Toolkit: diff shows version bump even if nothing else changed

[rix0rrr]

I was making changes, and to verify I didn't break anything I ran cdk diff. This was the output:

huijbers ~/W/P/cdk-ops(master)> cdk diff cdk-master
[~] 🛠 Updating CDKMetadata (type: AWS::CDK::Metadata)
 └─ [~] .Modules:
     ├─ [-] Old value: @aws-cdk/assets=0.7.4-beta,@aws-cdk/aws-cloudformation=0.
7.4-beta,@aws-cdk/aws-cloudwatch=0.7.4-beta,@aws-cdk/aws-codebuild=0.7.4-beta,@a
ws-cdk/aws-codebuild-codepipeline=0.7.4-beta,@aws-cdk/aws-codecommit-codepipelin
e=0.7.4-beta,@aws-cdk/aws-codepipeline=0.7.4-beta,@aws-cdk/aws-custom-resources=
0.7.4-beta,@aws-cdk/aws-events=0.7.4-beta,@aws-cdk/aws-iam=0.7.4-beta,@aws-cdk/a
ws-kms=0.7.4-beta,@aws-cdk/aws-lambda=0.7.4-beta,@aws-cdk/aws-s3=0.7.4-beta,@aws
-cdk/aws-sns=0.7.4-beta,@aws-cdk/cdk=0.7.4-beta,@aws-cdk/cx-api=0.7.4-beta,@aws-
cdk/util=0.7.4-beta,buildable=1.0.0,js-base64=2.4.5
     └─ [+] New value: @aws-cdk/assets=0.8.0,@aws-cdk/aws-cloudformation=0.8.0,@
aws-cdk/aws-cloudwatch=0.8.0,@aws-cdk/aws-codebuild=0.8.0,@aws-cdk/aws-codebuild
-codepipeline=0.8.0,@aws-cdk/aws-codecommit-codepipeline=0.8.0,@aws-cdk/aws-code
pipeline=0.8.0,@aws-cdk/aws-custom-resources=0.8.0,@aws-cdk/aws-events=0.8.0,@aw
s-cdk/aws-iam=0.8.0,@aws-cdk/aws-kms=0.8.0,@aws-cdk/aws-lambda=0.8.0,@aws-cdk/aw
s-s3=0.8.0,@aws-cdk/aws-sns=0.8.0,@aws-cdk/cdk=0.8.0,@aws-cdk/cx-api=0.8.0,@aws-
cdk/util=0.8.0,buildable=1.0.0,js-base64=2.4.5

The tool was answering my question "did anything change" literally correct, but I would still argue that this is not helpful and we shouldn't include the CDKMetadata resource in the diff:

• This resource is not about the USER's resources. They don't care about it, it doesn't fulfill any function for them.
• It actively harms--now I need to know what this resource means and need to do reading to convince myself that, no, it's not actually important to my infrastructure. Yes, we are all very aware about what it is and does, but any arbitrary user doesn't know and shouldn't need to know.
• In fact, it's an implementation detail. This is how we've chosen to communicate the version data back to the server. If it had been in the template's Metadata section, it would not have been part of the diff (even though the same data would have changed). Does that seem right to you?

There is one good counterargument to be made--if cdk diff shows no diff, you would expect cdk deploy to not do anything either, which would be broken by this change.

I am willing to take that hit, as am I willing to udpate the stackset change checker to disregard changes to the CDKMetadata resource.

[RomainMuller]

A possible middle-ground would be to ignore the CDKMetadata resource by default in the cdk diff output (filter it out, basically), but have a cdk diff --pedantic (come up with a better name if you can) that includes everything.

[rix0rrr]

Yes, I was thinking something like that as well.

[eladb]

Sounds good (--strict?)