* If we use the built-in YAQL function 'str' in a workflow then it
doesn't represent lists as '[item1, item3, ...]' but instead
creates '(item1, item2,...). This is because the standard YAQL
function 'yaql_utils.convert_input_data', which is needed to
convert a initial user data into an internal YAQL format,
converts all sequences (except strings) into tuples.
This patch overrides this behavior for sequences that are not
strings and tuples so that they now get converted into lists.
YAQL uses tuples because it needs to obtain a safe immutable
structure to make calculations upon. But in Mistral list is
more suitable because lots of users care about string
representations. Immutability is not so important because
Mistral code base guarantees that the initial data context
for an expression won't be changed while an expression is
being evaluated by YAQL.
* "str" YAQL function used to work well but it was broken in
https://review.openstack.org/#/c/477816/ that added additional
context preparation in order to fix the issue
https://bugs.launchpad.net/mistral/+bug/1772864
Change-Id: I69d32f8772418d586d6c414842bb54aada217481
Closes-Bug: #1815710
a39db2d3dc