Add wire codec roundtrip fuzz test generator#87
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dillonkearns wants to merge 1 commit intolamdera:lamdera-nextfrom
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Add wire codec roundtrip fuzz test generator#87dillonkearns wants to merge 1 commit intolamdera:lamdera-nextfrom
dillonkearns wants to merge 1 commit intolamdera:lamdera-nextfrom
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Adds an elm-pages + elm-codegen based generator that randomly creates Elm type definitions (unions, records, extensible records, alias chains, cross-module references) weighted toward edge cases, then generates elm-test fuzz tests proving the compiler-generated wire codecs are correct via roundtrip testing. Run with: cd test/scenario-alltypes && bash run-roundtrip-tests.sh The generator produces 15 type scenarios including extensible record alias chains, cross-module references, overlapping fields, deep alias chains, many-variant unions, and two-level extensible chains. The two-level extensible chain scenario surfaces a known bug where the wire codec generator loses fields when an extensible record extends another extensible record. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Thank you! This seems super useful! |
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Hey @supermario, I thought I'd add a random generator to try to surface any problematic permutations in types for the wire codecs. I was able to find one case that has errors, which I'll share in a separate issue or PR shortly.
For now, this PR adds an elm-pages + elm-codegen based generator that randomly creates Elm type definitions (unions, records, extensible records, alias chains, cross-module references) weighted toward edge cases, then generates
elm-testfuzz tests running the wire codecs in a roundtrip test.Run with:
cd test/scenario-alltypes && bash run-roundtrip-tests.shThe generator produces 15 type scenarios including extensible record alias chains, cross-module references, overlapping fields, deep alias chains, many-variant unions, and two-level extensible chains. The two-level extensible chain scenario surfaces a known bug where the wire codec generator loses fields when an extensible record extends another extensible record.
Happy to discuss if you have any feedback, and if you don't want to add this to the codebase no worries, still useful for running separately if you don't want to pull it in to this project directly! Just thought I'd share.