[src/trunk]: src/usr.bin/xlint/lint1 lint: don't warn about cast between poin...

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

details:   https://anonhg.NetBSD.org/src/rev/a841cafe3be5
branches:  trunk
changeset: 982301:a841cafe3be5
user:      rillig <rillig%NetBSD.org@localhost>
date:      Thu Apr 08 19:20:54 2021 +0000

description:
lint: don't warn about cast between pointers to compatible structs

diffstat:

 tests/usr.bin/xlint/lint1/msg_247.c   |   7 +++++--
 tests/usr.bin/xlint/lint1/msg_247.exp |   1 -
 usr.bin/xlint/lint1/tree.c            |  21 ++++++++++++++++-----
 3 files changed, 21 insertions(+), 8 deletions(-)

diffs (72 lines):

diff -r d25aa5b1c6d4 -r a841cafe3be5 tests/usr.bin/xlint/lint1/msg_247.c
--- a/tests/usr.bin/xlint/lint1/msg_247.c       Thu Apr 08 19:08:17 2021 +0000
+++ b/tests/usr.bin/xlint/lint1/msg_247.c       Thu Apr 08 19:20:54 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: msg_247.c,v 1.9 2021/04/08 19:08:17 rillig Exp $       */
+/*     $NetBSD: msg_247.c,v 1.10 2021/04/08 19:20:54 rillig Exp $      */
 # 3 "msg_247.c"
 
 // Test for message: pointer cast from '%s' to '%s' may be troublesome [247]
@@ -112,7 +112,10 @@
 void
 counter_increment(struct counter *counter)
 {
-       /* expect+1: 247 */
+       /*
+        * Before tree.c 1.272 from 2021-04-08, lint warned about the cast
+        * from 'struct counter' to 'struct counter_impl'.
+        */
        struct counter_impl *impl = (struct counter_impl *)counter;
        impl->saved_count = impl->public_part.count;
        impl->public_part.count++;
diff -r d25aa5b1c6d4 -r a841cafe3be5 tests/usr.bin/xlint/lint1/msg_247.exp
--- a/tests/usr.bin/xlint/lint1/msg_247.exp     Thu Apr 08 19:08:17 2021 +0000
+++ b/tests/usr.bin/xlint/lint1/msg_247.exp     Thu Apr 08 19:20:54 2021 +0000
@@ -1,3 +1,2 @@
 msg_247.c(31): warning: pointer cast from 'pointer to struct Other' to 'pointer to struct <unnamed>' may be troublesome [247]
 msg_247.c(70): warning: pointer cast from 'pointer to struct Other' to 'pointer to signed char' may be troublesome [247]
-msg_247.c(116): warning: pointer cast from 'pointer to struct counter' to 'pointer to struct counter_impl' may be troublesome [247]
diff -r d25aa5b1c6d4 -r a841cafe3be5 usr.bin/xlint/lint1/tree.c
--- a/usr.bin/xlint/lint1/tree.c        Thu Apr 08 19:08:17 2021 +0000
+++ b/usr.bin/xlint/lint1/tree.c        Thu Apr 08 19:20:54 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: tree.c,v 1.271 2021/04/06 21:59:58 rillig Exp $        */
+/*     $NetBSD: tree.c,v 1.272 2021/04/08 19:20:54 rillig Exp $        */
 
 /*
  * Copyright (c) 1994, 1995 Jochen Pohl
@@ -37,7 +37,7 @@
 
 #include <sys/cdefs.h>
 #if defined(__RCSID) && !defined(lint)
-__RCSID("$NetBSD: tree.c,v 1.271 2021/04/06 21:59:58 rillig Exp $");
+__RCSID("$NetBSD: tree.c,v 1.272 2021/04/08 19:20:54 rillig Exp $");
 #endif
 
 #include <float.h>
@@ -2023,11 +2023,22 @@
 }
 
 static bool
-should_warn_about_pointer_cast(const type_t *tp, tspec_t nst,
-                              const tnode_t *tn, tspec_t ost)
+should_warn_about_pointer_cast(const type_t *ntp, tspec_t nst,
+                              const tnode_t *otn, tspec_t ost)
 {
+       /*
+        * Casting a pointer to 'struct S' to a pointer to another struct that
+        * has 'struct S' as its first member is ok, see msg_247.c, 'struct
+        * counter'.
+        */
+       if (nst == STRUCT && ost == STRUCT &&
+           ntp->t_subt->t_str->sou_first_member != NULL &&
+           ntp->t_subt->t_str->sou_first_member->s_type ==
+           otn->tn_type->t_subt)
+               return false;
+
        if (nst == STRUCT || nst == UNION)
-               if (tp->t_subt->t_str != tn->tn_type->t_subt->t_str)
+               if (ntp->t_subt->t_str != otn->tn_type->t_subt->t_str)
                        return true;
 
        if (nst == CHAR || nst == UCHAR)