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 +723,30 @@ 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() }
+  /**
+   * A local variable definition at the top level of a pattern.
+   */
+  class TopLevelPatternDefinition extends PatternDefinition {
+    TopLevelPatternDefinition() { lvpd.isTopLevel() }
+  }
+
+  /**
+   * A local variable definition in a tuple pattern.
+   */
+  class TuplePatternDefinition extends PatternDefinition {
+    TuplePatternDefinition() { lvpd.isInTuple() }
+  }
+
+  /**
+   * A local variable definition in a property pattern.
+   */
+  class PropertyPatternDefinition extends PatternDefinition {
+    PropertyPatternDefinition() { lvpd.getParent() instanceof PropertyPatternExpr }
   }
 
   /**

csharp/ql/lib/semmle/code/csharp/dataflow/Nullness.qll

@@ -104,7 +104,7 @@ private predicate nonNullDef(Ssa::ExplicitDefinition def) {
   def.getADefinition().getSource() instanceof NonNullExpr
   or
   exists(AssignableDefinition ad | ad = def.getADefinition() |
-    ad instanceof AssignableDefinitions::PatternDefinition
+    ad instanceof AssignableDefinitions::TopLevelPatternDefinition
     or
     ad =
       any(AssignableDefinitions::LocalVariableDefinition d |

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

@@ -640,31 +640,30 @@ module LocalFlow {
       def.getSource() = e and
       (
         scope = def.getExpr() and
-        isSuccessor = true
+        isSuccessor = true and
+        (
+          not def instanceof AssignableDefinitions::PatternDefinition or
+          def instanceof AssignableDefinitions::TopLevelPatternDefinition
+        )
+        or
+        scope = def.(AssignableDefinitions::TopLevelPatternDefinition).getMatch().(IsExpr) and
+        isSuccessor = false
         or
-        exists(AssignableDefinitions::PatternDefinition def0 | def = def0 and def0.isTopLevel() |
-          scope = def0.getMatch().(IsExpr) and
-          isSuccessor = false
+        exists(Switch s |
+          s.getACase() = def.(AssignableDefinitions::TopLevelPatternDefinition).getMatch() and
+          isSuccessor = true
+        |
+          scope = s.getExpr()
           or
-          exists(Switch s |
-            s.getACase() = def0.getMatch() and
-            isSuccessor = true
-          |
-            scope = s.getExpr()
-            or
-            scope = s.getACase()
-          )
+          scope = s.getACase()
         )
       )
       or
       // Needed for read steps for pattern matching involving properties.
       scope = def.getExpr() and
       exactScope = false and
       isSuccessor = false and
-      def =
-        any(AssignableDefinitions::PatternDefinition apd |
-          e = apd.getDeclaration() and not apd.isTopLevel()
-        )
+      e = def.(AssignableDefinitions::PropertyPatternDefinition).getDeclaration()
     }
   }
 
@@ -2508,7 +2507,7 @@ private class ReadStepConfiguration extends ControlFlowReachabilityConfiguration
     or
     scope =
       any(TuplePatternExpr te |
-        te.getAnArgument() = defTo.(AssignableDefinitions::PatternDefinition).getDeclaration() and
+        te.getAnArgument() = defTo.(AssignableDefinitions::TuplePatternDefinition).getDeclaration() and
         e = te and
         exactScope = false and
         isSuccessor = false
@@ -2558,7 +2557,7 @@ private predicate readContentStep(Node node1, Content c, Node node2) {
       or
       // item = variable in node1 = (..., variable, ...) in a case/is var (..., ...)
       te = any(TuplePatternExpr pe).getAChildExpr*() and
-      exists(AssignableDefinitions::PatternDefinition lvd |
+      exists(AssignableDefinitions::TuplePatternDefinition lvd |
         node2.(AssignableDefinitionNode).getDefinition() = lvd and
         lvd.getDeclaration() = item and
         hasNodePath(x, node1, node2)
@@ -2990,10 +2989,8 @@ class CastNode extends Node {
   CastNode() {
     this.asExpr() instanceof Cast
     or
-    this.(AssignableDefinitionNode)
-        .getDefinition()
-        .(AssignableDefinitions::PatternDefinition)
-        .isTopLevel()
+    this.(AssignableDefinitionNode).getDefinition() instanceof
+      AssignableDefinitions::TopLevelPatternDefinition
   }
 }