` : filename;
 		callback(content, filename, fullPath);
 		if (typeof content === "object") {