fix: use Knip version from installed dependency (#1792)

## PR Checklist

- [x] Addresses an existing open issue: fixes #1638
- [x] That issue was marked as [`status: accepting
prs`](https://github.com/JoshuaKGoldberg/create-typescript-app/issues?q=is%3Aopen+is%3Aissue+label%3A%22status%3A+accepting+prs%22)
- [x] Steps in
[CONTRIBUTING.md](https://github.com/JoshuaKGoldberg/create-typescript-app/blob/main/.github/CONTRIBUTING.md)
were taken

## Overview

Uses the same `readFileSafeAsJson` strategy as `writePackageJson`.

💖

knip.json

@@ -1,5 +1,5 @@
 {
-	"$schema": "https://unpkg.com/knip@latest/schema.json",
+	"$schema": "https://unpkg.com/knip@5.41.0/schema.json",
 	"entry": ["script/*e2e.js", "src/index.ts!", "src/**/*.test.*"],
 	"ignoreDependencies": ["all-contributors-cli"],
 	"ignoreExportsUsedInFile": { "interface": true, "type": true },

script/__snapshots__/migrate-test-e2e.ts.snap

@@ -212,7 +212,7 @@ exports[`expected file changes > knip.json 1`] = `
 +++ b/knip.json
 @@ ... @@
  {
- 	"$schema": "https://unpkg.com/knip@latest/schema.json",
+ 	"$schema": "https://unpkg.com/knip@5.41.0/schema.json",
 -	"entry": ["script/*e2e.js", "src/index.ts!", "src/**/*.test.*"],
 -	"ignoreDependencies": ["all-contributors-cli"],
 +	"entry": ["src/index.ts!"],

src/next/blocks/blockKnip.ts

@@ -2,7 +2,7 @@ import { base } from "../base.js";
 import { blockDevelopmentDocs } from "./blockDevelopmentDocs.js";
 import { blockGitHubActionsCI } from "./blockGitHubActionsCI.js";
 import { blockPackageJson } from "./blockPackageJson.js";
-import { getPackageDependencies } from "./packageData.js";
+import { getPackageDependencies, getPackageDependency } from "./packageData.js";
 
 export const blockKnip = base.createBlock({
 	about: {
@@ -41,7 +41,7 @@ export const blockKnip = base.createBlock({
 			],
 			files: {
 				"knip.json": JSON.stringify({
-					$schema: "https://unpkg.com/knip@latest/schema.json",
+					$schema: `https://unpkg.com/knip@${getPackageDependency("knip")}/schema.json`,
 					entry: ["src/index.ts!"],
 					ignoreExportsUsedInFile: {
 						interface: true,

src/next/blocks/packageData.ts

@@ -6,28 +6,33 @@ const packageData =
 	// Importing from above src/ would expand the TS build rootDir
 	require("../../../package.json") as typeof import("../../../package.json");
 
-const getPackageInner = (
+export function getPackageDependencies(...names: string[]) {
+	return Object.fromEntries(
+		names.map((name) => {
+			return [name, getPackageDependency(name)];
+		}),
+	);
+}
+
+export function getPackageDependency(name: string) {
+	const version =
+		getPackageInner("devDependencies", name) ??
+		getPackageInner("dependencies", name);
+
+	if (!version) {
+		throw new Error(
+			`'${name} is neither in package.json's dependencies nor its devDependencies.`,
+		);
+	}
+
+	return version;
+}
+
+function getPackageInner(
 	key: "dependencies" | "devDependencies",
 	name: string,
-) => {
+) {
 	const inner = packageData[key];
 
 	return inner[name as keyof typeof inner] as string | undefined;
-};
-
-export const getPackageDependencies = (...names: string[]) =>
-	Object.fromEntries(
-		names.map((name) => {
-			const version =
-				getPackageInner("devDependencies", name) ??
-				getPackageInner("dependencies", name);
-
-			if (!version) {
-				throw new Error(
-					`'${name} is neither in package.json's dependencies nor its devDependencies.`,
-				);
-			}
-
-			return [name, version];
-		}),
-	);
+}

src/steps/writing/creation/createKnipConfig.test.ts

@@ -0,0 +1,66 @@
+import { describe, expect, it, vi } from "vitest";
+
+import { createKnipConfig } from "./createKnipConfig.js";
+
+const mockReadFileSafeAsJson = vi.fn();
+
+vi.mock("../../../shared/readFileSafeAsJson.js", () => ({
+	get readFileSafeAsJson() {
+		return mockReadFileSafeAsJson;
+	},
+}));
+
+describe("createKnipConfig", () => {
+	it("uses uses the knip version from package.json devDependencies when it exists", async () => {
+		const version = "1.2.3";
+		mockReadFileSafeAsJson.mockResolvedValueOnce({
+			devDependencies: { knip: version },
+		});
+
+		const packageJson = await createKnipConfig();
+
+		expect(JSON.parse(packageJson)).toEqual({
+			$schema: `https://unpkg.com/knip@${version}/schema.json`,
+			entry: ["src/index.ts!"],
+			ignoreExportsUsedInFile: {
+				interface: true,
+				type: true,
+			},
+			project: ["src/**/*.ts!"],
+		});
+	});
+
+	it("uses version 'latest' when the package.json does not exist", async () => {
+		mockReadFileSafeAsJson.mockResolvedValueOnce(undefined);
+
+		const packageJson = await createKnipConfig();
+
+		expect(JSON.parse(packageJson)).toEqual({
+			$schema: `https://unpkg.com/knip@latest/schema.json`,
+			entry: ["src/index.ts!"],
+			ignoreExportsUsedInFile: {
+				interface: true,
+				type: true,
+			},
+			project: ["src/**/*.ts!"],
+		});
+	});
+
+	it("uses version 'latest' when the package.json exists but does not have knip in devDependencies", async () => {
+		mockReadFileSafeAsJson.mockResolvedValueOnce({
+			dependencies: {},
+		});
+
+		const packageJson = await createKnipConfig();
+
+		expect(JSON.parse(packageJson)).toEqual({
+			$schema: `https://unpkg.com/knip@latest/schema.json`,
+			entry: ["src/index.ts!"],
+			ignoreExportsUsedInFile: {
+				interface: true,
+				type: true,
+			},
+			project: ["src/**/*.ts!"],
+		});
+	});
+});

src/steps/writing/creation/createKnipConfig.ts

@@ -0,0 +1,19 @@
+import { readFileSafeAsJson } from "../../../shared/readFileSafeAsJson.js";
+import { PartialPackageData } from "../../../shared/types.js";
+import { formatJson } from "./formatters/formatJson.js";
+
+export async function createKnipConfig() {
+	const existingPackageJson = (await readFileSafeAsJson(
+		"./package.json",
+	)) as null | PartialPackageData;
+
+	return await formatJson({
+		$schema: `https://unpkg.com/knip@${existingPackageJson?.devDependencies?.knip ?? "latest"}/schema.json`,
+		entry: ["src/index.ts!"],
+		ignoreExportsUsedInFile: {
+			interface: true,
+			type: true,
+		},
+		project: ["src/**/*.ts!"],
+	});
+}

src/steps/writing/creation/rootFiles.ts

@@ -2,6 +2,7 @@ import { Options } from "../../../shared/types.js";
 import { createCSpellConfig } from "./createCSpellConfig.js";
 import { createDotGitignore } from "./createDotGitignore.js";
 import { createESLintConfig } from "./createESLintConfig.js";
+import { createKnipConfig } from "./createKnipConfig.js";
 import { createTsupConfig } from "./createTsupConfig.js";
 import { formatIgnoreFile } from "./formatters/formatIgnoreFile.js";
 import { formatJson } from "./formatters/formatJson.js";
@@ -96,15 +97,7 @@ SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 			"cspell.json": await createCSpellConfig(options),
 		}),
 		...(!options.excludeLintKnip && {
-			"knip.json": await formatJson({
-				$schema: "https://unpkg.com/knip@latest/schema.json",
-				entry: ["src/index.ts!"],
-				ignoreExportsUsedInFile: {
-					interface: true,
-					type: true,
-				},
-				project: ["src/**/*.ts!"],
-			}),
+			"knip.json": await createKnipConfig(),
 		}),
 		"package.json": await writePackageJson(options),
 		"tsconfig.json": await formatJson({