.dockerignore documentation claims /bla entry will ignore directory named "bla" in root, but it doesn't

[ghost]

Description

.dockerignore documentation https://docs.docker.com/engine/reference/builder/#dockerignore-file claims /bla entry will ignore directory named "bla" in root, but when I actually tested this, only bla will work as an entry, and /bla won't. Since I believe this is inconsistent with a .gitignore, I wonder if this is a docker bug? (If it isn't a docker bug, then I suggest it should be fixed in the documentation.)

Steps to reproduce the issue:

1. Create a new folder, inside add "Dockerfile" and "bla" folder and ".dockerignore" file
2. Put "/bla" into .dockerignore as a new line (without quotes)
3. Build the Dockerfile

Describe the results you received:
"bla" is uploaded to docker daemon, despite "/bla" entry in ".dockerignore" file

Describe the results you expected:
"bla" is not uploaded to docker daemon, because of "/bla" entry in ".dockerignore" file. Alternatively, the docs shouldn't suggest that this works (which they do now, at least as far as my reading comprehension goes, of the /foo/bar example entry that is mentioned)

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

Output of docker version:

Client:
 Version:         1.13.1
 API version:     1.26
 Package version: docker-1.13.1-44.git584d391.fc27.x86_64
 Go version:      go1.9.1
 Git commit:      caba767-unsupported
 Built:           Thu Nov 23 21:17:26 2017
 OS/Arch:         linux/amd64

Server:
 Version:         1.13.1
 API version:     1.26 (minimum version 1.12)
 Package version: docker-1.13.1-44.git584d391.fc27.x86_64
 Go version:      go1.9.1
 Git commit:      caba767-unsupported
 Built:           Thu Nov 23 21:17:26 2017
 OS/Arch:         linux/amd64
 Experimental:    false

Output of docker info:

Containers: 26
 Running: 1
 Paused: 0
 Stopped: 25
Images: 615
Server Version: 1.13.1
Storage Driver: devicemapper
 Pool Name: docker-253:1-704589-pool
 Pool Blocksize: 65.54 kB
 Base Device Size: 10.74 GB
 Backing Filesystem: xfs
 Data file: /dev/loop0
 Metadata file: /dev/loop1
 Data Space Used: 7.63 GB
 Data Space Total: 107.4 GB
 Data Space Available: 24.61 GB
 Metadata Space Used: 21.66 MB
 Metadata Space Total: 2.147 GB
 Metadata Space Available: 2.126 GB
 Thin Pool Minimum Free Space: 10.74 GB
 Udev Sync Supported: true
 Deferred Removal Enabled: true
 Deferred Deletion Enabled: true
 Deferred Deleted Device Count: 0
 Data loop file: /var/lib/docker/devicemapper/devicemapper/data
 WARNING: Usage of loopback devices is strongly discouraged for production use. Use `--storage-opt dm.thinpooldev` to specify a custom block storage device.
 Metadata loop file: /var/lib/docker/devicemapper/devicemapper/metadata
 Library Version: 1.02.144 (2017-10-06)
Logging Driver: journald
Cgroup Driver: systemd
Plugins: 
 Volume: local
 Network: bridge host macvlan null overlay
 Authorization: rhel-push-plugin
Swarm: inactive
Runtimes: oci runc
Default Runtime: oci
Init Binary: /usr/libexec/docker/docker-init-current
containerd version: caba7670d38dc7cddb0c19bcd97cc27fdd65a789 (expected: aa8187dbd3b7ad67d8e5e3a15115d3eef43a7ed1)
runc version: caba7670d38dc7cddb0c19bcd97cc27fdd65a789-dirty (expected: 9df8b306d01f59d3a8029be411de015b7304dd8f)
init version: N/A (expected: 949e6facb77383876aeff8a6944dde66b3089574)
Security Options:
 seccomp
  WARNING: You're not using the default seccomp profile
  Profile: /etc/docker/seccomp.json
 selinux
Kernel Version: 4.15.9-300.fc27.x86_64
Operating System: Fedora 27 (Workstation Edition)
OSType: linux
Architecture: x86_64
Number of Docker Hooks: 3
CPUs: 12
Total Memory: 15.65 GiB
Name: falcon
ID: NKWR:ZVET:EPGZ:CT3X:BVQH:XY34:4TBN:5PXO:LNQI:T3NB:K44I:WCL7
Docker Root Dir: /var/lib/docker
Debug Mode (client): false
Debug Mode (server): false
Registry: https://index.docker.io/v1/
Experimental: false
Insecure Registries:
 127.0.0.0/8
Live Restore Enabled: false
Registries: docker.io (secure), registry.fedoraproject.org (secure), registry.access.redhat.com (secure), docker.io (secure)

Additional environment details (AWS, VirtualBox, physical, etc.):
tested on a physical dev machine (zen / AMD64, runs fedora 27)

[thaJeztah]

Looks like you're running an unsupported Red Hat fork of Docker, not the official packages;

 Package version: docker-1.13.1-44.git584d391.fc27.x86_64
 Go version:      go1.9.1
 Git commit:      caba767-unsupported

Also note that Docker 1.13 has reached end of life in May of last year, and has not been maintained since.

Can you try installing a current version of the official package? https://docs.docker.com/install/linux/docker-ce/fedora/

I tried on a current version of Docker, and am not able to reproduce:

mkdir repro-36660 && cd repro-36660

mkdir bla
echo '/bla' > .dockerignore

cat > Dockerfile -<<EOF
FROM busybox
RUN mkdir /copied/
COPY . /copied/
RUN ls -la /copied/
EOF

docker build --no-cache .

Which shows:

Sending build context to Docker daemon  3.072kB
Step 1/4 : FROM busybox
 ---> f6e427c148a7
Step 2/4 : RUN mkdir /copied/
 ---> Running in 5d6e0120fe63
Removing intermediate container 5d6e0120fe63
 ---> cb5349747106
Step 3/4 : COPY . /copied/
 ---> 367453e2c2bf
Step 4/4 : RUN ls -la /copied/
 ---> Running in 3989ba0cc064
total 16
drwxr-xr-x    1 root     root          4096 Mar 22 00:55 .
drwxr-xr-x    1 root     root          4096 Mar 22 00:55 ..
-rw-r--r--    1 root     root             5 Mar 22 00:48 .dockerignore
-rw-r--r--    1 root     root            68 Mar 22 00:48 Dockerfile
Removing intermediate container 3989ba0cc064
 ---> 97947ba13f22
Successfully built 97947ba13f22

I'm closing this issue, because this does not appear to be reproducible on a current version of Docker, but feel free to continue the conversation

[ghost]

Ok, I tested your neat reproduction script and indeed it gives a wrong result here. I filed a ticket with Red Hat about this: https://bugzilla.redhat.com/show_bug.cgi?id=1559274

[runcom]

This has been fixed by 1cde87c#diff-c87a8ca60f0891b79d192fa86f019916

We're updating the package in Fedora with that commit