tpl/partials: Add templates.Exists

Fixes #5010

tpl/templates/templates.go

@@ -0,0 +1,39 @@
+// Copyright 2018 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 partials
+
+import (
+	"github.com/gohugoio/hugo/deps"
+)
+
+// New returns a new instance of the templates-namespaced template functions.
+func New(deps *deps.Deps) *Namespace {
+	return &Namespace{
+		deps: deps,
+	}
+}
+
+// Namespace provides template functions for the "templates" namespace.
+type Namespace struct {
+	deps *deps.Deps
+}
+
+// Exists returns whether the template with the given name exists.
+// Note that this is the Unix-styled relative path including filename suffix,
+// e.g. partials/header.html
+func (ns *Namespace) Exists(name string) bool {
+	_, found := ns.deps.Tmpl.Lookup(name)
+	return found
+
+}