From 9edb2459fd9d2bc7c8869d21ddc8ff20aeb55c39 Mon Sep 17 00:00:00 2001
From: Jon Meow <46229924+jonmeow@users.noreply.github.com>
Date: Mon, 20 Sep 2021 13:51:20 -0700
Subject: [PATCH] Remove BisonWrap, which was a Ptr-specific feature (#836)

---
 executable_semantics/syntax/BUILD        |  7 ---
 executable_semantics/syntax/bison_wrap.h | 44 -----------------
 executable_semantics/syntax/parser.ypp   | 60 ++++++++++++------------
 3 files changed, 29 insertions(+), 82 deletions(-)
 delete mode 100644 executable_semantics/syntax/bison_wrap.h

diff --git a/executable_semantics/syntax/BUILD b/executable_semantics/syntax/BUILD
index adb7a63af58d..ccfb4db827ed 100644
--- a/executable_semantics/syntax/BUILD
+++ b/executable_semantics/syntax/BUILD
@@ -6,12 +6,6 @@ load("@mypy_integration//:mypy.bzl", "mypy_test")
 
 package(default_visibility = ["//executable_semantics:__pkg__"])
 
-cc_library(
-    name = "bison_wrap",
-    hdrs = ["bison_wrap.h"],
-    deps = ["//common:check"],
-)
-
 cc_library(
     name = "syntax",
     srcs = [
@@ -33,7 +27,6 @@ cc_library(
         "-Wno-writable-strings",
     ],
     deps = [
-        ":bison_wrap",
         "//common:check",
         "//common:ostream",
         "//common:string_helpers",
diff --git a/executable_semantics/syntax/bison_wrap.h b/executable_semantics/syntax/bison_wrap.h
deleted file mode 100644
index c6917470b775..000000000000
--- a/executable_semantics/syntax/bison_wrap.h
+++ /dev/null
@@ -1,44 +0,0 @@
-// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
-// Exceptions. See /LICENSE for license information.
-// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-
-#ifndef EXECUTABLE_SEMANTICS_SYNTAX_BISON_WRAP_H_
-#define EXECUTABLE_SEMANTICS_SYNTAX_BISON_WRAP_H_
-
-#include <optional>
-
-#include "common/check.h"
-
-namespace Carbon {
-
-// Bison requires that types be default initializable for use with its variant
-// semantics. This wraps arbitrary types to support a default constructor, while
-// still requiring they be properly initialized.
-template <typename T>
-class BisonWrap {
- public:
-  // Assigning a value initializes the wrapper.
-  BisonWrap& operator=(T&& rhs) {
-    val = std::move(rhs);
-    return *this;
-  }
-
-  // Support transparent conversion to the wrapped type.
-  operator T() { return Release(); }
-
-  // Deliberately releases the contained value. Errors if not initialized.
-  // Called directly in parser.ypp when releasing pairs.
-  auto Release() -> T {
-    CHECK(val.has_value());
-    T ret = std::move(*val);
-    val.reset();
-    return ret;
-  }
-
- private:
-  std::optional<T> val;
-};
-
-}  // namespace Carbon
-
-#endif  // EXECUTABLE_SEMANTICS_SYNTAX_BISON_WRAP_H_
diff --git a/executable_semantics/syntax/parser.ypp b/executable_semantics/syntax/parser.ypp
index bce5c9de1b51..4f88da2a8019 100644
--- a/executable_semantics/syntax/parser.ypp
+++ b/executable_semantics/syntax/parser.ypp
@@ -73,7 +73,6 @@
   #include "executable_semantics/ast/pattern.h"
   #include "executable_semantics/common/arena.h"
   #include "executable_semantics/common/ptr.h"
-  #include "executable_semantics/syntax/bison_wrap.h"
 
   namespace Carbon {
   class ParseAndLexContext;
@@ -98,42 +97,42 @@
 %type <std::vector<LibraryName>> import_directives
 %type <std::string> optional_library_path
 %type <bool> api_or_impl
-%type <BisonWrap<Nonnull<const Declaration*>>> declaration
-%type <BisonWrap<Nonnull<const FunctionDefinition*>>> function_declaration
-%type <BisonWrap<Nonnull<const FunctionDefinition*>>> function_definition
+%type <Nonnull<const Declaration*>> declaration
+%type <Nonnull<const FunctionDefinition*>> function_declaration
+%type <Nonnull<const FunctionDefinition*>> function_definition
 %type <std::vector<Nonnull<const Declaration*>>> declaration_list
-%type <BisonWrap<Nonnull<const Statement*>>> statement
-%type <BisonWrap<Nonnull<const Statement*>>> if_statement
+%type <Nonnull<const Statement*>> statement
+%type <Nonnull<const Statement*>> if_statement
 %type <std::optional<Nonnull<const Statement*>>> optional_else
-%type <BisonWrap<std::pair<Nonnull<const Expression*>, bool>>> return_expression
-%type <BisonWrap<Nonnull<const Statement*>>> block
+%type <std::pair<Nonnull<const Expression*>, bool>> return_expression
+%type <Nonnull<const Statement*>> block
 %type <std::optional<Nonnull<const Statement*>>> statement_list
-%type <BisonWrap<Nonnull<const Expression*>>> expression
-%type <BisonWrap<GenericBinding>> generic_binding
+%type <Nonnull<const Expression*>> expression
+%type <GenericBinding> generic_binding
 %type <std::vector<GenericBinding>> deduced_params
 %type <std::vector<GenericBinding>> deduced_param_list
-%type <BisonWrap<Nonnull<const Pattern*>>> pattern
-%type <BisonWrap<Nonnull<const Pattern*>>> non_expression_pattern
-%type <BisonWrap<std::pair<Nonnull<const Expression*>, bool>>> return_type
-%type <BisonWrap<Nonnull<const Expression*>>> paren_expression
-%type <BisonWrap<Nonnull<const Expression*>>> tuple
+%type <Nonnull<const Pattern*>> pattern
+%type <Nonnull<const Pattern*>> non_expression_pattern
+%type <std::pair<Nonnull<const Expression*>, bool>> return_type
+%type <Nonnull<const Expression*>> paren_expression
+%type <Nonnull<const Expression*>> tuple
 %type <std::optional<std::string>> binding_lhs
-%type <BisonWrap<Nonnull<const BindingPattern*>>> variable_declaration
-%type <BisonWrap<Nonnull<Member*>>> member
+%type <Nonnull<const BindingPattern*>> variable_declaration
+%type <Nonnull<Member*>> member
 %type <std::vector<Nonnull<Member*>>> member_list
-%type <BisonWrap<ParenContents<Expression>::Element>> paren_expression_element
+%type <ParenContents<Expression>::Element> paren_expression_element
 %type <ParenContents<Expression>> paren_expression_base
 %type <ParenContents<Expression>> paren_expression_contents
-%type <BisonWrap<Nonnull<const Pattern*>>> paren_pattern
-%type <BisonWrap<Nonnull<const TuplePattern*>>> tuple_pattern
-%type <BisonWrap<Nonnull<const TuplePattern*>>> maybe_empty_tuple_pattern
+%type <Nonnull<const Pattern*>> paren_pattern
+%type <Nonnull<const TuplePattern*>> tuple_pattern
+%type <Nonnull<const TuplePattern*>> maybe_empty_tuple_pattern
 %type <ParenContents<Pattern>> paren_pattern_base
-%type <BisonWrap<ParenContents<Pattern>::Element>> paren_pattern_element
+%type <ParenContents<Pattern>::Element> paren_pattern_element
 %type <ParenContents<Pattern>> paren_pattern_contents
-%type <BisonWrap<std::pair<std::string, Nonnull<const Expression*>>>> alternative
+%type <std::pair<std::string, Nonnull<const Expression*>>> alternative
 %type <std::vector<std::pair<std::string, Nonnull<const Expression*>>>> alternative_list
 %type <std::vector<std::pair<std::string, Nonnull<const Expression*>>>> alternative_list_contents
-%type <BisonWrap<std::pair<Nonnull<const Pattern*>, Nonnull<const Statement*>>>> clause
+%type <std::pair<Nonnull<const Pattern*>, Nonnull<const Statement*>>> clause
 %type <std::vector<std::pair<Nonnull<const Pattern*>, Nonnull<const Statement*>>>> clause_list
 
 %token
@@ -375,7 +374,7 @@ expression:
     }
 | FNTY tuple return_type
     {
-      auto [return_exp, is_omitted_exp] = $3.Release();
+      auto [return_exp, is_omitted_exp] = $3;
       $$ = arena->New<FunctionTypeLiteral>(context.SourceLoc(), $2, return_exp,
                                            is_omitted_exp);
     }
@@ -469,9 +468,8 @@ paren_pattern_contents:
 | paren_pattern_contents COMMA paren_expression_element
     {
       $$ = $1;
-      auto el = $3.Release();
-      $$.elements.push_back({.name = el.name,
-                             .term = arena->New<ExpressionPattern>(el.term)});
+      $$.elements.push_back({.name = $3.name,
+                             .term = arena->New<ExpressionPattern>($3.term)});
     }
 | paren_pattern_contents COMMA paren_pattern_element
     {
@@ -541,7 +539,7 @@ statement:
     { $$ = arena->New<Continue>(context.SourceLoc()); }
 | RETURN return_expression SEMICOLON
     {
-      auto [return_exp, is_omitted_exp] = $2.Release();
+      auto [return_exp, is_omitted_exp] = $2;
       $$ = arena->New<Return>(context.SourceLoc(), return_exp, is_omitted_exp);
     }
 | block
@@ -617,7 +615,7 @@ deduced_params:
 function_definition:
   FN identifier deduced_params maybe_empty_tuple_pattern return_type block
     {
-      auto [return_exp, is_omitted_exp] = $5.Release();
+      auto [return_exp, is_omitted_exp] = $5;
       $$ = arena->New<FunctionDefinition>(
           context.SourceLoc(), $2, $3, $4,
           arena->New<ExpressionPattern>(return_exp), is_omitted_exp, $6);
@@ -636,7 +634,7 @@ function_definition:
 function_declaration:
   FN identifier deduced_params maybe_empty_tuple_pattern return_type SEMICOLON
     {
-      auto [return_exp, is_omitted_exp] = $5.Release();
+      auto [return_exp, is_omitted_exp] = $5;
       $$ = arena->New<FunctionDefinition>(
           context.SourceLoc(), $2, $3, $4,
           arena->New<ExpressionPattern>(return_exp), is_omitted_exp,