Error in -Ycheck:typer when refining String on StringOps defs
#17465
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timotheeandres
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itype:bug
stat:needs triage
nicolasstucki
added
area:typer
and removed
stat:needs triage
Minimizationimport reflect.Selectable.reflectiveSelectable
def f[T](x: T{ def *(y: Int): T }): T = x * 2
def test = f[scala.collection.StringOps | String]("Hello") |
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Maybe it is because |
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This issue was picked for the Issue Spree No. 31 of 30 May 2023 which takes place in 2 days. @Linyxus, @hamzaremmal, @TheElectronWill will be working on it. If you have any insight into the issue or guidance on how to fix it, please leave it here. |
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Relevant documentation: |
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Linyxus
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this issue
Jul 20, 2023
Fixes #17465. In TypeComparer, `fourthTry` calls `isNewSubType` and `isCovered` to detect the subtype queries that have been covered by previous attempts and prune them. However, the pruning is spurious when both sides contain union types, as exemplified by the following subtype trace before the PR: ``` ==> isSubType (test1 : (Int | String){def foo(x: Int): Int}) <:< Int | String? ==> isSubType (Int | String){def foo(x: Int): Int} <:< Int | String? ==> isSubType (Int | String){def foo(x: Int): Int} <:< Int? <== isSubType (Int | String){def foo(x: Int): Int} <:< Int = false ==> isSubType (Int | String){def foo(x: Int): Int} <:< String? ==> isSubType (Int | String){def foo(x: Int): Int} <:< String? <== isSubType (Int | String){def foo(x: Int): Int} <:< String = false <== isSubType (Int | String){def foo(x: Int): Int} <:< String = false // (1): follow-up subtype checks are pruned here by isNewSubType <== isSubType (Int | String){def foo(x: Int): Int} <:< Int | String = false <== isSubType (test1 : (Int | String){def foo(x: Int): Int}) <:< Int | String = false ``` At `(1)`, the pruning condition is met, and follow-up recursions are skipped. However, in this case, only after `(1)` are the refinement on LHS dropped and the subtype between two identical OrTypes are accepted. The pruning is spurious. This PR tempers the pruning conditions specified in `isCovered` and `isNewSubType` to fix these false negatives.
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Compiler version
3.3.0-RC4
Minimized code
Compile this code with the
-Ycheck:typerflag.Edit: further minimization (thanks to @nicolasstucki):
Output
Expectation
The code compiles both with and without the
-Ycheck:typerflag.More information
This seems to be related to the widening of
Stringtoscala.collection.StringOps | String, as this issue does not arise with a homemade class: the following code passes the check.The text was updated successfully, but these errors were encountered: