all: Add receive only folder type (#5027)

Adds a receive only folder type that does not send changes, and where the user can optionally revert local changes. Also changes some of the icons to make the three folder types distinguishable.

lib/db/meta_test.go

@@ -0,0 +1,82 @@
+// Copyright (C) 2018 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at https://mozilla.org/MPL/2.0/.
+
+package db
+
+import (
+	"math/bits"
+	"sort"
+	"testing"
+
+	"github.com/syncthing/syncthing/lib/protocol"
+)
+
+func TestEachFlagBit(t *testing.T) {
+	cases := []struct {
+		flags      uint32
+		iterations int
+	}{
+		{0, 0},
+		{1<<0 | 1<<3, 2},
+		{1 << 0, 1},
+		{1 << 31, 1},
+		{1<<10 | 1<<20 | 1<<30, 3},
+	}
+
+	for _, tc := range cases {
+		var flags uint32
+		iterations := 0
+
+		eachFlagBit(tc.flags, func(f uint32) {
+			iterations++
+			flags |= f
+			if bits.OnesCount32(f) != 1 {
+				t.Error("expected exactly one bit to be set in every call")
+			}
+		})
+
+		if flags != tc.flags {
+			t.Errorf("expected 0x%x flags, got 0x%x", tc.flags, flags)
+		}
+		if iterations != tc.iterations {
+			t.Errorf("expected %d iterations, got %d", tc.iterations, iterations)
+		}
+	}
+}
+
+func TestMetaDevices(t *testing.T) {
+	d1 := protocol.DeviceID{1}
+	d2 := protocol.DeviceID{2}
+	meta := newMetadataTracker()
+
+	meta.addFile(d1, protocol.FileInfo{Sequence: 1})
+	meta.addFile(d1, protocol.FileInfo{Sequence: 2, LocalFlags: 1})
+	meta.addFile(d2, protocol.FileInfo{Sequence: 1})
+	meta.addFile(d2, protocol.FileInfo{Sequence: 2, LocalFlags: 2})
+	meta.addFile(protocol.LocalDeviceID, protocol.FileInfo{Sequence: 1})
+
+	// There are five device/flags combos
+	if l := len(meta.counts.Counts); l < 5 {
+		t.Error("expected at least five buckets, not", l)
+	}
+
+	// There are only two non-local devices
+	devs := meta.devices()
+	if l := len(devs); l != 2 {
+		t.Fatal("expected two devices, not", l)
+	}
+
+	// Check that we got the two devices we expect
+	sort.Slice(devs, func(a, b int) bool {
+		return devs[a].Compare(devs[b]) == -1
+	})
+	if devs[0] != d1 {
+		t.Error("first device should be d1")
+	}
+	if devs[1] != d2 {
+		t.Error("second device should be d2")
+	}
+}