Speed up enry.IsVendor (#15213)

`enry.IsVendor` is kinda slow as it simply iterates across all regexps.
This PR ajdusts the regexps to combine them to make this process a
little quicker.

Related #15143

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/analyze/vendor.go

@@ -0,0 +1,70 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package analyze
+
+import (
+	"regexp"
+	"sort"
+	"strings"
+
+	"github.com/go-enry/go-enry/v2/data"
+)
+
+var isVendorRegExp *regexp.Regexp
+
+func init() {
+	matchers := data.VendorMatchers
+
+	caretStrings := make([]string, 0, 10)
+	caretShareStrings := make([]string, 0, 10)
+
+	matcherStrings := make([]string, 0, len(matchers))
+	for _, matcher := range matchers {
+		str := matcher.String()
+		if str[0] == '^' {
+			caretStrings = append(caretStrings, str[1:])
+		} else if str[0:5] == "(^|/)" {
+			caretShareStrings = append(caretShareStrings, str[5:])
+		} else {
+			matcherStrings = append(matcherStrings, str)
+		}
+	}
+
+	sort.Strings(caretShareStrings)
+	sort.Strings(caretStrings)
+	sort.Strings(matcherStrings)
+
+	sb := &strings.Builder{}
+	sb.WriteString("(?:^(?:")
+	sb.WriteString(caretStrings[0])
+	for _, matcher := range caretStrings[1:] {
+		sb.WriteString(")|(?:")
+		sb.WriteString(matcher)
+	}
+	sb.WriteString("))")
+	sb.WriteString("|")
+	sb.WriteString("(?:(?:^|/)(?:")
+	sb.WriteString(caretShareStrings[0])
+	for _, matcher := range caretShareStrings[1:] {
+		sb.WriteString(")|(?:")
+		sb.WriteString(matcher)
+	}
+	sb.WriteString("))")
+	sb.WriteString("|")
+	sb.WriteString("(?:")
+	sb.WriteString(matcherStrings[0])
+	for _, matcher := range matcherStrings[1:] {
+		sb.WriteString(")|(?:")
+		sb.WriteString(matcher)
+	}
+	sb.WriteString(")")
+	combined := sb.String()
+	isVendorRegExp = regexp.MustCompile(combined)
+}
+
+// IsVendor returns whether or not path is a vendor path.
+func IsVendor(path string) bool {
+	return isVendorRegExp.MatchString(path)
+}