bake: copy remote context contents to root

When resolving remote contexts locally in bake, then we need to ensure
that we properly unpack the contents of that context to the root
directory, instead of leaving it in the subdirectory.

Otherwise, any files will be found in the wrong location. Along with
this change, we also need a change to the dockerfile location lookup to
ensure that it is found at the root instead of in the subdirectory.

Signed-off-by: Justin Chadwell <me@jedevc.com>

bake/bake.go

@@ -951,7 +951,12 @@ func updateContext(t *build.Inputs, inp *Input) {
 	if build.IsRemoteURL(t.ContextPath) {
 		return
 	}
-	st := llb.Scratch().File(llb.Copy(*inp.State, t.ContextPath, "/"), llb.WithCustomNamef("set context to %s", t.ContextPath))
+	st := llb.Scratch().File(
+		llb.Copy(*inp.State, t.ContextPath, "/", &llb.CopyInfo{
+			CopyDirContentsOnly: true,
+		}),
+		llb.WithCustomNamef("set context to %s", t.ContextPath),
+	)
 	t.ContextState = &st
 }
 
@@ -1027,9 +1032,6 @@ func toBuildOpt(t *Target, inp *Input) (*build.Options, error) {
 	if t.Dockerfile != nil {
 		dockerfilePath = *t.Dockerfile
 	}
-	if !build.IsRemoteURL(contextPath) && !path.IsAbs(dockerfilePath) {
-		dockerfilePath = path.Join(contextPath, dockerfilePath)
-	}
 
 	bi := build.Inputs{
 		ContextPath:    contextPath,
@@ -1040,6 +1042,9 @@ func toBuildOpt(t *Target, inp *Input) (*build.Options, error) {
 		bi.DockerfileInline = *t.DockerfileInline
 	}
 	updateContext(&bi, inp)
+	if !build.IsRemoteURL(bi.ContextPath) && bi.ContextState == nil && !path.IsAbs(bi.DockerfilePath) {
+		bi.DockerfilePath = path.Join(bi.ContextPath, bi.DockerfilePath)
+	}
 	if strings.HasPrefix(bi.ContextPath, "cwd://") {
 		bi.ContextPath = path.Clean(strings.TrimPrefix(bi.ContextPath, "cwd://"))
 	}