Ruby: fix CFG and toString for anonymous '*' and '**'

Author: aibaars

ruby/ql/lib/codeql/ruby/ast/Parameter.qll

@@ -183,7 +183,11 @@ class HashSplatParameter extends NamedParameter, THashSplatParameter {
 
   final override LocalVariable getVariable() { result = TLocalVariableReal(_, _, g.getName()) }
 
-  final override string toString() { result = "**" + this.getName() }
+  final override string toString() {
+    result = "**" + this.getName()
+    or
+    not exists(g.getName()) and result = "**"
+  }
 
   final override string getName() { result = g.getName().getValue() }
 }
@@ -305,7 +309,11 @@ class SplatParameter extends NamedParameter, TSplatParameter {
 
   final override LocalVariable getVariable() { result = TLocalVariableReal(_, _, g.getName()) }
 
-  final override string toString() { result = "*" + this.getName() }
+  final override string toString() {
+    result = "*" + this.getName()
+    or
+    not exists(g.getName()) and result = "*"
+  }
 
   final override string getName() { result = g.getName().getValue() }
 }

ruby/ql/lib/codeql/ruby/controlflow/internal/ControlFlowGraphImpl.qll

@@ -139,10 +139,16 @@ module Trees {
   abstract private class NonDefaultValueParameterTree extends ControlFlowTree, NamedParameter {
     final override predicate first(AstNode first) {
       this.getDefiningAccess().(ControlFlowTree).first(first)
+      or
+      not exists(this.getDefiningAccess()) and first = this
     }
 
     final override predicate last(AstNode last, Completion c) {
       this.getDefiningAccess().(ControlFlowTree).last(last, c)
+      or
+      not exists(this.getDefiningAccess()) and
+      last = this and
+      c.isValidFor(this)
     }
 
     override predicate propagatesAbnormal(AstNode child) {

ruby/ql/test/library-tests/controlflow/graph/Cfg.expected

@@ -3719,9 +3719,12 @@ cfg.rb:
 #-----|  -> exit do ... end
 
 #  208| elem
-#-----|  -> rest
+#-----|  -> *
 
-#  208| rest
+#  208| *
+#-----|  -> **
+
+#  208| **
 #-----|  -> elem
 
 #  209| elem

ruby/ql/test/library-tests/controlflow/graph/cfg.rb

@@ -205,7 +205,7 @@ def forward_param(a, b, ...)
 foo&.bar(1,2) { |x| x }
 
 def filter_nil list
-  list.reject do |elem, *rest|
+  list.reject do |elem, *, **|
     elem.nil?
   end
 end