dockerfile: allow lowercase dockerfile name

frontend/dockerfile/builder/build.go

@@ -130,8 +130,15 @@ func Build(ctx context.Context, c client.Client) (*client.Result, error) {
 
 	name := "load build definition from " + filename
 
+	filenames := []string{filename, filename + ".dockerignore"}
+
+	// dockerfile is also supported casing moby/moby#10858
+	if path.Base(filename) == defaultDockerfileName {
+		filenames = append(filenames, path.Join(path.Dir(filename), strings.ToLower(defaultDockerfileName)))
+	}
+
 	src := llb.Local(localNameDockerfile,
-		llb.FollowPaths([]string{filename, filename + ".dockerignore"}),
+		llb.FollowPaths(filenames),
 		llb.SessionID(c.BuildOpts().SessionID),
 		llb.SharedKeyHint(localNameDockerfile),
 		dockerfile2llb.WithInternalName(name),
@@ -258,7 +265,19 @@ func Build(ctx context.Context, c client.Client) (*client.Result, error) {
 			Filename: filename,
 		})
 		if err != nil {
-			return errors.Wrapf(err, "failed to read dockerfile")
+			fallback := false
+			if path.Base(filename) == defaultDockerfileName {
+				var err1 error
+				dtDockerfile, err1 = ref.ReadFile(ctx2, client.ReadRequest{
+					Filename: path.Join(path.Dir(filename), strings.ToLower(defaultDockerfileName)),
+				})
+				if err1 == nil {
+					fallback = true
+				}
+			}
+			if !fallback {
+				return errors.Wrapf(err, "failed to read dockerfile")
+			}
 		}
 
 		sourceMap = llb.NewSourceMap(&src, filename, dtDockerfile)

frontend/dockerfile/dockerfile_test.go

@@ -107,6 +107,7 @@ var allTests = []integration.Test{
 	testFrontendSubrequests,
 	testDockefileCheckHostname,
 	testDefaultShellAndPath,
+	testDockerfileLowercase,
 }
 
 var fileOpTests = []integration.Test{
@@ -2732,6 +2733,34 @@ COPY . .
 	}
 }
 
+// moby/moby#10858
+func testDockerfileLowercase(t *testing.T, sb integration.Sandbox) {
+	f := getFrontend(t, sb)
+
+	dockerfile := []byte(`FROM scratch
+`)
+
+	dir, err := tmpdir(
+		fstest.CreateFile("dockerfile", dockerfile, 0600),
+	)
+	require.NoError(t, err)
+	defer os.RemoveAll(dir)
+
+	ctx := context.TODO()
+
+	c, err := client.New(ctx, sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	_, err = f.Solve(ctx, c, client.SolveOpt{
+		LocalDirs: map[string]string{
+			builder.DefaultLocalNameDockerfile: dir,
+			builder.DefaultLocalNameContext:    dir,
+		},
+	}, nil)
+	require.NoError(t, err)
+}
+
 func testExportedHistory(t *testing.T, sb integration.Sandbox) {
 	skipDockerd(t, sb)
 	f := getFrontend(t, sb)