Load a single template (view) along with all layouts (_layout.gohtml) from directories, starting from the top and going down to the current directory

views.go

package web

import (
	"errors"
	"fmt"
	"html/template"
	"io/fs"
	"os"
	"path"
	"strings"
)

// LoadFS is the same as Load but using new empty template as root.
func LoadFS(store fs.FS, view string) (*template.Template, error) {
	return Load(template.New(""), store, view)
}

// Load single template (view) and all layouts (_layout.gohtml) from all dirs starting from the top
// and until the current dir.
//
// If embedded FS is used, glob suffix in go:embed (/** or *) MUST be used, otherwise files with underscore will
// not be included by Go compiler.
func Load(root *template.Template, store fs.FS, view string) (*template.Template, error) {
	const layoutName = "_layout.gohtml"
	dirs := strings.Split(strings.Trim(view, "/"), "/")
	dirs = dirs[:len(dirs)-1] // last segment is view itself
	// parse layouts from all dirs starting from the top and until the current dir
	for i := range dirs {
		fpath := path.Join(path.Join(dirs[:i+1]...), layoutName)
		content, err := fs.ReadFile(store, fpath)
		if errors.Is(err, os.ErrNotExist) || errors.Is(err, fs.ErrNotExist) {
			continue // layout does not exists - skipping
		}
		if err != nil {
			return nil, fmt.Errorf("read layouad %q: %w", fpath, err)
		}

		child, err := root.Parse(string(content))
		if err != nil {
			return nil, fmt.Errorf("parse %q: %w", fpath, err)
		}
		root = child
	}
	// parse view it self
	content, err := fs.ReadFile(store, view)
	if err != nil {
		return nil, fmt.Errorf("parse view %q: %w", view, err)
	}
	return root.Parse(string(content))
}

As a library https://github.com/reddec/view