[PATCH] D24289: Add warning when assigning enums to bitfields without an explicit unsigned underlying type

[Nico Weber via cfe-commits]

thakis added a comment.

Works for me if rnk likes it :-)

(We could bikeshed on if this should be one of the -Wmicrosoft warnings, but the warning can't be both in -Wall and -Wmicrosoft, so let's don't).

I do have a question about the test (the first commit below):


================
Comment at: test/SemaCXX/warn-msvc-enum-bitfield.cpp:12
@@ +11,3 @@
+
+  s.e2 = E2;
+  s.f2 = F2;
----------------
Shouldn't this be the version that warns? The assignment with E1 assigns 0 which is portable, but this assigns 1 which overflows, right?

================
Comment at: test/SemaCXX/warn-msvc-enum-bitfield.cpp:39
@@ +38,3 @@
+  s.e2 = E2;
+  s.f2 = F2;
+}
----------------
We have -Wconversion warnings for similar cases; maybe we should have this here too (but not in this change):

Nicos-MBP:llvm-build thakis$ cat test2.cc
enum E {e1, e2};

struct S {
  E e1 : 1;
};
void f() {
  short s1 = 65536;
  short s2 = 32769;

  S s;
  s.e1 = e2;
}
Nicos-MBP:llvm-build thakis$ clang -Wconversion -c test2.cc
test2.cc:8:14: warning: implicit conversion changes signedness: 'int' to 'short' [-Wsign-conversion]
  short s2 = 32769;
        ~~   ^~~~~
test2.cc:7:14: warning: implicit conversion from 'int' to 'short' changes value from 65536 to 0 [-Wconstant-conversion]
  short s1 = 65536;
        ~~   ^~~~~
2 warnings generated.


https://reviews.llvm.org/D24289