Add `auto' linking option to Python jgo

Fixes #22

jgo/jgo.py

@@ -146,13 +146,30 @@ def executable_path_or_raise(tool):
 def executable_path(tool):
     return shutil.which(tool)
 
-def link(source, link_name, link_type="hard"):
-    if link_type.lower() == "soft":
-        os.symlink(source, link_name)
-    elif link_type.lower() == "hard":
-        os.link(source, link_name)
-    else:
-        shutil.copyfile(source, link_name)
+def link(source, link_name, link_type='auto'):
+    _logger.debug("Linking source %s to target %s with link_type %s", source, link_name, link_type)
+    if link_type.lower() == 'soft':
+        return os.symlink(source, link_name)
+    elif link_type.lower() == 'hard':
+        return os.link(source, link_name)
+    elif link_type.lower() == 'copy':
+        return shutil.copyfile(source, link_name)
+    elif link_type.lower() == 'auto':
+        try:
+            return link(source=source, link_name=link_name, link_type='hard')
+        except OSError as e:
+            if e.errno != 18:
+                raise e
+        try:
+            return link(source=source, link_name=link_name, link_type='soft')
+        except OSError as e:
+            pass
+
+        return link(source=source, link_name=link_name, link_type='copy')
+
+    raise Exception('Unable to link source {} to target {} with link_type {}', source, link_name, link_type)
+
+
 
 def m2_path():
     return os.getenv("M2_REPO", (pathlib.Path.home() / '.m2').absolute())
@@ -225,7 +242,7 @@ def jgo_main(argv=sys.argv[1:]):
     parser.add_argument('-a', '--additional-jars', nargs='+', help='Add additional jars to classpath', default=[], required=False)
     parser.add_argument( '--additional-endpoints', nargs='+', help='Add additional endpoints', default=[], required=False)
     parser.add_argument('--ignore-jgorc', action='store_true', help='Ignore ~/.jgorc')
-    parser.add_argument('--link-type', default=None, type=str, help='How to link from local maven repository into jgo cache. Defaults to the `links\' setting in ~/.jrunrc or \'hard\' if not specified.', choices=('hard', 'soft', 'copy'))
+    parser.add_argument('--link-type', default=None, type=str, help='How to link from local maven repository into jgo cache. Defaults to the `links\' setting in ~/.jrunrc or \'auto\' if not specified.', choices=('hard', 'soft', 'copy', 'auto'))
 
 
     try:
@@ -271,7 +288,7 @@ def default_config():
     config.add_section('settings')
     config.set('settings', 'm2Repo', os.path.join(str(pathlib.Path.home()), '.m2', 'repository'))
     config.set('settings', 'cacheDir', os.path.join(str(pathlib.Path.home()), '.jgo'))
-    config.set('settings', 'links', 'hard')
+    config.set('settings', 'links', 'auto')
 
     # repositories
     config.add_section('repositories')
@@ -345,7 +362,7 @@ def resolve_dependencies(
         endpoint_string,
         cache_dir,
         m2_repo,
-        link_type='hard',
+        link_type='auto',
         update_cache=False,
         force_update=False,
         manage_dependencies=False,