[src/trunk]: src/usr.bin/xlint/lint1 lint: fix wrong warning about main falli...

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

details:   https://anonhg.NetBSD.org/src/rev/750c8a56ab9a
branches:  trunk
changeset: 952918:750c8a56ab9a
user:      rillig <rillig%NetBSD.org@localhost>
date:      Sun Feb 21 09:17:55 2021 +0000

description:
lint: fix wrong warning about main falling off the bottom in C99 mode

This gets lint a small step closer to implementing C99.

diffstat:

 tests/usr.bin/xlint/lint1/d_cvt_constant.c   |   6 ++----
 tests/usr.bin/xlint/lint1/d_cvt_constant.exp |   1 -
 tests/usr.bin/xlint/lint1/msg_217.c          |  14 +++++++++++++-
 usr.bin/xlint/lint1/func.c                   |  26 +++++++++++++++++++-------
 4 files changed, 34 insertions(+), 13 deletions(-)

diffs (102 lines):

diff -r 6ad2a08a1851 -r 750c8a56ab9a tests/usr.bin/xlint/lint1/d_cvt_constant.c
--- a/tests/usr.bin/xlint/lint1/d_cvt_constant.c        Sun Feb 21 09:07:58 2021 +0000
+++ b/tests/usr.bin/xlint/lint1/d_cvt_constant.c        Sun Feb 21 09:17:55 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: d_cvt_constant.c,v 1.4 2021/02/21 09:07:58 rillig Exp $        */
+/*     $NetBSD: d_cvt_constant.c,v 1.5 2021/02/21 09:17:55 rillig Exp $        */
 # 3 "d_cvt_constant.c"
 
 /* the second assignment assumes failed before */
@@ -9,6 +9,4 @@
        int foo = 0;
        if (foo)
                x = 1;
-}                              /* expect: 217 */
-// FIXME: Since C99, main may fall off the bottom without returning a value.
-//  Therefore there should be no warning 217.
+}
diff -r 6ad2a08a1851 -r 750c8a56ab9a tests/usr.bin/xlint/lint1/d_cvt_constant.exp
--- a/tests/usr.bin/xlint/lint1/d_cvt_constant.exp      Sun Feb 21 09:07:58 2021 +0000
+++ b/tests/usr.bin/xlint/lint1/d_cvt_constant.exp      Sun Feb 21 09:17:55 2021 +0000
@@ -1,2 +1,1 @@
 d_cvt_constant.c(8): warning: x set but not used in function main [191]
-d_cvt_constant.c(12): warning: function main falls off bottom without returning value [217]
diff -r 6ad2a08a1851 -r 750c8a56ab9a tests/usr.bin/xlint/lint1/msg_217.c
--- a/tests/usr.bin/xlint/lint1/msg_217.c       Sun Feb 21 09:07:58 2021 +0000
+++ b/tests/usr.bin/xlint/lint1/msg_217.c       Sun Feb 21 09:17:55 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: msg_217.c,v 1.3 2021/01/31 13:33:10 rillig Exp $       */
+/*     $NetBSD: msg_217.c,v 1.4 2021/02/21 09:17:55 rillig Exp $       */
 # 3 "msg_217.c"
 
 // Test for message: function %s falls off bottom without returning value [217]
@@ -30,3 +30,15 @@
                return i;
        } while (/*CONSTCOND*/0);       /*FIXME*//* expect: 193 */
 }                                      /*FIXME*//* expect: 217 */
+
+/*
+ * C99 5.1.2.2.3 "Program termination" p1 defines that as a special exception,
+ * the function 'main' does not have to return a value, reaching the bottom
+ * is equivalent to returning 0.
+ *
+ * Before func.c 1.72 from 2021-02-21, lint had wrongly warned about this.
+ */
+int
+main(void)
+{
+}
diff -r 6ad2a08a1851 -r 750c8a56ab9a usr.bin/xlint/lint1/func.c
--- a/usr.bin/xlint/lint1/func.c        Sun Feb 21 09:07:58 2021 +0000
+++ b/usr.bin/xlint/lint1/func.c        Sun Feb 21 09:17:55 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: func.c,v 1.71 2021/02/19 22:27:49 rillig Exp $ */
+/*     $NetBSD: func.c,v 1.72 2021/02/21 09:17:55 rillig Exp $ */
 
 /*
  * Copyright (c) 1994, 1995 Jochen Pohl
@@ -37,7 +37,7 @@
 
 #include <sys/cdefs.h>
 #if defined(__RCSID) && !defined(lint)
-__RCSID("$NetBSD: func.c,v 1.71 2021/02/19 22:27:49 rillig Exp $");
+__RCSID("$NetBSD: func.c,v 1.72 2021/02/21 09:17:55 rillig Exp $");
 #endif
 
 #include <stdlib.h>
@@ -337,6 +337,22 @@
        reached = true;
 }
 
+static void
+check_missing_return_value(void)
+{
+       if (funcsym->s_type->t_subt->t_tspec == VOID)
+               return;
+       if (funcsym->s_return_type_implicit_int)
+               return;
+
+       /* C99 5.1.2.2.3 "Program termination" p1 */
+       if (Sflag && strcmp(funcsym->s_name, "main") == 0)
+               return;
+
+       /* function %s falls off bottom without returning value */
+       warning(217, funcsym->s_name);
+}
+
 /*
  * Called at the end of a function definition.
  */
@@ -348,11 +364,7 @@
 
        if (reached) {
                cstmt->c_had_return_noval = true;
-               if (funcsym->s_type->t_subt->t_tspec != VOID &&
-                   !funcsym->s_return_type_implicit_int) {
-                       /* func. %s falls off bottom without returning value */
-                       warning(217, funcsym->s_name);
-               }
+               check_missing_return_value();
        }
 
        /*