Unexpected `CopyIgnoredFile` warning

[ro0NL]

Description

We started to see CopyIgnoredFile warning since recent for COPY . .

This is a neat shortcut to copy everyting included, given your dockerignore contains something like

/*
!/some

Reproduce

docker build .

Expected behavior

No response

docker version

$ docker version
Client: Docker Engine - Community
 Version:           29.2.0
 API version:       1.53
 Go version:        go1.25.6
 Git commit:        0b9d198
 Built:             Mon Jan 26 19:27:07 2026
 OS/Arch:           linux/amd64
 Context:           default

Server: Docker Engine - Community
 Engine:
  Version:          29.2.0
  API version:      1.53 (minimum version 1.44)
  Go version:       go1.25.6
  Git commit:       9c62384
  Built:            Mon Jan 26 19:27:07 2026
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          v2.2.1
  GitCommit:        dea7da592f5d1d2b7755e3a161be07f43fad8f75
 runc:
  Version:          1.3.4
  GitCommit:        v1.3.4-0-gd6d73eb8
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

docker info

$ docker info
Client: Docker Engine - Community
 Version:    29.2.0
 Context:    default
 Debug Mode: false
 Plugins:
  buildx: Docker Buildx (Docker Inc.)
    Version:  v0.31.1
    Path:     /usr/libexec/docker/cli-plugins/docker-buildx
  compose: Docker Compose (Docker Inc.)
    Version:  v5.0.2
    Path:     /usr/libexec/docker/cli-plugins/docker-compose

Server:
 Containers: 7
  Running: 5
  Paused: 0
  Stopped: 2
 Images: 65
 Server Version: 29.2.0
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Using metacopy: false
  Native Overlay Diff: true
  userxattr: false
 Logging Driver: json-file
 Cgroup Driver: systemd
 Cgroup Version: 2
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local splunk syslog
 CDI spec directories:
  /etc/cdi
  /var/run/cdi
 Swarm: inactive
 Runtimes: io.containerd.runc.v2 runc
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: dea7da592f5d1d2b7755e3a161be07f43fad8f75
 runc version: v1.3.4-0-gd6d73eb8
 init version: de40ad0
 Security Options:
  apparmor
  seccomp
   Profile: builtin
  cgroupns
 Kernel Version: 6.14.0-37-generic
 Operating System: Ubuntu 24.04.3 LTS
 OSType: linux
 Architecture: x86_64
 CPUs: 12
 Total Memory: 15.29GiB
 Name: roland
 ID: d25654b8-8a03-41f4-832e-ca0958fec624
 Docker Root Dir: /var/lib/docker
 Debug Mode: false
 Username: etriasnl
 Experimental: false
 Insecure Registries:
  ::1/128
  127.0.0.0/8
 Live Restore Enabled: false

Additional Info

No response

[Best2Two]

The fix for this issue was merged in moby/buildkit#6356 on November 13, 2025, but it's not yet in any official Docker release. Docker Engine 29.2.0 uses BuildKit v0.27.0, Just wait for the update. This issue is not related to CLI either

[thaJeztah]

Looking at moby/buildkit#6356, I see it's part of BuildKit v0.27.0, which is used by Docker 29.2, so I think it's the reverse and that PR to have introduced the problem, not solved it.

The change in behavior is in the Dockerfile frontend moby/buildkit@143a046, so the parsing used for the Dockerfile, and part of dockerfile v1.21.0

mkdir test && cd test

cat > .dockerignore <<'EOF'
/*
!/some
EOF


cat > Dockerfile <<'EOF'
FROM scratch
COPY . .
EOF

With the above, I get the warning:

docker build --no-cache .
# ...
# => => unpacking to moby-dangling@sha256:ff039ba2427511592c8627270aca2b70975589bf58a46d25e12a837f437a14  0.0s
#
# 1 warning found (use docker --debug to expand):
# - CopyIgnoredFile: Attempting to Copy file "." that is excluded by .dockerignore (line 2)

Updating the Dockerfile to use the previous (v1.20.0) syntax;

cat > Dockerfile <<'EOF'
# syntax=docker/dockerfile:1.20.0

FROM scratch
COPY . .
EOF

Doesn't produce the warning;

docker build --no-cache .
# ...
#  => => unpacking to moby-dangling@sha256:436b8636ddbcfeeff19131f2a420ee1222441f1471e54a55ad0b8d90ee21ff  0.0s

In general, I wouldn't recommend pinning to an older version of the syntax, but it's a possible workaround if this is causing issues.

[thaJeztah]

Looks like a ticket was opened in the BuildKit repository as well, so let me mark this as duplicate;

• CopyIgnoredFile linter triggers with negated matches and "COPY . $target" moby/buildkit#6512