Swift: introduce Node.asPattern()

swift/ql/lib/codeql/swift/controlflow/CfgNodes.qll

@@ -118,6 +118,16 @@ class ExprCfgNode extends CfgNode {
   Expr getExpr() { result = e }
 }
 
+/** A control-flow node that wraps a pattern. */
+class PatternCfgNode extends CfgNode {
+  Pattern p;
+
+  PatternCfgNode() { p = this.getNode().asAstNode() }
+
+  /** Gets the underlying pattern. */
+  Pattern getPattern() { result = p }
+}
+
 /** A control-flow node that wraps a property getter. */
 class PropertyGetterCfgNode extends CfgNode {
   override PropertyGetterElement n;

swift/ql/lib/codeql/swift/dataflow/internal/DataFlowPrivate.qll

@@ -40,6 +40,14 @@ private class ExprNodeImpl extends ExprNode, NodeImpl {
   override DataFlowCallable getEnclosingCallable() { result = TDataFlowFunc(n.getScope()) }
 }
 
+private class PatternNodeImpl extends PatternNode, NodeImpl {
+  override Location getLocationImpl() { result = pattern.getLocation() }
+
+  override string toStringImpl() { result = pattern.toString() }
+
+  override DataFlowCallable getEnclosingCallable() { result = TDataFlowFunc(n.getScope()) }
+}
+
 private class SsaDefinitionNodeImpl extends SsaDefinitionNode, NodeImpl {
   override Location getLocationImpl() { result = def.getLocation() }
 
@@ -63,6 +71,7 @@ private module Cached {
   cached
   newtype TNode =
     TExprNode(CfgNode n, Expr e) { hasExprNode(n, e) } or
+    TPatternNode(CfgNode n, Pattern p) { hasPatternNode(n, p) } or
     TSsaDefinitionNode(Ssa::Definition def) or
     TInoutReturnNode(ParamDecl param) { modifiableParam(param) } or
     TSummaryNode(FlowSummary::SummarizedCallable c, FlowSummaryImpl::Private::SummaryNodeState state) {
@@ -231,6 +240,11 @@ private predicate hasExprNode(CfgNode n, Expr e) {
   n.(PropertyObserverCfgNode).getAssignExpr() = e
 }
 
+private predicate hasPatternNode(PatternCfgNode n, Pattern p) {
+  n.getPattern() = p and
+  p = p.resolve() // no need to turn hidden-AST patterns (`let`s, parens) into data flow nodes
+}
+
 import Cached
 
 /** Holds if `n` should be hidden from path explanations. */

swift/ql/lib/codeql/swift/dataflow/internal/DataFlowPublic.qll

@@ -37,6 +37,11 @@ class Node extends TNode {
    */
   Expr asExpr() { none() }
 
+  /**
+   * Gets this node's underlying pattern, if any.
+   */
+  Pattern asPattern() { none() }
+
   /**
    * Gets this data flow node's corresponding control flow node.
    */
@@ -66,6 +71,20 @@ class ExprNode extends Node, TExprNode {
   override ControlFlowNode getCfgNode() { result = n }
 }
 
+/**
+ * A pattern, viewed as a node in a data flow graph.
+ */
+class PatternNode extends Node, TPatternNode {
+  CfgNode n;
+  Pattern pattern;
+
+  PatternNode() { this = TPatternNode(n, pattern) }
+
+  override Pattern asPattern() { result = pattern }
+
+  override ControlFlowNode getCfgNode() { result = n }
+}
+
 /**
  * The value of a parameter at function entry, viewed as a node in a data
  * flow graph.