Avoid treating labels and macros differently in column 1 (#1515)

Fixes #1512

man/rgbasm.5

@@ -41,7 +41,6 @@ or
 Labels tie a name to a specific location within a section (see
 .Sx Labels
 below).
-They must come first in the line.
 .Pp
 Instructions are assembled into Game Boy opcodes.
 Multiple instructions on one line can be separated by double colons

src/asm/lexer.cpp

@@ -1849,7 +1849,19 @@ static Token yylex_NORMAL() {
 					}
 				}
 
-				if (token.type == T_(ID) && (lexerState->atLineStart || peek() == ':'))
+				// This is a "lexer hack"! We need it to distinguish between label definitions
+				// (which start with `LABEL`) and macro invocations (which start with `ID`).
+				//
+				// If we had one `IDENTIFIER` token, the parser would need to perform "lookahead"
+				// to determine which rule applies. But since macros need to enter "raw" mode to
+				// parse their arguments, which may not even be valid tokens in "normal" mode, we
+				// cannot use lookahead to check for the presence of a `COLON`.
+				//
+				// Instead, we have separate `ID` and `LABEL` tokens, lexing as a `LABEL` if a ':'
+				// character *immediately* follows the identifier. Thus, at the beginning of a line,
+				// "Label:" and "mac:" are treated as label definitions, but "Label :" and "mac :"
+				// are treated as macro invocations.
+				if (token.type == T_(ID) && peek() == ':')
 					token.type = T_(LABEL);
 
 				return token;

src/asm/parser.y

@@ -433,22 +433,6 @@ line:
 		fstk_StopRept();
 		yyerrok;
 	}
-	// Hint about unindented macros parsed as labels
-	| LABEL error {
-		lexer_SetMode(LEXER_NORMAL);
-		lexer_ToggleStringExpansion(true);
-	} endofline {
-		Symbol *macro = sym_FindExactSymbol($1);
-
-		if (macro && macro->type == SYM_MACRO)
-			fprintf(
-			    stderr,
-			    "    To invoke `%s` as a macro it must be indented\n",
-			    $1.c_str()
-			);
-		fstk_StopRept();
-		yyerrok;
-	}
 ;
 
 endofline: NEWLINE | EOB;

test/asm/lexer-hack.asm

@@ -0,0 +1,28 @@
+MACRO mac
+	println "got {d:_NARG} args: \#"
+ENDM
+
+; indented, these were always macro invocations
+	mac
+	mac ro
+	mac : ld a, 1
+
+; in column 1, we historically treated these as labels
+mac
+mac ro
+mac : ld b, 2
+
+SECTION "test", ROM0
+
+; a colon makes these into labels
+	Label1: ld c, 3
+Label2: ld d, 4
+
+; a macro invocation when already defined as a label
+	Label1 args
+; and a label definition when already defined as a macro
+mac: ld e, 5
+
+; the space before the colon matters!
+	undef :
+undef :

test/asm/lexer-hack.err

@@ -0,0 +1,9 @@
+error: lexer-hack.asm(22):
+    "Label1" is not a macro
+error: lexer-hack.asm(24):
+    'mac' already defined at lexer-hack.asm(1)
+error: lexer-hack.asm(27):
+    Macro "undef" not defined
+error: lexer-hack.asm(28):
+    Macro "undef" not defined
+error: Assembly aborted (4 errors)!

test/asm/lexer-hack.out

@@ -0,0 +1,6 @@
+got 0 args: 
+got 1 args: ro
+got 2 args: : ld a,1
+got 0 args: 
+got 1 args: ro
+got 2 args: : ld b,2

test/asm/syntax-error-after-syntax-error.asm

@@ -1,10 +1,11 @@
-MACRO mac
-	println "got {d:_NARG} args"
-ENDM
-	mac
-	mac 42
-notmac
-mac
-mac 42
-mac::
-mac ::
+def x = 1 ; so far so good...
+def n equ 2 + * / ^ 3 ; oops
+def s equs "no closing quote, lol
+section "test", rom0 ; good again
+ld a, 42 ; keep going...
+ld xor, ret ; oh no :(
+label1: ; yes...
+label2:: ; yes...
+label3::: ; no!
+halt stop abort ; please
+println "finally!"

test/asm/syntax-error-after-syntax-error.err

@@ -1,13 +1,11 @@
+error: syntax-error-after-syntax-error.asm(2):
+    syntax error, unexpected *
+error: syntax-error-after-syntax-error.asm(3):
+    Unterminated string
 error: syntax-error-after-syntax-error.asm(6):
-    syntax error, unexpected newline, expecting : or ::
-error: syntax-error-after-syntax-error.asm(7):
-    syntax error, unexpected newline, expecting : or ::
-    To invoke `mac` as a macro it must be indented
-error: syntax-error-after-syntax-error.asm(8):
-    syntax error, unexpected number, expecting : or ::
-    To invoke `mac` as a macro it must be indented
+    syntax error, unexpected xor
 error: syntax-error-after-syntax-error.asm(9):
-    'mac' already defined at syntax-error-after-syntax-error.asm(1)
+    syntax error, unexpected :
 error: syntax-error-after-syntax-error.asm(10):
-    'mac' already defined at syntax-error-after-syntax-error.asm(1)
+    syntax error, unexpected stop, expecting newline or end of buffer or ::
 error: Assembly aborted (5 errors)!

test/asm/syntax-error-after-syntax-error.out

@@ -1,2 +1 @@
-got 0 args
-got 1 args
+finally!