fix: Don't replace malformed appmap.yml, warn and use defaults

src/__tests__/config.test.ts

@@ -1,4 +1,4 @@
-import { mkdirSync, writeFileSync } from "node:fs";
+import { mkdirSync, readFileSync, writeFileSync } from "node:fs";
 import { basename } from "node:path";
 import { chdir, cwd } from "node:process";
 
@@ -101,6 +101,17 @@ describe(Config, () => {
     });
   });
 
+  it("does not replace malformed appmap.yml but uses defaults", () => {
+    const malformedAppMapFileContent = "{ appmap-dir: 'abc/xyz' ";
+    writeFileSync("appmap.yml", malformedAppMapFileContent);
+
+    const cfg = new Config();
+    expect(cfg.fileIsMalformed).toEqual(true);
+    expect(cfg.relativeAppmapDir).toEqual("tmp/appmap");
+
+    expect(readFileSync("appmap.yml").toString()).toEqual(malformedAppMapFileContent);
+  });
+
   let dir: string;
   beforeEach(() => {
     chdir((dir = tmp.dirSync().name));

src/bin.ts

@@ -9,7 +9,7 @@ import json5 from "json5";
 import YAML from "yaml";
 
 import config from "./config";
-import { info } from "./message";
+import { info, warn } from "./message";
 import { version } from "./metadata";
 import forwardSignals from "./util/forwardSignals";
 import { readPkgUp } from "./util/readPkgUp";
@@ -30,7 +30,9 @@ export function main() {
   if (config.default) {
     info("Writing default config to %s", config.configPath);
     writeFileSync(config.configPath, YAML.stringify(config));
-  } else info("Using config file %s", config.configPath);
+  } else if (config.fileIsMalformed)
+    warn("Malformed config file %s, using default values instead", config.configPath);
+  else info("Using config file %s", config.configPath);
   config.export();
 
   // FIXME: Probably there should be a way to remove this altogether

src/config.ts

@@ -21,6 +21,7 @@ export class Config {
   public readonly root: string;
   public readonly configPath: string;
   public readonly default: boolean;
+  public readonly fileIsMalformed: boolean;
   public readonly packages: PackageMatcher;
   public readonly responseBodyMaxLength: number;
 
@@ -34,8 +35,10 @@ export class Config {
     const root = (this.root = process.env.APPMAP_ROOT ?? configDir ?? packageDir() ?? pwd);
 
     this.configPath = join(root, "appmap.yml");
-    const config = readConfigFile(this.configPath);
+    const readConfigFileResult = readConfigFile(this.configPath);
+    const config = readConfigFileResult != "malformed" ? readConfigFileResult : undefined;
     this.default = !config;
+    this.fileIsMalformed = readConfigFileResult == "malformed" ?? false;
 
     this.relativeAppmapDir = config?.appmap_dir ?? "tmp/appmap";
 
@@ -94,12 +97,16 @@ interface ConfigFile {
   name?: string;
   packages?: Package[];
   response_body_max_length?: number;
+  malformed?: boolean;
 }
 
-function readConfigFile(path: string | undefined): ConfigFile | undefined {
+function readConfigFile(path: string | undefined): ConfigFile | "malformed" | undefined {
   if (!path) return;
-  const config = tryOr(() => YAML.parse(readFileSync(path, "utf8")) as unknown);
+  const fileContent = tryOr(() => readFileSync(path, "utf8"));
+  if (!fileContent) return;
+  const config = tryOr(() => YAML.parse(fileContent) as unknown, "malformed");
   if (!config) return;
+  if (config == "malformed") return "malformed";
 
   const result: ConfigFile = {};
   assert(typeof config === "object");
@@ -110,6 +117,7 @@ function readConfigFile(path: string | undefined): ConfigFile | undefined {
     const value = parseInt(String(config.response_body_max_length));
     result.response_body_max_length = value >= 0 ? value : undefined;
   }
+  if ("malformed" in config) result.malformed = true;
 
   return result;
 }

src/util/tryOr.ts

@@ -1,7 +1,7 @@
-export default function tryOr<T>(fn: () => T): T | undefined {
+export default function tryOr<T, E = undefined>(fn: () => T, elseReturn?: E): T | E | undefined {
   try {
     return fn();
   } catch (e) {
-    return undefined;
+    return elseReturn;
   }
 }