http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58062
Bug ID: 58062
Summary: [C++11] bogus __func__ lookup in lambda body
Product: gcc
Version: 4.8.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: hstong at ca dot ibm.com
In the case below, the __func__ identifier appears within a lambda body at
namespace scope.
GCC seems to find __func__ from somewhere, but the behaviour does not appear to
be supported by the Standard. MSVC gives the expected error.
When we are told by C++11 subclause 5.1.2 [expr.prim.lambda] paragraph 7 that
the compound-statement "yields" the function-body of the function call
operator, it can be taken that it means that a function-body is produced from
the compound-statement and that the latter is not an actual function-body. We
are also told that for the purposes of name lookup, the compound-statement is
considered in the context of the lambda-expression.
We find that, in the absence of a function-body, __func__ is not a specified to
be a predefined variable (8.4.1 [dcl.fct.def.general] paragraphs 7-8). We also
note that the form of a function definition (8.4.1 paragraph 1) is not present
in the above program and that the wording in subclauses 3.3.2
[basic.scope.pdecl] and 3.3.3 [basic.scope.block] (paragraphs 8 and 2,
respectively) covers only function-local predefined variables in function
definitions.
The conclusion is that __func__ in a lambda body is bound using the context of
the lambda-expression, and not bound later to be the function-local predefined
variable which would exist in the context of the function-call operator's
compiler-generated definition.
In the case of the code below, it means that the lookup for __func__ fails and
renders the program ill-formed.
## Small test:
namespace K {
auto ff = [] { return __func__; };
}
## Actual output:
Clean compile.
## Expected output:
main.cpp: In lambda function:
main.cpp:2:26: error: ‘__func__’ was not declared in this scope
auto ff = [] { return __func__; };
^
## g++ -v:
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.8/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
4.8.1-2ubuntu1~12.04' --with-bugurl=file:///usr/share/doc/gcc-4.8/README.Bugs
--enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr
--program-suffix=-4.8 --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--with-gxx-include-dir=/usr/include/c++/4.8 --libdir=/usr/lib --enable-nls
--with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --enable-gnu-unique-object --enable-plugin
--with-system-zlib --disable-browser-plugin --enable-java-awt=gtk
--enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64/jre
--enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.8-amd64
--with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar
--enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686
--with-abi=m64 --with-multilib-list=m32,m64 --with-tune=generic
--enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu
--target=x86_64-linux-gnu
Thread model: posix
gcc version 4.8.1 (Ubuntu 4.8.1-2ubuntu1~12.04)
