Fix bugs surrounding adding funcs to a template

environment.go

@@ -2,8 +2,10 @@ package step
 
 import "os"
 import "io"
+import "fmt"
 import "time"
 import "io/fs"
+import "errors"
 import "context"
 import "path/filepath"
 import "html/template"
@@ -107,28 +109,47 @@ func (this *Environment) parse (name string, modTime time.Time, input io.Reader)
 		document.Extends = extends
 	}
 
+	// add template functions
+	funcMap := make(template.FuncMap)
+	for name, function := range this.funcMap {
+		funcMap[name] = function
+	}
+	for _, provider := range this.FuncProviders {
+		provider, ok := provider.(FuncProviderFor)
+		if !ok { continue }
+		funcMapFor := provider.FuncMapFor(document)
+		if funcMapFor == nil { continue }
+		for name, function := range funcMapFor {
+			funcMap[name] = function
+		}
+	}
+	err = this.addFuncsTo(document, funcMap)
+	if err != nil { return nil, err }
+
 	// parse template from the body
-	document.template.Funcs(this.funcMap)
 	// TODO catch template errors here and offset their row number by the
 	// number of rows taken up by the front matter
 	_, err = document.template.Parse(body)
 	if err != nil { return nil, err }
 
-	// add template functions which need a document pointer for context
-	for _, provider := range this.FuncProviders {
-		provider, ok := provider.(FuncProviderFor)
-		if !ok { continue }
-		funcMap := provider.FuncMapFor(document)
-		if funcMap == nil { continue }
-		for name, function := range funcMap {
-			this.funcMap[name] = function
-		}
-	}
-
 	documents[name] = document
 	return document, nil
 }
 
+func (this *Environment) addFuncsTo (document *Document, funcs template.FuncMap) (err error) {
+	defer func () {
+		if r := recover(); r != nil {
+			if rerr, ok := err.(error); ok {
+				err = rerr
+			} else {
+				err = errors.New(fmt.Sprint(r))
+			}
+		}
+	} ()
+	document.template.Funcs(funcs)
+	return err
+}
+
 // GetFS returns the effective filesystem that the environment uses.
 func (this *Environment) GetFS () fs.FS {
 	if this.FS == nil {