filter: make [^...] in globs exclude / and document it

A glob like file[^a].txt was translated to (^|/)file[^a]\.txt$ in path
mode, so it matched file/.txt across a directory boundary, unlike ?
and the [!...] form.

Treat a leading ^ in a character class the same as a leading !: in
path mode it now also excludes /, and [^] is rejected as an empty
character class. Document both negation forms in the filtering
grammar.

docs/content/filtering.md

@@ -43,7 +43,7 @@ Rclone matching rules follow a glob style:
 *         matches any sequence of non-separator (/) characters
 **        matches any sequence of characters including / separators
 ?         matches any single non-separator (/) character
-[ [ ! ] { character-range } ]
+[ [ ! | ^ ] { character-range } ]
           character class (must be non-empty)
 { pattern-list }
           pattern alternatives

fs/filter/filter_test.go

@@ -627,22 +627,26 @@ func TestNewFilterMatchesRegexp(t *testing.T) {
 }
 
 func TestNewFilterMatchesNegatedCharacterClass(t *testing.T) {
-	f, err := NewFilter(nil)
-	require.NoError(t, err)
-	add := func(s string) {
-		err := f.AddRule(s)
-		require.NoError(t, err)
+	for _, negate := range []string{"!", "^"} {
+		t.Run(negate, func(t *testing.T) {
+			f, err := NewFilter(nil)
+			require.NoError(t, err)
+			add := func(s string) {
+				err := f.AddRule(s)
+				require.NoError(t, err)
+			}
+			add("+ file[" + negate + "a].txt")
+			add("- *")
+			testInclude(t, f, []includeTest{
+				{"fileb.txt", 100, 0, true},
+				{"sub/fileb.txt", 100, 0, true},
+				{"filea.txt", 100, 0, false},
+				{"file" + negate + ".txt", 100, 0, true},
+				{"file/.txt", 100, 0, false},
+			})
+			assert.False(t, f.InActive())
+		})
 	}
-	add("+ file[!a].txt")
-	add("- *")
-	testInclude(t, f, []includeTest{
-		{"fileb.txt", 100, 0, true},
-		{"sub/fileb.txt", 100, 0, true},
-		{"filea.txt", 100, 0, false},
-		{"file!.txt", 100, 0, true},
-		{"file/.txt", 100, 0, false},
-	})
-	assert.False(t, f.InActive())
 }
 
 func TestNewFilterHashFilter(t *testing.T) {

fs/filter/glob.go

@@ -86,7 +86,7 @@ func globToRegexp(glob string, pathMode bool, addAnchors bool, ignoreCase bool)
 	braceDepth := 0
 	inBrackets := 0
 	bracketStart := false   // just opened a character class
-	bracketNegated := false // just read the ! of a [! character class
+	bracketNegated := false // just read the ! or ^ of a [! or [^ character class
 	slashed := false
 	inRegexp := false    // inside {{ ... }}
 	inRegexpEnd := false // have received }} waiting for more
@@ -127,10 +127,10 @@ func globToRegexp(glob string, pathMode bool, addAnchors bool, ignoreCase bool)
 			}
 		}
 		if inBrackets > 0 {
-			if bracketStart && c == '!' {
-				// [!...] is a negated character class in glob
-				// syntax, which is [^...] in a regexp. Like ?, it
-				// does not match the / separator in path mode.
+			if bracketStart && (c == '!' || c == '^') {
+				// [!...] and [^...] are negated character classes
+				// in glob syntax, which is [^...] in a regexp. Like
+				// ?, they do not match the / separator in path mode.
 				bracketStart = false
 				bracketNegated = true
 				_ = re.WriteByte('^')

fs/filter/glob_test.go

@@ -25,6 +25,10 @@ func TestGlobStringToRegexp(t *testing.T) {
 		{`potat[![:alpha:]]or`, `potat[^[:alpha:]]or`, ``},
 		{`potat[a!]`, `potat[a!]`, ``},
 		{`potat[!]`, ``, `empty character class`},
+		{`potat[^oa]`, `potat[^oa]`, ``},
+		{`potat[^[:alpha:]]or`, `potat[^[:alpha:]]or`, ``},
+		{`potat[a^]`, `potat[a^]`, ``},
+		{`potat[^]`, ``, `empty character class`},
 		{`'.' '+' '(' ')' '|' '^' '$'`, `'\.' '\+' '\(' '\)' '\|' '\^' '\$'`, ``},
 		{`*.jpg`, `.*\.jpg`, ``},
 		{`a{b,c,d}e`, `a(b|c|d)e`, ``},
@@ -99,6 +103,10 @@ func TestGlobPathToRegexp(t *testing.T) {
 		{`potat[![:alpha:]]or`, `(^|/)potat[^/[:alpha:]]or$`, ``},
 		{`potat[a!]`, `(^|/)potat[a!]$`, ``},
 		{`potat[!]`, ``, `empty character class`},
+		{`potat[^oa]`, `(^|/)potat[^/oa]$`, ``},
+		{`potat[^[:alpha:]]or`, `(^|/)potat[^/[:alpha:]]or$`, ``},
+		{`potat[a^]`, `(^|/)potat[a^]$`, ``},
+		{`potat[^]`, ``, `empty character class`},
 		{`'.' '+' '(' ')' '|' '^' '$'`, `(^|/)'\.' '\+' '\(' '\)' '\|' '\^' '\$'$`, ``},
 		{`*.jpg`, `(^|/)[^/]*\.jpg$`, ``},
 		{`a{b,c,d}e`, `(^|/)a(b|c|d)e$`, ``},