misc-static-assert generates incorrect fixes

[llvmbot]

Bugzilla Link	23692
Version	unspecified
OS	Linux
Reporter	LLVM Bugzilla Contributor

Extended Description

A couple of cases where a static_assert can't be used:

1. expressions with addresses of struct members:
   =====
   $ cat q.cc
   #include

void f() {
struct {
int a;
int b;
} s;
assert(&s.b - &s.a == 1);
}
$ clang-tidy q.cc -- -std=c++11
1 warning generated.
q.cc:8:3: warning: found assert() that could be replaced by static_assert() [misc-static-assert]
assert(&s.b - &s.a == 1);
^
static_assert , ""

The expression can be rewritten using offsetof(), so that it will be suitable for the static_assert. Thus the check should continue to warn, but it should provide no fixit in this case.

2. some "not constant enough" expressions:
   =====
   $ cat q.cc
   #include

const double x = 1;
void f() {
assert(x > 0);
}
$ clang-tidy -fix q.cc -- -std=c++11
1 warning generated.
q.cc:5:3: warning: found assert() that could be replaced by static_assert() [misc-static-assert]
assert(x > 0);
^
static_assert , ""
q.cc:5:3: note: FIX-IT applied suggested code changes
assert(x > 0);
^
q.cc:5:15: note: FIX-IT applied suggested code changes
assert(x > 0);
^
clang-tidy applied 2 of 2 suggested fixes.
google3$ clang-check q.cc -- -std=c++11
q.cc:5:17: error: static_assert expression is not an integral constant expression
static_assert(x > 0, "");
^~~~~
q.cc:5:17: note: read of non-constexpr variable 'x' is not allowed in a constant expression
q.cc:3:14: note: declared here
const double x = 1;
^
1 error generated.
Error while processing q.cc.

Same here. It's fine to flag this assert, maybe with a slightly different message. But the fixit shouldn't be there.

[PiotrZSL]

https://reviews.llvm.org/D158657