implement RFC495 semantics for slice patterns

non-MIR translation is still not supported for these and will happily ICE.

This is a [breaking-change] for many uses of slice_patterns.

1 files changed, 15 insertions, 6 deletions

diff --git a/src/libstd/sys/common/wtf8.rs b/src/libstd/sys/common/wtf8.rs
index 55e485e5811..5519230890c 100644
--- a/src/libstd/sys/common/wtf8.rs
+++ b/src/libstd/sys/common/wtf8.rs
@@ -560,15 +560,20 @@ impl Wtf8 {
         }
     }
 
+    // FIXME(stage0): use slice patterns after snapshot
     #[inline]
     fn final_lead_surrogate(&self) -> Option<u16> {
         let len = self.len();
         if len < 3 {
             return None
         }
-        match &self.bytes[(len - 3)..] {
-            [0xED, b2 @ 0xA0...0xAF, b3] => Some(decode_surrogate(b2, b3)),
-            _ => None
+        if self.bytes[len-3] == 0xed &&
+            self.bytes[len-2] > 0xa0 &&
+            self.bytes[len-2] <= 0xaf
+        {
+            Some(decode_surrogate(self.bytes[len-2], self.bytes[len-1]))
+        } else {
+            None
         }
     }
 
@@ -578,9 +583,13 @@ impl Wtf8 {
         if len < 3 {
             return None
         }
-        match &self.bytes[..3] {
-            [0xED, b2 @ 0xB0...0xBF, b3] => Some(decode_surrogate(b2, b3)),
-            _ => None
+        if self.bytes[len-3] == 0xed &&
+            self.bytes[len-2] > 0xb0 &&
+            self.bytes[len-2] <= 0xbf
+        {
+            Some(decode_surrogate(self.bytes[len-2], self.bytes[len-1]))
+        } else {
+            None
         }
     }
 }