C#: Some more precise flow.

Author: michaelnebel

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

@@ -286,6 +286,9 @@ module AssignableInternal {
     /** Holds if the local variable definition is at the top level of the pattern. */
     predicate isTopLevel() { this = pm.getPattern().(BindingPatternExpr).getVariableDeclExpr() }
 
+    /** Holds of this local variable definition is a part of a tuple pattern. */
+    predicate isInTuple() { this.getParent() instanceof TuplePatternExpr }
+
     /** Gets the pattern match that this local variable declaration (pattern) belongs to. */
     PatternMatch getMatch() { result = pm }
   }
@@ -720,12 +723,15 @@ module AssignableDefinitions {
     /** Gets the underlying local variable declaration. */
     LocalVariableDeclExpr getDeclaration() { result = lvpd }
 
-    override Expr getSource() { this.isTopLevel() and result = this.getMatch().getExpr() }
+    override Expr getSource() { result = this.getMatch().getExpr() }
 
     override string toString() { result = this.getDeclaration().toString() }
 
     /** Holds if the local variable definition is at the top level of the pattern. */
     predicate isTopLevel() { lvpd.isTopLevel() }
+
+    /** Holds of this local variable definition is a part of a tuple pattern. */
+    predicate isInTuple() { lvpd.isInTuple() }
   }
 
   /**

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

@@ -640,7 +640,8 @@ module LocalFlow {
       def.getSource() = e and
       (
         scope = def.getExpr() and
-        isSuccessor = true
+        isSuccessor = true and
+        not def instanceof AssignableDefinitions::PatternDefinition
         or
         exists(AssignableDefinitions::PatternDefinition def0 | def = def0 and def0.isTopLevel() |
           scope = def0.getMatch().(IsExpr) and
@@ -663,7 +664,7 @@ module LocalFlow {
       isSuccessor = false and
       def =
         any(AssignableDefinitions::PatternDefinition apd |
-          e = apd.getDeclaration() and not apd.isTopLevel()
+          e = apd.getDeclaration() and not apd.isTopLevel() and not apd.isInTuple()
         )
     }
   }