Don't interpolate downwards to Nothing #7130
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odersky
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Aug 29, 2019
If the result of a covariant type variable interpolation would be a bottom type,
wait instead. This could make the variable be inferred to its upper bound after all,
if we do not need a fully instantiated type right away.
This makes a difference for indentation whereever we have a situation like this:
```
def foo: T =
bla.asInstanceOf
```
With indentation on, this is now equivalent to
```
def foo: T = {
bla.asInstanceof
}
```
This means there is now an added opportunity for an interpolation step, of
the asInstanceOf, which would go downwards to Nothing. So indentation changes
the inferred type, which is very bad. With the commit the problem is
avoided.
The commit is broken out separately into PR scala#7130.
odersky
added a commit
to dotty-staging/dotty
that referenced
this pull request
Aug 29, 2019
If the result of a covariant type variable interpolation would be a bottom type,
wait instead. This could make the variable be inferred to its upper bound after all,
if we do not need a fully instantiated type right away.
This makes a difference for indentation whereever we have a situation like this:
```
def foo: T =
bla.asInstanceOf
```
With indentation on, this is now equivalent to
```
def foo: T = {
bla.asInstanceof
}
```
This means there is now an added opportunity for an interpolation step, of
the asInstanceOf, which would go downwards to Nothing. So indentation changes
the inferred type, which is very bad. With the commit the problem is
avoided.
The commit is broken out separately into PR scala#7130.
odersky
changed the title
If the result of a covariant type variable interpolation would be a bottom type, wait instead. This could make the variable be inferred to its upper bound after all, if we do not need a fully instantiated type right away.
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odersky
added a commit
to dotty-staging/dotty
that referenced
this pull request
Aug 29, 2019
If the result of a covariant type variable interpolation would be a bottom type,
wait instead. This could make the variable be inferred to its upper bound after all,
if we do not need a fully instantiated type right away.
This makes a difference for indentation whereever we have a situation like this:
```
def foo: T =
bla.asInstanceOf
```
With indentation on, this is now equivalent to
```
def foo: T = {
bla.asInstanceof
}
```
This means there is now an added opportunity for an interpolation step, of
the asInstanceOf, which would go downwards to Nothing. So indentation changes
the inferred type, which is very bad. With the commit the problem is
avoided.
The commit is broken out separately into PR scala#7130.
i536.scala previously compiled since the type argument was inferred to be Nothing. But that inference is useless; it just hides a runtime failure. The issue scala#536 only complained that the compiler crashed, so having a negative outcome is permissible.
odersky
added a commit
to dotty-staging/dotty
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Aug 29, 2019
This was referenced Aug 29, 2019
odersky
added a commit
to dotty-staging/dotty
that referenced
this pull request
Aug 29, 2019
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This was merged as part of #7114 |
odersky
added a commit
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Sep 3, 2019
Undo the change where we do not interpolate a type variable if its lower bound is nothing. It turned out this broke type inference.
odersky
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to dotty-staging/dotty
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Sep 3, 2019
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If the result of a covariant type variable interpolation would be type Nothing,
wait instead. This could make the variable be inferred to its upper bound after all,
if we do not need a fully instantiated type right away.