1 files changed, 78 insertions, 0 deletions
diff --git a/identity/predicate_identity.go b/identity/predicate_identity.go
new file mode 100644
index 000000000..bad247867
--- /dev/null
+++ b/identity/predicate_identity.go
@@ -0,0 +1,78 @@
+// Copyright 2024 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 provides ways to identify values in Hugo. Used for dependency tracking etc.
+package identity
+
+import (
+	"fmt"
+	"sync/atomic"
+
+	hglob "github.com/gohugoio/hugo/hugofs/glob"
+)
+
+// NewGlobIdentity creates a new Identity that
+// is probably dependent on any other Identity
+// that matches the given pattern.
+func NewGlobIdentity(pattern string) Identity {
+	glob, err := hglob.GetGlob(pattern)
+	if err != nil {
+		panic(err)
+	}
+
+	predicate := func(other Identity) bool {
+		return glob.Match(other.IdentifierBase())
+	}
+
+	return NewPredicateIdentity(predicate, nil)
+}
+
+var predicateIdentityCounter = &atomic.Uint32{}
+
+type predicateIdentity struct {
+	id                 string
+	probablyDependent  func(Identity) bool
+	probablyDependency func(Identity) bool
+}
+
+var (
+	_ IsProbablyDependencyProvider = &predicateIdentity{}
+	_ IsProbablyDependentProvider  = &predicateIdentity{}
+)
+
+// NewPredicateIdentity creates a new Identity that implements both IsProbablyDependencyProvider and IsProbablyDependentProvider
+// using the provided functions, both of which are optional.
+func NewPredicateIdentity(
+	probablyDependent func(Identity) bool,
+	probablyDependency func(Identity) bool,
+) *predicateIdentity {
+	if probablyDependent == nil {
+		probablyDependent = func(Identity) bool { return false }
+	}
+	if probablyDependency == nil {
+		probablyDependency = func(Identity) bool { return false }
+	}
+	return &predicateIdentity{probablyDependent: probablyDependent, probablyDependency: probablyDependency, id: fmt.Sprintf("predicate%d", predicateIdentityCounter.Add(1))}
+}
+
+func (id *predicateIdentity) IdentifierBase() string {
+	return id.id
+}
+
+func (id *predicateIdentity) IsProbablyDependent(other Identity) bool {
+	return id.probablyDependent(other)
+}
+
+func (id *predicateIdentity) IsProbablyDependency(other Identity) bool {
+	return id.probablyDependency(other)
+}