[Expr] Allow OpaqueValueExpr to store an underlying expression

Author: hborla

include/swift/AST/Expr.h

@@ -4021,11 +4021,14 @@ class DynamicTypeExpr : public Expr {
 /// subexpressions of that AST node.
 class OpaqueValueExpr : public Expr {
   SourceRange Range;
+  Expr *UnderlyingValue;
 
 public:
   explicit OpaqueValueExpr(SourceRange Range, Type Ty,
-                           bool isPlaceholder = false)
-      : Expr(ExprKind::OpaqueValue, /*Implicit=*/true, Ty), Range(Range) {
+                           bool isPlaceholder = false,
+                           Expr *underlyingValue = nullptr)
+      : Expr(ExprKind::OpaqueValue, /*Implicit=*/true, Ty),
+        Range(Range), UnderlyingValue(underlyingValue) {
     Bits.OpaqueValueExpr.IsPlaceholder = isPlaceholder;
   }
 
@@ -4038,6 +4041,14 @@ class OpaqueValueExpr : public Expr {
     Bits.OpaqueValueExpr.IsPlaceholder = value;
   }
 
+  Expr *getUnderlyingValue() const {
+    return UnderlyingValue;
+  }
+
+  void setUnderlyingValue(Expr *value) {
+    UnderlyingValue = value;
+  }
+
   SourceRange getSourceRange() const { return Range; }
 
   static bool classof(const Expr *E) {

lib/AST/ASTDumper.cpp

@@ -2498,6 +2498,10 @@ class PrintExpr : public ExprVisitor<PrintExpr> {
 
   void visitOpaqueValueExpr(OpaqueValueExpr *E) {
     printCommon(E, "opaque_value_expr") << " @ " << (void*)E;
+    if (auto *underlyingValue = E->getUnderlyingValue()) {
+      OS << '\n';
+      printRec(underlyingValue);
+    }
     PrintWithColorRAII(OS, ParenthesisColor) << ')';
   }
 

lib/AST/ASTWalker.cpp

@@ -506,7 +506,15 @@ class Traversal : public ASTVisitor<Traversal, Expr*, Stmt*,
     return E; 
   }
 
-  Expr *visitOpaqueValueExpr(OpaqueValueExpr *E) { return E; }
+  Expr *visitOpaqueValueExpr(OpaqueValueExpr *E) {
+    if (E->getUnderlyingValue()) {
+      if (auto *newValue = doIt(E->getUnderlyingValue()))
+        E->setUnderlyingValue(newValue);
+      else
+        return nullptr;
+    }
+    return E;
+  }
 
   Expr *visitDefaultArgumentExpr(DefaultArgumentExpr *E) { return E; }