Implement . string constant for the current label scope (gbdev#1499)

include/asm/symbol.hpp

@@ -36,10 +36,11 @@ struct Symbol {
 	uint32_t fileLine;                  // Line where the symbol was defined
 
 	std::variant<
-	    int32_t,                     // If isNumeric()
-	    int32_t (*)(),               // If isNumeric() and has a callback
-	    ContentSpan,                 // For SYM_MACRO
-	    std::shared_ptr<std::string> // For SYM_EQUS
+	    int32_t,                           // If isNumeric()
+	    int32_t (*)(),                     // If isNumeric() via a callback
+	    ContentSpan,                       // For SYM_MACRO
+	    std::shared_ptr<std::string>,      // For SYM_EQUS
+	    std::shared_ptr<std::string> (*)() // For SYM_EQUS via a callback
 	    >
 	    data;
 

man/rgbasm.5

@@ -1526,6 +1526,7 @@ The following symbols are defined by the assembler:
 .Bl -column -offset indent "__ISO_8601_LOCAL__" "EQUS"
 .It Sy Name Ta Sy Type Ta Sy Contents
 .It Dv @ Ta Ic EQU Ta PC value (essentially, the current memory address)
+.It Dv . Ta Ic EQUS Ta The current global label scope
 .It Dv _RS Ta Ic = Ta _RS Counter
 .It Dv _NARG Ta Ic EQU Ta Number of arguments passed to macro, updated by Ic SHIFT
 .It Dv __DATE__ Ta Ic EQUS Ta Today's date

src/asm/lexer.cpp

@@ -327,8 +327,6 @@ static std::unordered_map<std::string, int, CaseInsensitive, CaseInsensitive> ke
     {"POPO",          T_(POP_POPO)         },
 
     {"OPT",           T_(POP_OPT)          },
-
-    {".",             T_(PERIOD)           },
 };
 
 static bool isWhitespace(int c) {
@@ -1173,6 +1171,10 @@ static Token readIdentifier(char firstChar, bool raw) {
 			return Token(search->second);
 	}
 
+	// Label scope `.` is the only nonlocal identifier that starts with a dot
+	if (identifier.find_first_not_of('.') == identifier.npos)
+		tokenType = T_(ID);
+
 	return Token(tokenType, identifier);
 }
 

src/asm/parser.y

@@ -107,7 +107,6 @@
 %token EOB "end of buffer"
 
 // General punctuation
-%token PERIOD "."
 %token COMMA ","
 %token COLON ":" DOUBLE_COLON "::"
 %token LBRACK "[" RBRACK "]"

src/asm/symbol.cpp

@@ -25,6 +25,7 @@ std::unordered_set<std::string> purgedSymbols;
 static Symbol const *labelScope = nullptr; // Current section's label scope
 static Symbol *PCSymbol;
 static Symbol *NARGSymbol;
+static Symbol *labelScopeSymbol;
 static Symbol *RSSymbol;
 static char savedTIME[256];
 static char savedDATE[256];
@@ -50,6 +51,14 @@ static int32_t NARGCallback() {
 	}
 }
 
+static std::shared_ptr<std::string> labelScopeCallback() {
+	if (!labelScope) {
+		error("\".\" has no value outside of a label scope\n");
+		return std::make_shared<std::string>("");
+	}
+	return std::make_shared<std::string>(labelScope->name);
+}
+
 static int32_t PCCallback() {
 	return sect_GetSymbolSection()->org + sect_GetSymbolOffset();
 }
@@ -78,7 +87,12 @@ ContentSpan const &Symbol::getMacro() const {
 }
 
 std::shared_ptr<std::string> Symbol::getEqus() const {
-	assume(std::holds_alternative<std::shared_ptr<std::string>>(data));
+	assume(
+	    std::holds_alternative<std::shared_ptr<std::string>>(data)
+	    || std::holds_alternative<std::shared_ptr<std::string> (*)()>(data)
+	);
+	if (auto *callback = std::get_if<std::shared_ptr<std::string> (*)()>(&data); callback)
+		return (*callback)();
 	return std::get<std::shared_ptr<std::string>>(data);
 }
 
@@ -126,9 +140,14 @@ static void redefinedError(Symbol const &sym) {
 	}
 }
 
+static void assumeAlreadyExpanded(std::string const &symName) {
+	// Either the symbol name is `Global.local` or entirely '.'s (for global scope `.`),
+	// but cannot be unqualified `.local`
+	assume(!symName.starts_with('.') || symName.find_first_not_of('.') == symName.npos);
+}
+
 static Symbol &createSymbol(std::string const &symName) {
-	// The symbol name should have been expanded already
-	assume(!symName.starts_with('.'));
+	assumeAlreadyExpanded(symName);
 
 	static uint32_t nextDefIndex = 0;
 
@@ -156,6 +175,10 @@ static bool isAutoScoped(std::string const &symName) {
 	if (dotPos == std::string::npos)
 		return false;
 
+	// Label scope `.` is the only nonlocal identifier that starts with a dot
+	if (dotPos == 0 && symName.find_first_not_of('.') == symName.npos)
+		return false;
+
 	// Check for nothing after the dot
 	if (dotPos == symName.length() - 1)
 		fatalerror("'%s' is a nonsensical reference to an empty local label\n", symName.c_str());
@@ -176,8 +199,7 @@ static bool isAutoScoped(std::string const &symName) {
 }
 
 Symbol *sym_FindExactSymbol(std::string const &symName) {
-	// The symbol name should have been expanded already
-	assume(!symName.starts_with('.'));
+	assumeAlreadyExpanded(symName);
 
 	auto search = symbols.find(symName);
 	return search != symbols.end() ? &search->second : nullptr;
@@ -198,6 +220,11 @@ Symbol *sym_FindScopedValidSymbol(std::string const &symName) {
 	if (sym == NARGSymbol && !fstk_GetCurrentMacroArgs()) {
 		return nullptr;
 	}
+	// `.` has no value outside of a label scope
+	if (sym == labelScopeSymbol && !labelScope) {
+		return nullptr;
+	}
+
 	return sym;
 }
 
@@ -231,8 +258,7 @@ void sym_Purge(std::string const &symName) {
 }
 
 bool sym_IsPurgedExact(std::string const &symName) {
-	// The symbol name should have been expanded already
-	assume(!symName.starts_with('.'));
+	assumeAlreadyExpanded(symName);
 
 	return purgedSymbols.find(symName) != purgedSymbols.end();
 }
@@ -391,8 +417,7 @@ Symbol *sym_AddVar(std::string const &symName, int32_t value) {
 }
 
 static Symbol *addLabel(std::string const &symName) {
-	// The symbol name should have been expanded already
-	assume(!symName.starts_with('.'));
+	assumeAlreadyExpanded(symName);
 
 	Symbol *sym = sym_FindExactSymbol(symName);
 
@@ -541,6 +566,11 @@ void sym_Init(time_t now) {
 	NARGSymbol->data = NARGCallback;
 	NARGSymbol->isBuiltin = true;
 
+	labelScopeSymbol = &createSymbol("."s);
+	labelScopeSymbol->type = SYM_EQUS;
+	labelScopeSymbol->data = labelScopeCallback;
+	labelScopeSymbol->isBuiltin = true;
+
 	RSSymbol = sym_AddVar("_RS"s, 0);
 	RSSymbol->isBuiltin = true;
 

test/asm/builtin-reserved.asm

@@ -11,5 +11,23 @@ REDEF _NARG = 78
 DEF _NARG EQUS "hello"
 REDEF _NARG EQUS "world"
 
-SECTION "test", ROM0
+SECTION "_NARG", ROM0
 _NARG:
+ENDSECTION
+
+ASSERT !DEF(.)
+
+PURGE .
+
+DEF . EQU 12
+REDEF . EQU 34
+
+DEF . = 56
+REDEF . = 78
+
+DEF . EQUS "hello"
+REDEF . EQUS "world"
+
+SECTION ".", ROM0
+.:
+ENDSECTION

test/asm/builtin-reserved.err

@@ -14,4 +14,20 @@ error: builtin-reserved.asm(12):
     '_NARG' is reserved for a built-in symbol
 error: builtin-reserved.asm(15):
     '_NARG' is reserved for a built-in symbol
-error: Assembly aborted (8 errors)!
+error: builtin-reserved.asm(20):
+    '.' not defined
+error: builtin-reserved.asm(22):
+    '.' is reserved for a built-in symbol
+error: builtin-reserved.asm(23):
+    '.' is reserved for a built-in symbol
+error: builtin-reserved.asm(25):
+    '.' is reserved for a built-in symbol
+error: builtin-reserved.asm(26):
+    '.' is reserved for a built-in symbol
+error: builtin-reserved.asm(28):
+    '.' is reserved for a built-in symbol
+error: builtin-reserved.asm(29):
+    '.' is reserved for a built-in symbol
+error: builtin-reserved.asm(32):
+    "." has no value outside of a label scope
+error: Assembly aborted (16 errors)!

test/asm/label-scope.asm

@@ -0,0 +1,12 @@
+ASSERT !DEF(@) && !DEF(.)
+
+PURGE @, .
+
+SECTION "test", ROM0[42]
+Foobar:
+
+PURGE @, .
+
+ASSERT DEF(@) && DEF(.) && DEF(Foobar)
+
+PRINTLN "PC: {#05X:@}; label scope: \"{.}\"; {.}: {#05X:{.}}"

test/asm/label-scope.err

@@ -0,0 +1,9 @@
+error: label-scope.asm(3):
+    '@' not defined
+error: label-scope.asm(3):
+    '.' not defined
+error: label-scope.asm(8):
+    Built-in symbol '@' cannot be purged
+error: label-scope.asm(8):
+    Built-in symbol '.' cannot be purged
+error: Assembly aborted (4 errors)!

test/asm/label-scope.out

@@ -0,0 +1 @@
+PC: $002A; label scope: "Foobar"; Foobar: $002A

test/asm/period.asm

@@ -2,4 +2,5 @@ section "period", rom0
 
 global1: db 1
 .local   db 2
-.        db 3
+.        db 3 ; this...
+global1  db 4 ; ...expands to this

test/asm/period.err

@@ -1,3 +1,5 @@
 error: period.asm(5):
-    syntax error, unexpected .
-error: Assembly aborted (1 error)!
+    syntax error, unexpected DB, expecting : or ::
+error: period.asm(6):
+    syntax error, unexpected DB, expecting : or ::
+error: Assembly aborted (2 errors)!

test/asm/undefined-builtins.asm

@@ -3,6 +3,11 @@ assert !DEF(@)
 println @
 println "{@}?"
 
+; not inside a label scope
+assert !DEF(.)
+println .
+println "{.}?"
+
 ; not inside a macro
 assert !DEF(_NARG)
 println _NARG
@@ -13,6 +18,11 @@ assert DEF(@)
 println @
 println "{@}!"
 
+LabelScope:
+assert DEF(.)
+println .
+println "{.}!"
+
 MACRO m
 	assert DEF(_NARG)
 	println _NARG

test/asm/undefined-builtins.err

@@ -3,7 +3,11 @@ error: undefined-builtins.asm(3):
 error: undefined-builtins.asm(4):
     Interpolated symbol "@" does not exist
 error: undefined-builtins.asm(8):
-    _NARG has no value outside of a macro
+    "." has no value outside of a label scope
 error: undefined-builtins.asm(9):
+    Interpolated symbol "." does not exist
+error: undefined-builtins.asm(13):
+    _NARG has no value outside of a macro
+error: undefined-builtins.asm(14):
     Interpolated symbol "_NARG" does not exist
-error: Assembly aborted (4 errors)!
+error: Assembly aborted (6 errors)!

test/asm/undefined-builtins.out

@@ -1,8 +1,12 @@
 $0
+?
+
 ?
 $0
 ?
 $42
 $42!
+$42
+LabelScope!
 $3
 $3!