https://llvm.org/bugs/show_bug.cgi?id=30636
Bug ID: 30636
Summary: an impossible case for -Wimplicit-fallthrough and
[[clang::fallthrough]]
Product: clang
Version: unspecified
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: C++
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
Classification: Unclassified
Here is a function that I have reduced from some real-life code that I am
unable to compile with -Wimplicit-fallthrough.
% cat foo.cc
template<bool param>
int fun(int i)
{
switch (i)
{
case 1:
if (param)
return 3;
// [[clang::fallthrough]];
case 2:
return 4;
default:
return 5;
}
}
template int fun<true>(int);
template int fun<false>(int);
% clang++-3.9 -std=c++11 -Wimplicit-fallthrough foo.cc -cfoo.cc:10:5: warning:
unannotated fall-through between switch labels [-Wimplicit-fallthrough]
case 2:
^
foo.cc:18:14: note: in instantiation of function template specialization
'fun<false>' requested here
template int fun<false>(int);
^
foo.cc:10:5: note: insert '[[clang::fallthrough]];' to silence this warning
[...]
Unfortunately, inserting [[clang::fallthrough]] gives a different error:
% clang++-3.9 -std=c++11 -Wimplicit-fallthrough foo.cc -c
foo.cc:9:7: warning: fallthrough annotation in unreachable code
[-Wimplicit-fallthrough]
[[clang::fallthrough]];
^
foo.cc:17:14: note: in instantiation of function template specialization
'fun<true>' requested here
template int fun<true>(int);
^
1 warning generated.
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