Add --parents flag for ADD/COPY instructions

[DYefimov]

partially fixes: #2917

.parents_test.sh:

#!/usr/bin/env sh
set -e

TMP_DIR=$(mktemp -dt parents_test.XXXXXXXX)

echo "Created \"$TMP_DIR\""
trap "echo \"Removing \\\"$TMP_DIR\\\"\"; rm -rf \"$TMP_DIR\"" EXIT

mkdir -p $TMP_DIR/src/dir1
mkdir -p $TMP_DIR/src/dir2/subdir2

touch $TMP_DIR/src/dir1/file1-1.py
touch $TMP_DIR/src/dir1/file1-2.go
touch $TMP_DIR/src/dir2/subdir2/file2-1.go
touch $TMP_DIR/src/dir2/subdir2/file2-2.js

cat << DOCKERFILE > $TMP_DIR/dockerfile
# syntax=dyefimov/dockerfile:copy_parents-labs

FROM scratch

COPY ./src/*/*/*.go ./dst1/
COPY --parents ./src/*/*/*.go ./dst2/

CMD ["echo", "hello-world"]
DOCKERFILE

echo "======================================================="
SOCKET_DIR=$(realpath $(dirname $0))/.tmp
mkdir -p $SOCKET_DIR
sudo buildctl \
    --addr=unix://$SOCKET_DIR/buildkitd.socket \
    build \
        --frontend=dockerfile.v0 \
        --local context=$TMP_DIR \
        --local dockerfile=$TMP_DIR \
        --no-cache \
        --output=type=docker,name=test_parents | docker load

echo "======================================================="
echo "source:"
find $TMP_DIR/src -printf '%P\n' | grep -v '^[[:space:]]*$' | sort

echo "======================================================="
docker container rm -f test_parents > /dev/null 2>&1
docker container create --name=test_parents test_parents > /dev/null 2>&1
echo "COPY:"
docker container export test_parents | tar tf - | grep "dst1" | sed 's#^dst1/##' | grep -v '^[[:space:]]*$' | sort
echo "COPY --parents:"
docker container export test_parents | tar tf - | grep "dst2" | sed 's#^dst2/##' | grep -v '^[[:space:]]*$' | sort
docker container rm -f test_parents > /dev/null 2>&1

echo "======================================================="

.parents_test.sh output:

$ ./.parents_test.sh 
Created "/tmp/parents_test.XduwOh8Y"
=======================================================
[+] Building 34.9s (8/8) FINISHED                                                                                      
 => [internal] load build definition from Dockerfile                                                              0.2s
 => => transferring dockerfile: 196B                                                                              0.0s
 => [internal] load .dockerignore                                                                                 0.2s
 => => transferring context: 2B                                                                                   0.0s
 => resolve image config for docker.io/dyefimov/dockerfile:copy_parents-labs                                      3.5s
 => docker-image://docker.io/dyefimov/dockerfile:copy_parents-labs@sha256:d610b759d921bc35515d468718f2609cd6a43  20.0s
 => => resolve docker.io/dyefimov/dockerfile:copy_parents-labs@sha256:d610b759d921bc35515d468718f2609cd6a436327e  0.0s
 => => sha256:9b5f69abec23db87906aa36405c32438ee46fa07539bab74519bbc1df4f7f43b 10.50MB / 10.50MB                 19.3s
 => => extracting sha256:9b5f69abec23db87906aa36405c32438ee46fa07539bab74519bbc1df4f7f43b                         0.6s
 => [internal] load build context                                                                                 0.0s
 => => transferring context: 137B                                                                                 0.0s
 => [1/2] COPY ./src/*/*/*.go ./dst1/                                                                             5.4s
 => [2/2] COPY --parents ./src/*/*/*.go ./dst2/                                                                   4.7s
 => exporting to oci image format                                                                                 0.4s
 => => exporting layers                                                                                           0.3s
 => => exporting manifest sha256:561ee1a533640037d09124564cc0c87a8b83f2afb6c295388396aee90c358b41                 0.0s
 => => exporting config sha256:e8e6fb69968b721a8025df93212bf37429781089a3be88f0f73f275c3023c096                   0.0s
 => => sending tarball                                                                                            0.0s
374816127ac7: Loading layer [==================================================>]     138B/138B
d46573954a71: Loading layer [==================================================>]     186B/186B
The image test_parents:latest already exists, renaming the old one with ID sha256:623c1fa1a66cc452143122dfce26062f698284b8428baf59cf25da8ab6416890 to empty string
Loaded image: test_parents:latest
=======================================================
source:
dir1
dir1/file1-1.py
dir1/file1-2.go
dir2
dir2/subdir2
dir2/subdir2/file2-1.go
dir2/subdir2/file2-2.js
=======================================================
COPY:
file2-1.go
COPY --parents:
src/
src/dir2/
src/dir2/subdir2/
src/dir2/subdir2/file2-1.go
=======================================================
Removing "/tmp/parents_test.XduwOh8Y"