gnome: Distinguish between internal and external linker flags

When an older version of the library being built is installed in the
same prefix as external dependencies, we have to be careful to construct
the linker or compiler command line. If a -L flag from external
dependencoes comes before a -L flag pointing to builddir, it is possible
for the linker to load older libraries from the installation prefix
instead of the newly built ones, which is likely to cause undefined
reference error.

Since the order of dependencies is not significant, we cannot expect
internal dependencies to appear before external dependencies when
recursively iterating the list of dependencies. To make it harder to
make mistakes, linker flags come from internal and external
dependencies are now stored in different order sets. Code using
_get_dependencies_flags are expected to follow the order when
constructing linker command line:

  1. Internal linker flags
  2. LDFLAGS set by users
  3. External linker flags

It is similar to what automake and libtool do for autotools projects.

mesonbuild/modules/gnome.py

@@ -316,7 +316,8 @@ class GnomeModule(ExtensionModule):
     def _get_dependencies_flags(self, deps, state, depends, include_rpath=False,
                                 use_gir_args=False):
         cflags = OrderedSet()
-        ldflags = OrderedSet()
+        internal_ldflags = OrderedSet()
+        external_ldflags = OrderedSet()
         gi_includes = OrderedSet()
         deps = mesonlib.listify(deps, unholder=True)
 
@@ -326,17 +327,19 @@ class GnomeModule(ExtensionModule):
                 for lib in dep.libraries:
                     if hasattr(lib, 'held_object'):
                         lib = lib.held_object
-                    ldflags.update(self._get_link_args(state, lib, depends, include_rpath))
+                    internal_ldflags.update(self._get_link_args(state, lib, depends, include_rpath))
                     libdepflags = self._get_dependencies_flags(lib.get_external_deps(), state, depends, include_rpath,
                                                                use_gir_args)
                     cflags.update(libdepflags[0])
-                    ldflags.update(libdepflags[1])
-                    gi_includes.update(libdepflags[2])
+                    internal_ldflags.update(libdepflags[1])
+                    external_ldflags.update(libdepflags[2])
+                    gi_includes.update(libdepflags[3])
                 extdepflags = self._get_dependencies_flags(dep.ext_deps, state, depends, include_rpath,
                                                            use_gir_args)
                 cflags.update(extdepflags[0])
-                ldflags.update(extdepflags[1])
-                gi_includes.update(extdepflags[2])
+                internal_ldflags.update(extdepflags[1])
+                external_ldflags.update(extdepflags[2])
+                gi_includes.update(extdepflags[3])
                 for source in dep.sources:
                     if hasattr(source, 'held_object'):
                         source = source.held_object
@@ -351,9 +354,9 @@ class GnomeModule(ExtensionModule):
                             # For PkgConfigDependency only:
                             getattr(dep, 'is_libtool', False)):
                         lib_dir = os.path.dirname(lib)
-                        ldflags.update(["-L%s" % lib_dir])
+                        external_ldflags.update(["-L%s" % lib_dir])
                         if include_rpath:
-                            ldflags.update(['-Wl,-rpath {}'.format(lib_dir)])
+                            external_ldflags.update(['-Wl,-rpath {}'.format(lib_dir)])
                         libname = os.path.basename(lib)
                         if libname.startswith("lib"):
                             libname = libname[3:]
@@ -362,7 +365,7 @@ class GnomeModule(ExtensionModule):
                     # Hack to avoid passing some compiler options in
                     if lib.startswith("-W"):
                         continue
-                    ldflags.update([lib])
+                    external_ldflags.update([lib])
 
                 if isinstance(dep, PkgConfigDependency):
                     girdir = dep.get_pkgconfig_variable("girdir", {'default': ''})
@@ -376,14 +379,17 @@ class GnomeModule(ExtensionModule):
                 continue
 
         if gir_has_extra_lib_arg(self.interpreter) and use_gir_args:
-            fixed_ldflags = OrderedSet()
-            for ldflag in ldflags:
-                if ldflag.startswith("-l"):
-                    fixed_ldflags.add(ldflag.replace('-l', '--extra-library=', 1))
-                else:
-                    fixed_ldflags.add(ldflag)
-            ldflags = fixed_ldflags
-        return cflags, ldflags, gi_includes
+            def fix_ldflags(ldflags):
+                fixed_ldflags = OrderedSet()
+                for ldflag in ldflags:
+                    if ldflag.startswith("-l"):
+                        fixed_ldflags.add(ldflag.replace('-l', '--extra-library=', 1))
+                    else:
+                        fixed_ldflags.add(ldflag)
+                return fixed_ldflags
+            internal_ldflags = fix_ldflags(internal_ldflags)
+            external_ldflags = fix_ldflags(external_ldflags)
+        return cflags, internal_ldflags, external_ldflags, gi_includes
 
     @FeatureNewKwargs('build target', '0.40.0', ['build_by_default'])
     @permittedKwargs({'sources', 'nsversion', 'namespace', 'symbol_prefix', 'identifier_prefix',
@@ -487,7 +493,8 @@ class GnomeModule(ExtensionModule):
                         'Gir includes must be str, GirTarget, or list of them')
 
         cflags = []
-        ldflags = []
+        internal_ldflags = []
+        external_ldflags = []
         for lang, compiler in girtarget.compilers.items():
             # XXX: Can you use g-i with any other language?
             if lang in ('c', 'cpp', 'objc', 'objcpp', 'd'):
@@ -504,7 +511,7 @@ class GnomeModule(ExtensionModule):
                 sanitize = state.environment.coredata.base_options['b_sanitize'].value
                 cflags += compilers.sanitizer_compile_args(sanitize)
                 if 'address' in sanitize.split(','):
-                    ldflags += ['-lasan']
+                    external_ldflags += ['-lasan']
                 # FIXME: Linking directly to libasan is not recommended but g-ir-scanner
                 # does not understand -f LDFLAGS. https://bugzilla.gnome.org/show_bug.cgi?id=783892
                 # ldflags += compilers.sanitizer_link_args(sanitize)
@@ -565,10 +572,11 @@ class GnomeModule(ExtensionModule):
         # ldflags will be misinterpreted by gir scanner (showing
         # spurious dependencies) but building GStreamer fails if they
         # are not used here.
-        dep_cflags, dep_ldflags, gi_includes = self._get_dependencies_flags(deps, state, depends,
-                                                                            use_gir_args=True)
+        dep_cflags, dep_internal_ldflags, dep_external_ldflags, gi_includes = \
+            self._get_dependencies_flags(deps, state, depends, use_gir_args=True)
         cflags += list(dep_cflags)
-        ldflags += list(dep_ldflags)
+        internal_ldflags += list(dep_internal_ldflags)
+        external_ldflags += list(dep_external_ldflags)
         scan_command += ['--cflags-begin']
         scan_command += cflags
         scan_command += state.environment.coredata.get_external_args(lang)
@@ -578,7 +586,7 @@ class GnomeModule(ExtensionModule):
         # ones.
         if isinstance(girtarget, build.SharedLibrary):
             scan_command += ["-L@PRIVATE_OUTDIR_ABS_%s@" % girtarget.get_id()]
-        scan_command += list(ldflags)
+        scan_command += list(internal_ldflags)
         for i in gi_includes:
             scan_command += ['--add-include-path=%s' % i]
 
@@ -606,6 +614,7 @@ class GnomeModule(ExtensionModule):
         for link_arg in state.environment.coredata.get_external_link_args(lang):
             if link_arg.startswith('-L'):
                 scan_command.append(link_arg)
+        scan_command += list(external_ldflags)
 
         scankwargs = {'output': girfile,
                       'command': scan_command,
@@ -832,7 +841,8 @@ This will become a hard error in the future.''')
     def _get_build_args(self, kwargs, state, depends):
         args = []
         deps = extract_as_list(kwargs, 'dependencies', unholder=True)
-        cflags, ldflags, gi_includes = self._get_dependencies_flags(deps, state, depends, include_rpath=True)
+        cflags, internal_ldflags, external_ldflags, gi_includes = \
+            self._get_dependencies_flags(deps, state, depends, include_rpath=True)
         inc_dirs = mesonlib.extract_as_list(kwargs, 'include_directories')
         for incd in inc_dirs:
             if not isinstance(incd.held_object, (str, build.IncludeDirs)):
@@ -840,7 +850,10 @@ This will become a hard error in the future.''')
                     'Gir include dirs should be include_directories().')
         cflags.update(get_include_args(inc_dirs))
         cflags.update(state.environment.coredata.get_external_args('c'))
+        ldflags = OrderedSet()
+        ldflags.update(internal_ldflags)
         ldflags.update(state.environment.coredata.get_external_link_args('c'))
+        ldflags.update(external_ldflags)
         if cflags:
             args += ['--cflags=%s' % ' '.join(cflags)]
         if ldflags:

test cases/frameworks/22 gir link order/fake-gthread/fake-gthread.c

@@ -0,0 +1,6 @@
+#include "fake-gthread.h"
+
+int fake_gthread_fake_function (void)
+{
+  return 7;
+}

test cases/frameworks/22 gir link order/fake-gthread/fake-gthread.h

@@ -0,0 +1,6 @@
+#ifndef FAKE_GTHREAD_H
+#define FAKE_GTHREAD_H
+
+int fake_gthread_fake_function (void);
+
+#endif /* FAKE_GTHREAD_H */

test cases/frameworks/22 gir link order/fake-gthread/meson.build

@@ -0,0 +1,12 @@
+fake_gthread_sources = ['fake-gthread.c', 'fake-gthread.h']
+fake_gthread_lib = shared_library(
+  'gthread-2.0',
+  sources : fake_gthread_sources,
+  install : false,
+)
+
+fake_gthread_includes = include_directories('.')
+fake_gthread = declare_dependency(
+  include_directories : fake_gthread_includes,
+  link_with : fake_gthread_lib,
+)

test cases/frameworks/22 gir link order/get-prgname/get-prgname.c

@@ -0,0 +1,8 @@
+#include "get-prgname.h"
+
+#include <glib.h>
+
+const char *get_prgname_get_name (void)
+{
+  return g_get_prgname ();
+}

test cases/frameworks/22 gir link order/get-prgname/get-prgname.h

@@ -0,0 +1,6 @@
+#ifndef GET_PRGNAME_H
+#define GET_PRGNAME_H
+
+const char *get_prgname_get_name (void);
+
+#endif /* GET_PRGNAME_H */

test cases/frameworks/22 gir link order/get-prgname/meson.build

@@ -0,0 +1,13 @@
+get_prgname_sources = ['get-prgname.c', 'get-prgname.h']
+get_prgname_lib = shared_library(
+  'get-prgname',
+  sources : get_prgname_sources,
+  dependencies : [glib],
+  install : false,
+)
+
+get_prgname_includes = include_directories('.')
+get_prgname = declare_dependency(
+  include_directories : get_prgname_includes,
+  link_with : get_prgname_lib,
+)

test cases/frameworks/22 gir link order/meson-sample.c

@@ -0,0 +1,48 @@
+#include "meson-sample.h"
+
+#include "get-prgname.h"
+#include "fake-gthread.h"
+
+struct _MesonSample {
+  GObject parent_instance;
+};
+
+G_DEFINE_TYPE (MesonSample, meson_sample, G_TYPE_OBJECT)
+
+/**
+ * meson_sample_new:
+ *
+ * Allocates a new #MesonSample.
+ *
+ * Returns: (transfer full): a #MesonSample.
+ */
+MesonSample *
+meson_sample_new (void)
+{
+  return g_object_new (MESON_TYPE_SAMPLE, NULL);
+}
+
+static void
+meson_sample_class_init (MesonSampleClass *klass)
+{
+}
+
+static void
+meson_sample_init (MesonSample *self)
+{
+}
+
+/**
+ * meson_sample_print_message:
+ * @self: a #MesonSample.
+ *
+ * Prints a message.
+ */
+void
+meson_sample_print_message (MesonSample *self)
+{
+  g_return_if_fail (MESON_IS_SAMPLE (self));
+
+  g_print ("Message: %s\n", get_prgname_get_name ());
+  g_print ("Message: %d\n", fake_gthread_fake_function ());
+}

test cases/frameworks/22 gir link order/meson-sample.h

@@ -0,0 +1,17 @@
+#ifndef MESON_SAMPLE_H
+#define MESON_SAMPLE_H
+
+#include <glib-object.h>
+
+G_BEGIN_DECLS
+
+#define MESON_TYPE_SAMPLE (meson_sample_get_type())
+
+G_DECLARE_FINAL_TYPE (MesonSample, meson_sample, MESON, SAMPLE, GObject)
+
+MesonSample *meson_sample_new           (void);
+void         meson_sample_print_message (MesonSample *self);
+
+G_END_DECLS
+
+#endif /* MESON_SAMPLE_H */

test cases/frameworks/22 gir link order/meson.build

@@ -0,0 +1,41 @@
+project('gir link order', 'c')
+
+if not dependency('glib-2.0', required : false).found()
+  error('MESON_SKIP_TEST glib not found.')
+endif
+
+gnome = import('gnome')
+glib = dependency('glib-2.0')
+gobject = dependency('gobject-2.0')
+
+# get-prgname is a shared library which uses a function from glib-2.0. It is
+# used to introduce external -L flags which may cause -L order problems.
+subdir('get-prgname')
+
+# fake-gthread is a shared library which has the same name as gthread-2.0 from
+# GLib. This is used to simulate the case where an older or unrelated version
+# of a library is already installed on the system. Our meson sample library
+# defined below uses a function from fake-gthread. If meson messes up -L order,
+# the linker will find libgthread-2.0.so installed on the system and fail to
+# find the symbol our meson sample library uses.
+subdir('fake-gthread')
+
+meson_sample_sources = ['meson-sample.c', 'meson-sample.h']
+meson_sample_lib = shared_library(
+  'sample',
+  sources : meson_sample_sources,
+  dependencies : [gobject, get_prgname, fake_gthread],
+  install : false,
+)
+
+gnome.generate_gir(
+  meson_sample_lib,
+  sources : meson_sample_sources,
+  nsversion : '1.0',
+  namespace : 'Meson',
+  symbol_prefix : 'meson',
+  identifier_prefix : 'Meson',
+  includes : ['GObject-2.0'],
+  install : false,
+  build_by_default: true,
+)