From 6f9083050fd2aa04490cdd5fb6e52120fb3e74f8 Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Tue, 11 Dec 2018 20:00:49 +0900 Subject: [PATCH 1/1] 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. Signed-off-by: Masahiro Yamada Signed-off-by: Christian Lamparter --- config/zconf.l | 21 +++++++++++++++++++++ config/zconf.y | 18 +++--------------- 2 files changed, 24 insertions(+), 15 deletions(-) diff --git a/config/zconf.l b/config/zconf.l index 323fb55..bbbef0c 100644 --- a/config/zconf.l +++ b/config/zconf.l @@ -16,6 +16,8 @@ #include "lkc.h" +#define YY_DECL static int yylex1(void) + #define START_STRSIZE 16 static struct { @@ -23,6 +25,7 @@ static struct { int lineno; } current_pos; +static int prev_token = T_EOL; static char *text; static int text_size, text_asize; @@ -268,6 +271,24 @@ n [A-Za-z0-9_-] } %% + +/* second stage lexer */ +int yylex(void) +{ + int token; + +repeat: + token = yylex1(); + + /* Do not pass unneeded T_EOL to the parser. */ + if ((prev_token == T_EOL || prev_token == T_HELPTEXT) && token == T_EOL) + goto repeat; + + prev_token = token; + + return token; +} + static char *expand_token(const char *in, size_t n) { char *out; diff --git a/config/zconf.y b/config/zconf.y index 4aa5ad8..be5d689 100644 --- a/config/zconf.y +++ b/config/zconf.y @@ -31,7 +31,7 @@ struct symbol *symbol_hash[SYMBOL_HASHSIZE]; static struct menu *current_menu, *current_entry; %} -%expect 29 +%expect 21 %union { @@ -111,9 +111,7 @@ static struct menu *current_menu, *current_entry; %} %% -input: nl start | start; - -start: mainmenu_stmt stmt_list | stmt_list; +input: mainmenu_stmt stmt_list | stmt_list; /* mainmenu entry */ @@ -141,8 +139,7 @@ option_name: ; common_stmt: - T_EOL - | if_stmt + if_stmt | comment_stmt | config_stmt | menuconfig_stmt @@ -193,7 +190,6 @@ config_option_list: | config_option_list depends | config_option_list help | config_option_list option_error - | config_option_list T_EOL ; config_option: T_TYPE prompt_stmt_opt T_EOL @@ -293,7 +289,6 @@ choice_option_list: | choice_option_list choice_option | choice_option_list depends | choice_option_list help - | choice_option_list T_EOL | choice_option_list option_error ; @@ -443,7 +438,6 @@ help: help_start T_HELPTEXT depends_list: /* empty */ | depends_list depends - | depends_list T_EOL | depends_list option_error ; @@ -458,7 +452,6 @@ depends: T_DEPENDS T_ON expr T_EOL visibility_list: /* empty */ | visibility_list visible - | visibility_list T_EOL ; visible: T_VISIBLE if_expr T_EOL @@ -484,11 +477,6 @@ end: T_ENDMENU T_EOL { $$ = $1; } | T_ENDIF T_EOL { $$ = $1; } ; -nl: - T_EOL - | nl T_EOL -; - if_expr: /* empty */ { $$ = NULL; } | T_IF expr { $$ = $2; } ; -- 2.31.1