[src/trunk]: src/usr.bin/xlint/lint1 lint: proof-read the C grammar, remove u...

[rillig <rillig%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/93fef2cf853c
branches:  trunk
changeset: 984199:93fef2cf853c
user:      rillig <rillig%NetBSD.org@localhost>
date:      Sun Jun 27 18:03:05 2021 +0000

description:
lint: proof-read the C grammar, remove unnecessary %type

After the fix from the previous commit (a missing assignment to $$ in an
error case), make sure that there are no other bugs of the same kind, by
manually checking that each rule with a %type assigns $$ in each and
every case.  There is one more instance in block_item_list, but that
does not lead to a crash since it affects only a boolean variable, not a
pointer.

It should not be necessary to check for this class of bugs manually, but
neither BSD yacc nor GNU Bison provide any warning option to help with
this scenario.  They should have remarked that the %type for
type_attribute is never used, since that is easy to detect.  They should
have also warned that the rule for block_item_list does not mention $$
at all.

Detecting the bug from the previous commit would probably be too much to
ask since it involves control flow analysis in the C code.  In this
particular case, it would have been necessary to visit each possible
branch from the 'if' statement and ensure that there is a $$ on the
left-hand side of an assignment.

While here, note down several small inconsistencies in the grammar that
should be fixed in follow-up commits.

diffstat:

 usr.bin/xlint/lint1/cgram.y |  28 +++++++++++++++++++++++-----
 1 files changed, 23 insertions(+), 5 deletions(-)

diffs (145 lines):

diff -r ce9eed0ab4b2 -r 93fef2cf853c usr.bin/xlint/lint1/cgram.y
--- a/usr.bin/xlint/lint1/cgram.y       Sun Jun 27 16:24:52 2021 +0000
+++ b/usr.bin/xlint/lint1/cgram.y       Sun Jun 27 18:03:05 2021 +0000
@@ -1,5 +1,5 @@
 %{
-/* $NetBSD: cgram.y,v 1.232 2021/06/27 13:59:29 rillig Exp $ */
+/* $NetBSD: cgram.y,v 1.233 2021/06/27 18:03:05 rillig Exp $ */
 
 /*
  * Copyright (c) 1996 Christopher G. Demetriou.  All Rights Reserved.
@@ -35,7 +35,7 @@
 
 #include <sys/cdefs.h>
 #if defined(__RCSID) && !defined(lint)
-__RCSID("$NetBSD: cgram.y,v 1.232 2021/06/27 13:59:29 rillig Exp $");
+__RCSID("$NetBSD: cgram.y,v 1.233 2021/06/27 18:03:05 rillig Exp $");
 #endif
 
 #include <limits.h>
@@ -284,7 +284,6 @@
 %type  <y_type>        notype_typespec
 %type  <y_type>        struct_spec
 %type  <y_type>        enum_spec
-%type  <y_type>        type_attribute
 %type  <y_sym>         struct_tag
 %type  <y_sym>         enum_tag
 %type  <y_tspec>       struct
@@ -1072,6 +1071,7 @@
          }
        ;
 
+/* TODO: move below type_decl */
 notype_direct_decl:
          T_NAME {
                $$ = declarator_name(getsym($1));
@@ -1094,6 +1094,7 @@
                block_level--;
          }
        | notype_direct_decl type_attribute_list
+/* TODO: either add { $$ = $1 } everywhere or remove it everywhere. */
        ;
 
 type_decl:
@@ -1105,6 +1106,10 @@
          }
        ;
 
+/*
+ * TODO: document whether T_NAME here vs. identifier in notype_direct_decl
+ *  is on purpose.
+ */
 type_direct_decl:
          identifier {
                $$ = declarator_name(getsym($1));
@@ -1145,6 +1150,7 @@
          }
        ;
 
+/* TODO: consistently use 'opt' either as prefix or as suffix */
 opt_type_qualifier_list:
          /* empty */
        | type_qualifier_list
@@ -1216,11 +1222,14 @@
          }
        ;
 
+/* TODO: rename 'pointer' to something less ambiguous, maybe 'pointer_level' */
 pointer:
          asterisk {
                $$ = $1;
          }
        | asterisk type_qualifier_list {
+               /* TODO: rename pqinf_t to be more expressive */
+               /* TODO: then rename the merge function */
                $$ = merge_pointers_and_qualifiers($1, $2);
          }
        | asterisk pointer {
@@ -1239,6 +1248,7 @@
          }
        ;
 
+/* TODO: try whether type_qualifier_list_opt makes the code simpler */
 type_qualifier_list:
          type_qualifier {
                $$ = $1;
@@ -1434,6 +1444,7 @@
        | designator_list designator
        ;
 
+/* TODO: order from big to small */
 designation:                   /* C99 6.7.8 "Initialization" */
          designator_list T_ASSIGN
        | identifier T_COLON {
@@ -1479,6 +1490,7 @@
          }
        ;
 
+/* TODO: abstract_declaration and abstract_decl sound too similar */
 abstract_decl:
          pointer {
                $$ = add_pointer(abstract_name(), $1);
@@ -1596,6 +1608,7 @@
                if (!Sflag && $1 && !$2)
                        /* declarations after statements is a C99 feature */
                        c99ism(327);
+               /* TODO: $$ = $1 || $2; */
        }
        ;
 
@@ -1666,6 +1679,7 @@
          }
        ;
 
+/* TODO: rename to generic-association, as in C11 6.5.1.1 */
 association:
          type_name T_COLON expr
        | T_DEFAULT T_COLON expr
@@ -1676,13 +1690,17 @@
        | association_list T_COMMA association
        ;
 
+/* TODO: sort from big to small, as in C11 6.5.1.1 */
+/* TODO: rename to generic_expression, as in C11 6.5.1.1 */
+/* TODO: C11 6.5.1.1 says "assignment-expression", not plain "expr". */
+/* TODO: c11ism */
 generic_expr:
          T_GENERIC T_LPAREN expr T_COMMA association_list T_RPAREN {
                $$ = $3;
          }
        ;
 
-do_statement:
+do_statement:                  /* C99 6.8.5 */
          do statement {
                clear_warning_flags();
          }
@@ -2040,7 +2058,7 @@
                        expr($1, false, false, false, false);
                        seen_fallthrough = false;
                }
-       }
+         }
        ;
 
 string: