C#: Prototype breaking pattern assignments into multiple steps.

Author: michaelnebel

csharp/ql/lib/semmle/code/csharp/Assignable.qll

@@ -700,6 +700,8 @@ module AssignableDefinitions {
 
   /**
    * A local variable definition in a pattern, for example `x is int i`.
+   *
+   * TODO: SHOULD THIS BE RENAMED OR SHOULD IT GENERALIZED TO ALL PATTERN DEFINITIONS?
    */
   class PatternDefinition extends AssignableDefinition, TPatternDefinition {
     TopLevelPatternDecl tlpd;
@@ -712,8 +714,7 @@ module AssignableDefinitions {
     /** Gets the underlying local variable declaration. */
     LocalVariableDeclExpr getDeclaration() { result = tlpd }
 
-    override Expr getSource() { result = this.getMatch().getExpr() }
-
+    //override Expr getSource() { result = this.getMatch().getExpr() }
     override string toString() { result = this.getDeclaration().toString() }
   }
 

csharp/ql/lib/semmle/code/csharp/dataflow/internal/DataFlowPrivate.qll

@@ -601,6 +601,13 @@ module LocalFlow {
           e2 = we
         )
         or
+        exists(IsExpr ie |
+          scope = ie and
+          isSuccessor = true and
+          e1 = ie.getExpr() and
+          e2 = ie.getPattern()
+        )
+        or
         scope = any(AssignExpr ae | ae.getLValue().(TupleExpr) = e2 and ae.getRValue() = e1) and
         isSuccessor = false
         or
@@ -624,9 +631,9 @@ module LocalFlow {
         scope = def.getExpr() and
         isSuccessor = true
         or
-        scope = def.(AssignableDefinitions::PatternDefinition).getMatch().(IsExpr) and
-        isSuccessor = false
-        or
+        // or
+        // scope = def.(AssignableDefinitions::PatternDefinition).getMatch().(IsExpr) and
+        // isSuccessor = false
         exists(Switch s |
           s.getACase() = def.(AssignableDefinitions::PatternDefinition).getMatch() and
           isSuccessor = true
@@ -639,10 +646,13 @@ module LocalFlow {
       or
       // Needed for read steps for pattern matching involving properties.
       scope = def.getExpr() and
-      e.(VariablePatternExpr).getVariableDeclExpr() =
-        def.(AssignableDefinitions::LocalVariableDefinition).getExpr() and
+      e.(VariablePatternExpr).getVariableDeclExpr() = def.getExpr() and
       exactScope = false and
-      isSuccessor = false
+      isSuccessor = false and
+      (
+        def instanceof AssignableDefinitions::PatternDefinition or
+        def instanceof AssignableDefinitions::LocalVariableDefinition
+      )
     }
   }