Add Claude Code hooks to prevent common development mistakes (#23241)

## Summary

Added Claude Code hooks to prevent common development mistakes when
working on the Bun codebase.

## Changes

- Created `.claude/hooks/pre-bash-zig-build.js` - A pre-bash hook that
validates commands
- Created `.claude/settings.json` - Hook configuration

## Prevented Mistakes

1. **Running `zig build obj` directly** → Redirects to use `bun bd`
2. **Using `bun test` in development** → Must use `bun bd test` (or set
`USE_SYSTEM_BUN=1`)
3. **Combining snapshot updates with test filters** → Prevents
`-u`/`--update-snapshots` with `-t`/`--test-name-pattern`
4. **Running `bun bd` with timeout** → Build needs time to complete
without timeout
5. **Running `bun bd test` from repo root** → Must specify a test file
path to avoid running all tests

## Test plan

- [x] Tested all validation rules with various command combinations
- [x] Verified USE_SYSTEM_BUN=1 bypass works
- [x] Verified file path detection works correctly

🤖 Generated with [Claude Code](https://claude.com/claude-code)

---------

Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Jarred Sumner <jarred@jarredsumner.com>

.claude/hooks/post-edit-zig-format.js

@@ -0,0 +1,90 @@
+#!/usr/bin/env bun
+import { extname } from "path";
+import { spawnSync } from "child_process";
+
+const input = await Bun.stdin.json();
+
+const toolName = input.tool_name;
+const toolInput = input.tool_input || {};
+const filePath = toolInput.file_path;
+
+// Only process Write, Edit, and MultiEdit tools
+if (!["Write", "Edit", "MultiEdit"].includes(toolName)) {
+  process.exit(0);
+}
+
+const ext = extname(filePath);
+
+// Only format known files
+if (!filePath) {
+  process.exit(0);
+}
+
+function formatZigFile() {
+  try {
+    // Format the Zig file
+    const result = spawnSync("vendor/zig/zig.exe", ["fmt", filePath], {
+      cwd: process.env.CLAUDE_PROJECT_DIR || process.cwd(),
+      encoding: "utf-8",
+    });
+
+    if (result.error) {
+      console.error(`Failed to format ${filePath}: ${result.error.message}`);
+      process.exit(0);
+    }
+
+    if (result.status !== 0) {
+      console.error(`zig fmt failed for ${filePath}:`);
+      if (result.stderr) {
+        console.error(result.stderr);
+      }
+      process.exit(0);
+    }
+  } catch (error) {}
+}
+
+function formatTypeScriptFile() {
+  try {
+    // Format the TypeScript file
+    const result = spawnSync(
+      "./node_modules/.bin/prettier",
+      ["--plugin=prettier-plugin-organize-imports", "--config", ".prettierrc", "--write", filePath],
+      {
+        cwd: process.env.CLAUDE_PROJECT_DIR || process.cwd(),
+        encoding: "utf-8",
+      },
+    );
+  } catch (error) {}
+}
+
+if (ext === ".zig") {
+  formatZigFile();
+} else if (
+  [
+    ".cjs",
+    ".css",
+    ".html",
+    ".js",
+    ".json",
+    ".jsonc",
+    ".jsx",
+    ".less",
+    ".mjs",
+    ".pcss",
+    ".postcss",
+    ".sass",
+    ".scss",
+    ".styl",
+    ".stylus",
+    ".toml",
+    ".ts",
+    ".tsx",
+    ".yaml",
+  ].includes(ext)
+) {
+  formatTypeScriptFile();
+} else if (ext === ".cpp" || ext === ".c" || ext === ".h") {
+  formatCppFile();
+}
+
+process.exit(0);

.claude/hooks/pre-bash-zig-build.js

@@ -0,0 +1,175 @@
+#!/usr/bin/env bun
+import { basename, extname } from "path";
+
+const input = await Bun.stdin.json();
+
+const toolName = input.tool_name;
+const toolInput = input.tool_input || {};
+const command = toolInput.command || "";
+const timeout = toolInput.timeout;
+const cwd = input.cwd || "";
+
+// Get environment variables from the hook context
+// Note: We check process.env directly as env vars are inherited
+let useSystemBun = process.env.USE_SYSTEM_BUN;
+
+if (toolName !== "Bash" || !command) {
+  process.exit(0);
+}
+
+function denyWithReason(reason) {
+  const output = {
+    hookSpecificOutput: {
+      hookEventName: "PreToolUse",
+      permissionDecision: "deny",
+      permissionDecisionReason: reason,
+    },
+  };
+  console.log(JSON.stringify(output));
+  process.exit(0);
+}
+
+// Parse the command to extract argv0 and positional args
+let tokens;
+try {
+  // Simple shell parsing - split on spaces but respect quotes (both single and double)
+  tokens = command.match(/(?:[^\s"']+|"[^"]*"|'[^']*')+/g)?.map(t => t.replace(/^['"]|['"]$/g, "")) || [];
+} catch {
+  process.exit(0);
+}
+
+if (tokens.length === 0) {
+  process.exit(0);
+}
+
+// Strip inline environment variable assignments (e.g., FOO=1 bun test)
+const inlineEnv = new Map();
+let commandStart = 0;
+while (
+  commandStart < tokens.length &&
+  /^[A-Za-z_][A-Za-z0-9_]*=/.test(tokens[commandStart]) &&
+  !tokens[commandStart].includes("/")
+) {
+  const [name, value = ""] = tokens[commandStart].split("=", 2);
+  inlineEnv.set(name, value);
+  commandStart++;
+}
+if (commandStart >= tokens.length) {
+  process.exit(0);
+}
+tokens = tokens.slice(commandStart);
+useSystemBun = inlineEnv.get("USE_SYSTEM_BUN") ?? useSystemBun;
+
+// Get the executable name (argv0)
+const argv0 = basename(tokens[0], extname(tokens[0]));
+
+// Check if it's zig or zig.exe
+if (argv0 === "zig") {
+  // Filter out flags (starting with -) to get positional arguments
+  const positionalArgs = tokens.slice(1).filter(arg => !arg.startsWith("-"));
+
+  // Check if the positional args contain "build" followed by "obj"
+  if (positionalArgs.length >= 2 && positionalArgs[0] === "build" && positionalArgs[1] === "obj") {
+    denyWithReason("error: Use `bun bd` to build Bun and wait patiently");
+  }
+}
+
+// Check if argv0 is timeout and the command is "bun bd"
+if (argv0 === "timeout") {
+  // Find the actual command after timeout and its arguments
+  const timeoutArgEndIndex = tokens.slice(1).findIndex(t => !t.startsWith("-") && !/^\d/.test(t));
+  if (timeoutArgEndIndex === -1) {
+    process.exit(0);
+  }
+
+  const actualCommandIndex = timeoutArgEndIndex + 1;
+  if (actualCommandIndex >= tokens.length) {
+    process.exit(0);
+  }
+
+  const actualCommand = basename(tokens[actualCommandIndex]);
+  const restArgs = tokens.slice(actualCommandIndex + 1);
+
+  // Check if it's "bun bd" or "bun-debug bd" without other positional args
+  if (actualCommand === "bun" || actualCommand.includes("bun-debug")) {
+    const positionalArgs = restArgs.filter(arg => !arg.startsWith("-"));
+    if (positionalArgs.length === 1 && positionalArgs[0] === "bd") {
+      denyWithReason("error: Run `bun bd` without a timeout");
+    }
+  }
+}
+
+// Check if command is "bun .* test" or "bun-debug test" with -u/--update-snapshots AND -t/--test-name-pattern
+if (argv0 === "bun" || argv0.includes("bun-debug")) {
+  const allArgs = tokens.slice(1);
+
+  // Check if "test" is in positional args or "bd" followed by "test"
+  const positionalArgs = allArgs.filter(arg => !arg.startsWith("-"));
+  const hasTest = positionalArgs.includes("test") || (positionalArgs[0] === "bd" && positionalArgs[1] === "test");
+
+  if (hasTest) {
+    const hasUpdateSnapshots = allArgs.some(arg => arg === "-u" || arg === "--update-snapshots");
+    const hasTestNamePattern = allArgs.some(arg => arg === "-t" || arg === "--test-name-pattern");
+
+    if (hasUpdateSnapshots && hasTestNamePattern) {
+      denyWithReason("error: Cannot use -u/--update-snapshots with -t/--test-name-pattern");
+    }
+  }
+}
+
+// Check if timeout option is set for "bun bd" command
+if (timeout !== undefined && (argv0 === "bun" || argv0.includes("bun-debug"))) {
+  const positionalArgs = tokens.slice(1).filter(arg => !arg.startsWith("-"));
+  if (positionalArgs.length === 1 && positionalArgs[0] === "bd") {
+    denyWithReason("error: Run `bun bd` without a timeout");
+  }
+}
+
+// Check if running "bun test <file>" without USE_SYSTEM_BUN=1
+if ((argv0 === "bun" || argv0.includes("bun-debug")) && useSystemBun !== "1") {
+  const allArgs = tokens.slice(1);
+  const positionalArgs = allArgs.filter(arg => !arg.startsWith("-"));
+
+  // Check if it's "test" (not "bd test")
+  if (positionalArgs.length >= 1 && positionalArgs[0] === "test" && positionalArgs[0] !== "bd") {
+    denyWithReason(
+      "error: In development, use `bun bd test <file>` to test your changes. If you meant to use a release version, set USE_SYSTEM_BUN=1",
+    );
+  }
+}
+
+// Check if running "bun bd test" from bun repo root or test folder without a file path
+if (argv0 === "bun" || argv0.includes("bun-debug")) {
+  const allArgs = tokens.slice(1);
+  const positionalArgs = allArgs.filter(arg => !arg.startsWith("-"));
+
+  // Check if it's "bd test"
+  if (positionalArgs.length >= 2 && positionalArgs[0] === "bd" && positionalArgs[1] === "test") {
+    // Check if cwd is the bun repo root or test folder
+    const isBunRepoRoot = cwd === "/workspace/bun" || cwd.endsWith("/bun");
+    const isTestFolder = cwd.endsWith("/bun/test");
+
+    if (isBunRepoRoot || isTestFolder) {
+      // Check if there's a file path argument (looks like a path: contains / or has test extension)
+      const hasFilePath = positionalArgs
+        .slice(2)
+        .some(
+          arg =>
+            arg.includes("/") ||
+            arg.endsWith(".test.ts") ||
+            arg.endsWith(".test.js") ||
+            arg.endsWith(".test.tsx") ||
+            arg.endsWith(".test.jsx"),
+        );
+
+      if (!hasFilePath) {
+        denyWithReason(
+          "error: `bun bd test` from repo root or test folder will run all tests. Use `bun bd test <path>` with a specific test file.",
+        );
+      }
+    }
+  }
+}
+
+// Allow the command to proceed
+process.exit(0);

.claude/settings.json

@@ -0,0 +1,26 @@
+{
+  "hooks": {
+    "PreToolUse": [
+      {
+        "matcher": "Bash",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "\"$CLAUDE_PROJECT_DIR\"/.claude/hooks/pre-bash-zig-build.js"
+          }
+        ]
+      }
+    ],
+    "PostToolUse": [
+      {
+        "matcher": "Write|Edit|MultiEdit",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "\"$CLAUDE_PROJECT_DIR\"/.claude/hooks/post-edit-zig-format.js"
+          }
+        ]
+      }
+    ]
+  }
+}