Implement 'character' literals (#1747)

man/rgbasm.5

@@ -280,7 +280,7 @@ There are a number of numeric formats.
 .It Binary Ta Li % , 0b , 0B Ta 01
 .It Fixed-point Ta none Ta 01234.56789
 .It Precise fixed-point Ta none Ta 12.34q8
-.It Character constant Ta none Ta \(dqABYZ\(dq
+.It Character constant Ta none Ta 'ABYZ'
 .It Game Boy graphics Ta Li \` Ta 0123
 .El
 .Pp
@@ -293,11 +293,14 @@ or
 The "character constant" form yields the value the character maps to in the current charmap.
 For example, by default
 .Pq refer to Xr ascii 7
-.Sq \(dqA\(dq
+.Sq 'A'
 yields 65.
+A character constant must represent a single value, so it cannot include multiple characters, or characters which map to multiple values.
 See
 .Sx Character maps
-for information on charmaps.
+for information on charmaps, and
+.Sx String expressions
+for information on escape characters allowed in character constants.
 .Pp
 The last one, Game Boy graphics, is quite interesting and useful.
 After the backtick, 8 digits between 0 and 3 are expected, corresponding to pixel values.
@@ -538,7 +541,8 @@ There are a number of escape sequences you can use within a string:
 .Bl -column -offset indent "Sequence"
 .It Sy Sequence Ta Sy Meaning
 .It Ql \e\e Ta Backslash Pq escapes the escape character itself
-.It Ql \e" Ta Double quote Pq does not terminate the string
+.It Ql \e" Ta Double quote Pq does not terminate a string
+.It Ql \e' Ta Single quote Pq does not terminate a character literal
 .It Ql \e{ Ta Open curly brace Pq does not start interpolation
 .It Ql \e} Ta Close curly brace Pq does not end interpolation
 .It Ql \en Ta Newline Pq ASCII $0A

src/asm/lexer.cpp

@@ -1428,6 +1428,7 @@ static void appendExpandedString(std::string &str, std::string const &expanded)
 			break;
 		case '\\':
 		case '"':
+		case '\'':
 		case '{':
 			str += '\\';
 			[[fallthrough]];
@@ -1448,6 +1449,7 @@ static void appendCharInLiteral(std::string &str, int c) {
 		// Character escape
 		case '\\':
 		case '"':
+		case '\'':
 		case '{':
 		case '}':
 			if (rawMode) {
@@ -1518,7 +1520,7 @@ static void appendCharInLiteral(std::string &str, int c) {
 		break;
 
 	case '{': // Symbol interpolation
-		// We'll be exiting the string scope, so re-enable expansions
+		// We'll be exiting the string/character scope, so re-enable expansions
 		// (Not interpolations, since they're handled by the function itself...)
 		lexerState->disableMacroArgs = false;
 		if (auto interpolation = readInterpolation(0); interpolation) {
@@ -1614,6 +1616,42 @@ static void readString(std::string &str, bool rawString) {
 	}
 }
 
+static void readCharacter(std::string &str) {
+	// This is essentially a simplified `readString`
+	Defer reenableExpansions = scopedDisableExpansions();
+
+	bool rawMode = lexerState->mode == LEXER_RAW;
+
+	// We reach this function after reading a single quote
+	if (rawMode) {
+		str += '\'';
+	}
+
+	for (;;) {
+		int c = peek();
+
+		// '\r', '\n' or EOF ends a character early
+		if (c == EOF || c == '\r' || c == '\n') {
+			error("Unterminated character");
+			return;
+		}
+
+		// We'll be staying in the character, so we can safely consume the char
+		shiftChar();
+
+		// Close the character and return if it's terminated
+		if (c == '\'') {
+			if (rawMode) {
+				str += c;
+			}
+			return;
+		}
+
+		// Append the character or handle special ones
+		appendCharInLiteral(str, c);
+	}
+}
+
 // Lexer core
 
 static Token yylex_SKIP_TO_ENDC(); // forward declaration for yylex_NORMAL
@@ -1896,7 +1934,7 @@ static Token yylex_NORMAL() {
 		case '`': // Gfx constant
 			return Token(T_(NUMBER), readGfxConstant());
 
-			// Handle strings
+			// Handle string and character literals
 
 		case '"': {
 			std::string str;
@@ -1904,6 +1942,12 @@ static Token yylex_NORMAL() {
 			return Token(T_(STRING), str);
 		}
 
+		case '\'': {
+			std::string chr;
+			readCharacter(chr);
+			return Token(T_(CHARACTER), chr);
+		}
+
 			// Handle newlines and EOF
 
 		case '\r':
@@ -2036,6 +2080,11 @@ static Token yylex_RAW() {
 			readString(str, false);
 			break;
 
+		case '\'': // Character literals inside macro args
+			shiftChar();
+			readCharacter(str);
+			break;
+
 		case '#': // Raw string literals inside macro args
 			str += c;
 			shiftChar();
@@ -2093,6 +2142,7 @@ backslash:
 			case ')':
 			case '\\': // Escapes shared with string literals
 			case '"':
+			case '\'':
 			case '{':
 			case '}':
 				break;

src/asm/parser.y

@@ -339,6 +339,7 @@
 // Literals
 %token <int32_t> NUMBER "number"
 %token <std::string> STRING "string"
+%token <std::string> CHARACTER "character"
 %token <std::string> SYMBOL "symbol"
 %token <std::string> LABEL "label"
 %token <std::string> LOCAL "local label"
@@ -1415,6 +1416,15 @@ relocexpr_no_str:
 	NUMBER {
 		$$.makeNumber($1);
 	}
+	| CHARACTER {
+		std::vector<int32_t> output = charmap_Convert($1);
+		if (output.size() == 1) {
+			$$.makeNumber(static_cast<uint32_t>(output[0]));
+		} else {
+			::error("Character literals must be a single charmap unit");
+			$$.makeNumber(0);
+		}
+	}
 	| OP_LOGICNOT relocexpr %prec NEG {
 		$$.makeUnaryOp(RPN_LOGNOT, std::move($2));
 	}

src/link/script.y

@@ -293,7 +293,7 @@ yy::parser::symbol_type yylex() {
 					c = '\r';
 				} else if (c == 't') {
 					c = '\t';
-				} else if (c != '\\' && c != '"') {
+				} else if (c != '\\' && c != '"' && c != '\'') {
 					scriptError(context, "Cannot escape character %s", printChar(c));
 				}
 				context.file.sbumpc();

test/asm/character-literals.asm

@@ -0,0 +1,34 @@
+def s equs "d"
+
+charmap "A", 1
+charmap "B", 2
+charmap "c{s}e", 3
+charmap "F", 4, 5, 6
+charmap "'", 42
+charmap "\"", 1234
+charmap "\n\r\t\0", 1337
+charmap "',\",\\", 99
+
+MACRO char
+	assert (\1) == (\2)
+ENDM
+
+char 'A', 1
+char 'B', 2
+char 'c{s}e', 3
+char '\'', 42
+char '"', 1234
+char '\n\r\t\0', 1337
+char '\',",\\', 99
+
+char charval("c{s}e", 0), 'c{s}e'
+
+def v equs "\n\r\t\0"
+def x = '{v}'
+char x, '\n\r\t\0'
+
+; errors
+char '?', $3f ; ASCII
+char 'F', 0
+char 'ABF', 0
+char '\n\r\t', 0

test/asm/character-literals.err

@@ -0,0 +1,15 @@
+warning: character-literals.asm(31) -> character-literals.asm::char(13): [-Wunmapped-char]
+    Unmapped character '?'
+error: character-literals.asm(32) -> character-literals.asm::char(13):
+    Character literals must be a single charmap unit
+error: character-literals.asm(33) -> character-literals.asm::char(13):
+    Character literals must be a single charmap unit
+warning: character-literals.asm(34) -> character-literals.asm::char(13): [-Wunmapped-char]
+    Unmapped character '\n'
+warning: character-literals.asm(34) -> character-literals.asm::char(13): [-Wunmapped-char]
+    Unmapped character '\r'
+warning: character-literals.asm(34) -> character-literals.asm::char(13): [-Wunmapped-char]
+    Unmapped character '\t'
+error: character-literals.asm(34) -> character-literals.asm::char(13):
+    Character literals must be a single charmap unit
+Assembly aborted with 3 errors!

test/asm/garbage_sequence.asm

@@ -1,3 +1,3 @@
 assert 1 +# 1 == 2
-assert 2 '?* 2 == 4
+assert 2 ?<EFBFBD>* 2 == 4
-assert 3 **?''?##?? 3 == 27
+assert 3 **?<EFBFBD>?##?? 3 == 27

test/asm/garbage_sequence.err

@@ -1,9 +1,9 @@
 error: garbage_sequence.asm(1):
     Unknown character '#'
 error: garbage_sequence.asm(2):
-    Unknown characters ''', '?'
+    Unknown characters '?', 0xFF
 error: garbage_sequence.asm(3):
-    Unknown characters '?', ''', ''', '?'
+    Unknown characters '?', 0xFF, '?'
 error: garbage_sequence.asm(3):
     Unknown character '#'
 error: garbage_sequence.asm(3):