Description

wildcard directory matching in dockerignore (the double asterisk **) is not implemented correctly and buggy in some cases

Steps to reproduce the issue:

1. Dockerfile:

FROM busybox
WORKDIR /src
ADD . .
RUN find .

2. .dockerignore:

**/c
!a/b/c/include.txt
.git

3. Create files "a/b/c/include.txt" and "a/b/c/exclude.txt"

4. Run docker build --no-cache .

Describe the results you received:

a/b/c/exclude.txt should be ignored

Describe the results you expected:

a/b/c/exclude.txt is included in the docker context

Additional information you deem important (e.g. issue happens only occasionally):

This repo has a more complete explanation of the bug:

https://github.com/tilt-dev/dockerignore-wildcard-bug

The underlying bug is this code:

https://github.com/moby/moby/blob/v19.03.12/pkg/fileutils/fileutils.go#L83

which assumes that the number of directory separators in the pattern can be used to determine the "directory" length, which is not a correct assumption when wildcards are present.

Interestingly, the exclude pattern is necessary to reproduce this problem. That's because this code:

https://github.com/moby/moby/blob/v19.03.12/pkg/archive/archive.go#L843

skips directories purely as an optimization. Adding an exclusion pattern (!a/b/c/include.txt) makes this code go down the "slow" codepath.

Output of docker version:

Client: Docker Engine - Community
 Version:           19.03.11
 API version:       1.40
 Go version:        go1.13.10
 Git commit:        42e35e61f3
 Built:             Mon Jun  1 09:12:22 2020
 OS/Arch:           linux/amd64
 Experimental:      false

Server: Docker Engine - Community
 Engine:
  Version:          19.03.11
  API version:      1.40 (minimum version 1.12)
  Go version:       go1.13.10
  Git commit:       42e35e61f3
  Built:            Mon Jun  1 09:10:54 2020
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.2.13
  GitCommit:        7ad184331fa3e55e52b890ea95e65ba581ae3429
 runc:
  Version:          1.0.0-rc10
  GitCommit:        dc9208a3303feef5b3839f4323d9beb36df0a9dd
 docker-init:
  Version:          0.18.0
  GitCommit:        fec3683