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/filter_test.go

@@ -135,6 +135,11 @@ func TestFilters(t *testing.T) {
 				corpus[8],
 			},
 		},
+		{
+			name:      "LabelValueNoAltQuoting",
+			input:     "labels.|foo|==omg_asdf.asdf-qwer",
+			errString: "filters: parse error: [labels. >|||< foo|==omg_asdf.asdf-qwer]: invalid quote encountered",
+		},
 		{
 			name:  "Name",
 			input: "name==bar",
@@ -178,6 +183,27 @@ func TestFilters(t *testing.T) {
 				corpus[7],
 			},
 		},
+		{
+			name:  "RegexpQuotedValue",
+			input: "other~=/[abc]+/,name!=foo",
+			expected: []interface{}{
+				corpus[6],
+				corpus[7],
+			},
+		},
+		{
+			name:  "RegexpQuotedValue",
+			input: "other~=/[abc]{1,2}/,name!=foo",
+			expected: []interface{}{
+				corpus[6],
+				corpus[7],
+			},
+		},
+		{
+			name:  "RegexpQuotedValueGarbage",
+			input: "other~=/[abc]{0,1}\"\\//,name!=foo",
+			// valid syntax, but doesn't match anything
+		},
 		{
 			name:  "NameAndLabelValue",
 			input: "name==bar,labels.bar==true",