lsp: handle missing modules gracefully

Also removed hard install requirement of pygls where users are not
interested in using pyang as an LSP server.

Signed-off-by: Siddharth Sharma <[email protected]>

dev-requirements.txt

@@ -4,4 +4,3 @@ pyflakes
 flake8
 pylint
 virtualenv
-pygls

pyang/lsp/__init__.py

@@ -1,4 +1 @@
 """pyang library to serve Microsoft LSP"""
-
-__version__ = "0.0.1"
-__date__ = "2024-05-10"

pyang/lsp/server.py

@@ -1,7 +1,6 @@
 """pyang LSP handling"""
 
 from __future__ import absolute_import
-import io
 import optparse
 import tempfile
 from pathlib import Path
@@ -14,9 +13,15 @@
 from pyang.translators import yang
 
 from lsprotocol import types as lsp
-
 from pygls.server import LanguageServer
 
+import importlib
+ext_deps = ['lsprotocol.types', 'pygls.server']
+def try_import_deps():
+    """Throws ModuleNotFoundError if external module dependencies are missing"""
+    for dep in ext_deps:
+        importlib.import_module(dep)
+
 SERVER_NAME = "pyangls"
 SERVER_VERSION = "v0.1"
 

pyang/scripts/pyang_tool.py

@@ -341,8 +341,15 @@ def run():
         p.pre_load_modules(ctx)
 
     if o.lsp:
-        pyangls.start_server(o, ctx, fmts)
-        sys.exit(0)
+        try:
+            pyangls.try_import_deps()
+            pyangls.start_server(o, ctx, fmts)
+            sys.exit(0)
+        except ModuleNotFoundError as e:
+            print("LSP feature required external dependencies are missing")
+            print(str(e))
+            print("Please resolve dependencies to use pyang as an LSP server")
+            sys.exit(1)
 
     exit_code = 0
     modules = []

requirements.txt

@@ -1,2 +1 @@
 lxml
-pygls

setup.py

@@ -60,7 +60,7 @@ def run_commands(self):
       " Provides a framework for plugins that can convert YANG modules" + \
       "to other formats.",
       url='https://github.com/mbj4668/pyang',
-      install_requires = ["lxml", "pygls"],
+      install_requires = ["lxml"],
       license='BSD',
       classifiers=[
             'Development Status :: 5 - Production/Stable',