diff options
Diffstat (limited to 'src/compiler/scala/tools/nsc/transform/patmat/Logic.scala')
-rw-r--r-- | src/compiler/scala/tools/nsc/transform/patmat/Logic.scala | 39 |
1 files changed, 28 insertions, 11 deletions
diff --git a/src/compiler/scala/tools/nsc/transform/patmat/Logic.scala b/src/compiler/scala/tools/nsc/transform/patmat/Logic.scala index 92b7700c04..7508843a48 100644 --- a/src/compiler/scala/tools/nsc/transform/patmat/Logic.scala +++ b/src/compiler/scala/tools/nsc/transform/patmat/Logic.scala @@ -384,18 +384,35 @@ trait ScalaLogic extends Interface with Logic with TreeAndTypeAnalysis { // else debug.patmat("NOT implies: "+(lower, upper)) - /* does V = C preclude V having value `other`? - (1) V = null is an exclusive assignment, - (2) V = A and V = B, for A and B value constants, are mutually exclusive unless A == B - we err on the safe side, for example: - - assume `val X = 1; val Y = 1`, then - (2: Int) match { case X => case Y => <falsely considered reachable> } - - V = 1 does not preclude V = Int, or V = Any, it could be said to preclude V = String, but we don't model that - - (3) for types we could try to do something fancy, but be conservative and just say no + /** Does V=A preclude V=B? + * + * (0) A or B must be in the domain to draw any conclusions. + * + * For example, knowing the the scrutinee is *not* true does not + * statically exclude it from being `X`, because that is an opaque + * Boolean. + * + * val X = true + * (true: Boolean) match { case true => case X <reachable> } + * + * (1) V = null excludes assignment to any other constant (modulo point #0). This includes + * both values and type tests (which are both modelled here as `Const`) + * (2) V = A and V = B, for A and B domain constants, are mutually exclusive unless A == B + * + * (3) We only reason about test tests as being excluded by null assignments, otherwise we + * only consider value assignments. + * TODO: refine this, a == 0 excludes a: String, or `a: Int` excludes `a: String` + * (since no value can be of both types. See also SI-7211) + * + * NOTE: V = 1 does not preclude V = Int, or V = Any, it could be said to preclude + * V = String, but we don't model that. */ - def excludes(a: Const, b: Const): Boolean = - a != b && ((a == NullConst || b == NullConst) || (a.isValue && b.isValue)) + def excludes(a: Const, b: Const): Boolean = { + val bothInDomain = domain exists (d => d(a) && d(b)) + val eitherIsNull = a == NullConst || b == NullConst + val bothAreValues = a.isValue && b.isValue + bothInDomain && (eitherIsNull || bothAreValues) && (a != b) + } // if(r) debug.patmat("excludes : "+(a, a.tp, b, b.tp)) // else debug.patmat("NOT excludes: "+(a, b)) |