command(bake): Specify local and remote bake files

This adds the ability to source additional local build definition files when
sourcing Bake files via a remote url.
Prefixing a file with 'cwd://' will source a bake file on the local
machine, instead of the remote location.
Local files will be read/have precedence before remote files.

Usage:
```
docker buildx bake https://github.com/example/upstream.git --file cwd://docker-bake.override.hcl --print
```
This will source a default file from the example/upstream repository,
and also source a build definition from the local machine.

Signed-off-by: Cameron Adams <pnzreba@gmail.com>

commands/bake.go

@@ -5,6 +5,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"os"
+	"strings"
 
 	"github.com/containerd/console"
 	"github.com/containerd/containerd/platforms"
@@ -142,11 +143,19 @@ func runBake(dockerCli command.Cli, targets []string, in bakeOptions, cFlags com
 			}
 		}
 	}()
-
+	localFilesArg, remoteFilesArg := getFilesArgs(in.files)
 	if url != "" {
-		files, inp, err = bake.ReadRemoteFiles(ctx, nodes, url, in.files, printer)
+		files, inp, err = bake.ReadRemoteFiles(ctx, nodes, url, remoteFilesArg, printer)
+		if len(localFilesArg) > 0 {
+			var localFiles []bake.File
+			localFiles, err = bake.ReadLocalFiles(localFilesArg, dockerCli.In())
+			files = append(files, localFiles...)
+		}
 	} else {
-		files, err = bake.ReadLocalFiles(in.files, dockerCli.In())
+		var filesArg []string
+		filesArg = append(filesArg, localFilesArg...)
+		filesArg = append(filesArg, remoteFilesArg...)
+		files, err = bake.ReadLocalFiles(filesArg, dockerCli.In())
 	}
 	if err != nil {
 		return err
@@ -257,3 +266,16 @@ func bakeCmd(dockerCli command.Cli, rootOpts *rootOptions) *cobra.Command {
 
 	return cmd
 }
+
+func getFilesArgs(s []string) ([]string, []string) {
+	var localFiles []string
+	var remoteFiles []string
+	for _, v := range s {
+		if strings.HasPrefix(v, "cwd://") {
+			localFiles = append(localFiles, strings.TrimPrefix(v, "cwd://"))
+		} else {
+			remoteFiles = append(remoteFiles, v)
+		}
+	}
+	return localFiles, remoteFiles
+}

tests/bake.go

@@ -21,6 +21,7 @@ var bakeTests = []func(t *testing.T, sb integration.Sandbox){
 	testBakeLocal,
 	testBakeRemote,
 	testBakeRemoteCmdContext,
+	testBakeRemoteLocalOverride,
 	testBakeRemoteCmdContextOverride,
 	testBakeRemoteContextSubdir,
 	testBakeRemoteCmdContextEscapeRoot,
@@ -48,6 +49,11 @@ target "default" {
 	require.NoError(t, err, out)
 
 	require.FileExists(t, filepath.Join(dirDest, "foo"))
+
+	out, err = bakeCmd(sb, withDir(dir), withArgs("--file", "cwd://docker-bake.hcl", "--set", "*.output=type=local,dest="+dirDest))
+	require.NoError(t, err, out)
+
+	require.FileExists(t, filepath.Join(dirDest, "foo"))
 }
 
 func testBakeRemote(t *testing.T, sb integration.Sandbox) {
@@ -80,6 +86,48 @@ EOT
 	require.FileExists(t, filepath.Join(dirDest, "foo"))
 }
 
+func testBakeRemoteLocalOverride(t *testing.T, sb integration.Sandbox) {
+	remoteBakefile := []byte(`
+target "default" {
+	dockerfile-inline = <<EOT
+FROM scratch
+COPY foo /foo
+EOT
+}
+`)
+	localBakefile := []byte(`
+target "default" {
+	dockerfile-inline = <<EOT
+FROM scratch
+COPY bar /bar
+EOT
+}
+`)
+	dirSpec := tmpdir(
+		t,
+		fstest.CreateFile("docker-bake.hcl", remoteBakefile, 0600),
+		fstest.CreateFile("bar", []byte("bar"), 0600),
+	)
+	dirSrc := tmpdir(
+		t,
+		fstest.CreateFile("local-docker-bake.hcl", localBakefile, 0600),
+	)
+	dirDest := t.TempDir()
+
+	git, err := gitutil.New(gitutil.WithWorkingDir(dirSpec))
+	require.NoError(t, err)
+
+	gitutil.GitInit(git, t)
+	gitutil.GitAdd(git, t, "docker-bake.hcl", "bar")
+	gitutil.GitCommit(git, t, "initial commit")
+	addr := gitutil.GitServeHTTP(git, t)
+
+	out, err := bakeCmd(sb, withDir(dirSrc), withArgs(addr, "--file", "cwd://local-docker-bake.hcl", "--set", "*.output=type=local,dest="+dirDest))
+	require.NoError(t, err, out)
+
+	require.FileExists(t, filepath.Join(dirDest, "bar"))
+}
+
 func testBakeRemoteCmdContext(t *testing.T, sb integration.Sandbox) {
 	bakefile := []byte(`
 target "default" {