tpl: Add docshelper for template funcs

And fix some other minor related issues.

Updates #3418

tpl/cast/docshelper.go

@@ -0,0 +1,41 @@
+// Copyright 2017 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 cast
+
+import (
+	"github.com/spf13/hugo/deps"
+	"github.com/spf13/hugo/docshelper"
+	"github.com/spf13/hugo/tpl/internal"
+)
+
+// This file provides documentation support and is randomly put into this package.
+func init() {
+	docsProvider := func() map[string]interface{} {
+		docs := make(map[string]interface{})
+		d := &deps.Deps{}
+
+		var namespaces []*internal.TemplateFuncsNamespace
+
+		for _, nsf := range internal.TemplateFuncsNamespaceRegistry {
+			nf := nsf(d)
+			namespaces = append(namespaces, nf)
+
+		}
+
+		docs["funcs"] = namespaces
+		return docs
+	}
+
+	docshelper.AddDocProvider("tpl", docsProvider)
+}