Add LocalFlags to FileInfo (#4952)

We have the invalid bit to indicate that a file isn't good. That's enough for remote devices. For ourselves, it would be good to know sometimes why the file isn't good - because it's an unsupported type, because it matches an ignore pattern, or because we detected the data is bad and we need to rescan it.

Or, and this is the main future reason for the PR, because it's a change detected on a receive only device. We will want something like the invalid flag for those changes, but marking them as invalid today means the scanner will rehash them. Hence something more fine grained is required.

This introduces a LocalFlags fields to the FileInfo where we can stash things that we care about locally. For example,

    FlagLocalUnsupported = 1 << 0 // The kind is unsupported, e.g. symlinks on Windows
    FlagLocalIgnored     = 1 << 1 // Matches local ignore patterns
    FlagLocalMustRescan  = 1 << 2 // Doesn't match content on disk, must be rechecked fully

The LocalFlags fields isn't sent over the wire; instead the Invalid attribute is calculated based on the flags at index sending time. It's on the FileInfo anyway because that's what we serialize to database etc.

The actual Invalid flag should after this just be considered when building the global state and figuring out availability for remote devices. It is not used for local file index entries.

lib/protocol/protocol_test.go

@@ -391,6 +391,28 @@ func BenchmarkBlockSize(b *testing.B) {
 	}
 }
 
+func TestLocalFlagBits(t *testing.T) {
+	var f FileInfo
+	if f.IsIgnored() || f.MustRescan() || f.IsInvalid() {
+		t.Error("file should have no weird bits set by default")
+	}
+
+	f.SetIgnored(42)
+	if !f.IsIgnored() || f.MustRescan() || !f.IsInvalid() {
+		t.Error("file should be ignored and invalid")
+	}
+
+	f.SetMustRescan(42)
+	if f.IsIgnored() || !f.MustRescan() || !f.IsInvalid() {
+		t.Error("file should be must-rescan and invalid")
+	}
+
+	f.SetUnsupported(42)
+	if f.IsIgnored() || f.MustRescan() || !f.IsInvalid() {
+		t.Error("file should be invalid")
+	}
+}
+
 func TestIsEquivalent(t *testing.T) {
 	b := func(v bool) *bool {
 		return &v
@@ -430,8 +452,8 @@ func TestIsEquivalent(t *testing.T) {
 			eq: false,
 		},
 		{
-			a:  FileInfo{Invalid: false},
-			b:  FileInfo{Invalid: true},
+			a:  FileInfo{RawInvalid: false},
+			b:  FileInfo{RawInvalid: true},
 			eq: false,
 		},
 		{
@@ -445,6 +467,31 @@ func TestIsEquivalent(t *testing.T) {
 			eq: false,
 		},
 
+		// Special handling of local flags and invalidity. "MustRescan"
+		// files are never equivalent to each other. Otherwise, equivalence
+		// is based just on whether the file becomes IsInvalid() or not, not
+		// the specific reason or flag bits.
+		{
+			a:  FileInfo{LocalFlags: FlagLocalMustRescan},
+			b:  FileInfo{LocalFlags: FlagLocalMustRescan},
+			eq: false,
+		},
+		{
+			a:  FileInfo{RawInvalid: true},
+			b:  FileInfo{RawInvalid: true},
+			eq: true,
+		},
+		{
+			a:  FileInfo{LocalFlags: FlagLocalUnsupported},
+			b:  FileInfo{LocalFlags: FlagLocalUnsupported},
+			eq: true,
+		},
+		{
+			a:  FileInfo{RawInvalid: true},
+			b:  FileInfo{LocalFlags: FlagLocalUnsupported},
+			eq: true,
+		},
+
 		// Difference in blocks is not OK
 		{
 			a:         FileInfo{Blocks: []BlockInfo{{Hash: []byte{1, 2, 3, 4}}}},