Don't generate CanThrow capabilities for catches with guards

Author: odersky

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -1745,7 +1745,7 @@ class Typer extends Namer
         .withSpan(expr.span)
     val caps =
       for
-        CaseDef(pat, _, _) <- cases
+        case CaseDef(pat, EmptyTree, _) <- cases
         if Feature.enabled(Feature.saferExceptions) && pat.tpe.widen.isCheckedException
       yield makeCanThrow(pat.tpe.widen)
     caps.foldLeft(expr)((e, g) => untpd.Block(g :: Nil, e))

tests/neg/i13849.scala

@@ -0,0 +1,16 @@
+import annotation.experimental
+import language.experimental.saferExceptions
+
+@experimental
+case class Ex(i: Int) extends Exception(s"Exception: $i")
+
+@experimental
+def foo(): Unit throws Ex = throw Ex(1)
+
+@experimental
+object Main:
+  def main(args: Array[String]): Unit =
+    try
+      foo() // error
+    catch
+      case _: Ex if false => println("Caught")