Fix #631: bun add throwing JSON lexer bug (#2041)

* add double-backslash to list of control chars

* update test

* stderr as string

2 files changed, 39 insertions, 1 deletions

diff --git a/src/js_lexer.zig b/src/js_lexer.zig
index c009a01db..f067392c4 100644
--- a/src/js_lexer.zig
+++ b/src/js_lexer.zig
@@ -624,7 +624,7 @@ fn NewLexer_(
 
                         switch (lexer.code_point) {
                             // 0 cannot be in this list because it may be a legacy octal literal
-                            'v', 'f', 't', 'r', 'n', '`', '\'', '"', 0x2028, 0x2029 => {
+                            'v', 'f', 't', 'r', 'n', '`', '\'', '"', '\\', 0x2028, 0x2029 => {
                                 lexer.step();
 
                                 continue :stringLiteral;
diff --git a/test/bun.js/repro_631.test.js b/test/bun.js/repro_631.test.js
new file mode 100644
index 000000000..b418306dd
--- /dev/null
+++ b/test/bun.js/repro_631.test.js
@@ -0,0 +1,38 @@
+import { expect, it } from "bun:test";
+import { bunExe } from "./bunExe.ts";
+import { bunEnv } from "./bunEnv.ts";
+import { mkdirSync, rmSync, writeFileSync, readFileSync } from "fs";
+
+it("JSON strings escaped properly", async () => {
+  const testDir = import.meta.dir + "/repro_631/";
+
+  // Clean up from prior runs if necessary
+  rmSync(testDir, { recursive: true });
+
+  // Create a directory with our test package file
+  mkdirSync(testDir);
+  writeFileSync(testDir + "package.json", String.raw`{"testRegex":"\\a\n\\b\\"}`);
+
+  // Attempt to add a package, causing the package file to be parsed, modified,
+  //  written, and reparsed.  This verifies that escaped backslashes in JSON
+  //  survive the roundtrip
+  const {exitCode, stderr} = Bun.spawnSync({
+    cmd: [bunExe(), "add", "left-pad"],
+    env: bunEnv,
+    cwd: testDir
+  });
+  console.log(stderr.toString());
+  expect(exitCode).toBe(0);
+
+  const packageContents = readFileSync(testDir + "package.json", { encoding: "utf8" });
+  expect(packageContents).toBe(String.raw
+`{
+  "testRegex": "\\a\n\\b\\",
+  "dependencies": {
+    "left-pad": "^1.3.0"
+  }
+}`);
+
+  //// If successful clean up test artifacts
+  rmSync(testDir, { recursive: true });
+})