Refactor template render (#36438)

modules/templates/vars/vars.go

@@ -10,25 +10,6 @@ import (
 	"unicode/utf8"
 )
 
-// ErrWrongSyntax represents a wrong syntax with a template
-type ErrWrongSyntax struct {
-	Template string
-}
-
-func (err ErrWrongSyntax) Error() string {
-	return "wrong syntax found in " + err.Template
-}
-
-// ErrVarMissing represents an error that no matched variable
-type ErrVarMissing struct {
-	Template string
-	Var      string
-}
-
-func (err ErrVarMissing) Error() string {
-	return fmt.Sprintf("the variable %s is missing for %s", err.Var, err.Template)
-}
-
 // Expand replaces all variables like {var} by `vars` map, it always returns the expanded string regardless of errors
 // if error occurs, the error part doesn't change and is returned as it is.
 func Expand(template string, vars map[string]string) (string, error) {
@@ -66,14 +47,14 @@ func Expand(template string, vars map[string]string) (string, error) {
 		posBegin = posEnd
 		if part == "{}" || part[len(part)-1] != '}' {
 			// treat "{}" or "{..." as error
-			err = ErrWrongSyntax{Template: template}
+			err = fmt.Errorf("wrong syntax found in %s", template)
 			buf.WriteString(part)
 		} else {
 			// now we get a valid key "{...}"
 			key := part[1 : len(part)-1]
 			keyFirst, _ := utf8.DecodeRuneInString(key)
 			if unicode.IsSpace(keyFirst) || unicode.IsPunct(keyFirst) || unicode.IsControl(keyFirst) {
-				// the if key doesn't start with a letter, then we do not treat it as a var now
+				// if the key doesn't start with a letter, then we do not treat it as a var now
 				buf.WriteString(part)
 			} else {
 				// look up in the map
@@ -82,7 +63,7 @@ func Expand(template string, vars map[string]string) (string, error) {
 				} else {
 					// write the non-existing var as it is
 					buf.WriteString(part)
-					err = ErrVarMissing{Template: template, Var: key}
+					err = fmt.Errorf("the variable %s is missing for %s", key, template)
 				}
 			}
 		}