Add script to reproduce moby/buildkit#2279 issue

.gitignore

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+.build/
+
+

Dockerfile

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+ARG BASE=alpine:edge
+
+FROM $BASE AS base
+# RUN command always produce layer with digest `sha256:bcca0bb7...`
+RUN echo "Hello, world!!!"; if [ "$(arch)" = "x86_64" ]; then sleep 1; fi; touch -d 2021-01-01 -t 00:00:00 /foo.txt
+# COPY command produce differ layer per platform because /opt has differ change time
+COPY .build/changed.txt /opt/changed.txt
+
+FROM $BASE
+COPY --from=base /opt/changed.txt /opt/copy.txt

registry.sh

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+#!/bin/bash -e
+
+PORT=5000
+
+# Start docker registry
+if [ "$(docker ps -q -f name=registry)" == "" ]; then
+  docker run --rm -d -p $PORT:$PORT --name registry registry:2
+fi
+
+# Wait docker registry is ready
+n=0
+until nc -z localhost $PORT; do
+  sleep 0.1
+  n=$((n + 1))
+  if [ "$n" -gt 300 ]; then
+    echo Waiting port $PORT timeout
+    exit 1
+  fi
+done
+
+# Reupload used images
+for image in moby/buildkit:master alpine:edge; do
+  local=localhost:$PORT/${image/:[[:alpha:]]*/:latest}
+  echo "Reupload: $image -> $local"
+  docker pull $image
+  docker tag $image $local
+  docker push $local
+done

test-pass.sh

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+#!/bin/bash -e
+PORT=5000
+REGISTRY=localhost:$PORT
+
+# Recreate builder for clear local cache
+docker buildx rm cachebug || true
+docker buildx create --name cachebug --driver docker-container --driver-opt image=$REGISTRY/moby/buildkit:latest,network=host
+docker buildx inspect cachebug --bootstrap
+
+# Create some changed file
+mkdir -p .build
+date > .build/changed.txt
+
+# Run with cache-to only
+docker buildx build \
+    --progress=plain \
+    --builder cachebug \
+    --build-arg BASE=$REGISTRY/alpine:latest \
+    --cache-to type=registry,ref=$REGISTRY/cachebug:buildcache,mode=max \
+    --platform linux/amd64 \
+    --platform linux/arm64 \
+    .
+
+# Recreate builder for clear local cache
+docker buildx rm cachebug || true
+docker buildx create --name cachebug --driver docker-container --driver-opt image=$REGISTRY/moby/buildkit:latest,network=host
+docker buildx inspect cachebug --bootstrap
+
+# Create some changed file
+date > .build/changed.txt
+
+# Run with cache-from only
+docker buildx build \
+    --progress=plain \
+    --builder cachebug \
+    --build-arg BASE=$REGISTRY/alpine:latest \
+    --cache-from type=registry,ref=$REGISTRY/cachebug:buildcache \
+    --platform linux/amd64 \
+    --platform linux/arm64 \
+    . 2>&1 | tee .build/build.log
+
+if ( grep "Hello, world" .build/build.log | grep -v RUN > /dev/null ); then
+    echo "Cache miss found"
+    exit 1
+fi

test.sh

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+#!/bin/bash -e
+
+./registry.sh
+
+TOTAL=0
+FAILED=0
+for pass in {1..100}; do
+    if ( ./test-pass.sh > /dev/null 2>&1 ); then
+        echo "[$pass] OK"
+    else
+        echo "[$pass] FAIL"
+        FAILED=$((FAILED + 1))
+    fi
+    TOTAL=$((TOTAL + 1))
+done
+
+docker kill registry
+
+if [ $FAILED -gt 0 ]; then
+    echo "FAILED $FAILED OF $TOTAL"
+    exit 1
+fi