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Warn constant promotions #8730

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Warn constant promotions #8730

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som-snytt
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@som-snytt som-snytt commented Feb 19, 2020 •
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Warn if widening of literal Int or Long is not safe,
which is defined as the conversion roundtrips, the
test used for harmonization.

Fixes scala/bug#10773

@scala-jenkins scala-jenkins added this to the 2.13.3 milestone Feb 19, 2020
@som-snytt som-snytt mentioned this pull request Feb 20, 2020
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@som-snytt
Warn constant promotions
b611820 
Warn if widening of literal Int or Long is not safe,
which is defined as the conversion roundtrips, the
test used for harmonization.

The test means that if I want to convert precisely back to my
original value, I can do so. It does not mean the converted
value maintains accuracy or number of significant digits.

An attachment is used to defer the warning, since typechecking
may consider expressions which are discarded, such as
conversions during implicit search.
@som-snytt
Harmonize deprecated conversion warnings
a188207
@som-snytt som-snytt mentioned this pull request Feb 20, 2020
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@som-snytt som-snytt marked this pull request as ready for review February 21, 2020 01:37
@som-snytt som-snytt mentioned this pull request Feb 26, 2020
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@som-snytt som-snytt requested a review from lrytz February 26, 2020 21:49
@lrytz lrytz modified the milestones: 2.13.3, 2.13.2 Feb 28, 2020
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lrytz commented Mar 3, 2020

After comparing this PR with #8757, I have a tendency for the simpler solution over there. This PR introduces a warning when calling def +(x: Int): Float, but only if the receiver is a literal, which seems a bit ad-hoc to me.

Whether to do the roundtrip or based on the number of bits, I'm fine with both.

The commit message mentions to avoid warnings during implicit search, can you give an example? I wonder if this affects the other PR.

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@lrytz the issue on the original PR #7405 (comment) was whether the warning could be an ordinary deprecation, but n max 42 in the test would trigger it. The use an attachment to trigger the warning on the tree that survives typer is the workaround. I have no opinion on whether to warn on binary op of literals, who does that anyway?

@SethTisue SethTisue added the release-notes worth highlighting in next release notes label Mar 4, 2020
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lrytz commented Mar 4, 2020

OK thanks, I remember the deprecation issue now. Maybe extending ContextReporter to buffer deprecations is more uniform with what we already have?

I integrated the changes from this PR into #8757.

@lrytz lrytz closed this Mar 4, 2020
@SethTisue SethTisue removed the release-notes worth highlighting in next release notes label Mar 4, 2020
@SethTisue SethTisue removed this from the 2.13.2 milestone Mar 4, 2020
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