fix(resolver): show warning when tsconfig extends non-existent file

Previously, when a tsconfig.json's "extends" field referenced a non-existent
file, Bun silently ignored it (only logging at debug level). This made it
difficult for users to diagnose configuration issues.

Now, a warning is shown when the extended config file cannot be found,
similar to TypeScript's behavior. Warnings are suppressed for tsconfig files
inside node_modules to avoid noise from third-party packages.

Fixes #2804

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/resolver/resolver.zig

@@ -4203,12 +4203,19 @@ pub const Resolver = struct {
                         const ts_dir_name = Dirname.dirname(current.abs_path);
                         const abs_path = ResolvePath.joinAbsStringBuf(ts_dir_name, bufs(.tsconfig_path_abs), &[_]string{ ts_dir_name, current.extends }, .auto);
                         const parent_config_maybe = r.parseTSConfig(abs_path, bun.invalid_fd) catch |err| {
-                            r.log.addDebugFmt(null, logger.Loc.Empty, r.allocator, "{s} loading tsconfig.json extends {f}", .{
-                                @errorName(err),
-                                bun.fmt.QuotedFormatter{
-                                    .text = abs_path,
-                                },
-                            }) catch {};
+                            // Only show warnings for tsconfig files outside of node_modules
+                            if (!info.isInsideNodeModules()) {
+                                if (err == error.ENOENT or err == error.FileNotFound) {
+                                    r.log.addWarningFmtLineCol(current.abs_path, 0, 0, r.allocator, "Cannot find base config file {f}", .{
+                                        bun.fmt.QuotedFormatter{ .text = current.extends },
+                                    }) catch {};
+                                } else if (err != error.ParseErrorAlreadyLogged and err != error.IsDir and err != error.EISDIR) {
+                                    r.log.addWarningFmtLineCol(current.abs_path, 0, 0, r.allocator, "Cannot read base config file {f}: {s}", .{
+                                        bun.fmt.QuotedFormatter{ .text = current.extends },
+                                        @errorName(err),
+                                    }) catch {};
+                                }
+                            }
                             break;
                         };
                         if (parent_config_maybe) |parent_config| {

test/regression/issue/02804.test.ts

@@ -0,0 +1,46 @@
+import { expect, test } from "bun:test";
+import { bunEnv, bunExe, tempDirWithFiles } from "harness";
+
+test("tsconfig extends non-existent file shows warning", () => {
+  const dir = tempDirWithFiles("02804", {
+    "tsconfig.json": JSON.stringify({
+      extends: "./nonexistent-config.json",
+      compilerOptions: {
+        strict: true,
+      },
+    }),
+    "index.ts": `const x: string = "hello"; console.log(x);`,
+  });
+
+  const proc = Bun.spawnSync([bunExe(), "index.ts"], {
+    env: bunEnv,
+    cwd: dir,
+    stderr: "pipe",
+    stdout: "pipe",
+  });
+
+  const stderr = proc.stderr.toString("utf-8");
+  expect(stderr).toContain('Cannot find base config file "./nonexistent-config.json"');
+  expect(stderr).toContain("warn:");
+});
+
+test("tsconfig extends inside node_modules does not warn", () => {
+  const dir = tempDirWithFiles("02804-node-modules", {
+    "index.ts": `import "./node_modules/foo/index.js"; console.log("done");`,
+    "node_modules/foo/tsconfig.json": JSON.stringify({
+      extends: "./nonexistent-config.json",
+    }),
+    "node_modules/foo/index.js": `console.log("foo");`,
+  });
+
+  const proc = Bun.spawnSync([bunExe(), "index.ts"], {
+    env: bunEnv,
+    cwd: dir,
+    stderr: "pipe",
+    stdout: "pipe",
+  });
+
+  const stderr = proc.stderr.toString("utf-8");
+  // Should NOT show warning for files inside node_modules
+  expect(stderr).not.toContain("Cannot find base config file");
+});