What causes "Failed to open " STRING_FORMAT ": %s\n" in bazelbuild/bazel?

Verify the printed path exists and is readable (type on Windows).

Failed to open " STRING_FORMAT ": %s\n

Error message

Failed to open " STRING_FORMAT ": %s\n

What it means

launcher_maker opens argv[1] — the base launcher binary shipped with Bazel — with std::ifstream in binary mode; if the stream is not good() it prints the path (wide-string aware via STRING_FORMAT '%ls' on Windows) plus strerror(errno) and exits 1. It means the launcher template file does not exist or is not readable at the moment the action runs.

Source

Thrown at src/tools/launcher/launcher_maker.cc:74

#define STRING_TYPE std::string
#define STRING_FORMAT "%s"
std::string convert_path(char* path) { return path; }

#endif  // _WIN32

int main(int argc, char** argv) {
  if (argc < 4) {
    fprintf(stderr, "Expected 3 arguments, got %d\n", argc);
    return 1;
  }

  STRING_TYPE launcher_path = convert_path(argv[1]);
  STRING_TYPE info_params = convert_path(argv[2]);
  STRING_TYPE output_path = convert_path(argv[3]);

  std::ifstream src(launcher_path.c_str(), std::ios::binary);
  if (!src.good()) {
    fprintf(stderr, "Failed to open " STRING_FORMAT ": %s\n",
            launcher_path.c_str(), strerror(errno));
    return 1;
  }
  std::ofstream dst(output_path.c_str(), std::ios::binary);
  if (!dst.good()) {
    fprintf(stderr, "Failed to create " STRING_FORMAT ": %s\n",
            output_path.c_str(), strerror(errno));
    return 1;
  }
  dst << src.rdbuf();

  std::ifstream info_file(info_params.c_str());
  if (!info_file.good()) {
    fprintf(stderr, "Failed to open " STRING_FORMAT ": %s\n",
            info_params.c_str(), strerror(errno));
    return 1;
  }
  int64_t bytes = 0;

View on GitHub (pinned to e6e199d060)

Solutions

Verify the printed path exists and is readable (type <path> on Windows).
Check the errno text: 'No such file or directory' → fix the argument; 'Permission denied' → fix ACLs or AV exclusions.
Ensure nothing deletes runfiles/output-base content concurrently (bazel clean while a build runs).
For custom rules, use a files= dep on the launcher so Bazel materializes it before the action.

Defensive patterns

Strategy: validation

Validate before calling

// verify the launcher input exists and is readable before running the action
struct stat st;
if (stat(launcher_path.c_str(), &st) != 0 || !(st.st_mode & S_IREAD)) {
  fprintf(stderr, "missing/unreadable launcher: %s\n", launcher_path.c_str());
  return 1;
}

Prevention

Declare the launcher binary as an action input so Bazel materializes it first.
Keep AV from quarantining Bazel-shipped binaries.
Do not prune the output base mid-build.

When it happens

Trigger: The launcher binary path argument points to a missing/moved file; the file exists but permissions deny read; the path contains characters mishandled by the shell so it resolves to a nonexistent name.

Common situations: Custom rules passing a wrong launcher location; antivirus quarantining the launcher exe; output base pruned mid-build by an external cleaner.

Related errors

AI-assisted analysis of bazelbuild/bazel@e6e199d060 (2026-08-14). Data as JSON: /api/errors/40f0d00009649dd6. Report an issue: GitHub.