Reimplement and simplify Hugo's template system

See #13541 for details.

Fixes #13545
Fixes #13515
Closes #7964
Closes #13365
Closes #12988
Closes #4891

tpl/tplimplinit/tplimplinit.go

@@ -0,0 +1,96 @@
+// Copyright 2025 The Hugo Authors. All rights reserved.
+//
+// Portions Copyright The Go 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.
+
+package tplimplinit
+
+import (
+	// Init the template funcs namespaces
+	"context"
+	"html/template"
+
+	"github.com/gohugoio/hugo/deps"
+	_ "github.com/gohugoio/hugo/tpl/cast"
+	_ "github.com/gohugoio/hugo/tpl/collections"
+	_ "github.com/gohugoio/hugo/tpl/compare"
+	_ "github.com/gohugoio/hugo/tpl/crypto"
+	_ "github.com/gohugoio/hugo/tpl/css"
+	_ "github.com/gohugoio/hugo/tpl/data"
+	_ "github.com/gohugoio/hugo/tpl/debug"
+	_ "github.com/gohugoio/hugo/tpl/diagrams"
+	_ "github.com/gohugoio/hugo/tpl/encoding"
+	_ "github.com/gohugoio/hugo/tpl/fmt"
+	_ "github.com/gohugoio/hugo/tpl/hash"
+	_ "github.com/gohugoio/hugo/tpl/hugo"
+	_ "github.com/gohugoio/hugo/tpl/images"
+	_ "github.com/gohugoio/hugo/tpl/inflect"
+	"github.com/gohugoio/hugo/tpl/internal"
+	_ "github.com/gohugoio/hugo/tpl/js"
+	_ "github.com/gohugoio/hugo/tpl/lang"
+	_ "github.com/gohugoio/hugo/tpl/math"
+	_ "github.com/gohugoio/hugo/tpl/openapi/openapi3"
+	_ "github.com/gohugoio/hugo/tpl/os"
+	_ "github.com/gohugoio/hugo/tpl/page"
+	_ "github.com/gohugoio/hugo/tpl/partials"
+	_ "github.com/gohugoio/hugo/tpl/path"
+	_ "github.com/gohugoio/hugo/tpl/reflect"
+	_ "github.com/gohugoio/hugo/tpl/resources"
+	_ "github.com/gohugoio/hugo/tpl/safe"
+	_ "github.com/gohugoio/hugo/tpl/site"
+	_ "github.com/gohugoio/hugo/tpl/strings"
+	_ "github.com/gohugoio/hugo/tpl/templates"
+	_ "github.com/gohugoio/hugo/tpl/time"
+	_ "github.com/gohugoio/hugo/tpl/transform"
+	_ "github.com/gohugoio/hugo/tpl/urls"
+)
+
+// CreateFuncMap creates a template.FuncMap with all of Hugo's template funcs,
+// excluding the Go built-ins.
+func CreateFuncMap(d *deps.Deps) map[string]any {
+	funcMap := template.FuncMap{}
+	nsMap := make(map[string]any)
+	var onCreated []func(namespaces map[string]any)
+
+	// Merge the namespace funcs
+	for _, nsf := range internal.TemplateFuncsNamespaceRegistry {
+		ns := nsf(d)
+		if _, exists := funcMap[ns.Name]; exists {
+			panic(ns.Name + " is a duplicate template func")
+		}
+		funcMap[ns.Name] = ns.Context
+		contextV, err := ns.Context(context.Background())
+		if err != nil {
+			panic(err)
+		}
+		nsMap[ns.Name] = contextV
+		for _, mm := range ns.MethodMappings {
+			for _, alias := range mm.Aliases {
+				if _, exists := funcMap[alias]; exists {
+					panic(alias + " is a duplicate template func")
+				}
+				funcMap[alias] = mm.Method
+			}
+		}
+
+		if ns.OnCreated != nil {
+			onCreated = append(onCreated, ns.OnCreated)
+		}
+	}
+
+	for _, f := range onCreated {
+		f(nsMap)
+	}
+
+	return funcMap
+}