From 018fde13ec361b5baf1a4d8fdb7ebe4ba477e76f Mon Sep 17 00:00:00 2001
From: Roberto Raggi <roberto.raggi@gmail.com>
Date: Sat, 19 Jul 2025 17:04:08 +0200
Subject: [PATCH] Fix increments and assignments to enums

Fixes #599

Signed-off-by: Roberto Raggi <roberto.raggi@gmail.com>
---
 src/parser/cxx/type_checker.cc    | 65 +++++++++++++++++++++----------
 tests/unit_tests/sema/incr_c_01.c | 22 +++++++++++
 2 files changed, 66 insertions(+), 21 deletions(-)
 create mode 100644 tests/unit_tests/sema/incr_c_01.c

diff --git a/src/parser/cxx/type_checker.cc b/src/parser/cxx/type_checker.cc
index 3ba81d27..8ee72f3a 100644
--- a/src/parser/cxx/type_checker.cc
+++ b/src/parser/cxx/type_checker.cc
@@ -50,6 +50,14 @@ struct TypeChecker::Visitor {
     return check.unit_->control();
   }
 
+  [[nodiscard]] auto is_parsing_c() const {
+    return check.unit_->language() == LanguageKind::kC;
+  }
+
+  [[nodiscard]] auto is_parsing_cxx() const {
+    return check.unit_->language() == LanguageKind::kCXX;
+  }
+
   void error(SourceLocation loc, std::string message) {
     if (!check.reportErrors_) return;
     check.unit_->error(loc, std::move(message));
@@ -498,7 +506,16 @@ void TypeChecker::Visitor::operator()(PostIncrExpressionAST* ast) {
   }
 
   auto incr_arithmetic = [&]() {
-    if (!control()->is_arithmetic(ast->baseExpression->type)) return false;
+    if (control()->is_const(ast->baseExpression->type)) return false;
+
+    if (is_parsing_cxx() &&
+        !control()->is_arithmetic(ast->baseExpression->type))
+      return false;
+
+    if (is_parsing_c() &&
+        !control()->is_arithmetic_or_unscoped_enum(ast->baseExpression->type))
+      return false;
+
     auto ty = control()->remove_cv(ast->baseExpression->type);
     if (type_cast<BoolType>(ty)) return false;
 
@@ -798,20 +815,23 @@ void TypeChecker::Visitor::operator()(UnaryExpressionAST* ast) {
         break;
       }
 
-      auto ty = ast->expression->type;
+      if (!control()->is_const(ast->expression->type)) {
+        const auto ty = ast->expression->type;
 
-      if (control()->is_arithmetic(ty) && !control()->is_const(ty)) {
-        ast->type = ty;
-        ast->valueCategory = ValueCategory::kLValue;
-        break;
-      }
-
-      if (auto ptrTy = type_cast<PointerType>(ty)) {
-        if (!control()->is_void(ptrTy->elementType())) {
-          ast->type = ptrTy;
+        if (is_parsing_cxx() ? control()->is_arithmetic(ty)
+                             : control()->is_arithmetic_or_unscoped_enum(ty)) {
+          ast->type = ty;
           ast->valueCategory = ValueCategory::kLValue;
           break;
         }
+
+        if (auto ptrTy = type_cast<PointerType>(ty)) {
+          if (!control()->is_void(ptrTy->elementType())) {
+            ast->type = ptrTy;
+            ast->valueCategory = ValueCategory::kLValue;
+            break;
+          }
+        }
       }
 
       error(ast->opLoc, std::format("cannot increment a value of type '{}'",
@@ -826,20 +846,23 @@ void TypeChecker::Visitor::operator()(UnaryExpressionAST* ast) {
         break;
       }
 
-      auto ty = ast->expression->type;
-
-      if (control()->is_arithmetic(ty) && !control()->is_const(ty)) {
-        ast->type = ty;
-        ast->valueCategory = ValueCategory::kLValue;
-        break;
-      }
+      if (!control()->is_const(ast->expression->type)) {
+        auto ty = ast->expression->type;
 
-      if (auto ptrTy = type_cast<PointerType>(ty)) {
-        if (ptrTy && !control()->is_void(ptrTy->elementType())) {
-          ast->type = ptrTy;
+        if (is_parsing_cxx() ? control()->is_arithmetic(ty)
+                             : control()->is_arithmetic_or_unscoped_enum(ty)) {
+          ast->type = ty;
           ast->valueCategory = ValueCategory::kLValue;
           break;
         }
+
+        if (auto ptrTy = type_cast<PointerType>(ty)) {
+          if (ptrTy && !control()->is_void(ptrTy->elementType())) {
+            ast->type = ptrTy;
+            ast->valueCategory = ValueCategory::kLValue;
+            break;
+          }
+        }
       }
 
       error(ast->opLoc, std::format("cannot decrement a value of type '{}'",
diff --git a/tests/unit_tests/sema/incr_c_01.c b/tests/unit_tests/sema/incr_c_01.c
new file mode 100644
index 00000000..ba43eaed
--- /dev/null
+++ b/tests/unit_tests/sema/incr_c_01.c
@@ -0,0 +1,22 @@
+// RUN: %cxx -verify -fcheck -xc %s
+
+enum E { a, b, c };
+
+int main() {
+  enum E e = a;
+  ++e;
+  --e;
+  e++;
+  e--;
+
+  const E ce = a;
+  // expected-error@1 {{cannot increment a value of type 'const E'}}
+  ++ce;
+  // expected-error@1 {{cannot decrement a value of type 'const E'}}
+  --ce;
+  // expected-error@1 {{cannot increment a value of type 'const E'}}
+  ce++;
+  // expected-error@1 {{cannot decrement a value of type 'const E'}}
+  ce--;
+  return 0;
+}