From 62713964b96f64f9c0fd0070c89aa6571679856d Mon Sep 17 00:00:00 2001
From: Jason Zaugg <jzaugg@gmail.com>
Date: Tue, 23 Apr 2013 23:55:05 +0200
Subject: SI-7369 Avoid spurious unreachable warnings in patterns

Unreachability analysis draws on the enumerated domain of types
(e.g sealed subclasses + null, or true/false), and also looks at all
stable identifier patterns tested for equality against the same 'slot'
in a pattern.

It was drawing the wrong conclusions about stable identifier patterns.
Unlike the domain constants, two such values may hold the same value,
so we can't assume that matching X precludes matching Y in the same
slot in a subsequent case.

For example:

    val X: Boolean = true; val Y: Boolean = true
    def m1(t1: Tuple1[Boolean]) = t1 match {
      case Tuple1(true) =>
      case Tuple1(false) =>
      case Tuple1(false) => // correctly unreachable
    }
    def m2(t1: Tuple1[Boolean]) = t1 match {
      case Tuple1(X) =>
      case Tuple1(Y) => // spurious unreachable warning
    }

    //
    // Before
    //
    reachability, vars:
    V2: Boolean ::= true | false// Set(false, Y, X, true) // = x1._1
    V1: (Boolean,) ::= null | ... // = x1
    equality axioms:
      V2=true#4  \/ V2=false#5  /\
     -V2=false#5 \/  -V2=Y#3    /\
     -V2=false#5 \/  -V2=X#2    /\
     -V2=false#5 \/ -V2=true#4  /\
       -V2=Y#3   \/  -V2=X#2    /\
       -V2=Y#3   \/ -V2=true#4  /\
       -V2=X#2   \/ -V2=true#4

    //
    // After
    //
    reachability, vars:
    V2: Boolean ::= true | false// Set(false, Y, X, true) // = x1._1
    V1: (Boolean,) ::= null | ... // = x1
    equality axioms:
      V2=true#4  \/ V2=false#5  /\
     -V2=false#5 \/ -V2=true#4
---
 test/files/neg/t7369.check | 13 +++++++++++++
 1 file changed, 13 insertions(+)
 create mode 100644 test/files/neg/t7369.check

(limited to 'test/files/neg/t7369.check')

diff --git a/test/files/neg/t7369.check b/test/files/neg/t7369.check
new file mode 100644
index 0000000000..4f101e145a
--- /dev/null
+++ b/test/files/neg/t7369.check
@@ -0,0 +1,13 @@
+t7369.scala:6: error: unreachable code
+    case Tuple1(X) => // unreachable
+                   ^
+t7369.scala:13: error: unreachable code
+    case Tuple1(true) => // unreachable
+                      ^
+t7369.scala:31: error: unreachable code
+    case Tuple1(X) => // unreachable
+                   ^
+t7369.scala:40: error: unreachable code
+    case Tuple1(null) => // unreachable
+                      ^
+four errors found
-- 
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