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The spec says that `case _: List[Int]` should be always issue
an unchecked warning:
> Types which are not of one of the forms described above are
> also accepted as type patterns. However, such type patterns
> will be translated to their erasure (§3.7). The Scala compiler
> will issue an “unchecked” warning for these patterns to flag
> the possible loss of type-safety.
But the implementation goes a little further to omit warnings
based on the static type of the scrutinee. As a trivial example:
def foo(s: Seq[Int]) = s match { case _: List[Int] => }
need not issue this warning.
These discriminating unchecked warnings are domain of
`CheckabilityChecker`.
Let's deconstruct the reported bug:
def nowarn[T] = (null: Any) match { case _: Some[T] => }
We used to determine that if the first case matched, the scrutinee
type would be `Some[Any]` (`Some` is covariant). If this statically
matches `Some[T]` in a pattern context, we don't need to issue an
unchecked warning. But, our blanket use of `existentialAbstraction`
in `matchesPattern` loosened the pattern type to `Some[Any]`, and
the scrutinee type was deemed compatible.
I've added a new method, `scrutConformsToPatternType` which replaces
pattern type variables by wildcards, but leaves other abstract
types intact in the pattern type. We have to use this inside
`CheckabilityChecker` only. If we were to make `matchesPattern`
stricter in the same way, tests like `pos/t2486.scala` would fail.
I have introduced a new symbol test to (try to) identify pattern
type variables introduced by `typedBind`. Its not pretty, and it
might be cleaner to reserve a new flag for these.
I've also included a test variation exercising with nested matches.
The pattern type of the inner case can't, syntactically, refer to the
pattern type variable of the enclosing case. If it could, we would
have to be more selective in our wildcarding in `ptMatchesPatternType`
by restricting ourselves to type variables associated with the closest
enclosing `CaseDef`.
As some further validation of the correctness of this patch,
four stray warnings have been teased out of
neg/unchecked-abstract.scala
I also had to changes `typeArgsInTopLevelType` to extract the type
arguments of `Array[T]` if `T` is an abstract type. This avoids the
"Checkability checker says 'Uncheckable', but uncheckable type
cannot be found" warning and consequent overly lenient analysis.
Without this change, the warning was suppressed for:
def warnArray[T] = (null: Any) match { case _: Array[T] => }
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* origin/2.10.0-wip:
MethodSymbol.params => MethodSymbol.paramss
SI-6471 Update jquery from 1.4.2 to 1.8.2
undeprecates manifests for 2.10.0
SI-6451: Rename classes in `unchecked-abstract.scala` test.
Put more implementation restrictions on value classes.
Fixed problem in SI-6408
Revised restrictions for value classes and unversal traits
SI-6436 Handle ambiguous string processors
fixes a bug in a weak cache in runtime reflection
Conflicts:
test/files/neg/classmanifests_new_deprecations.check
test/files/neg/unchecked-abstract.check
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As reported Miguel, `Con` is problematic name of a class on Windows
and makes this test to fail. Renamed classes to something else which
hopefully make Windows build happy again.
Closes SI-6451.
Review by @magarciaEPFL or @paulp.
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* 2.10.x: (37 commits)
Added logic and tests for unchecked refinements.
Moved isNonRefinementClassType somewhere logical.
Moved two tests to less breaky locations.
Nailed down the "impossible match" logic.
Finish docs for string interpolation.
moves Context.ParseError outside the cake
revives macros.Infrastructure
moves Context.runtimeUniverse to TreeBuild.mkRuntimeUniverseRef
a more precise type for Context.mirror
gets rid of macros.Infrastructure
simplifies Context.Run and Context.CompilationUnit
exposes Position.source as SourceFile
removes extraneous stuff from macros.Infrastructure
merges macros.CapturedVariables into macros.Universe
merges macros.Exprs and macros.TypeTags into Context
removes front ends from scala-reflect.jar
PositionApi => Position
hides BuildUtils from Scaladoc
MirrorOf => Mirror
docs.pre-lib now checks for mods in reflect
...
Conflicts:
test/files/neg/t4302.check
test/files/neg/unchecked.check
test/files/neg/unchecked2.check
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I will again defer to a comment.
/** Given classes A and B, can it be shown that nothing which is
* an A will ever be a subclass of something which is a B? This
* entails not only showing that !(A isSubClass B) but that the
* same is true of all their subclasses. Restated for symmetry:
* the same value cannot be a member of both A and B.
*
* 1) A must not be a subclass of B, nor B of A (the trivial check)
* 2) One of A or B must be completely knowable (see isKnowable)
* 3) Assuming A is knowable, the proposition is true if
* !(A' isSubClass B) for all A', where A' is a subclass of A.
*
* Due to symmetry, the last condition applies as well in reverse.
*/
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