From cf8e75fae7702855b3d81ed11b2fb480c31a7fde Mon Sep 17 00:00:00 2001
From: Julius Ikkala <julius.ikkala@gmail.com>
Date: Tue, 6 May 2025 20:56:18 +0300
Subject: Parse char literals as integers (#6989)

* Parse char literals as integers

* Fix formatting

* Parse escaped chars correctly

---------

Co-authored-by: Yong He <yonghe@outlook.com>
---
 source/compiler-core/slang-lexer.cpp | 38 +++++++++++++++++++++++++++++++++---
 source/compiler-core/slang-lexer.h   |  2 ++
 source/slang/slang-parser.cpp        | 15 ++++++++++++++
 3 files changed, 52 insertions(+), 3 deletions(-)

(limited to 'source')

diff --git a/source/compiler-core/slang-lexer.cpp b/source/compiler-core/slang-lexer.cpp
index d19ea388d..358a0ceff 100644
--- a/source/compiler-core/slang-lexer.cpp
+++ b/source/compiler-core/slang-lexer.cpp
@@ -6,6 +6,7 @@
 //
 
 #include "core/slang-char-encode.h"
+#include "core/slang-string-escape-util.h"
 #include "slang-core-diagnostics.h"
 #include "slang-name.h"
 #include "slang-source-loc.h"
@@ -829,17 +830,48 @@ FloatingPointLiteralValue getFloatingPointLiteralValue(
     return value;
 }
 
-static void _lexStringLiteralBody(Lexer* lexer, char quote)
+IntegerLiteralValue getCharLiteralValue(Token const& token)
 {
+    String unquotedContent = StringEscapeUtil::unquote('\'', token.getContent());
+    StringBuilder unescaped(4);
+    auto escapeHandler = StringEscapeUtil::getHandler(StringEscapeUtil::Style::Cpp);
+    escapeHandler->appendUnescaped(unquotedContent.getUnownedSlice(), unescaped);
+
+    char const* cursor = unescaped.getBuffer();
+
+    IntegerLiteralValue codepoint = getUnicodePointFromUTF8([&]() { return *cursor++; });
+    return codepoint;
+}
+
+static void _lexStringLiteralBody(Lexer* lexer, char quote, bool singleChar)
+{
+    int len = 0;
     for (;;)
     {
         int c = _peek(lexer);
         if (c == quote)
         {
+            if (singleChar && len == 0)
+            { // Empty char literal - size must be exactly 1.
+                if (auto sink = lexer->getDiagnosticSink())
+                {
+                    sink->diagnose(_getSourceLoc(lexer), LexerDiagnostics::illegalCharacterLiteral);
+                }
+            }
             _advance(lexer);
             return;
         }
 
+        len++;
+
+        if (singleChar && len == 2)
+        { // Char literal about to have more than 1 char.
+            if (auto sink = lexer->getDiagnosticSink())
+            {
+                sink->diagnose(_getSourceLoc(lexer), LexerDiagnostics::illegalCharacterLiteral);
+            }
+        }
+
         switch (c)
         {
         case kEOF:
@@ -1346,12 +1378,12 @@ static TokenType _lexTokenImpl(Lexer* lexer)
 
     case '\"':
         _advance(lexer);
-        _lexStringLiteralBody(lexer, '\"');
+        _lexStringLiteralBody(lexer, '\"', false);
         return TokenType::StringLiteral;
 
     case '\'':
         _advance(lexer);
-        _lexStringLiteralBody(lexer, '\'');
+        _lexStringLiteralBody(lexer, '\'', true);
         return TokenType::CharLiteral;
 
 
diff --git a/source/compiler-core/slang-lexer.h b/source/compiler-core/slang-lexer.h
index c39d130b7..99ad87681 100644
--- a/source/compiler-core/slang-lexer.h
+++ b/source/compiler-core/slang-lexer.h
@@ -184,6 +184,8 @@ IntegerLiteralValue getIntegerLiteralValue(
 FloatingPointLiteralValue getFloatingPointLiteralValue(
     Token const& token,
     UnownedStringSlice* outSuffix = 0);
+
+IntegerLiteralValue getCharLiteralValue(Token const& token);
 } // namespace Slang
 
 #endif
diff --git a/source/slang/slang-parser.cpp b/source/slang/slang-parser.cpp
index c17a086a7..7ff0a6a2f 100644
--- a/source/slang/slang-parser.cpp
+++ b/source/slang/slang-parser.cpp
@@ -7584,6 +7584,21 @@ static Expr* parseAtomicExpr(Parser* parser)
 
             return constExpr;
         }
+
+    case TokenType::CharLiteral:
+        {
+            IntegerLiteralExpr* constExpr = parser->astBuilder->create<IntegerLiteralExpr>();
+            parser->FillPosition(constExpr);
+
+            auto token = parser->tokenReader.advanceToken();
+            constExpr->token = token;
+
+            IntegerLiteralValue value = getCharLiteralValue(token);
+            constExpr->value = value;
+            constExpr->suffixType = BaseType::UInt;
+            return constExpr;
+        }
+
     case TokenType::CompletionRequest:
         {
             VarExpr* varExpr = parser->astBuilder->create<VarExpr>();
-- 
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