provider/aws: Add support for updating Lambda function

[radeksimko]

This supersedes #3825

To do:

• Working implementation of updates via source_code_hash = base64sha256()
• Test for updating local ZIP file
• Test cleanup - Replace generic function testAccCheckAWSLambdaAttributes() with more specific ones - testAccCheckAwsLambdaFunctionName & testAccCheckAwsLambdaFunctionArn
• Test for updating S3 version ID - would have been a lot cleaner if [WIP] helper/schema: implement ComputedWhen #4846 & Make use of ComputedWhen in aws_s3_bucket_object #5330 were merged
• Document how to trigger updates

[radeksimko]

Waiting for #5305 to be reviewed and merged. That should make writing acceptance test for S3 deployment much easier.

[radeksimko]

This is now ready for final review.

[phinze]

Because we're building up inputs for a single API call rather than making a bunch of smaller API calls, I believe the partial mode code is unnecessary. The update will either fully succeed or fully fail, there's no partial success here.

[radeksimko]

I was first thinking the same thing when I first saw this piece of code (it's not exactly my addition), but then I scrolled down to line 351. We actually send two API calls: https://github.com/hashicorp/terraform/pull/5239/files#diff-2dcdbaf0cd0066fa2112ca76a0c2135eR351

So I think the partial state handling here is actually useful, isn't it?

[phinze]

Ah sorry yes, missed that. So I think the pattern should then be to setPartial on all the attributes that would be successfully updated by UpdateFunctionCode once it completes successfully. In pseudocode:

enable partial mode
build up UpdateFunctionCode request
  if error, return and nothing is updated
  if successful, mark all FunctionCode related attributes successful
build up UpdateFunctionConfig request
  if error, return and only marked FunctionCode attrs will be picked up
  if successful, disable partial mode, since everything worked (perhaps mark specific attrs here anyways to prepare for a potential 3rd update API call down the road?)

Let me know if this makes sense!

[radeksimko]

Right, I think it does - basically it means I'll need to move all of the d.SetPartial( calls below conn.UpdateFunctionCode so these are only called when conn.UpdateFunctionCode is actually successful.

The same will apply to UpdateFunctionConfiguration and its related fields.

[phinze]

Yep exactly.

[radeksimko]

Done.

[phinze]

Few nits inline, but this is looking good!

[radeksimko]

@phinze are u happy with all the changes I made, especially around the partial state mgmt?

[phinze]

Yep this LGTM!

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