Show failed assertion trace

[hoangmaihuy]

/claim #354

Because the tests are macro-expansion from both Tests.apply and assertImpl so the original assertion position is lost after Tracer.apply converts test expressions into Expr[Unit]

utest/utest/src-3/utest/asserts/Tracer.scala

Line 24 in 76e7fe5

val trees: Expr[Seq[AssertEntry[T]]] = Expr.ofSeq(ess.map(e => makeAssertEntry(e, codeOf(e))))

This PR is an attempt to preserve original assertion's position by introducing pos: String field in AssertEntry, which is formatted as ${sourceFile}:${line} so that we can output failed assertion location under AssertionError like:

X test.utest.examples.HelloTests.test4 2ms
[113]   utest.AssertionError:  1 == 2
[113]   at .../utest/utest/test/src/test/utest/examples/HelloTests.scala:21
[113]     utest.asserts.Asserts$.assertImpl(Asserts.scala:31)
[113]     test.utest.examples.HelloTests$.$init$$$anonfun$1$$anonfun$4(HelloTests.scala:5)

[lihaoyi]

the original assertion position is lost after Tracer.apply converts test expressions into Expr[Unit]

Perhaps this is the thing we should focus on. The current PR that plumbs through the changes as runtime values works, but I don't think it's the right fix here. Why is Tracer.apply losing the assertion positions, and can we fix it?

[hoangmaihuy]

@lihaoyi I made futher debugging and see that Tracer.apply convert test expressions into Seq[AssertEntry[...]] in test file:

val esx: scala.collection.immutable.Seq[utest.asserts.AssertEntry[scala.Boolean]] = utest.asserts.AssertEntry.apply[scala.Boolean]("1 == 2", ((logger: scala.Function1[utest.TestValue, scala.Unit]) => false))

utest.asserts.Asserts.assertImpl(esx: _*)

And we have assertImpl is a function which actually evaluate those AssertEntry, that's why when assertImpl throw exception the stack trace only show

utest.asserts.Asserts$.assertImpl(Asserts.scala:31)
test.utest.examples.HelloTests$.$init$$$anonfun$1$$anonfun$4(HelloTests.scala:5)

because utest.asserts.Asserts.assertImpl(esx: _*) is already inlined into main source code. I think the difference in macro-expansion between scala 2 and 3 introduces this problem.

To fix this issue, assertion error should be thrown in AssertEntry function instead of assertImpl, but I haven't figured out how to implement that because it will affect scala 2 macro as well.

Besides, I think output full path of error location is not a bad choice because I can click on the path to jump into that location in editor/IDE just like scala's compile error.

[lihaoyi]

As far as the linked ticket is concerned, I won't accept the approach in this PR. It's a decent workaround, but it doesn't really address the root issue: neither fixing it nor investigating and explaining why it is unfixable. As much as I want a fix myself, I'll hold off for a deeper fix or investigation