Add option for prepending arbitrary cmd-line args

README.rst

@@ -21,6 +21,7 @@ Install into the same virtualenv as pyls itself.
 
 Configuration
 -------------
+``prepend`` (default is ``[]``) list of additional command-line options to prepend
 
 ``live_mode`` (default is True) provides type checking as you type.
 
@@ -41,7 +42,8 @@ Depending on your editor, the configuration should be roughly like this:
             "pyls_mypy":
             {
                 "enabled": true,
-                "live_mode": false
+                "live_mode": false,
+                "prepend": ["--python-executable", "/tmp/foo/bin/python"]
             }
         }
     }

pyls_mypy/plugin.py

@@ -72,6 +72,10 @@ def pyls_lint(config, workspace, document, is_saved):
     if settings.get('strict', False):
         args.append('--strict')
 
+    prepend = settings.get('prepend')
+    if prepend:
+        args = prepend + args
+
     report, errors, _ = mypy_api.run(args)
 
     diagnostics = []

test/test_plugin.py

@@ -65,3 +65,38 @@ def test_parse_line_with_context(monkeypatch, word, bounds):
     assert diag['message'] == '"Request" has no attribute "id"'
     assert diag['range']['start'] == {'line': 278, 'character': bounds[0]}
     assert diag['range']['end'] == {'line': 278, 'character': bounds[1]}
+
+
+def test_option_prepend(tmpdir, monkeypatch):
+    import sys
+    from textwrap import dedent
+
+    sentinel = tmpdir / 'ran'
+
+    source = dedent(
+        """\
+        #!/bin/sh
+        touch {}
+        exec {} "$@"
+        """
+    ).format(sentinel, sys.executable)
+
+    wrapper = tmpdir / 'bin/wrapper'
+    wrapper.write(source, ensure=True)
+    wrapper.chmod(0o700)
+
+    monkeypatch.setattr(
+        FakeConfig,
+        'plugin_settings',
+        lambda *_: {'prepend': ['--python-executable', wrapper.strpath]}
+    )
+
+    assert not sentinel.exists()
+    diags = plugin.pyls_lint(
+        config=FakeConfig(),
+        workspace=None,
+        document=Document(DOC_URI, DOC_TYPE_ERR),
+        is_saved=False,
+    )
+    assert len(diags) == 1
+    assert sentinel.exists()