chore: hide diffs of mangled unicode strings

[laverdet]

I am reopening this from #25525

and following up on my comments here:
#24557 (comment)
#24557 (comment)
#25008 (comment)
#25008 (comment)
#25008 (comment)
#25008 (comment)
#25008 (comment)
#25008 (comment)
#25525 (comment)
#25525 (comment)
🫠 #25525 (comment) 🫠

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Fixes #25309
Fixes #22203
Fixes #20212
Fixes #13634
Fixes #10523
Fixes #10219
See also: aws-cloudformation/cloudformation-coverage-roadmap#1220
See also: aws-cloudformation/cloudformation-coverage-roadmap#814

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👻 I have retitled this PR as a chore instead of a fix because @aws-cdk-automation keeps closing my PRs as abandoned even though they are clearly not abandoned.

This PR has been deemed to be abandoned, and will be automatically closed. Please create a new PR for these changes if you think this decision has been made in error.

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@otaviomacedo @rix0rrr @TheRealAmazonKendra - I'm happy to adjust the approach, add more tests, or do what else needs to be done. I'm not getting any feedback from the team so I'm not sure how to proceed. The diff noise with non-ASCII information in cdk diff makes it difficult to find meaningful changes to our stacks.

🗿🗞️📬 Crucially, this change only affects the CLI output and therefore an integration test isn't possible.

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CloudFormation's GetStackTemplate irrecoverably mangles any character not in the 7-bit ASCII range. This causes noisy output from cdk diff when a template contains non-English languages or emoji. We can detect this case and consider these strings equal.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

Many AWS services accept non-ASCII input, eg many "description" fields. CloudFormation will correctly dispatch these templates but when invoking GetStackTemplate the result is mangled. This causes annoying noise in the output of cdk diff:

Resources
[~] AWS::Lambda::Function Lambda/Resource
 └─ [~] Description
     ├─ [-] ?????
     └─ [+] 🤦🏻‍♂️

This change modifies the diff algorithm to consider the string equal if the lvalue is a mangled version of the rvalue.

Of course this runs the risk of hiding changesets which modify only a single non-ASCII character to another non-ASCII character, but these fields already tend to be informative in nature.

[gitpod-io]

[otaviomacedo]

Hi, @laverdet. Sorry for missing your previous PR. I understand that CloudFormation is lossy in this respect, by putting all non-ASCII characters in the same equivalence class. But this fact would become more evident to both users and developers if we separated transformation from comparison:

1. Transform the original local template into its mangled version (in memory).
2. Compare the mangled version with the CFN result using deepEquals() as it is today.
3. If original !== mangled, display a warning to let users know that the result of this diff may contain false negatives.

[laverdet]

@otaviomacedo thank you for following up. I agree that the suggested approach is more informative and now has no downsides. I've updated the PR to implement that idea, and piggy-backed on the --strict flag to switch it off.

Pull request has been modified.

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