Added ability to customize the resolution of context contained variables.

[blaubaer]

Added ability to customize the resolution of context contained variables, by:

1. NamedFieldResolver.GetNamedField(name) and IndexedFieldResolver.GetIndexedField(index) interfaces
2. Struct field pongo2:"..."

Plus: Added security enforcement to never use not exported fields.

Excerpt from the documentation

By the default sub variables are resolved by

1. Field names inside structs
2. Keys of values inside maps
3. Indexes of values inside slices

This behavior can be customized using either struct tag "pongo2" like:

type MyStruct struct {
    FieldA string `pongo2:"uh"`
    FieldB string `pongo2:"yeah"`
}

my.tmpl:

{{ myStruct.uh }} {{ myStruct.yeah }}

...or by implementing NamedFieldResolver or IndexedFieldResolver.

type MyStruct struct {
    fieldA string
}

// GetNamedField implements NamedFieldResolver
func (s MyStruct) GetNamedField(s string) (interface{}, error) {
    switch s {
    case "uh":
        return s.fieldA, nil
    case "yeah":
        return "YEAH!", nil
    default:
        return nil, pongo2.ErrNoSuchField
     }
}

// GetNamedField implements IndexedFieldResolver
func (s MyStruct) GetIndexedField(s int) (interface{}, error) {
    switch s {
    case 0:
        return s.fieldA, nil
    case 1:
        return "YEAH!", nil
    default:
        return nil, pongo2.ErrNoSuchField
    }
}

my.tmpl:

{{ myStruct.uh }} {{ myStruct.yeah }}
{{ myStruct.0 }} {{ myStruct.1 }}

[sonarqubecloud[bot]]

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[blaubaer]

@flosch any updates on this? 🙂

[flosch]

Thank you for your contribution. Please allow some more time for me to go through your PR.