utils: share the include/exclude regexp flag handling (#2737)

Signed-off-by: Jan-Otto Kröpke <mail@jkroepke.de>

internal/utils/regexp.go

@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: Apache-2.0
+//
+// Copyright The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build windows
+
+package utils
+
+import (
+	"fmt"
+	"regexp"
+	"slices"
+
+	"github.com/alecthomas/kingpin/v2"
+	"github.com/prometheus-community/windows_exporter/internal/types"
+)
+
+//nolint:gochecknoglobals
+var (
+	// matchAllExpressions are the expressions of an include filter that matches every name.
+	matchAllExpressions = []string{anchor(".+"), anchor(".*"), types.RegExpAny.String()}
+	// matchNoneExpressions are the expressions of an exclude filter that matches no name.
+	matchNoneExpressions = []string{anchor(""), types.RegExpEmpty.String()}
+)
+
+// anchor wraps expr, so that it must match the whole input.
+func anchor(expr string) string {
+	return "^(?:" + expr + ")$"
+}
+
+// CompileAnchored compiles expr, so that it must match the whole input.
+func CompileAnchored(expr string) (*regexp.Regexp, error) {
+	return regexp.Compile(anchor(expr))
+}
+
+// MustCompileAnchored is like [CompileAnchored], but panics if expr can't be parsed.
+func MustCompileAnchored(expr string) *regexp.Regexp {
+	return regexp.MustCompile(anchor(expr))
+}
+
+// IsMatchAll reports whether re is an include filter that matches every name:
+// the default of an include flag, [types.RegExpAny] or nil, which the New function of
+// a collector replaces with the default.
+func IsMatchAll(re *regexp.Regexp) bool {
+	return re == nil || slices.Contains(matchAllExpressions, re.String())
+}
+
+// IsMatchNone reports whether re is an exclude filter that matches no name:
+// the default of an exclude flag, [types.RegExpEmpty] or nil, which the New function
+// of a collector replaces with the default.
+func IsMatchNone(re *regexp.Regexp) bool {
+	return re == nil || slices.Contains(matchNoneExpressions, re.String())
+}
+
+// anchoredRegexpValue is a [kingpin.Value] which compiles its value with [CompileAnchored].
+type anchoredRegexpValue struct {
+	name   string
+	expr   string
+	target **regexp.Regexp
+}
+
+func (v *anchoredRegexpValue) Set(expr string) error {
+	re, err := CompileAnchored(expr)
+	if err != nil {
+		return fmt.Errorf("%s: %w", v.name, err)
+	}
+
+	v.expr = expr
+	*v.target = re
+
+	return nil
+}
+
+func (v *anchoredRegexpValue) String() string {
+	return v.expr
+}
+
+// RegexpFlag registers the flag name, whose value is a regular expression that
+// must match the whole name. The compiled expression is stored in target when
+// the flags are parsed, including the default and a value from the
+// configuration file. An invalid expression fails the parsing with an error
+// that starts with the name of the flag.
+func RegexpFlag(app *kingpin.Application, name, help, defaultValue string, target **regexp.Regexp) *kingpin.FlagClause {
+	flag := app.Flag(name, help).Default(defaultValue)
+	flag.SetValue(&anchoredRegexpValue{name: name, target: target})
+
+	return flag
+}