C#: Prototype of pattern match flow.

Author: michaelnebel

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

@@ -636,6 +636,11 @@ module LocalFlow {
           scope = s.getACase()
         )
       )
+      or
+      e.(VariablePatternExpr).getVariableDeclExpr().getVariable() =
+        def.(AssignableDefinitions::PatternDefinition).getTarget() and
+      exactScope = false and
+      isSuccessor = false
     }
   }
 
@@ -896,6 +901,18 @@ private predicate fieldOrPropertyStore(Expr e, ContentSet c, Expr src, Expr q, b
   )
 }
 
+private predicate patternPropertyRead(Expr e1, ContentSet c, LabeledPatternExpr e2) {
+  exists(IsExpr ie, RecursivePatternExpr p, TypeAccess ta, Property prop |
+    e1 = ie.getExpr() and
+    p = ie.getPattern() and
+    ta = p.getTypeAccess() and
+    e2 = p.getPropertyPatterns().getPattern(_) and
+    prop.getDeclaringType() = ta.getType() and
+    prop.getName() = e2.getLabel() and
+    c.isProperty(prop)
+  )
+}
+
 /**
  * Holds if `e2` is an expression that reads field or property `c` from
  * expression `e1`.
@@ -1124,6 +1141,8 @@ private module Cached {
           or
           dynamicPropertyRead(e, _, read)
           or
+          patternPropertyRead(e, _, read)
+          or
           arrayRead(e, read)
         )
       )
@@ -2415,6 +2434,11 @@ private class ReadStepConfiguration extends ControlFlowReachabilityConfiguration
     e2 = e1.(TupleExpr).getAnArgument() and
     scope = e1 and
     isSuccessor = false
+    or
+    exactScope = false and
+    isSuccessor = true and
+    patternPropertyRead(e1, _, e2) and
+    scope = e1
   }
 
   override predicate candidateDef(
@@ -2537,6 +2561,8 @@ predicate readStep(Node node1, ContentSet c, Node node2) {
     or
     dynamicPropertyRead(node1.asExpr(), c, node2.asExpr())
     or
+    patternPropertyRead(node1.asExpr(), c, node2.asExpr())
+    or
     node2.asExpr().(AwaitExpr).getExpr() = node1.asExpr() and
     c = getResultContent()
   )

csharp/ql/lib/semmle/code/csharp/exprs/Expr.qll

@@ -505,7 +505,10 @@ class RecursivePatternExpr extends BindingPatternExpr, @recursive_pattern_expr {
    */
   TypeAccess getTypeAccess() { result = this.getChild(1) }
 
-  override LocalVariableDeclExpr getVariableDeclExpr() { result = this.getChild(0) }
+  override LocalVariableDeclExpr getVariableDeclExpr() {
+    result = this.getChild(0) or
+    result = this.getPropertyPatterns().getPattern(_).(BindingPatternExpr).getVariableDeclExpr()
+  }
 }
 
 /** A property pattern. For example, `{ Length: 5 }`. */