Ruby: Switch from ssaDefAssigns/ssaDefInitializesParam to WriteDefSourceNode.

Author: aschackmull

ruby/ql/lib/codeql/ruby/dataflow/internal/DataFlowPrivate.qll

@@ -108,7 +108,12 @@ module SsaFlow {
     or
     result.(Impl::ExprPostUpdateNode).getExpr() = n.(PostUpdateNode).getPreUpdateNode().asExpr()
     or
-    n = toParameterNode(result.(Impl::ParameterNode).getParameter())
+    exists(SsaImpl::ParameterExt p |
+      n = toParameterNode(p) and
+      p.isInitializedBy(result.(Impl::WriteDefSourceNode).getDefinition())
+    )
+    or
+    result.(Impl::WriteDefSourceNode).getDefinition().(Ssa::WriteDefinition).assigns(n.asExpr())
   }
 
   predicate localFlowStep(

ruby/ql/lib/codeql/ruby/dataflow/internal/SsaImpl.qll

@@ -481,11 +481,9 @@ private module DataFlowIntegrationInput implements Impl::DataFlowIntegrationInpu
 
   Expr getARead(Definition def) { result = Cached::getARead(def) }
 
-  predicate ssaDefAssigns(WriteDefinition def, Expr value) {
-    def.(Ssa::WriteDefinition).assigns(value)
-  }
+  predicate ssaDefAssigns(WriteDefinition def, Expr value) { none() }
 
-  predicate ssaDefInitializesParam(WriteDefinition def, Parameter p) { p.isInitializedBy(def) }
+  predicate ssaDefInitializesParam(WriteDefinition def, Parameter p) { none() }
 
   class Guard extends Cfg::CfgNodes::AstCfgNode {
     /**