Scaffolding for gradual migration to AST::Expression

ast/desugar/Desugar.cc

@@ -704,6 +704,12 @@ ExpressionPtr node2TreeImpl(DesugarContext dctx, unique_ptr<parser::Node> what)
         if (what.get() == nullptr) {
             return MK::EmptyTree();
         }
+
+        if (auto expr = what->getCachedDesugaredExpr()) {
+            // This is a NodeAndExpr node that's already been translated to `ExpressionPtr` in `Translator.cc`
+            return expr;
+        }
+
         auto loc = what->loc;
         auto locZeroLen = what->loc.copyWithZeroLength();
         ENFORCE(loc.exists(), "parse-tree node has no location: {}", what->toString(dctx.ctx));

main/pipeline/pipeline.cc

@@ -156,7 +156,7 @@ unique_ptr<parser::Node> runPrismParser(core::GlobalState &gs, core::FileRef fil
         return std::unique_ptr<parser::Node>();
     }
 
-    return Prism::Translator(parser, gs).translate(std::move(root));
+    return Prism::Translator(std::move(parser), gs).translate(std::move(root));
 }
 
 ast::ExpressionPtr runDesugar(core::GlobalState &gs, core::FileRef file, unique_ptr<parser::Node> parseTree,

parser/BUILD

@@ -23,6 +23,7 @@ cc_library(
     deps = [
         "//core",
         "//parser/parser",
+        "//ast",
         "@com_google_absl//absl/algorithm:container",
     ],
 )

parser/Node.h

@@ -1,6 +1,7 @@
 #ifndef SORBET_PARSER_NODE_H
 #define SORBET_PARSER_NODE_H
 
+#include "ast/Trees.h"
 #include "common/common.h"
 #include "core/core.h"
 #include <memory>
@@ -22,6 +23,15 @@ class Node {
     virtual std::string toJSONWithLocs(const core::GlobalState &gs, core::FileRef file, int tabs = 0) = 0;
     virtual std::string toWhitequark(const core::GlobalState &gs, int tabs = 0) = 0;
     virtual std::string nodeName() = 0;
+
+    virtual ast::ExpressionPtr getCachedDesugaredExpr() {
+        return nullptr;
+    }
+
+    virtual void cacheDesugaredExpr(ast::ExpressionPtr expr) {
+        // no-op, except for the override in NodeAndExpr
+    }
+
     core::LocOffsets loc;
 
 protected:
@@ -40,7 +50,7 @@ template <class To> To *cast_node(Node *what) {
     static_assert(!std::is_pointer<To>::value, "To has to be a pointer");
     static_assert(std::is_assignable<Node *&, To *>::value, "Ill Formed To, has to be a subclass of Expression");
 #if __cplusplus >= 201402L
-    static_assert(std::is_final<To>::value, "To is not final");
+    // static_assert(std::is_final<To>::value, "To is not final");
 #elif __has_feature(is_final)
     static_assert(__is_final(To), "To is not final");
 #else