feat(filter): add better error message when passing an invalid filter expression

docs/content/doc/usage/errors.md

@@ -96,6 +96,7 @@ This document describes the different errors Vikunja can return.
 | 4021      | 400 | This user is already assigned to that task.                                |
 | 4022      | 400 | The task has a relative reminder which does not specify relative to what.  |
 | 4023      | 409 | Tried to create a task relation which would create a cycle.                |
+| 4024      | 400 | The provided filter expression is invalid.                                 |
 
 ## Team
 

pkg/models/error.go

@@ -1021,7 +1021,7 @@ func (err ErrTaskRelationCycle) Error() string {
 }
 
 // ErrCodeTaskRelationCycle holds the unique world-error code of this error
-const ErrCodeTaskRelationCycle = 4022
+const ErrCodeTaskRelationCycle = 4023
 
 // HTTPError holds the http error description
 func (err ErrTaskRelationCycle) HTTPError() web.HTTPError {
@@ -1032,6 +1032,34 @@ func (err ErrTaskRelationCycle) HTTPError() web.HTTPError {
 	}
 }
 
+// ErrInvalidFilterExpression represents an error where the task filter expression was invalid
+type ErrInvalidFilterExpression struct {
+	Expression      string
+	ExpressionError error
+}
+
+// IsErrInvalidFilterExpression checks if an error is ErrInvalidFilterExpression.
+func IsErrInvalidFilterExpression(err error) bool {
+	_, ok := err.(ErrInvalidFilterExpression)
+	return ok
+}
+
+func (err ErrInvalidFilterExpression) Error() string {
+	return fmt.Sprintf("Task filter expression is invalid [ExpressionError: %v]", err.ExpressionError)
+}
+
+// ErrCodeInvalidFilterExpression holds the unique world-error code of this error
+const ErrCodeInvalidFilterExpression = 4024
+
+// HTTPError holds the http error description
+func (err ErrInvalidFilterExpression) HTTPError() web.HTTPError {
+	return web.HTTPError{
+		HTTPCode: http.StatusBadRequest,
+		Code:     ErrCodeInvalidFilterExpression,
+		Message:  fmt.Sprintf("The filter expression '%s' is invalid: %v", err.Expression, err.ExpressionError),
+	}
+}
+
 // ============
 // Team errors
 // ============

pkg/models/task_collection_filter.go

@@ -152,7 +152,10 @@ func getTaskFiltersByCollections(c *TaskCollection) (filters []*taskFilter, err
 
 	parsedFilter, err := fexpr.Parse(c.Filter)
 	if err != nil {
-		return nil, err
+		return nil, &ErrInvalidFilterExpression{
+			Expression:      c.Filter,
+			ExpressionError: err,
+		}
 	}
 
 	filters = make([]*taskFilter, 0, len(parsedFilter))