Preserve -L -l pairings fetched from external deps

While adding link args for external deps, sometimes different
libraries come from different prefixes, and an older version of the
same library might be present in other prefixes and we don't want to
accidentally pick that up.

For example:

/usr/local/lib/libglib-2.0.so
/usr/local/lib/pkgconfig/glib-2.0.pc
/usr/local/lib/libz.so
/usr/local/lib/pkgconfig/zlib.pc
/home/mesonuser/.local/lib/libglib-2.0.so
/home/mesonuser/.local/lib/pkgconfig/glib-2.0.pc

PKG_CONFIG_PATH="/home/mesonuser/.local/lib/pkgconfig/:/usr/local/lib/pkgconfig/"

If a target uses `dependencies : [glib_dep, zlib_dep]`, it will end up
using /usr/local/lib/libglib-2.0.so instead of
/home/mesonuser/.local/lib/libglib-2.0.so despite using the pkg-config
file in /home/mesonuser/.local/lib/pkgconfig because we reorder the -L
flag and separate it from the -l flag.

With this change, external link arguments will be added to the
compiler list without de-dup or reordering.

Closes https://github.com/mesonbuild/meson/issues/1718

4 files changed, 31 insertions, 4 deletions

diff --git a/mesonbuild/backend/ninjabackend.py b/mesonbuild/backend/ninjabackend.py
index 8a2ee9a..9a48c4e 100644
--- a/mesonbuild/backend/ninjabackend.py
+++ b/mesonbuild/backend/ninjabackend.py
@@ -2294,11 +2294,13 @@ rule FORTRAN_DEP_HACK
             commands += target.link_args
             # External deps must be last because target link libraries may depend on them.
             for dep in target.get_external_deps():
-                commands += dep.get_link_args()
+                # Extend without reordering or de-dup to preserve `-L -l` sets
+                # https://github.com/mesonbuild/meson/issues/1718
+                commands.extend_direct(dep.get_link_args())
             for d in target.get_dependencies():
                 if isinstance(d, build.StaticLibrary):
                     for dep in d.get_external_deps():
-                        commands += dep.get_link_args()
+                        commands.extend_direct(dep.get_link_args())
         # Add link args for c_* or cpp_* build options. Currently this only
         # adds c_winlibs and cpp_winlibs when building for Windows. This needs
         # to be after all internal and external libraries so that unresolved
diff --git a/mesonbuild/backend/vs2010backend.py b/mesonbuild/backend/vs2010backend.py
index d4a7a19..57b0437 100644
--- a/mesonbuild/backend/vs2010backend.py
+++ b/mesonbuild/backend/vs2010backend.py
@@ -908,11 +908,13 @@ class Vs2010Backend(backends.Backend):
             extra_link_args += target.link_args
             # External deps must be last because target link libraries may depend on them.
             for dep in target.get_external_deps():
-                extra_link_args += dep.get_link_args()
+                # Extend without reordering or de-dup to preserve `-L -l` sets
+                # https://github.com/mesonbuild/meson/issues/1718
+                extra_link_args.extend_direct(dep.get_link_args())
             for d in target.get_dependencies():
                 if isinstance(d, build.StaticLibrary):
                     for dep in d.get_external_deps():
-                        extra_link_args += dep.get_link_args()
+                        extra_link_args.extend_direct(dep.get_link_args())
         # Add link args for c_* or cpp_* build options. Currently this only
         # adds c_winlibs and cpp_winlibs when building for Windows. This needs
         # to be after all internal and external libraries so that unresolved
diff --git a/mesonbuild/compilers.py b/mesonbuild/compilers.py
index 80d12a0..2b54cc8 100644
--- a/mesonbuild/compilers.py
+++ b/mesonbuild/compilers.py
@@ -465,6 +465,19 @@ class CompilerArgs(list):
                 self.insert(i + 1, '-Wl,--end-group')
         return self.compiler.unix_args_to_native(self)
 
+    def append_direct(self, arg):
+        '''
+        Append the specified argument without any reordering or de-dup
+        '''
+        super().append(arg)
+
+    def extend_direct(self, iterable):
+        '''
+        Extend using the elements in the specified iterable without any
+        reordering or de-dup
+        '''
+        super().extend(iterable)
+
     def __add__(self, args):
         new = CompilerArgs(self, self.compiler)
         new += args
diff --git a/run_unittests.py b/run_unittests.py
index dbfd638..9f39890 100755
--- a/run_unittests.py
+++ b/run_unittests.py
@@ -176,6 +176,16 @@ class InternalTests(unittest.TestCase):
         l += ['-lbar']
         self.assertEqual(l, ['-Lbardir', '-Lfoodir', '-lfoo', '-lbar'])
 
+        ## Test that 'direct' append and extend works
+        l = cargsfunc(c, ['-Lfoodir', '-lfoo'])
+        self.assertEqual(l, ['-Lfoodir', '-lfoo'])
+        # Direct-adding a library and a libpath appends both correctly
+        l.extend_direct(['-Lbardir', '-lbar'])
+        self.assertEqual(l, ['-Lfoodir', '-lfoo', '-Lbardir', '-lbar'])
+        # Direct-adding the same library again still adds it
+        l.append_direct('-lbar')
+        self.assertEqual(l, ['-Lfoodir', '-lfoo', '-Lbardir', '-lbar', '-lbar'])
+
     def test_commonpath(self):
         from os.path import sep
         commonpath = mesonbuild.mesonlib.commonpath