py: Add support for __debug__ constant.

__debug__ now resolves to True or False.  Its value needs to be set by
mp_set_debug().

TODO: call mp_set_debug in unix/ port.

TODO: optimise away "if False:" statements in compiler.

1 files changed, 19 insertions, 3 deletions

diff --git a/py/lexer.c b/py/lexer.c
index f736ef303..e2dfea78c 100644
--- a/py/lexer.c
+++ b/py/lexer.c
@@ -64,6 +64,13 @@ struct _mp_lexer_t {
     mp_token_t tok_cur;
 };
 
+// debug flag for __debug__ constant
+STATIC mp_token_kind_t mp_debug_value;
+
+void mp_set_debug(bool value) {
+    mp_debug_value = value ? MP_TOKEN_KW_TRUE : MP_TOKEN_KW_FALSE;
+}
+
 // TODO replace with a call to a standard function
 bool str_strn_equal(const char *str, const char *strn, int len) {
     uint i = 0;
@@ -303,7 +310,7 @@ STATIC const char *tok_kw[] = {
     "while",
     "with",
     "yield",
-    NULL,
+    "__debug__",
 };
 
 STATIC int hex_digit(unichar c) {
@@ -687,9 +694,18 @@ STATIC void mp_lexer_next_token_into(mp_lexer_t *lex, mp_token_t *tok, bool firs
 
     // check for keywords
     if (tok->kind == MP_TOKEN_NAME) {
-        for (int i = 0; tok_kw[i] != NULL; i++) {
+        // We check for __debug__ here and convert it to its value.  This is so
+        // the parser gives a syntax error on, eg, x.__debug__.  Otherwise, we
+        // need to check for this special token in many places in the compiler.
+        // TODO improve speed of these string comparisons
+        //for (int i = 0; tok_kw[i] != NULL; i++) {
+        for (int i = 0; i < ARRAY_SIZE(tok_kw); i++) {
             if (str_strn_equal(tok_kw[i], tok->str, tok->len)) {
-                tok->kind = MP_TOKEN_KW_FALSE + i;
+                if (i == ARRAY_SIZE(tok_kw) - 1) {
+                    tok->kind = mp_debug_value;
+                } else {
+                    tok->kind = MP_TOKEN_KW_FALSE + i;
+                }
                 break;
             }
         }