New loplugin:classmemaccess

...to complement and improve upon GCC's -Wclass-memaccess.  See the comment at
the head of compilerplugins/clang/classmemaccess.cxx for details.  (It is not
yet clear to me whether we would want to get this upstreamed into Clang.)

35d21e4bf6f66b3bbc7a44fcf184cb721b524a94 "Remove redundant memsets" was a case
that benefited from looking through toplevel casts to void*.  (Though the code
in include/basic/sbxvar.hxx needs a slightly more verbose way to deliberately
silence the warning now.)

d03041e19215592f21ba1222d3cfa29e1f94260a "Drop bogus memsets" is one example of
various cases that GCC -Wclass-memaccess failed to catch due to the use of array
instead of pointer types.

Change-Id: I6a9bfc34e3536834af35fdf4fb7ceeb31f31f8c0
Reviewed-on: https://gerrit.libreoffice.org/80421
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

1 files changed, 36 insertions, 0 deletions

diff --git a/compilerplugins/clang/test/classmemaccess.cxx b/compilerplugins/clang/test/classmemaccess.cxx
new file mode 100644
index 000000000000..05bb457f87e3
--- /dev/null
+++ b/compilerplugins/clang/test/classmemaccess.cxx
@@ -0,0 +1,36 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#include <cstring>
+
+void f(struct Incomplete* p1, struct S* p2);
+
+struct S
+{
+    S();
+};
+
+void f(struct Incomplete* p1, struct S* p2)
+{
+    S s;
+    // expected-error@+1 {{writing to an object of non-trivial type 'S'; use assignment instead [loplugin:classmemaccess]}}
+    std::memset(&s, 0, sizeof s);
+    // expected-error@+1 {{writing to an object of non-trivial type 'S'; use assignment instead [loplugin:classmemaccess]}}
+    std::memset(static_cast<void*>(&s), 0, sizeof s);
+    auto const disableWarning = static_cast<void*>(&s);
+    std::memset(disableWarning, 0, sizeof s);
+    S a[1][1];
+    // expected-error@+1 {{writing to an object of non-trivial type 'S'; use assignment instead [loplugin:classmemaccess]}}
+    std::memset(a, 0, sizeof a);
+    std::memset(p1, 0, 10); // conservatively assume Incomplete may be trivial
+    // expected-error@+1 {{writing to an object of non-trivial type 'S'; use assignment instead [loplugin:classmemaccess]}}
+    std::memset(p2, 0, 10);
+}
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab cinoptions=b1,g0,N-s cinkeys+=0=break: */