[imcc] document .lex "" limitation. add -d2 for MKCONST

Handle GH #1095 .lex corner cases with double-quotes.
Do not use it until refactored.

Add a new -d2 flag to print mk_const strings, useful to find
about quoting and escaping, or not. Was used for LEXER some years ago.

ChangeLog

@@ -1,9 +1,11 @@
 2014-11-18    release 6.10.0
     - Core
+      + Add imcc -d2 flag for MKCONST tracing.
     - Build
       + Set -mabi=64 for gcc --m=64 on mips, -m64 on powerpc #1110
       + Add --{en,dis}able-static #1104
     - Documentation
+      + Document .lex "" limitations
     - Tests
     - Community
 

compilers/imcc/debug.h

@@ -7,8 +7,7 @@
 
 
 #define DEBUG_PARROT 0x0001
-/* unused:
-#define DEBUG_LEXER  0x0002 */
+#define DEBUG_MKCONST 0x0002 /* was DEBUG_LEXER */
 #define DEBUG_PARSER 0x0004
 #define DEBUG_IMC    0x0008
 #define DEBUG_CFG    0x0010

compilers/imcc/imcc.y

@@ -495,6 +495,8 @@ mk_pmc_const_named(ARGMOD(imc_info_t *imcc), ARGMOD(IMC_Unit *unit),
         const_name = mem_sys_strdup(constant);
     }
 
+    /* That that an empty name here, like .const '' $Pxx = "constant"
+       can only be a Sub. name_length = 0 matches all */
     if ((strncmp(unquoted_name, "Sub",       name_length) == 0)
     ||  (strncmp(unquoted_name, "Coroutine", name_length) == 0)) {
         rhs = mk_const(imcc, const_name, 'p');
@@ -865,6 +867,7 @@ set_lexical(ARGMOD(imc_info_t *imcc), ARGMOD(SymReg *r), ARGMOD(SymReg *name))
 
     r->usage |= U_LEXICAL;
 
+    IMCC_debug(imcc, DEBUG_MKCONST, "#    .lex '%s'\n", name->name);
     if (name == r->reg)
         IMCC_fataly(imcc, EXCEPTION_SYNTAX_ERROR,
             "register %s already declared as lexical %s", r->name, name->name);