What causes "Duplicated file `{}` in {}" in rust-lang/rust?

Remove the duplicate entry from the bracketed list so each filename appears once.

rust-lang/rust · error · InvalidCheck

Duplicated file `{}` in {}

Error message

Duplicated file `{}` in {}

What it means

Raised as InvalidCheck by check_files_in_folder() when the same filename appears more than once in the bracketed list of a 'files' directive. The check builds a set and rejects duplicates before comparing against the directory contents, because a duplicate would otherwise cancel out a real missing/extra entry in the set arithmetic.

Source

Thrown at src/etc/htmldocck.py:488

            cache.get_tree(c.args[0]), pat, c.args[2], regexp, stop_at_first
        )


def check_files_in_folder(c, cache, folder, files):
    files = files.strip()
    if not files.startswith("[") or not files.endswith("]"):
        raise InvalidCheck(
            "Expected list as second argument of {} (ie '[]')".format(c.cmd)
        )

    folder = cache.get_absolute_path(folder)

    # First we create a set of files to check if there are duplicates.
    files = shlex.split(files[1:-1].replace(",", ""))
    files_set = set()
    for file in files:
        if file in files_set:
            raise InvalidCheck("Duplicated file `{}` in {}".format(file, c.cmd))
        files_set.add(file)
    folder_set = set([f for f in os.listdir(folder) if f != "." and f != ".."])

    # Then we remove entries from both sets (we clone `folder_set` so we can iterate it while
    # removing its elements).
    for entry in set(folder_set):
        if entry in files_set:
            files_set.remove(entry)
            folder_set.remove(entry)

    error = 0
    if len(files_set) != 0:
        print_err(
            c.lineno,
            c.context,
            "Entries not found in folder `{}`: `{}`".format(folder, files_set),
        )
        error += 1

View on GitHub (pinned to 7088e4b63a)

Solutions

Remove the duplicate entry from the bracketed list so each filename appears once.
Re-run the test to confirm the directive parses.

Example fix

// before
//@ files: mydir [a.html a.html b.html]

// after
//@ files: mydir [a.html b.html]

Defensive patterns

Strategy: validation

Validate before calling

def no_duplicate_files(files_str: str) -> bool:
    import shlex
    inner = files_str.strip()[1:-1].replace(",", "")
    entries = shlex.split(inner)
    return len(entries) == len(set(entries))

if not no_duplicate_files(files_arg):
    raise SystemExit(f"files directive contains duplicate entries: {files_arg!r}")

Type guard

def has_unique_entries(files_str: str) -> bool:
    import shlex
    inner = files_str.strip()[1:-1].replace(",", "")
    entries = shlex.split(inner)
    return len(entries) == len(set(entries))

Try / catch

from srcetc_htmldocck import InvalidCheck
try:
    check_files_in_folder(c, cache, folder, files)
except InvalidCheck as e:
    if "Duplicated file" in str(e):
        logging.error("de-duplicate the files list before re-running")
    raise

Prevention

De-duplicate file lists when editing files directives.
Add a lint rule that rejects repeated entries inside the brackets.
Generate files lists programmatically rather than hand-editing to avoid copy-paste dupes.

When it happens

Trigger: Authoring `//@ files: mydir [a.html a.html b.html]` (a.html listed twice). The loop at htmldocck.py:486-489 detects the repeat.

Common situations: Copy-paste error when editing a file list; merging two lists without de-duplicating; refactoring a directive and forgetting to remove the old entry.

Related errors

AI-assisted analysis of rust-lang/rust@7088e4b63a (2026-08-10). Data as JSON: /api/errors/7a910eaca8303b26. Report an issue: GitHub.