.dockerignore wildcard exceptions lose files inside excluded directories #3448

🤖 this issue description was generated by an LLM. i reviewed it before submitting. 🤖

I used Codex for the investigation, reproduction scripts, and this draft.

When I generate a build context with docker.utils.tar, the rules ** and !**/a.txt omit every nested a.txt. Docker's BuildKit keeps those files with the same input. The SDK therefore drops files that the exception explicitly includes.

Reproduction

Save this script as reproduce-wildcard.py:

import tarfile
from pathlib import Path
from tempfile import TemporaryDirectory

import docker
from docker.utils import tar

patterns = ['**', '!**/a.txt']
files = ['foo/a.txt', 'foo/bar/a.txt', 'target/a.txt']
with TemporaryDirectory() as directory:
    root = Path(directory)
    (root / 'Dockerfile').write_text('FROM scratch\nCOPY . /\n')
    (root / '.dockerignore').write_text('\n'.join(patterns) + '\n')
    for relative in files:
        path = root / relative
        path.parent.mkdir(parents=True, exist_ok=True)
        path.write_text(relative)
    with tar(str(root), exclude=patterns.copy()) as context:
        with tarfile.open(fileobj=context) as archive:
            actual = sorted(name for name in archive.getnames() if name in files)
    print('docker:', docker.__version__)
    print('patterns:', patterns)
    print('SDK context files:', actual)

I ran it in an isolated uv environment, using commit 56343ddf8f0c44281e151c2dad016c16cdb8393d:

uv run --isolated --no-project --no-config --no-cache \
  --python /home/jyn/.local/share/mise/installs/python/3.14.7/bin/python3 \
  --with 'docker @ git+https://github.com/docker/docker-py@56343ddf8f0c44281e151c2dad016c16cdb8393d' \
  python reproduce-wildcard.py

The --python path selects my tested Python installation; use the path to your Python executable on another machine. The pinned requirement selects the upstream SDK rather than an installed copy. I did not modify the SDK or replace its modules with mocks. This reproducer creates disposable files and examines the SDK's context tar without contacting a Docker daemon.

Expected behavior

The SDK should retain foo/a.txt, foo/bar/a.txt, and target/a.txt. I built the same files with FROM scratch and COPY . / using BuildKit, and its local output retained all three.

Actual output

docker: 7.2.1.dev26+g56343ddf8
patterns: ['**', '!**/a.txt']
SDK context files: []

BuildKit control

I ran the following standalone control with Docker's active lima context and lima builder. It creates the same input files, runs docker buildx build with a local filesystem export, and enumerates every exported regular file before removing the temporary directories. The command uses the active Docker context and builder; another machine can use its own working configuration.

import subprocess
from pathlib import Path
from tempfile import TemporaryDirectory

patterns = ['**', '!**/a.txt']
files = ['foo/a.txt', 'foo/bar/a.txt', 'target/a.txt']
with TemporaryDirectory() as directory:
    context = Path(directory) / 'input'
    context.mkdir()
    output = Path(directory) / 'output'
    (context / 'Dockerfile').write_text('FROM scratch\nCOPY . /\n')
    (context / '.dockerignore').write_text('\n'.join(patterns) + '\n')
    for relative in files:
        path = context / relative
        path.parent.mkdir(parents=True, exist_ok=True)
        path.write_text(relative)
    subprocess.run([
        'docker', 'buildx', 'build',
        '--progress=plain', '--provenance=false',
        '--output', f'type=local,dest={output}', str(context),
    ], check=True)
    print('BuildKit output files:', sorted(
        path.relative_to(output).as_posix()
        for path in output.rglob('*') if path.is_file()
    ))

python3 buildkit-control-wildcard.py

BuildKit output files: ['foo/a.txt', 'foo/bar/a.txt', 'target/a.txt']

Related report

A commenter described a similar wildcard-exception failure in the closed issue #1514. I can reproduce the minimized case below using the current upstream commit.

#1514 (comment)

Environment

• Docker SDK for Python: 7.2.1.dev26+g56343ddf8, using upstream commit 56343ddf8f0c44281e151c2dad016c16cdb8393d.
• Python: 3.14.7 (main, Sep 29 2026, 15:01:40) [Clang 22.1.3 ].
• OS/distribution: CachyOS Linux, rolling release (BUILD_ID=rolling; /etc/os-release does not define VERSION_ID).
• Kernel/platform: Linux-7.2.9-1-cachyos-x86_64-with-glibc2.44.
• Docker CLI: 29.8.2; Docker Engine: 29.8.0 (linux/amd64).
• Buildx: github.com/docker/buildx 0.37.2 2d379c0c3f22da0d2759d132a0ec81ca949098f0.
• The SDK tar reproducer requires no engine connection; the separate BuildKit comparison used the versions above.