Improve diff rendering with multi-line show instance #245
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zainab-ali
commented
Nov 6, 2025
| @@ -0,0 +1,6 @@ | |||
| package weaver | |||
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| object ScalaCompat { | |||
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These are only used in tests. We could move them to the test folder and define a test -> test relationship in SBT, but this would be best left to a different PR.
zainab-ali
commented
Nov 6, 2025
| private val comma: String = "," | ||
| private val indentStep = 1 | ||
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| private[weaver] def show[A]: Show[A] = (a: A) => { |
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This code uses explicit recursion and string builders, so is non-idiomatic for the weaver codebase.
However, I don't think we'll need to modify it much going forwards. If users have edge cases, they can support them with their own Show instances.
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I'm perfectly happy with String builders to be honest.
zainab-ali
commented
Nov 6, 2025
| """- (same with default show) 0ms | ||
| Values not equal: (src/main/DogFoodTests.scala:5) | ||
| => Diff (- obtained, + expected) |
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Scala 2.12 doesn't support field names, hence this test is different for different Scala versions.
Baccata
reviewed
Nov 7, 2025
| private[weaver] def productElementNames(p: Product): Iterator[String] = | ||
| p.productElementNames | ||
| private[weaver] def collectionClassName(i: Iterable[_]): String = i | ||
| .asInstanceOf[{ def collectionClassName: String }].collectionClassName |
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The current implementation of
Comparisonforexpect.sameandexpect.eqluses a defaultShow.fromToStringinstance.This prints the obtained or expected values on a single line. The Myers diff algorithm works on multi-line strings, not one-line strings, so the diff is hard to read.
This PR adapts munit's multi-line string printing logic to create a better default show instance.
Before
Running the test in:
After