Buildkit cache issue repro

go.mod

module github.com/aaronlehmann/bkcacherepro

go 1.16

require (
	github.com/moby/buildkit v0.9.0
	golang.org/x/sync v0.0.0-20210220032951-036812b2e83c
)

main.go

package main

import (
	"context"
	"fmt"
	"os"

	_ "github.com/moby/buildkit/client/connhelper/dockercontainer"

	"github.com/moby/buildkit/client"
	"github.com/moby/buildkit/client/llb"
	"github.com/moby/buildkit/util/appdefaults"
	"github.com/moby/buildkit/util/progress/progresswriter"
	"golang.org/x/sync/errgroup"
)

func main() {
	st := llb.Image("alpine")

	st = st.Run(
		llb.Shlex(`sh -c "mkdir -p /mnt/data/d1 && ln -s /mnt/data /data"`),
	).Root()

	st1 := st.Run(
		llb.Shlex(`sh -c "echo abc > /data/d1/foo"`),
	).Root()

	fmt.Println("Copying from st1 with a single file at /data/d1/foo:")
	if err := copyAndList(st1); err != nil {
		panic(err)
	}

	fmt.Println("Copying from stock alpine image - copy should not be cached!:")
	if err := copyAndList(llb.Image("alpine")); err != nil {
		panic(err)
	}
}

func copyAndList(st llb.State) error {
	copied := llb.Scratch().File(
		llb.Copy(st, "/mnt/data/d1", "/", &llb.CopyInfo{IncludePatterns: []string{"f*"}}),
	)

	findSt := llb.Image("alpine").Run(
		llb.Shlex(`sh -c "apk add -U findutils"`),
	).Root().Run(
		llb.Shlex(`sh -c "find . -ls"`),
		llb.AddMount("/d", copied),
		llb.Dir("/d"),
		llb.IgnoreCache,
	)

	ctx := context.Background()
	def, err := findSt.Marshal(ctx, llb.LinuxAmd64)
	if err != nil {
		return err
	}

	addr := os.Getenv("BUILDKIT_HOST")
	if addr == "" {
		addr = appdefaults.Address
	}

	c, err := client.New(ctx, addr, client.WithFailFast())
	if err != nil {
		return err
	}

	pw, err := progresswriter.NewPrinter(context.TODO(), os.Stderr, "plain")
	if err != nil {
		return err
	}
	mw := progresswriter.NewMultiWriter(pw)

	eg, ctx := errgroup.WithContext(ctx)

	cwd, err := os.Getwd()
	if err != nil {
		return err
	}

	eg.Go(func() error {
		solveOpt := client.SolveOpt{
			Exports: []client.ExportEntry{{
				Type:      client.ExporterLocal,
				OutputDir: cwd,
			}},
		}

		_, err := c.Solve(ctx, def, solveOpt, progresswriter.ResetTime(mw.WithPrefix("", false)).Status())
		return err
	})

	eg.Go(func() error {
		<-pw.Done()
		return pw.Err()
	})

	return eg.Wait()
}