feat: /diff command to view git diff (#426)

Adds `/diff` command to view git diff

codex-cli/src/utils/extract-applied-patches.ts

@@ -0,0 +1,36 @@
+import type { ResponseItem } from "openai/resources/responses/responses.mjs";
+
+/**
+ * Extracts the patch texts of all `apply_patch` tool calls from the given
+ * message history. Returns an empty string when none are found.
+ */
+export function extractAppliedPatches(items: Array<ResponseItem>): string {
+  const patches: Array<string> = [];
+
+  for (const item of items) {
+    if (item.type !== "function_call") {
+      continue;
+    }
+
+    const { name: toolName, arguments: argsString } = item as unknown as {
+      name: unknown;
+      arguments: unknown;
+    };
+
+    if (toolName !== "apply_patch" || typeof argsString !== "string") {
+      continue;
+    }
+
+    try {
+      const args = JSON.parse(argsString) as { patch?: string };
+      if (typeof args.patch === "string" && args.patch.length > 0) {
+        patches.push(args.patch.trim());
+      }
+    } catch {
+      // Ignore malformed JSON – we never want to crash the overlay.
+      continue;
+    }
+  }
+
+  return patches.join("\n\n");
+}

codex-cli/src/utils/get-diff.ts

@@ -0,0 +1,29 @@
+import { execSync } from "node:child_process";
+
+/**
+ * Returns the current Git diff for the working directory. If the current
+ * working directory is not inside a Git repository, `isGitRepo` will be
+ * false and `diff` will be an empty string.
+ */
+export function getGitDiff(): {
+  isGitRepo: boolean;
+  diff: string;
+} {
+  try {
+    // First check whether we are inside a git repository. `rev‑parse` exits
+    // with a non‑zero status code if not.
+    execSync("git rev-parse --is-inside-work-tree", { stdio: "ignore" });
+
+    // If the above call didn’t throw, we are inside a git repo. Retrieve the
+    // diff including color codes so that the overlay can render them.
+    const output = execSync("git diff --color", {
+      encoding: "utf8",
+      maxBuffer: 10 * 1024 * 1024, // 10 MB ought to be enough for now
+    });
+
+    return { isGitRepo: true, diff: output };
+  } catch {
+    // Either git is not installed or we’re not inside a repository.
+    return { isGitRepo: false, diff: "" };
+  }
+}

codex-cli/src/utils/slash-commands.ts

@@ -24,4 +24,9 @@ export const SLASH_COMMANDS: Array<SlashCommand> = [
   { command: "/model", description: "Open model selection panel" },
   { command: "/approval", description: "Open approval mode selection panel" },
   { command: "/bug", description: "Generate a prefilled GitHub bug report" },
+  {
+    command: "/diff",
+    description:
+      "Show git diff of the working directory (or applied patches if not in git)",
+  },
 ];