[lmi-commits] [lmi] master 1372a42 6/7: Use '-isystem' to suppress warnings in third-party headers

[Greg Chicares]

branch: master
commit 1372a42340285f6f3604db30a371142b54261991
Author: Gregory W. Chicares <gchicares@sbcglobal.net>
Commit: Gregory W. Chicares <gchicares@sbcglobal.net>

    Use '-isystem' to suppress warnings in third-party headers
    
    Some third-party headers elicit warnings, which '-Werror' turns into
    errors. There are several ways to avoid that:
    
    (1) Use pragmata to suppress the warnings before including such headers,
       and "pop" their suppression right after including them. That doesn't
       suppress warnings stemming from macros in those headers. In theory,
       each such macro expansion could be surrounded by pragmata, but that's
       tedious and ugly.
    
    (2) Same, but don't "pop". Then the warnings remain suppressed for lmi
       code that follows, so defects are hidden.
    
    (3) Include such headers with '-isystem', which yields the behavior
       described here:
    
      https://gcc.gnu.org/onlinedocs/cpp/System-Headers.html
    
    | All warnings, other than those generated by ‘#warning’ [...],
    | are suppressed while GCC is processing a system header.
    | Macros defined in a system header are immune to a few warnings
    | wherever they are expanded.
    
    Of those options, (1) gives false positives, (2) gives false negatives,
    and (3) seems workable.
---
 workhorse.make | 26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/workhorse.make b/workhorse.make
index 8ed48d9..8a73534 100644
--- a/workhorse.make
+++ b/workhorse.make
@@ -295,10 +295,12 @@ wx_config_check:
 #   http://lists.gnu.org/archive/html/lmi/2006-10/msg00046.html
 # for some discussion.
 
-all_include_directories := \
+lmi_include_directories := \
   $(srcdir) \
   $(srcdir)/tools/pete-2.1.1 \
   $(overriding_include_directories) \
+
+sys_include_directories := \
   $(compiler_include_directory) \
   $(wx_include_paths) \
   /opt/lmi/third_party/include \
@@ -855,7 +857,8 @@ endif
 # before or after '=' is an error.
 
 REQUIRED_CPPFLAGS = \
-  $(addprefix -I , $(all_include_directories)) \
+  $(addprefix -I , $(lmi_include_directories)) \
+  $(addprefix -isystem , $(sys_include_directories)) \
   $(lmi_wx_new_so_attributes) \
   $(actually_used_lmi_so_attributes) \
   $(platform_defines) \
@@ -924,19 +927,13 @@ REQUIRED_LDFLAGS = \
   $(REQUIRED_LIBS) \
 
 # The '--use-temp-file' windres option seems to be often helpful and
-# never harmful. The $(subst) workaround for '-I' isn't needed with
-#   GNU windres 2.15.91 20040904
-# and later versions, but is needed with
-#   GNU windres 2.13.90 20030111
-# and earlier versions. The $(subst) workaround for '-mno-cygwin' is
-# needed as long as
-#  - that option is included in $(ALL_CPPFLAGS), as it apparently
-#      should be because it affects the preprocessor; and
-#  - $(ALL_CPPFLAGS) is passed to 'windres', which seems common; and
-#  - 'windres' doesn't gracefully ignore that option.
+# never harmful.
+#
+# As seems customary, $(ALL_CPPFLAGS) is passed to 'windres', which
+# doesn't recognize '-isystem'--hence the $(subst) workaround.
 
 REQUIRED_RCFLAGS = \
-  $(subst -mno-cygwin,,$(subst -I,--include-dir ,$(ALL_CPPFLAGS))) \
+  $(subst -isystem,--include-dir,$(ALL_CPPFLAGS)) \
   --use-temp-file \
 
 # To create msw import libraries, use '-Wl,--out-implib,$@.a'. There
@@ -1617,7 +1614,8 @@ show_flags:
        @printf 'ALL_LDFLAGS             = "%s"\n' "$(ALL_LDFLAGS)"
        @printf 'ALL_RCFLAGS             = "%s"\n' "$(ALL_RCFLAGS)"
        @printf 'srcdir                  = "%s"\n' "$(srcdir)"
-       @printf 'all_include_directories = "%s"\n' "$(all_include_directories)"
+       @printf 'lmi_include_directories = "%s"\n' "$(lmi_include_directories)"
+       @printf 'sys_include_directories = "%s"\n' "$(sys_include_directories)"
        @printf 'all_source_directories  = "%s"\n' "$(all_source_directories)"
        @printf 'wx_include_paths        = "%s"\n' "$(wx_include_paths)"
        @printf 'wx_libraries            = "%s"\n' "$(wx_libraries)"