[Bug c++/71797] New: Spurious unused-variable warning with inline function and unrelated error

[r at queiro dot co.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71797

            Bug ID: 71797
           Summary: Spurious unused-variable warning with inline function
                    and unrelated error
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: r at queiro dot co.uk
  Target Milestone: ---

Created attachment 38854
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=38854&action=edit
test case

The unused-variable warning is only produced when another error is present and
FOO_CONSTANT is initialized with an inline function. Otherwise, no warning is
generated. Tested with g++ 4.8.4 and 4.9.3.

~ g++ -Wall foo.cc
In file included from foo.cc:2:0:
foo.h: In constructor ‘Foo::Foo()’:
foo.h:8:13: error: ‘create_a_compile_error’ was not declared in this scope
     Foo() { create_a_compile_error; };
             ^
foo.h: At global scope:
foo.h:5:16: warning: ‘FOO_CONSTANT’ defined but not used [-Wunused-variable]
 const unsigned FOO_CONSTANT = f(4);
                ^
~ 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
4.8.4-2ubuntu1~14.04.3' --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 --disable-libmudflap
--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,mx32 --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 4.8.4 (Ubuntu 4.8.4-2ubuntu1~14.04.3)

~ cat foo.ii 
# 1 "foo.cc"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "/usr/include/stdc-predef.h" 1 3 4
# 1 "<command-line>" 2
# 1 "foo.cc"
static inline unsigned f(unsigned x) {
    return x;
}

const unsigned FOO_CONSTANT = f(4);

class Foo {
    Foo() { create_a_compile_error; };
};