libarchive-sys-provided: let user override paths

let the user override assumed paths via environment.
Path to libarchive can be specified via
EXTRACTCODE_LIBARCHIVE_PATH environment variable.
If not found it falls back to previously calculation from
distro data.

With this patch it possible to run scancode is buildsystems like YOCTO,
which heaviily rely on overriding paths via environment to pick the
correct implementation from the build workspace

Signed-off-by: Konrad Weihmann <kweihmann@outlook.com>

Author: priv-kweihmann

builtins/extractcode_libarchive_system_provided/README.rst

@@ -1 +1,5 @@
-A ScanCode Toolkit plugin to use pre-installed system binary libraries and utilities.
+A ScanCode Toolkit plugin to use pre-installed libarchive library
+=================================================================
+
+the path of libarchive.so is either determined by distro data or explicitily
+taken from ``EXTRACTCODE_LIBARCHIVE_PATH`` environment variable

builtins/extractcode_libarchive_system_provided/src/extractcode_libarchive/__init__.py

@@ -7,8 +7,9 @@
 # See https://aboutcode.org for more information about nexB OSS projects.
 #
 
-from os import path
 import platform
+from os import environ
+from os import path
 
 from plugincode.location_provider import LocationProviderPlugin
 
@@ -20,30 +21,35 @@ def get_locations(self):
         locations of the libarchive shared library as installed on various Linux
         distros or on FreeBSD.
         """
-        system_arch = platform.machine()
-        mainstream_system = platform.system().lower()
-        if mainstream_system == 'linux':
-            distribution = platform.linux_distribution()[0].lower()
-            debian_based_distro = ['ubuntu', 'mint', 'debian']
-            rpm_based_distro = ['fedora', 'redhat']
-
-            if distribution in debian_based_distro:
-                lib_dir = '/usr/lib/'+system_arch+'-linux-gnu'
-
-            elif distribution in rpm_based_distro:
-                lib_dir = '/usr/lib64'
-
-            else:
-                raise Exception('Unsupported system: {}'.format(distribution))
-
-        elif mainstream_system == 'freebsd':
-            if path.isdir('/usr/local/'):
-                lib_dir = '/usr/local/lib'
-            else:
-                lib_dir = '/usr/lib'
+        lib_archive = environ.get('EXTRACTCODE_LIBARCHIVE_PATH')
+        if not lib_archive:
+            system_arch = platform.machine()
+            mainstream_system = platform.system().lower()
+            if mainstream_system == 'linux':
+                distribution = platform.linux_distribution()[0].lower()
+                debian_based_distro = ['ubuntu', 'mint', 'debian']
+                rpm_based_distro = ['fedora', 'redhat']
+
+                if distribution in debian_based_distro:
+                    lib_dir = '/usr/lib/'+system_arch+'-linux-gnu'
+
+                elif distribution in rpm_based_distro:
+                    lib_dir = '/usr/lib64'
+
+                else:
+                    raise Exception('Unsupported system: {}'.format(distribution))
+
+            elif mainstream_system == 'freebsd':
+                if path.isdir('/usr/local/'):
+                    lib_dir = '/usr/local/lib'
+                else:
+                    lib_dir = '/usr/lib'
+            lib_archive = path.join(lib_dir, 'libarchive.so')
+        else:
+            lib_dir = path.dirname(lib_archive)
 
         locations = {
             'extractcode.libarchive.libdir': lib_dir,
-            'extractcode.libarchive.dll': path.join(lib_dir, 'libarchive.so'),
+            'extractcode.libarchive.dll': lib_archive,
         }
         return locations