set up config['ndk_paths'] on demand by reading source.properties

ndk_paths is set up right after installing the NDK and right before
ndk_paths is used in Build.ndk_path().

A proper NDK install always has a _source.properties_ which declares
the revision and release strings. That is used as the source of
revision and release.  This only reads from the local filesystem, and
reads the official source of version info (_source.properties_),
thereby avoiding any potential network calls that sdkmanager might
do. This implementation was inspired by @uniqx's:

ed931d47d7 (27b997d583cd1c0a05b2213437e0d9fe6536bfe3)

tests/source-files/ndk/11.1.2683735/source.properties

@@ -0,0 +1,2 @@
+Pkg.Desc = Android NDK
+Pkg.Revision = 11.1.2683735

tests/source-files/ndk/29.0.14033849/source.properties

@@ -0,0 +1,4 @@
+Pkg.Desc = Android NDK
+Pkg.Revision = 29.0.14033849-beta4
+Pkg.BaseRevision = 29.0.14033849
+Pkg.ReleaseName = r29-beta4

tests/source-files/ndk/29.0.14206865/source.properties

@@ -0,0 +1,4 @@
+Pkg.Desc = Android NDK
+Pkg.Revision = 29.0.14206865
+Pkg.BaseRevision = 29.0.14206865
+Pkg.ReleaseName = r29

tests/test_common.py

@@ -2522,6 +2522,7 @@ class CommonTest(SetUpTearDownMixin, unittest.TestCase):
     def test_ndk_paths_in_config_must_be_strings(self):
         """All paths in config must be strings, and never pathlib.Path instances"""
         fdroidserver.common.config = {
+            'sdk_path': 'ignored',
             'ndk_paths': {'r21d': Path('/opt/android-sdk/ndk/r21d')}
         }
         build = fdroidserver.metadata.Build()
@@ -2610,7 +2611,7 @@ class CommonTest(SetUpTearDownMixin, unittest.TestCase):
         )
 
     def test_no_zero_length_ndk_path_prefixes(self):
-        fdroidserver.common.config = {'ndk_paths': {}}
+        fdroidserver.common.config = {'sdk_path': 'ignored', 'ndk_paths': dict()}
         build = fdroidserver.metadata.Build()
 
         with mock.patch.dict(os.environ, clear=True):
@@ -3705,3 +3706,54 @@ class VirtContainerTypeTest(unittest.TestCase):
             with self.assertRaises(SystemExit):
                 fdroidserver.common.get_virt_container_type(self.options)
             self.assertIn(testvalue, logs.output[0])
+
+
+class ParseNdkTest(unittest.TestCase):
+    """Test parsing installed NDKs."""
+
+    def setUp(self):
+        os.chdir(os.path.join(basedir, 'source-files/ndk'))
+
+    def tearDown(self):
+        fdroidserver.common.config = None
+
+    def test_parse_ndk_revision_release_release(self):
+        testvalue = '29.0.14206865'
+        self.assertEqual(
+            (testvalue, 'r29'),
+            fdroidserver.common._parse_ndk_revision_release(testvalue),
+        )
+
+    def test_parse_ndk_revision_release_beta(self):
+        testvalue = '29.0.14033849'
+        self.assertEqual(
+            (testvalue, 'r29-beta4'),
+            fdroidserver.common._parse_ndk_revision_release(testvalue),
+        )
+
+    def test_init_ndk_paths(self):
+        sdk_path = os.path.dirname(os.getcwd())
+        fdroidserver.common.config = {'sdk_path': sdk_path}
+        fdroidserver.common.init_ndk_paths()
+        self.assertEqual(
+            fdroidserver.common.config,
+            {
+                'ndk_paths': {
+                    '11.1.2683735': f'{sdk_path}/ndk/11.1.2683735',
+                    '29.0.14033849': f'{sdk_path}/ndk/29.0.14033849',
+                    '29.0.14206865': f'{sdk_path}/ndk/29.0.14206865',
+                    'r11b': f'{sdk_path}/ndk/11.1.2683735',
+                    'r29': f'{sdk_path}/ndk/29.0.14206865',
+                    'r29-beta4': f'{sdk_path}/ndk/29.0.14033849',
+                },
+                'sdk_path': sdk_path,
+            },
+        )
+
+    def test_build_ndk_path(self):
+        testvalue = '29.0.14033849'
+        sdk_path = os.path.dirname(os.getcwd())
+        fdroidserver.common.config = {'sdk_path': sdk_path}
+        build = fdroidserver.metadata.Build()
+        build.ndk = testvalue
+        self.assertEqual(build.ndk_path(), f'{sdk_path}/ndk/{testvalue}')

tests/test_metadata.py

@@ -1850,7 +1850,7 @@ class MetadataTest(unittest.TestCase):
 
     def test_build_ndk_path_only_accepts_str(self):
         """Paths in the config must be strings, never pathlib.Path instances"""
-        config = {'ndk_paths': {'r24': Path('r24')}}
+        config = {'sdk_path': 'ignored', 'ndk_paths': {'r24': Path('r24')}}
         fdroidserver.common.config = config
         build = fdroidserver.metadata.Build()
         build.ndk = 'r24'