Add support optional input

[pingsutw]

TL;DR

flyteorg/flyte#2426

Type

• Bug Fix
• Feature
• Plugin

Are all requirements met?

• Code completed
• Smoke tested
• Unit tests added
• Code documentation added
• Any pending items have an associated Issue

Complete description

How did you fix the bug, make the feature etc. Link to any design docs etc

Tracking Issue

Follow-up issue

NA

[codecov]

Codecov Report

Merging #452 (9e4dd9e) into master (24e93cd) will increase coverage by 0.25%.
The diff coverage is n/a.

❗ Current head 9e4dd9e differs from pull request most recent head 55cbe7b. Consider uploading reports for the commit 55cbe7b to get more accurate results

[pingsutw]

cc @EngHabu @kumare3

[hamersaw]

I am having trouble understanding how FlytePropeller resolves bindings for Union types. It doesn't look like there were any changes to the binding resolver in the original Union PR. It seems to me that a change would be necessary for the case that the value does not exist to pass nil or something rather than error? Can you help me understand how FlytePropeller resolves bindings in the test case you have (ie. Union[int, none])?

[pingsutw]

Let's say we have a task like the below.

@task
def t1(x: typing.Union[int, none]):
     ...

@workflow
def wf():
    t1()

In flytekit, We will not add any binding to the t1 node if calling t1() without input, so, Here I have to check if the params that aren't in providedBindings are optional type.

flytepropeller/pkg/compiler/validators/bindings.go

Line 228 in 55cbe7b

if !providedBindings.Has(paramName) && !IsOptionalType(*Variable) {

And Resolver return empty literalmap because the bindings is a empty list.

As a result, I only add "y" to VariableMap in the test, but didn't add "y" in the bindinds