} else {
                throw DocumentedFailure.builder()
                    .withSummary("Using internal convention mapping with a Provider backed property.")
                    .withUpgradeGuideSection(7, "convention_mapping")
                    .build();
            }
        } else {
            _mappings.put(propertyName, mapping);
        }
        return mapping;
    }

                @Input
                def String prop
                void doStuff(Action<Task> action) { action.execute(this) }
            }
            tasks.withType(GroovyTask) { conventionMapping.prop = { '[default]' } }
            task test(type: GroovyTask)
            assert test.prop == '[default]'
            test {
                description 'does something'
                prop 'value'