Preserve singleton types for final val aliases to Java enum constants by zielinsky · Pull Request #24980 · scala/scala3

zielinsky · 2026-01-14T22:58:17Z

som-snytt · 2026-01-14T23:13:36Z

I mentioned on the ticket that they can't be used in annotations. I tried one approach that was too clever, rewriting them as inline transparent def. Just in case there's an easy fix to the type, since enums are not constant (any more).

Edit: I guess the singleton type will be visible in the back end, at least, which is currently widened!

zielinsky · 2026-01-15T10:51:23Z

I mentioned on the ticket that they can't be used in annotations. I tried one approach that was too clever, rewriting them as inline transparent def. Just in case there's an easy fix to the type, since enums are not constant (any more).

Edit: I guess the singleton type will be visible in the back end, at least, which is currently widened!

@som-snytt now they can! Look at 7fee34d !:> Used exactly your insight - the singleton type is visible in backend. Should I mark this as fixing #21881?

som-snytt · 2026-01-15T16:33:52Z

@zielinsky that's amazing, thanks. I took a look yesterday and didn't formulate it correctly.

Yes, I think this is sufficient for the use case in #21881.

Edit: I just deleted my local branch issue/21881-post-zielinsky.

som-snytt · 2026-01-16T18:11:08Z

FSR I get the complement in the warn test.

It would fail on pattern case: NANOSECONDS, MICROSECONDS, MILLISECONDS, SECONDS, MINUTES, HOURS

I was about to inspect the back end fix.

Clean build (?) has similar warning in Duration.scala.

Edit: the difference is bootstrapped.

sbt:scala3-bootstrapped> scalac tests/pos/i24750.scala
[info] running (fork) dotty.tools.dotc.Main -d /home/amarki/projects/scala3/out/default-last-scalac-out.jar -classpath /home/amarki/projects/scala3/library/target/scala-library-bootstrapped/scala-library-3.8.2-RC1-bin-SNAPSHOT.jar tests/pos/i24750.scala
[success] Total time: 7 s, completed Jan 16, 2026, 5:34:38 PM
sbt:scala3-bootstrapped> project scala3-nonbootstrapped
[info] set current project to scala3-nonbootstrapped (in build file:/home/amarki/projects/scala3/)
sbt:scala3-nonbootstrapped> scalac tests/pos/i24750.scala
[info] running (fork) dotty.tools.dotc.Main -d /home/amarki/projects/scala3/out/default-last-scalac-out.jar -classpath /home/amarki/projects/scala3/library/target/scala-library-nonbootstrapped/scala-library-3.8.2-RC1-bin-SNAPSHOT-nonbootstrapped.jar tests/pos/i24750.scala
-- [E029] Pattern Match Exhaustivity Warning: tests/pos/i24750.scala:7:13 ------
7 |    duration.unit match
  |    ^^^^^^^^^^^^^
  |match may not be exhaustive.
  |
  |It would fail on pattern case: NANOSECONDS, MICROSECONDS, MILLISECONDS, SECONDS, MINUTES, HOURS
  |(More unmatched cases are elided)
  |
  | longer explanation available when compiling with `-explain`
1 warning found
[success] Total time: 5 s, completed Jan 16, 2026, 5:35:01 PM

som-snytt · 2026-01-17T03:27:20Z

          av.visitEnum(name, edesc, evalue)
+        // Handle final val aliases to Java enum values.
+        // Check if the symbol's pre-erasure type was a singleton of a Java enum value.
+        case t: tpd.RefTree if atPhase(erasurePhase) {


I wonder if there is a reason to prefer atPhaseBeforeTransforms or conversely to avoid it.

I see to my chagrin that braceless colon syntax does not work, atPhaseBeforeTransforms:.

som-snytt

"Better you than me!"

…pped-only. (#25102) Re-enable non-bootstrapped CI tests (revert 69a9094) move i24750 tests to bootstrapped-only (#24980).

…#24980) Fixes #24750 Fixes #21881 [Cherry-picked 2f8bbdc][modified]

… constants" to 3.8.2 (#25190) Backports #24980 to the 3.8.2-RC2. PR submitted by the release tooling. [skip ci]

scala/scala3#24980

…scala#24980) Fixes scala#24750 Fixes scala#21881 [Cherry-picked 2f8bbdc][modified]

scala/scala3#24980

som-snytt reviewed Jan 14, 2026

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Comment thread compiler/src/dotty/tools/dotc/typer/Namer.scala Outdated

for final variables pointing to java enum values preserve singleton type

09af60f

zielinsky force-pushed the i24750v3 branch from d488803 to 09af60f Compare January 15, 2026 09:29

zielinsky marked this pull request as ready for review January 15, 2026 09:39

support final val aliases to Java enums in annotations

7fee34d

zielinsky requested a review from som-snytt January 15, 2026 13:25

zielinsky requested review from odersky and removed request for som-snytt January 15, 2026 20:45

som-snytt reviewed Jan 16, 2026

View reviewed changes

Comment thread compiler/src/dotty/tools/dotc/typer/Namer.scala

som-snytt reviewed Jan 17, 2026

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som-snytt approved these changes Jan 17, 2026

View reviewed changes

address review

c9cbc97

zielinsky enabled auto-merge (squash) January 19, 2026 13:16

zielinsky merged commit 2f8bbdc into scala:main Jan 19, 2026
56 checks passed

This was referenced Jan 26, 2026

Re-enable non-bootstrapped CI tests and move i24750 tests to bootstrapped-only. #25102

Merged

Move i24750 tests back to tests/pos and tests/warn after release #25103

Closed

zielinsky added a commit that referenced this pull request Jan 26, 2026

Re-enable non-bootstrapped CI tests and move i24750 tests to bootstra…

c64261d

…pped-only. (#25102) Re-enable non-bootstrapped CI tests (revert 69a9094) move i24750 tests to bootstrapped-only (#24980).

WojciechMazur added the backport:nominated If we agree to backport this PR, replace this tag with "backport:accepted", otherwise delete it. label Feb 3, 2026

WojciechMazur added this to the 3.8.2 milestone Feb 3, 2026

WojciechMazur added a commit that referenced this pull request Feb 4, 2026

Preserve singleton types for final val aliases to Java enum constants (…

a9e7bce

…#24980) Fixes #24750 Fixes #21881 [Cherry-picked 2f8bbdc][modified]

WojciechMazur mentioned this pull request Feb 4, 2026

Backport "Preserve singleton types for final val aliases to Java enum constants" to 3.8.2 #25190

Merged

WojciechMazur added backport:accepted This PR needs to be backported, once it's been backported replace this tag by "backport:done" and removed backport:nominated If we agree to backport this PR, replace this tag with "backport:accepted", otherwise delete it. labels Feb 4, 2026

WojciechMazur added a commit that referenced this pull request Feb 5, 2026

Backport "Preserve singleton types for final val aliases to Java enum…

305577f

… constants" to 3.8.2 (#25190) Backports #24980 to the 3.8.2-RC2. PR submitted by the release tooling. [skip ci]

WojciechMazur added backport:done This PR was successfully backported. and removed backport:accepted This PR needs to be backported, once it's been backported replace this tag by "backport:done" labels Feb 5, 2026

bjaglin added a commit to bjaglin/scalafix that referenced this pull request Feb 14, 2026

work around change in compiler for java enums

6c0b00d

scala/scala3#24980

bjaglin mentioned this pull request Feb 14, 2026

build and test against scala 3.8.2 scalacenter/scalafix#2373

Merged

tgodzik added a commit to scala/scala3-lts that referenced this pull request Feb 17, 2026

Preserve singleton types for final val aliases to Java enum constants (…

54d5e3b

…scala#24980) Fixes scala#24750 Fixes scala#21881 [Cherry-picked 2f8bbdc][modified]

tgodzik mentioned this pull request Feb 17, 2026

Backport "Preserve singleton types for final val aliases to Java enum constants" to 3.3 LTS scala/scala3-lts#730

Merged

bjaglin added a commit to bjaglin/scalafix that referenced this pull request Feb 25, 2026

work around change in compiler for java enums

54e5cad

scala/scala3#24980

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Preserve singleton types for final val aliases to Java enum constants#24980

Preserve singleton types for final val aliases to Java enum constants#24980
zielinsky merged 3 commits intoscala:mainfrom
zielinsky:i24750v3

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zielinsky commented Jan 14, 2026 •

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