[gspell] build: add visibility handling

[Sébastien Wilmet <swilmet src gnome org>]

commit 74d5a68cf3eabcc7a2cb3fef9848794f80fc23c9
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Thu Apr 13 18:38:26 2017 +0200

    build: add visibility handling
    
    The -export-dynamic LDFLAG was not sufficient.
    
    Code copied from libsoup.
    
    Running:
    $ nm -D libgspell-1.so | grep T
    before and after this commit shows that the only difference is that
    gspell_get_resource() is no longer exported. It was exported by mistake,
    it's for the internal GResources.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=761921

 configure.ac       |   31 +++++++++++++++++++++++++++++++
 gspell/Makefile.am |    4 +++-
 2 files changed, 34 insertions(+), 1 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 23e0ef8..b93e0e8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -155,6 +155,37 @@ AX_CODE_COVERAGE
 AX_REQUIRE_DEFINED([AX_VALGRIND_CHECK])
 AX_VALGRIND_CHECK
 
+# Visibility handling
+# This requires that every gspell/*.c file #includes config.h.
+GSPELL_HIDDEN_VISIBILITY_CFLAGS=""
+case "$host" in
+    *-*-mingw*)
+        dnl on mingw32 we do -fvisibility=hidden and __declspec(dllexport)
+        AC_DEFINE([_GSPELL_EXTERN], [__attribute__((visibility("default"))) __declspec(dllexport) extern],
+                  [defines how to decorate public symbols while building])
+        GSPELL_HIDDEN_VISIBILITY_CFLAGS="-fvisibility=hidden"
+        ;;
+    *)
+        dnl on other compilers, check if we can do -fvisibility=hidden
+        SAVED_CFLAGS="${CFLAGS}"
+        CFLAGS="-fvisibility=hidden"
+        AC_MSG_CHECKING([for -fvisibility=hidden compiler flag])
+        AC_TRY_COMPILE([], [int main (void) { return 0; }],
+                       AC_MSG_RESULT(yes)
+                       enable_fvisibility_hidden=yes,
+                       AC_MSG_RESULT(no)
+                       enable_fvisibility_hidden=no)
+        CFLAGS="${SAVED_CFLAGS}"
+
+        AS_IF([test "${enable_fvisibility_hidden}" = "yes"], [
+            AC_DEFINE([_GSPELL_EXTERN], [__attribute__((visibility("default"))) extern],
+                      [defines how to decorate public symbols while building])
+            GSPELL_HIDDEN_VISIBILITY_CFLAGS="-fvisibility=hidden"
+        ])
+        ;;
+esac
+AC_SUBST(GSPELL_HIDDEN_VISIBILITY_CFLAGS)
+
 # Check for Mac OS X platform
 AC_MSG_CHECKING([for Mac OS X platform])
 case "$host" in
diff --git a/gspell/Makefile.am b/gspell/Makefile.am
index 009bad7..88f6577 100644
--- a/gspell/Makefile.am
+++ b/gspell/Makefile.am
@@ -94,7 +94,8 @@ nodist_libgspell_core_la_SOURCES = \
 libgspell_core_la_LIBADD =     \
        $(CODE_COVERAGE_LIBS)
 
-libgspell_core_la_CFLAGS =     \
+libgspell_core_la_CFLAGS =                     \
+       $(GSPELL_HIDDEN_VISIBILITY_CFLAGS)      \
        $(CODE_COVERAGE_CFLAGS)
 
 libgspell_core_la_LDFLAGS =    \
@@ -113,6 +114,7 @@ libgspell_@GSPELL_API_VERSION@_la_LIBADD =  \
        $(CODE_COVERAGE_LIBS)
 
 libgspell_@GSPELL_API_VERSION@_la_CFLAGS =     \
+       $(GSPELL_HIDDEN_VISIBILITY_CFLAGS)      \
        $(CODE_COVERAGE_CFLAGS)
 
 libgspell_@GSPELL_API_VERSION@_la_LDFLAGS =    \