filters: supporting alternative characters for quote

The regexp syntax can have some nasty characters to handle quoting
correctly, in practice. In certain scenarios a double quote works well,
but it can affect readability for certain regexps. This introduces a
quoting mode that treats `/` and `|` as a double quote to make the
quoting in regular expressions more familiar and readable.

This change is introduced in a backwards compatible manner, so existing
regexp quoting is not affected.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

filters/scanner_test.go

@@ -95,6 +95,20 @@ func TestScanner(t *testing.T) {
 				{pos: 22, token: tokenEOF},
 			},
 		},
+		{
+			name:  "RegexpQuotedValue",
+			input: `name~=/[abc]{0,2}/,foo=test`,
+			expected: []tokenResult{
+				{pos: 0, token: tokenField, text: "name"},
+				{pos: 4, token: tokenOperator, text: "~="},
+				{pos: 6, token: tokenQuoted, text: "/[abc]{0,2}/"},
+				{pos: 18, token: tokenSeparator, text: ","},
+				{pos: 19, token: tokenField, text: "foo"},
+				{pos: 22, token: tokenOperator, text: "="},
+				{pos: 23, token: tokenValue, text: "test"},
+				{pos: 27, token: tokenEOF},
+			},
+		},
 		{
 			name:  "Cowsay",
 			input: "name~=牛,labels.moo=true",
@@ -111,6 +125,22 @@ func TestScanner(t *testing.T) {
 				{pos: 25, token: tokenEOF},
 			},
 		},
+		{
+			name:  "CowsayRegexpQuoted",
+			input: "name~=|牛|,labels.moo=true",
+			expected: []tokenResult{
+				{pos: 0, token: tokenField, text: "name"},
+				{pos: 4, token: tokenOperator, text: "~="},
+				{pos: 6, token: tokenQuoted, text: "|牛|"},
+				{pos: 11, token: tokenSeparator, text: ","},
+				{pos: 12, token: tokenField, text: "labels"},
+				{pos: 18, token: tokenSeparator, text: "."},
+				{pos: 19, token: tokenField, text: "moo"},
+				{pos: 22, token: tokenOperator, text: "="},
+				{pos: 23, token: tokenValue, text: "true"},
+				{pos: 27, token: tokenEOF},
+			},
+		},
 		{
 			name:  "Escapes",
 			input: `name~="asdf\n\tfooo"`,
@@ -187,15 +217,45 @@ func TestScanner(t *testing.T) {
 		},
 		{
 			name:  "MissingValue",
-			input: "input==,id?=ff",
+			input: "input==,id!=ff",
 			expected: []tokenResult{
 				{pos: 0, token: tokenField, text: "input"},
 				{pos: 5, token: tokenOperator, text: "=="},
 				{pos: 7, token: tokenSeparator, text: ","},
-				{pos: 8, token: tokenValue, text: "id?=ff"},
+				{pos: 8, token: tokenField, text: "id"},
+				{pos: 10, token: tokenOperator, text: "!="},
+				{pos: 12, token: tokenValue, text: "ff"},
 				{pos: 14, token: tokenEOF},
 			},
 		},
+		{
+			name:  "QuotedRegexp",
+			input: "input~=/foo\\/bar/,id!=ff",
+			expected: []tokenResult{
+				{pos: 0, token: tokenField, text: "input"},
+				{pos: 5, token: tokenOperator, text: "~="},
+				{pos: 7, token: tokenQuoted, text: "/foo\\/bar/"},
+				{pos: 17, token: tokenSeparator, text: ","},
+				{pos: 18, token: tokenField, text: "id"},
+				{pos: 20, token: tokenOperator, text: "!="},
+				{pos: 22, token: tokenValue, text: "ff"},
+				{pos: 24, token: tokenEOF},
+			},
+		},
+		{
+			name:  "QuotedRegexpAlt",
+			input: "input~=|foo/bar|,id!=ff",
+			expected: []tokenResult{
+				{pos: 0, token: tokenField, text: "input"},
+				{pos: 5, token: tokenOperator, text: "~="},
+				{pos: 7, token: tokenQuoted, text: "|foo/bar|"},
+				{pos: 16, token: tokenSeparator, text: ","},
+				{pos: 17, token: tokenField, text: "id"},
+				{pos: 19, token: tokenOperator, text: "!="},
+				{pos: 21, token: tokenValue, text: "ff"},
+				{pos: 23, token: tokenEOF},
+			},
+		},
 	} {
 		t.Run(testcase.name, func(t *testing.T) {
 			var sc scanner