[src/trunk]: src/usr.bin/xlint/lint1 lint: explain why !finite(x) is not allo...

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

details:   https://anonhg.NetBSD.org/src/rev/be016a35c40f
branches:  trunk
changeset: 950281:be016a35c40f
user:      rillig <rillig%NetBSD.org@localhost>
date:      Sun Jan 24 07:58:48 2021 +0000

description:
lint: explain why !finite(x) is not allowed in strict bool mode

diffstat:

 tests/usr.bin/xlint/lint1/d_c99_bool_strict_syshdr.c   |  47 +++++++++++++++--
 tests/usr.bin/xlint/lint1/d_c99_bool_strict_syshdr.exp |   5 +-
 usr.bin/xlint/lint1/lex.c                              |   6 +-
 3 files changed, 46 insertions(+), 12 deletions(-)

diffs (105 lines):

diff -r f7ca05bf40e4 -r be016a35c40f tests/usr.bin/xlint/lint1/d_c99_bool_strict_syshdr.c
--- a/tests/usr.bin/xlint/lint1/d_c99_bool_strict_syshdr.c      Sun Jan 24 07:36:53 2021 +0000
+++ b/tests/usr.bin/xlint/lint1/d_c99_bool_strict_syshdr.c      Sun Jan 24 07:58:48 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: d_c99_bool_strict_syshdr.c,v 1.6 2021/01/23 23:11:40 rillig Exp $      */
+/*     $NetBSD: d_c99_bool_strict_syshdr.c,v 1.7 2021/01/24 07:58:48 rillig Exp $      */
 # 3 "d_c99_bool_strict_syshdr.c"
 
 /*
@@ -122,17 +122,50 @@
 }
 
 /*
- * If a function from a system header has return type int, which has
- * traditionally been used for the missing type bool, it may be used
- * in controlling expressions.
+ * There are several functions from system headers that have return type
+ * int.  For this return type there are many API conventions:
+ *
+ *     * isspace: 0 means no, non-zero means yes
+ *     * open: 0 means success, -1 means failure
+ *     * main: 0 means success, non-zero means failure
+ *     * strcmp: 0 means equal, < 0 means less than, > 0 means greater than
+ *
+ * Without a detailed list of individual functions, it's not possible to
+ * guess what the return value means.  Therefore in strict bool mode, the
+ * return value of these functions cannot be implicitly converted to bool,
+ * not even in a context where the result is compared to 0.  Allowing that
+ * would allow expressions like !strcmp(s1, s2), which is not correct since
+ * strcmp returns an "ordered comparison result", not a bool.
  */
 
 # 1 "math.h" 3 4
 extern int finite(double);
-# 133 "d_c99_bool_strict_syshdr.c"
+# 1 "string.h" 3 4
+extern int strcmp(const char *, const char *);
+# 146 "d_c99_bool_strict_syshdr.c"
+
+/*ARGSUSED*/
+_Bool
+call_finite_bad(double d)
+{
+       return finite(d);       /* expect: 211 */
+}
 
 _Bool
-call_finite(double d)          /*FIXME*//* expect: 231 */
+call_finite_good(double d)
+{
+       return finite(d) != 0;
+}
+
+/*ARGSUSED*/
+_Bool
+str_equal_bad(const char *s1, const char *s2)
 {
-       return finite(d);       /*FIXME*//* expect: 211 */
+       return !strcmp(s1, s2); /* expect: 330, 214 */
 }
+
+_Bool
+str_equal_good(const char *s1, const char *s2)
+{
+       return strcmp(s1, s2) == 0;
+}
diff -r f7ca05bf40e4 -r be016a35c40f tests/usr.bin/xlint/lint1/d_c99_bool_strict_syshdr.exp
--- a/tests/usr.bin/xlint/lint1/d_c99_bool_strict_syshdr.exp    Sun Jan 24 07:36:53 2021 +0000
+++ b/tests/usr.bin/xlint/lint1/d_c99_bool_strict_syshdr.exp    Sun Jan 24 07:58:48 2021 +0000
@@ -1,5 +1,6 @@
 d_c99_bool_strict_syshdr.c(32): controlling expression must be bool, not 'int' [333]
 d_c99_bool_strict_syshdr.c(42): controlling expression must be bool, not 'int' [333]
 d_c99_bool_strict_syshdr.c(76): operands of '=' have incompatible types (_Bool != int) [107]
-d_c99_bool_strict_syshdr.c(137): return value type mismatch (_Bool) and (int) [211]
-d_c99_bool_strict_syshdr.c(135): warning: argument d unused in function call_finite [231]
+d_c99_bool_strict_syshdr.c(151): return value type mismatch (_Bool) and (int) [211]
+d_c99_bool_strict_syshdr.c(164): operand of '!' must be bool, not 'int' [330]
+d_c99_bool_strict_syshdr.c(164): warning: function str_equal_bad expects to return value [214]
diff -r f7ca05bf40e4 -r be016a35c40f usr.bin/xlint/lint1/lex.c
--- a/usr.bin/xlint/lint1/lex.c Sun Jan 24 07:36:53 2021 +0000
+++ b/usr.bin/xlint/lint1/lex.c Sun Jan 24 07:58:48 2021 +0000
@@ -1,4 +1,4 @@
-/* $NetBSD: lex.c,v 1.4 2021/01/24 00:02:38 christos Exp $ */
+/* $NetBSD: lex.c,v 1.5 2021/01/24 07:58:48 rillig Exp $ */
 
 /*
  * Copyright (c) 1996 Christopher G. Demetriou.  All Rights Reserved.
@@ -38,7 +38,7 @@
 
 #include <sys/cdefs.h>
 #if defined(__RCSID) && !defined(lint)
-__RCSID("$NetBSD: lex.c,v 1.4 2021/01/24 00:02:38 christos Exp $");
+__RCSID("$NetBSD: lex.c,v 1.5 2021/01/24 07:58:48 rillig Exp $");
 #endif
 
 #include <ctype.h>
@@ -770,7 +770,7 @@
 
        if (typ == FLOAT) {
                f = (float)d;
-               if (!finite(f)) {
+               if (finite(f) == 0) {
                        /* floating-point constant out of range */
                        warning(248);
                        f = f > 0 ? FLT_MAX : -FLT_MAX;