fix(strings): ignore unnamed capture groups

capture() built a map key from SubexpNames() for every submatch; unnamed groups (name "") became an empty-string key (and duplicate keys for several). jq returns only named captures.

pkg/yqlib/operator_strings.go

@@ -365,8 +365,14 @@ func capture(matchPrefs matchPreferences, regEx *regexp.Regexp, candidate *Candi
 
 		_, submatches := matches[0], matches[1:]
 		for j, submatch := range submatches {
-
+			name := subNames[j+1]
-			keyNode := createScalarNode(subNames[j+1], subNames[j+1])
+			// jq only returns named capture groups; unnamed groups (whose
+			// SubexpNames entry is "") must be skipped so they don't become
+			// map entries with an empty-string key.
+			if name == "" {
+				continue
+			}
+			keyNode := createScalarNode(name, name)
 			var valueNode *CandidateNode
 
 			offset := allIndices[i][2+j*2]

pkg/yqlib/operator_strings_test.go

@@ -364,6 +364,15 @@ var stringsOperatorScenarios = []expressionScenario{
 			"D0, P[], (!!seq)::[\"1\", \"true\", \"null\", \"~\", cat, \"{an: object}\", \"[array, 2]\"]\n",
 		},
 	},
+	{
+		skipDoc:     true,
+		description: "Capture ignores unnamed groups",
+		document:    `foobar`,
+		expression:  `capture("(foo)(?P<rest>bar)")`,
+		expected: []string{
+			"D0, P[], (!!map)::rest: bar\n",
+		},
+	},
 }
 
 func TestStringsOperatorScenarios(t *testing.T) {