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authorAdriaan Moors <adriaan.moors@typesafe.com>2013-04-27 10:37:56 -0700
committerAdriaan Moors <adriaan.moors@typesafe.com>2013-04-27 10:37:56 -0700
commit3da1abe3a2e2752588ca8e2c7e889a321dae2037 (patch)
tree6357dcd07c064d80059283db67fe87c8a0bf8519 /src/compiler
parent0a23852d9b434d7aef734687474b1c3e79881a9b (diff)
parent62713964b96f64f9c0fd0070c89aa6571679856d (diff)
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Merge pull request #2439 from retronym/ticket/7369
SI-7369 Avoid spurious unreachable warnings in patterns
Diffstat (limited to 'src/compiler')
-rw-r--r--src/compiler/scala/tools/nsc/transform/patmat/Logic.scala39
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 0fab48028e..dbe08315f4 100644
--- a/src/compiler/scala/tools/nsc/transform/patmat/Logic.scala
+++ b/src/compiler/scala/tools/nsc/transform/patmat/Logic.scala
@@ -385,18 +385,35 @@ 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))