Names of libraries included in typelib files are opened by dlopen.
Here we add the full path.

This patch was provided by Luca Bruno <lucabru@src.gnome.org>,
for 'gobject-introspection' 1.40.0 in Nix.

It has since been updated to work with newer versions of
gobject-introspection.

diff --git a/giscanner/scannermain.py b/giscanner/scannermain.py
index 1d39ab84..e12ed24e 100644
--- a/giscanner/scannermain.py
+++ b/giscanner/scannermain.py
@@ -95,6 +95,39 @@ def get_windows_option_group(parser):
     return group
 
 
+def _get_default_fallback_libpath():
+    # Newer multiple-output-optimized stdenv has an environment variable
+    # $outputLib which in turn specifies another variable which then is used as
+    # the destination for the library contents (${!outputLib}/lib).
+    store_path = os.environ.get(os.environ.get("outputLib")) if "outputLib" in os.environ else None
+    if store_path is None:
+        outputs = os.environ.get("outputs", "out").split()
+        if "lib" in outputs:
+            # For multiple output derivations let's try whether there is a $lib
+            # environment variable and use that as the base store path.
+            store_path = os.environ.get("lib")
+        elif "out" in outputs:
+            # Otherwise we have a single output derivation, so the libraries
+            # most certainly will end up in "$out/lib".
+            store_path = os.environ.get("out")
+
+    if store_path is not None:
+        # Even if we have a $lib as output, there still should be a $lib/lib
+        # directory.
+        return os.path.join(store_path, 'lib')
+    else:
+        # If we haven't found a possible scenario, let's return an empty string
+        # so that the shared library won't be prepended with a path.
+        #
+        # Note that this doesn't mean that all hope is lost, because after all
+        # we can still use --fallback-library-path to set one.
+        #
+        # Also, we're not returning None, because that would make it very
+        # difficult to disable adding fallback paths altogether using something
+        # like: --fallback-library-path=""
+        return ""
+
+
 def _get_option_parser():
     parser = optparse.OptionParser('%prog [options] sources',
                                    version='%prog ' + giscanner.__version__)
@@ -220,6 +253,10 @@ match the namespace prefix.""")
     parser.add_option("", "--compiler",
                       action="store", dest="compiler", default=None,
                       help="the C compiler to use internally")
+    parser.add_option("", "--fallback-library-path",
+                      action="store", dest="fallback_libpath",
+                      default=_get_default_fallback_libpath(),
+                      help="Path to prepend to unknown shared libraries")
 
     group = get_preprocessor_option_group(parser)
     parser.add_option_group(group)
diff --git a/giscanner/shlibs.py b/giscanner/shlibs.py
index 9f8ab5df..8aa37c99 100644
--- a/giscanner/shlibs.py
+++ b/giscanner/shlibs.py
@@ -57,6 +57,14 @@ def _ldd_library_pattern(library_name):
     $""" % re.escape(library_name), re.VERBOSE)
 
 
+def _ldd_library_guix_pattern(library_name):
+    store_dir = re.escape(
+      os.environ.get("NIX_STORE", default="/gnu/store")
+    )
+    pattern = r'(%s(?:/[^/]*)+lib%s[^A-Za-z0-9_-][^\s\(\)]*)'
+    return re.compile(pattern % (store_dir, re.escape(library_name)))
+
+
 # This is a what we do for non-la files. We assume that we are on an
 # ELF-like system where ldd exists and the soname extracted with ldd is
 # a filename that can be opened with dlopen().
@@ -108,7 +116,8 @@ def _resolve_non_libtool(options, binary, libraries):
             output = output.decode("utf-8", "replace")
 
         shlibs = resolve_from_ldd_output(libraries, output)
-        return list(map(sanitize_shlib_path, shlibs))
+        fallback_libpath = options.fallback_libpath or "";
+        return list(map(lambda p: os.path.join(fallback_libpath, p), map(sanitize_shlib_path, shlibs)))
 
 
 def sanitize_shlib_path(lib):
@@ -117,19 +126,18 @@ def sanitize_shlib_path(lib):
     # In case we get relative paths on macOS (like @rpath) then we fall
     # back to the basename as well:
     # https://gitlab.gnome.org/GNOME/gobject-introspection/issues/222
-    if sys.platform == "darwin":
-        if not os.path.isabs(lib):
-            return os.path.basename(lib)
-        return lib
-    else:
+
+    # Always use absolute paths if available
+    if not os.path.isabs(lib):
         return os.path.basename(lib)
+    return lib
 
 
 def resolve_from_ldd_output(libraries, output):
     patterns = {}
     for library in libraries:
         if not os.path.isfile(library):
-            patterns[library] = _ldd_library_pattern(library)
+            patterns[library] = (_ldd_library_pattern(library), _ldd_library_guix_pattern(library))
     if len(patterns) == 0:
         return []
 
@@ -141,8 +149,12 @@ def resolve_from_ldd_output(libraries, output):
         if line.endswith(':'):
             continue
         for word in line.split():
-            for library, pattern in patterns.items():
-                m = pattern.match(word)
+            for library, (pattern, guix_pattern) in patterns.items():
+                store_dir = os.environ.get("NIX_STORE", default="/gnu/store")
+                if line.find(store_dir) != -1:
+                    m = guix_pattern.match(word)
+                else:
+                    m = pattern.match(word)
                 if m:
                     del patterns[library]
                     shlibs.append(m.group())
diff --git a/giscanner/utils.py b/giscanner/utils.py
index 31c7ea48..630002a8 100644
--- a/giscanner/utils.py
+++ b/giscanner/utils.py
@@ -114,16 +114,11 @@ def extract_libtool_shlib(la_file):
     if dlname is None:
         return None
 
-    # Darwin uses absolute paths where possible; since the libtool files never
-    # contain absolute paths, use the libdir field
-    if platform.system() == 'Darwin':
-        dlbasename = os.path.basename(dlname)
-        libdir = _extract_libdir_field(la_file)
-        if libdir is None:
-            return dlbasename
-        return libdir + '/' + dlbasename
-    # Older libtools had a path rather than the raw dlname
-    return os.path.basename(dlname)
+    dlbasename = os.path.basename(dlname)
+    libdir = _extract_libdir_field(la_file)
+    if libdir is None:
+        return dlbasename
+    return libdir + '/' + dlbasename
 
 
 # Returns arguments for invoking libtool, if applicable, otherwise None
diff --git a/tests/scanner/test_shlibs.py b/tests/scanner/test_shlibs.py
index a8337c60..7f123103 100644
--- a/tests/scanner/test_shlibs.py
+++ b/tests/scanner/test_shlibs.py
@@ -40,7 +40,8 @@ class TestLddParser(unittest.TestCase):
 
         self.assertEqual(
             sanitize_shlib_path('/foo/bar'),
-            '/foo/bar' if sys.platform == 'darwin' else 'bar')
+            # Always use an absolute filename for Guix
+            '/foo/bar')
 
     def test_unresolved_library(self):
         output = ''