Translate C++ enums as Rust integers (#325)

The previous translation, C++ enums -> Rust enums had two weak points:
* it did not allow enums that have equal variants, for example `enum E {
A = 1, B = A }`
* operations on the enum could not be used in const context, for
example: `int global = E::A != E::B`. `!=` for enums is not const so it
cannot be used in const expressions like initializing a global variable

The new translation does C++ enums -> Rust integers and the name of the
values becomes `E_A` instead of `E::A`.

Author: lucic71

cpp2rust/converter/converter.cpp

@@ -2070,25 +2070,24 @@ bool Converter::VisitCXXBoolLiteralExpr(clang::CXXBoolLiteralExpr *expr) {
 
 void Converter::ConvertIntegerToEnumeralCast(clang::Expr *to,
                                              clang::Expr *from) {
-  // Short circuit `Enum::from(X as i32)` to `X`
+  // Short circuit `(X as i32) as Enum` to `X`
   if (auto ref =
           clang::dyn_cast<clang::DeclRefExpr>(from->IgnoreParenImpCasts())) {
     if (auto ec = clang::dyn_cast<clang::EnumConstantDecl>(ref->getDecl())) {
       auto src_enum = clang::dyn_cast<clang::EnumDecl>(ec->getDeclContext());
       auto dst_enum = to->getType()->getAs<clang::EnumType>();
       if (src_enum && dst_enum && dst_enum->getDecl() == src_enum) {
-        StrCat(std::format("{}::{}", GetRecordName(src_enum),
-                           std::string_view(ec->getName())));
+        StrCat(EnumeratorName(ec));
         return;
       }
     }
   }
-  StrCat(GetUnsafeTypeAsString(to->getType()), "::from");
   PushParen paren(*this);
-  Convert(from);
-  if (!from->getType()->isSpecificBuiltinType(clang::BuiltinType::Int)) {
-    StrCat(keyword::kAs, "i32");
+  {
+    PushParen inner(*this);
+    Convert(from);
   }
+  StrCat(keyword::kAs, GetUnsafeTypeAsString(to->getType()));
 }
 
 void Converter::ConvertIntegralToBooleanCast(clang::ImplicitCastExpr *expr) {
@@ -2107,11 +2106,7 @@ void Converter::ConvertIntegralToBooleanCast(clang::ImplicitCastExpr *expr) {
   PushParen paren(*this);
   Convert(sub_expr);
   StrCat(token::kDiff);
-  if (sub_expr->getType()->isEnumeralType()) {
-    StrCat(GetUnsafeTypeAsString(sub_expr->getType()), "::from(0)");
-  } else /* sub_expr->getType()->isIntegerType() */ {
-    StrCat(token::kZero);
-  }
+  StrCat(token::kZero);
 }
 
 bool Converter::IsCastRedundantInRust(clang::Expr *expr,
@@ -2657,14 +2652,11 @@ std::string Converter::ConvertDeclRefExpr(clang::DeclRefExpr *expr) {
   }
 
   if (auto enum_constant = clang::dyn_cast<clang::EnumConstantDecl>(decl)) {
-    auto qualified = std::format("{}::{}",
-                                 GetRecordName(clang::dyn_cast<clang::EnumDecl>(
-                                     enum_constant->getDeclContext())),
-                                 std::string_view(enum_constant->getName()));
+    auto name = EnumeratorName(enum_constant);
     if (!expr->getType()->isEnumeralType()) {
-      return std::format("({} as i32)", qualified);
+      return std::format("({} as i32)", name);
     }
-    return qualified;
+    return name;
   }
 
   if (IsGlobalVar(expr)) {
@@ -3237,50 +3229,23 @@ bool Converter::VisitEnumDecl(clang::EnumDecl *decl) {
     return false;
   }
   Mapper::AddRuleForUserDefinedType(decl);
-  Mapper::SetDerives(ctx_.getCanonicalTagType(decl),
-                     {"Clone", "Copy", "PartialEq", "Debug", "Default"});
-  StrCat("#[derive(Clone, Copy, PartialEq, Debug, Default)]");
-  StrCat(std::format("enum {}", GetRecordName(decl)));
-  StrCat('{');
-  bool first_enumerator = true;
+  auto name = GetRecordName(decl);
+  StrCat(std::format("pub type {} = {};", name,
+                     GetUnsafeTypeAsString(decl->getIntegerType())));
   for (auto e : decl->enumerators()) {
     llvm::SmallVector<char, 32> init;
     e->getInitVal().toString(init, 10);
-    if (first_enumerator) {
-      StrCat("#[default]");
-      first_enumerator = false;
-    }
-    StrCat(std::format("{} = {},", std::string_view(e->getName()),
+    StrCat(std::format("pub const {}: {} = {};", EnumeratorName(e), name,
                        std::string_view(init.data(), init.size())));
   }
-  StrCat('}');
-
-  AddFromImpl(decl);
-  AddIncDecImpls(decl);
-  AddByteReprTrait(decl);
   return false;
 }
 
-void Converter::AddFromImpl(clang::EnumDecl *decl) {
-  auto name = GetRecordName(decl);
-  StrCat(std::format("impl From<i32> for {}", name));
-  PushBrace impl(*this);
-  StrCat(std::format("fn from(n: i32) -> {}", name));
-  PushBrace fn(*this);
-  StrCat("match n");
-  PushBrace match(*this);
-  for (auto e : decl->enumerators()) {
-    llvm::SmallVector<char, 32> init;
-    e->getInitVal().toString(init, 10);
-    StrCat(std::format("{} => {}::{},",
-                       std::string_view(init.data(), init.size()), name,
-                       std::string_view(e->getName())));
-  }
-  StrCat(std::format("_ => panic!(\"invalid {} value: {{}}\", n),", name));
-}
-
-void Converter::AddIncDecImpls(clang::EnumDecl *decl) {
-  StrCat(std::format("libcc2rs::impl_enum_inc_dec!({});", GetRecordName(decl)));
+std::string
+Converter::EnumeratorName(const clang::EnumConstantDecl *decl) const {
+  auto *enum_decl = clang::cast<clang::EnumDecl>(decl->getDeclContext());
+  return std::format("{}_{}", GetRecordName(enum_decl),
+                     std::string_view(decl->getName()));
 }
 
 bool Converter::VisitCXXDefaultArgExpr(clang::CXXDefaultArgExpr *expr) {
@@ -3570,9 +3535,10 @@ std::string Converter::GetDefaultAsStringFallback(clang::QualType qual_type) {
 
   if (qual_type->isEnumeralType()) {
     auto enum_decl = qual_type->castAs<clang::EnumType>()->getDecl();
-    return std::format(
-        "{}::{}", GetRecordName(enum_decl),
-        std::string_view(enum_decl->enumerator_begin()->getName()));
+    if (enum_decl->enumerators().empty()) {
+      return std::string(1, token::kZero);
+    }
+    return EnumeratorName(*enum_decl->enumerator_begin());
   }
 
   return std::format("<{}>::default()", ToString(qual_type));
@@ -4049,8 +4015,6 @@ void Converter::EmitDefaultStructLiteral(const clang::RecordDecl *decl) {
 
 void Converter::AddByteReprTrait(const clang::RecordDecl *decl) {}
 
-void Converter::AddByteReprTrait(const clang::EnumDecl *decl) {}
-
 void Converter::ConvertUnsignedArithBinaryOperator(clang::BinaryOperator *op,
                                                    clang::Expr *expr) {
   StrCat(token::kDot);

cpp2rust/converter/converter.h

@@ -374,9 +374,7 @@ class Converter : public clang::RecursiveASTVisitor<Converter> {
 
   virtual bool VisitEnumDecl(clang::EnumDecl *decl);
 
-  virtual void AddFromImpl(clang::EnumDecl *decl);
-
-  virtual void AddIncDecImpls(clang::EnumDecl *decl);
+  virtual std::string EnumeratorName(const clang::EnumConstantDecl *decl) const;
 
   virtual bool VisitCXXDefaultArgExpr(clang::CXXDefaultArgExpr *expr);
 
@@ -560,8 +558,6 @@ class Converter : public clang::RecursiveASTVisitor<Converter> {
 
   virtual void AddByteReprTrait(const clang::RecordDecl *decl);
 
-  virtual void AddByteReprTrait(const clang::EnumDecl *decl);
-
   virtual void
   ConvertUnsignedArithBinaryOperator(clang::BinaryOperator *binary_operator,
                                      clang::Expr *expr);

cpp2rust/converter/models/converter_refcount.cpp

@@ -654,17 +654,6 @@ void ConverterRefCount::AddByteReprTrait(const clang::RecordDecl *decl) {
   }
 }
 
-void ConverterRefCount::AddByteReprTrait(const clang::EnumDecl *decl) {
-  auto name = GetRecordName(decl);
-  StrCat(std::format("impl ByteRepr for {}", name));
-  PushBrace impl_brace(*this);
-  StrCat(
-      "fn to_bytes(&self, buf: &mut [u8]) { (*self as i32).to_bytes(buf); }");
-  StrCat(std::format("fn from_bytes(buf: &[u8]) -> Self {{ "
-                     "<{}>::from(i32::from_bytes(buf)) }}",
-                     name));
-}
-
 std::string
 ConverterRefCount::GetSelfMaybeWithMut(const clang::CXXMethodDecl *decl) {
   return "&self";

cpp2rust/converter/models/converter_refcount.h

@@ -45,8 +45,6 @@ class ConverterRefCount final : public Converter {
 
   void AddByteReprTrait(const clang::RecordDecl *decl) override;
 
-  void AddByteReprTrait(const clang::EnumDecl *decl) override;
-
   bool
   VisitUnaryExprOrTypeTraitExpr(clang::UnaryExprOrTypeTraitExpr *expr) override;
 

libcc2rs/src/inc.rs

@@ -124,38 +124,6 @@ impl<T> UnsafePrefixInc for *mut T {
     }
 }
 
-#[macro_export]
-macro_rules! impl_enum_inc_dec {
-    ($t:ty) => {
-        impl PostfixInc for $t {
-            fn postfix_inc(&mut self) -> Self {
-                let copy = *self;
-                *self = <$t>::from((*self as i32).wrapping_add(1));
-                copy
-            }
-        }
-        impl PrefixInc for $t {
-            fn prefix_inc(&mut self) -> Self {
-                *self = <$t>::from((*self as i32).wrapping_add(1));
-                *self
-            }
-        }
-        impl PostfixDec for $t {
-            fn postfix_dec(&mut self) -> Self {
-                let copy = *self;
-                *self = <$t>::from((*self as i32).wrapping_sub(1));
-                copy
-            }
-        }
-        impl PrefixDec for $t {
-            fn prefix_dec(&mut self) -> Self {
-                *self = <$t>::from((*self as i32).wrapping_sub(1));
-                *self
-            }
-        }
-    };
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;

tests/multi-file/cross_tu_anon_enum_collision/out/refcount/cross_tu_anon_enum_collision.rs

@@ -6,31 +6,11 @@ use std::io::prelude::*;
 use std::io::{Read, Seek, Write};
 use std::os::fd::AsFd;
 use std::rc::{Rc, Weak};
-#[derive(Clone, Copy, PartialEq, Debug, Default)]
-enum anon_0 {
-    #[default]
-    ALPHA = 7,
-}
-impl From<i32> for anon_0 {
-    fn from(n: i32) -> anon_0 {
-        match n {
-            7 => anon_0::ALPHA,
-            _ => panic!("invalid anon_0 value: {}", n),
-        }
-    }
-}
-libcc2rs::impl_enum_inc_dec!(anon_0);
-impl ByteRepr for anon_0 {
-    fn to_bytes(&self, buf: &mut [u8]) {
-        (*self as i32).to_bytes(buf);
-    }
-    fn from_bytes(buf: &[u8]) -> Self {
-        <anon_0>::from(i32::from_bytes(buf))
-    }
-}
+pub type anon_0 = u32;
+pub const anon_0_ALPHA: anon_0 = 7;
 pub fn a_value_1() -> i32 {
     let x: Value<i32> = Rc::new(RefCell::new(0));
-    (*x.borrow_mut()) |= (anon_0::ALPHA as i32);
+    (*x.borrow_mut()) |= (anon_0_ALPHA as i32);
     return (*x.borrow());
 }
 pub fn main() {
@@ -41,30 +21,10 @@ fn main_0() -> i32 {
     assert!((((({ b_value_2() }) == 9) as i32) != 0));
     return 0;
 }
-#[derive(Clone, Copy, PartialEq, Debug, Default)]
-enum anon_3 {
-    #[default]
-    BETA = 9,
-}
-impl From<i32> for anon_3 {
-    fn from(n: i32) -> anon_3 {
-        match n {
-            9 => anon_3::BETA,
-            _ => panic!("invalid anon_3 value: {}", n),
-        }
-    }
-}
-libcc2rs::impl_enum_inc_dec!(anon_3);
-impl ByteRepr for anon_3 {
-    fn to_bytes(&self, buf: &mut [u8]) {
-        (*self as i32).to_bytes(buf);
-    }
-    fn from_bytes(buf: &[u8]) -> Self {
-        <anon_3>::from(i32::from_bytes(buf))
-    }
-}
+pub type anon_3 = u32;
+pub const anon_3_BETA: anon_3 = 9;
 pub fn b_value_2() -> i32 {
     let x: Value<i32> = Rc::new(RefCell::new(0));
-    (*x.borrow_mut()) |= (anon_3::BETA as i32);
+    (*x.borrow_mut()) |= (anon_3_BETA as i32);
     return (*x.borrow());
 }

tests/multi-file/cross_tu_anon_enum_collision/out/unsafe/cross_tu_anon_enum_collision.rs

@@ -6,23 +6,11 @@ use std::collections::BTreeMap;
 use std::io::{Read, Seek, Write};
 use std::os::fd::{AsFd, FromRawFd, IntoRawFd};
 use std::rc::Rc;
-#[derive(Clone, Copy, PartialEq, Debug, Default)]
-enum anon_0 {
-    #[default]
-    ALPHA = 7,
-}
-impl From<i32> for anon_0 {
-    fn from(n: i32) -> anon_0 {
-        match n {
-            7 => anon_0::ALPHA,
-            _ => panic!("invalid anon_0 value: {}", n),
-        }
-    }
-}
-libcc2rs::impl_enum_inc_dec!(anon_0);
+pub type anon_0 = u32;
+pub const anon_0_ALPHA: anon_0 = 7;
 pub unsafe fn a_value_1() -> i32 {
     let mut x: i32 = 0;
-    x |= (anon_0::ALPHA as i32);
+    x |= (anon_0_ALPHA as i32);
     return x;
 }
 pub fn main() {
@@ -35,22 +23,10 @@ unsafe fn main_0() -> i32 {
     assert!(((((unsafe { b_value_2() }) == (9)) as i32) != 0));
     return 0;
 }
-#[derive(Clone, Copy, PartialEq, Debug, Default)]
-enum anon_3 {
-    #[default]
-    BETA = 9,
-}
-impl From<i32> for anon_3 {
-    fn from(n: i32) -> anon_3 {
-        match n {
-            9 => anon_3::BETA,
-            _ => panic!("invalid anon_3 value: {}", n),
-        }
-    }
-}
-libcc2rs::impl_enum_inc_dec!(anon_3);
+pub type anon_3 = u32;
+pub const anon_3_BETA: anon_3 = 9;
 pub unsafe fn b_value_2() -> i32 {
     let mut x: i32 = 0;
-    x |= (anon_3::BETA as i32);
+    x |= (anon_3_BETA as i32);
     return x;
 }

tests/multi-file/cross_tu_tag_collision/out/refcount/cross_tu_tag_collision.rs

@@ -43,33 +43,11 @@ fn main_0() -> i32 {
     assert!((((({ b_value_1() }) == 2) as i32) != 0));
     return 0;
 }
-#[derive(Clone, Copy, PartialEq, Debug, Default)]
-enum widget_enum {
-    #[default]
-    WIDGET_A = 0,
-    WIDGET_B = 1,
-    WIDGET_C = 2,
-}
-impl From<i32> for widget_enum {
-    fn from(n: i32) -> widget_enum {
-        match n {
-            0 => widget_enum::WIDGET_A,
-            1 => widget_enum::WIDGET_B,
-            2 => widget_enum::WIDGET_C,
-            _ => panic!("invalid widget_enum value: {}", n),
-        }
-    }
-}
-libcc2rs::impl_enum_inc_dec!(widget_enum);
-impl ByteRepr for widget_enum {
-    fn to_bytes(&self, buf: &mut [u8]) {
-        (*self as i32).to_bytes(buf);
-    }
-    fn from_bytes(buf: &[u8]) -> Self {
-        <widget_enum>::from(i32::from_bytes(buf))
-    }
-}
+pub type widget_enum = u32;
+pub const widget_enum_WIDGET_A: widget_enum = 0;
+pub const widget_enum_WIDGET_B: widget_enum = 1;
+pub const widget_enum_WIDGET_C: widget_enum = 2;
 pub fn b_value_1() -> i32 {
-    let w: Value<widget_enum> = Rc::new(RefCell::new(widget_enum::WIDGET_C));
+    let w: Value<widget_enum> = Rc::new(RefCell::new(widget_enum_WIDGET_C));
     return ((*w.borrow()) as i32);
 }