Allow cascade to be a slice with a _target discriminator

Fixes #7782

resources/page/page_matcher.go

@@ -0,0 +1,91 @@
+// Copyright 2020 The Hugo Authors. All rights reserved.
+//
+// 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.
+
+package page
+
+import (
+	"path/filepath"
+	"strings"
+
+	"github.com/pkg/errors"
+
+	"github.com/gohugoio/hugo/hugofs/glob"
+	"github.com/mitchellh/mapstructure"
+)
+
+// A PageMatcher can be used to match a Page with Glob patterns.
+// Note that the pattern matching is case insensitive.
+type PageMatcher struct {
+	// A Glob pattern matching the content path below /content.
+	// Expects Unix-styled slashes.
+	// Note that this is the virtual path, so it starts at the mount root
+	// with a leading "/".
+	Path string
+
+	// A Glob pattern matching the Page's Kind(s), e.g. "{home,section}"
+	Kind string
+
+	// A Glob pattern matching the Page's language, e.g. "{en,sv}".
+	Lang string
+}
+
+// Matches returns whether p matches this matcher.
+func (m PageMatcher) Matches(p Page) bool {
+
+	if m.Kind != "" {
+		g, err := glob.GetGlob(m.Kind)
+		if err == nil && !g.Match(p.Kind()) {
+			return false
+		}
+	}
+
+	if m.Lang != "" {
+		g, err := glob.GetGlob(m.Lang)
+		if err == nil && !g.Match(p.Lang()) {
+			return false
+		}
+	}
+
+	if m.Path != "" {
+		g, err := glob.GetGlob(m.Path)
+		// TODO(bep) Path() vs filepath vs leading slash.
+		p := strings.ToLower(filepath.ToSlash(p.Path()))
+		if !(strings.HasPrefix(p, "/")) {
+			p = "/" + p
+		}
+		if err == nil && !g.Match(p) {
+			return false
+		}
+	}
+
+	return true
+}
+
+// DecodePageMatcher decodes m into v.
+func DecodePageMatcher(m interface{}, v *PageMatcher) error {
+	if err := mapstructure.WeakDecode(m, v); err != nil {
+		return err
+	}
+
+	v.Kind = strings.ToLower(v.Kind)
+	if v.Kind != "" {
+		if _, found := kindMap[v.Kind]; !found {
+			return errors.Errorf("%q is not a valid Page Kind", v.Kind)
+		}
+	}
+
+	v.Path = filepath.ToSlash(strings.ToLower(v.Path))
+
+	return nil
+
+}