Java: Teach guards that exceptions in catch-clauses are non-null.

Author: aschackmull

java/ql/lib/semmle/code/java/controlflow/Guards.qll

@@ -141,6 +141,7 @@ private predicate isNonFallThroughPredecessor(SwitchCase sc, ControlFlowNode pre
 
 private module GuardsInput implements SharedGuards::InputSig<Location> {
   private import java as J
+  private import semmle.code.java.dataflow.internal.BaseSSA
   private import semmle.code.java.dataflow.NullGuards as NullGuards
   import SuccessorType
 
@@ -216,6 +217,12 @@ private module GuardsInput implements SharedGuards::InputSig<Location> {
         f.isFinal() and
         f.getInitializer() = NullGuards::baseNotNullExpr()
       )
+      or
+      exists(CatchClause cc, LocalVariableDeclExpr decl, BaseSsaUpdate v |
+        decl = cc.getVariable() and
+        decl = v.getDefiningExpr() and
+        this = v.getAUse()
+      )
     }
   }