[src/trunk]: src/usr.bin/xlint/lint1 lint: warn about unreachable null statem...

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

details:   https://anonhg.NetBSD.org/src/rev/9a5527c848fb
branches:  trunk
changeset: 359667:9a5527c848fb
user:      rillig <rillig%NetBSD.org@localhost>
date:      Sat Jan 15 23:21:34 2022 +0000

description:
lint: warn about unreachable null statements

This warning flags the second semicolon of 'return;;' as being
unreachable.  It does not warn about these superfluous semicolons in
general though.

Seen in usr.bin/make/bmake_malloc.c.

diffstat:

 tests/usr.bin/xlint/lint1/msg_193.c   |  27 +++++++++++++++++++++------
 tests/usr.bin/xlint/lint1/msg_193.exp |   1 +
 tests/usr.bin/xlint/lint1/msg_249.c   |   3 ++-
 tests/usr.bin/xlint/lint1/msg_249.exp |   5 +++--
 usr.bin/xlint/lint1/cgram.y           |   5 +++--
 5 files changed, 30 insertions(+), 11 deletions(-)

diffs (105 lines):

diff -r 10a7e9970621 -r 9a5527c848fb tests/usr.bin/xlint/lint1/msg_193.c
--- a/tests/usr.bin/xlint/lint1/msg_193.c       Sat Jan 15 22:18:04 2022 +0000
+++ b/tests/usr.bin/xlint/lint1/msg_193.c       Sat Jan 15 23:21:34 2022 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: msg_193.c,v 1.15 2022/01/15 22:12:35 rillig Exp $      */
+/*     $NetBSD: msg_193.c,v 1.16 2022/01/15 23:21:34 rillig Exp $      */
 # 3 "msg_193.c"
 
 // Test for message: statement not reached [193]
@@ -658,12 +658,27 @@
 }
 
 /*
- * Since at least 2002, lint does not detect a double semicolon.  See
- * cgram.y, expression_statement, T_SEMI.
+ * Since at least 2002 and before cgram.y 1.379 from 2022-01-16, lint did not
+ * detect a double semicolon.  See cgram.y, expression_statement, T_SEMI.
  */
 int
-test_empty_statement(int x)
+test_null_statement(void)
 {
-       /* TODO: expect+1: warning: statement not reachable [193] */
-       return x > 0 ? x : -x;;
+       /*
+        * The following 2 semicolons are superfluous but lint doesn't warn
+        * about them.  Probably it should.  A null statement as part of a
+        * block-list has no use.
+        */
+       ;;
+
+       /*
+        * A stand-alone null statement, on the other hand, has its purpose.
+        * Without it, the 'for' loop would not be complete.  The NetBSD
+        * style is to use 'continue;' instead of a simple ';'.
+        */
+       for (int i = 0; i < 10; i++)
+               ;
+
+       /* expect+1: warning: statement not reached [193] */
+       return 0;;
 }
diff -r 10a7e9970621 -r 9a5527c848fb tests/usr.bin/xlint/lint1/msg_193.exp
--- a/tests/usr.bin/xlint/lint1/msg_193.exp     Sat Jan 15 22:18:04 2022 +0000
+++ b/tests/usr.bin/xlint/lint1/msg_193.exp     Sat Jan 15 23:21:34 2022 +0000
@@ -87,3 +87,4 @@
 msg_193.c(606): warning: statement not reached [193]
 msg_193.c(627): warning: statement not reached [193]
 msg_193.c(655): warning: statement not reached [193]
+msg_193.c(683): warning: statement not reached [193]
diff -r 10a7e9970621 -r 9a5527c848fb tests/usr.bin/xlint/lint1/msg_249.c
--- a/tests/usr.bin/xlint/lint1/msg_249.c       Sat Jan 15 22:18:04 2022 +0000
+++ b/tests/usr.bin/xlint/lint1/msg_249.c       Sat Jan 15 23:21:34 2022 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: msg_249.c,v 1.8 2021/07/10 17:35:54 rillig Exp $       */
+/*     $NetBSD: msg_249.c,v 1.9 2022/01/15 23:21:34 rillig Exp $       */
 # 3 "msg_249.c"
 
 // Test for message: syntax error '%s' [249]
@@ -28,6 +28,7 @@
 void
 function(void)
 {
+       /* expect+2: warning: statement not reached [193] */
        if (0)
                ;
        );                      /* expect: syntax error ')' */
diff -r 10a7e9970621 -r 9a5527c848fb tests/usr.bin/xlint/lint1/msg_249.exp
--- a/tests/usr.bin/xlint/lint1/msg_249.exp     Sat Jan 15 22:18:04 2022 +0000
+++ b/tests/usr.bin/xlint/lint1/msg_249.exp     Sat Jan 15 23:21:34 2022 +0000
@@ -1,4 +1,5 @@
 msg_249.c(10): error: syntax error '"' [249]
 msg_249.c(19): error: syntax error '"' [249]
-msg_249.c(33): error: syntax error ')' [249]
-msg_249.c(58): error: syntax error 'member without type' [249]
+msg_249.c(33): warning: statement not reached [193]
+msg_249.c(34): error: syntax error ')' [249]
+msg_249.c(59): error: syntax error 'member without type' [249]
diff -r 10a7e9970621 -r 9a5527c848fb usr.bin/xlint/lint1/cgram.y
--- a/usr.bin/xlint/lint1/cgram.y       Sat Jan 15 22:18:04 2022 +0000
+++ b/usr.bin/xlint/lint1/cgram.y       Sat Jan 15 23:21:34 2022 +0000
@@ -1,5 +1,5 @@
 %{
-/* $NetBSD: cgram.y,v 1.378 2021/12/26 18:16:41 christos Exp $ */
+/* $NetBSD: cgram.y,v 1.379 2022/01/15 23:21:34 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 1.378 2021/12/26 18:16:41 christos Exp $");
+__RCSID("$NetBSD: cgram.y,v 1.379 2022/01/15 23:21:34 rillig Exp $");
 #endif
 
 #include <limits.h>
@@ -1731,6 +1731,7 @@
                seen_fallthrough = false;
          }
        | T_SEMI {
+               check_statement_reachable();
                seen_fallthrough = false;
          }
        ;