kconfig: fix ambiguous grammar in terms of new lines

This commit decreases 8 shift/reduce conflicts. A certain amount of grammatical ambiguity comes from how to reduce excessive T_EOL tokens. Let's take a look at the example code below: 1 config A 2 bool "a" 3 4 depends on B 5 6 config B 7 def_bool y The line 3 is melt into "config_option_list", but the line 5 can be either a part of "config_option_list" or "common_stmt" by itself. Currently, the lexer converts '\n' to T_EOL verbatim. In Kconfig, a new line works as a statement terminator, but new lines in empty lines are not critical since empty lines (or lines that contain only whitespaces/comments) are just no-op. If the lexer simply discards no-op lines, the parser will not be bothered by excessive T_EOL tokens. Of course, this means we are shifting the complexity from the parser to the lexer, but it is much easier than tackling on shift/reduce conflicts. I introduced the second stage lexer to tweak the behavior. Discard T_EOL if the previous token is T_EOL or T_HELPTEXT. Two T_EOL tokens in a row is meaningless. T_HELPTEXT is a special token that is reduced without T_EOL.

Masahiro Yamada committed 7 years ago

Commit cc66bca1 parent 21c5ecf2 files · +24 −15Browse files

Showing the changes to scripts (2 of 2 files). Show all

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2 files

scripts/kconfig/zconf.l +21 −0
scripts/kconfig/zconf.y +3 −15

scripts/kconfig/zconf.l+21−0

@@ -16,6 +16,8 @@ · 15 unmodified lines
16	16
17	17	#include "lkc.h"
18	18
	19	+#define YY_DECL static int yylex1(void)
	20	+
19	21	#define START_STRSIZE 16
20	22
21	23	static struct {
@@ -23,6 +25,7 @@ static struct { · 1 unmodified line
23	25	int lineno;
24	26	} current_pos;
25	27
	28	+static int prev_token = T_EOL;
26	29	static char *text;
27	30	static int text_size, text_asize;
28	31
@@ -268,6 +271,24 @@ n [A-Za-z0-9_-] · 239 unmodified lines
268	271	}
269	272
270	273	%%
	274	+
	275	+/* second stage lexer */
	276	+int yylex(void)
	277	+{
	278	+ int token;
	279	+
	280	+repeat:
	281	+ token = yylex1();
	282	+
	283	+ /* Do not pass unneeded T_EOL to the parser. */
	284	+ if ((prev_token == T_EOL \|\| prev_token == T_HELPTEXT) && token == T_EOL)
	285	+ goto repeat;
	286	+
	287	+ prev_token = token;
	288	+
	289	+ return token;
	290	+}
	291	+
271	292	static char expand_token(const char in, size_t n)
272	293	{
273	294	char *out;

scripts/kconfig/zconf.y+3−15

@@ -31,7 +31,7 @@ struct symbol *symbol_hash[SYMBOL_HASHSIZE]; · 30 unmodified lines
31	31	static struct menu current_menu, current_entry;
32	32
33	33	%}
34		−%expect 29
	34	+%expect 21
35	35
36	36	%union
37	37	{
@@ -111,9 +111,7 @@ static struct menu current_menu, current_entry; · 73 unmodified lines
111	111	%}
112	112
113	113	%%
114		−input: nl start \| start;
115		−
116		−start: mainmenu_stmt stmt_list \| stmt_list;
	114	+input: mainmenu_stmt stmt_list \| stmt_list;
117	115
118	116	/* mainmenu entry */
119	117
@@ -141,8 +139,7 @@ option_name: · 21 unmodified lines
141	139	;
142	140
143	141	common_stmt:
144		− T_EOL
145		− \| if_stmt
	142	+ if_stmt
146	143	\| comment_stmt
147	144	\| config_stmt
148	145	\| menuconfig_stmt
@@ -193,7 +190,6 @@ config_option_list: · 44 unmodified lines
193	190	\| config_option_list depends
194	191	\| config_option_list help
195	192	\| config_option_list option_error
196		− \| config_option_list T_EOL
197	193	;
198	194
199	195	config_option: T_TYPE prompt_stmt_opt T_EOL
@@ -293,7 +289,6 @@ choice_option_list: · 93 unmodified lines
293	289	\| choice_option_list choice_option
294	290	\| choice_option_list depends
295	291	\| choice_option_list help
296		− \| choice_option_list T_EOL
297	292	\| choice_option_list option_error
298	293	;
299	294
@@ -443,7 +438,6 @@ help: help_start T_HELPTEXT · 143 unmodified lines
443	438	depends_list:
444	439	/* empty */
445	440	\| depends_list depends
446		− \| depends_list T_EOL
447	441	\| depends_list option_error
448	442	;
449	443
@@ -458,7 +452,6 @@ depends: T_DEPENDS T_ON expr T_EOL · 8 unmodified lines
458	452	visibility_list:
459	453	/* empty */
460	454	\| visibility_list visible
461		− \| visibility_list T_EOL
462	455	;
463	456
464	457	visible: T_VISIBLE if_expr T_EOL
@@ -484,11 +477,6 @@ end: T_ENDMENU T_EOL { $$ = $1; } · 19 unmodified lines
484	477	\| T_ENDIF T_EOL { $$ = $1; }
485	478	;
486	479
487		−nl:
488		− T_EOL
489		− \| nl T_EOL
490		−;
491		−
492	480	if_expr: /* empty */ { $$ = NULL; }
493	481	\| T_IF expr { $$ = $2; }
494	482	;