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From:   Daniel Latypov <dlatypov@google.com>
Date:   Fri, 28 Jan 2022 13:36:55 -0800
Message-ID: <CAGS_qxoSn16TgDUvQTUpamu1xzY85Cbqy7Qg94fyKwjE4jw7Fg@mail.gmail.com>
Subject: Re: [PATCH] kunit: cleanup assertion macro internal variables
To:     Brendan Higgins <brendanhiggins@google.com>
Cc:     davidgow@google.com, linux-kernel@vger.kernel.org,
        kunit-dev@googlegroups.com, linux-kselftest@vger.kernel.org,
        skhan@linuxfoundation.org
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On Fri, Jan 28, 2022 at 1:21 PM Brendan Higgins
<brendanhiggins@google.com> wrote:
>
> On Thu, Jan 27, 2022 at 4:52 PM Daniel Latypov <dlatypov@google.com> wrot=
e:
> >
> > All the operands should be tagged `const`.
> > We're only assigning them to variables so that we can compare them (e.g=
.
> > check if left =3D=3D right, etc.) and avoid evaluating expressions mult=
iple
> > times.
> >
> > There's no need for them to be mutable.
>
> Agreed.
>
> > Also rename the helper variable `loc` to `__loc` like we do with
> > `__assertion` and `__strs` to avoid potential name collisions with user
> > code.
>
> Probably not necessary since we create a new code block (we are inside
> of an if-statement, do-while-loop, etc), but I don't really care
> either way.

You're totally right that this doesn't matter with our current macros.

given
int loc =3D 42;
KUNIT_EXPECT_TRUE(test, loc);
KUNIT_EXPECT_EQ(test, loc, 42);

becomes
do {
        if (__builtin_expect(!!(!(!!(loc) =3D=3D !!true)), 0)) {
                /* we don't use the operands in here, so `loc` is fine */
                static const struct kunit_loc loc =3D {
                        .file =3D "lib/kunit/kunit-example-test.c", .line =
=3D 25
                };
...
do {
        typeof(loc) __left =3D (loc);
        typeof(42) __right =3D (42);
        do {
                /* We never reference the expression again, so `loc` is fin=
e */
                if (__builtin_expect(!!(!(__left =3D=3D __right)), 0)) {
                        static const struct kunit_loc loc =3D {
                                .file =3D "lib/kunit/kunit-example-test.c",
                                .line =3D 24
                        };

But reminder: this was *not* the case until very recently.
Sau we didn't have my earlier patch to move the `if(!(passed))` check
into the macro.
Then we'd have issues, e.g.
../lib/kunit/kunit-example-test.c: In function =E2=80=98example_simple_test=
=E2=80=99:
../include/kunit/test.h:828:26: error: wrong type argument to unary
exclamation mark
  828 |                         !!(condition) =3D=3D !!expected_true,
                \
      |
...
../lib/kunit/kunit-example-test.c:25:9: note: in expansion of macro
=E2=80=98KUNIT_EXPECT_TRUE=E2=80=99
   25 |         KUNIT_EXPECT_TRUE(test, loc);
      |         ^~~~~~~~~~~~~~~~~

So being defensive here lets us change up our implementation more freely.

>
> > Signed-off-by: Daniel Latypov <dlatypov@google.com>
>
> Reviewed-by: Brendan Higgins <brendanhiggins@google.com>