Issue 4950 - Add -fpermissive to allow building on recent gcc.This is caused by V8 code.Possibly…

common.gypi

 {
   'variables': {
     'visibility%': 'hidden',
     'library%': 'static_library',
     'component%': '',
     'want_separate_host_toolset': 0,
     'v8_optimized_debug': 0,
     'v8_enable_i18n_support': 0,
   },
 
   'conditions': [
     ['OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="solaris" \
        or OS=="netbsd" or OS=="android"', {
       'target_defaults': {
+        # V8 headers cause a build error on recent gcc.
+        # Adding -fpermissive to solve this.
+        # See https://issues.adblockplus.org/ticket/4950
+        # We might be able to do without after upgrading V8.
         'cflags': [ '-Wall', '-W', '-Wno-unused-parameter',
                     '-Wnon-virtual-dtor', '-pthread', '-fno-rtti',
                     '-pedantic', '-std=c++0x', '-fexceptions', '-fpermissive' ],

[Felix Dahlke, 2017/03/06 17:00:41]

I'm a bit rusty with this build logic, but:

1. Is GCC only possible to use on the systems listed above? Not on macOS? AKA:
Is this the only place where we need to add the flag?
2. Can we do comments in this file (I know it's JSON...)? We should point out
that we want to get rid of `-fpermissive` after the V8 upgrade.

[hub, 2017/03/06 17:41:41]

There is no GCC with C++11 support in macOS (they stop at a badly patched 4.2.1,
because 4.2.2 changed licensing), unless you manually install it (ith Homebrew
for example). Below, the settings are for clang which is what it will default
too. Note: the BSD have moved to clang recently I think, but clang accepts
-fpermissive too.

We can do comments in the .gypi file:
https://gyp.gsrc.io/docs/InputFormatReference.md#Comments

So if you want, I can add the comment.

[Felix Dahlke, 2017/03/07 07:29:59]

I just checked and when I build on my Ubuntu system it actually uses Clang. I
couldn't figure out how to force the build to use GCC instead so I couldn't
reproduce this issue.

I'm not entirely happy with adding `-fpermissive` on an OS basis
(linux/freebsd/openbsd/solaris/netbsd/android) when it is actually needed just
for GCC (regardless of the system). Could you look into whether we could only
set this when GCC is used? If that's not possible this is alright by me though.
Yes please add one, referring to issue 4950.

[hub, 2017/03/07 16:36:18]

I haven't figured out how to do that with gyp. There don't seem to be any way to
select based on the compiler. :-/

         'cflags!': [ '-Werror', ],
         'ldflags': [ '-pthread', ],
       },
     }],
     ['OS=="mac"', {
       'xcode_settings': {
         'CLANG_CXX_LANGUAGE_STANDARD': 'c++11',
         'CLANG_CXX_LIBRARY': 'libc++',
         'OTHER_CPLUSPLUSFLAGS' : ['-std=c++11', '-stdlib=libc++'],
       },
@@ skipping 14 matching lines @@
     'msvs_cygwin_shell': 0,
     'target_conditions': [[
       'OS=="mac" and _type=="executable"', {
         'xcode_settings': {
           'OTHER_LDFLAGS': ['-stdlib=libc++'],
         },
       }
     ]],
   }
 }