Start doc server if local doc is available

Author: kwankyu

src/bin/sage-notebook

@@ -186,30 +186,24 @@ def trac_23428_browser_workaround():
 
 @contextmanager
 def sage_doc_server():
-    from sage.env import SAGE_DOC_SERVER_URL
-
-    if SAGE_DOC_SERVER_URL:
-        print(f'Sage doc server running at {SAGE_DOC_SERVER_URL}')
-        yield
-    else:
-        from functools import partial
-        from http.server import SimpleHTTPRequestHandler, ThreadingHTTPServer
-        from threading import Thread
+    from functools import partial
+    from http.server import SimpleHTTPRequestHandler, ThreadingHTTPServer
+    from threading import Thread
 
-        from sage.env import SAGE_DOC, SAGE_DOC_LOCAL_PORT as port
+    from sage.env import SAGE_DOC, SAGE_DOC_LOCAL_PORT as port
 
-        server = ThreadingHTTPServer(('localhost', int(port)),
-            partial(SimpleHTTPRequestHandler, directory=SAGE_DOC))
-        server_thread = Thread(target=server.serve_forever, name="sage_doc_server")
-        server_thread.start()
-        print(f'Sage doc server started running at http://localhost:{port}')
+    server = ThreadingHTTPServer(('localhost', int(port)),
+        partial(SimpleHTTPRequestHandler, directory=SAGE_DOC))
+    server_thread = Thread(target=server.serve_forever, name="sage_doc_server")
+    server_thread.start()
+    print(f'Sage doc server started running at http://localhost:{port}')
 
-        try:
-            yield
-        finally:
-            server.shutdown()
-            server_thread.join()
-            print(f'Sage doc server stopped runnning at http://localhost:{port}')
+    try:
+        yield
+    finally:
+        server.shutdown()
+        server_thread.join()
+        print(f'Sage doc server stopped runnning at http://localhost:{port}')
 
 
 if __name__ == '__main__':
@@ -254,5 +248,17 @@ if __name__ == '__main__':
 
     banner()
 
-    with sage_doc_server():
+    # Start a Sage doc server if the Sage documentation is available locally.
+    # See the corresponding code in src/sage/repl/ipython_kernel/kernel.py.
+
+    from sage.env import SAGE_DOC_SERVER_URL
+    from sage.features.sagemath import sagemath_doc_html
+
+    if SAGE_DOC_SERVER_URL:
+        print(f'Sage doc server running at {SAGE_DOC_SERVER_URL}')
+        launcher(unknown)
+    elif sagemath_doc_html().is_present():
+        with sage_doc_server():
+            launcher(unknown)
+    else:
         launcher(unknown)

src/sage/repl/ipython_kernel/kernel.py

@@ -103,16 +103,24 @@ def help_links(self):
               'url': '.../html/en/index.html'},
              ...]
         """
-        from sage.env import SAGE_DOC_SERVER_URL as url
+        # A Sage doc server starts when Jupyter notebook launches if the Sage
+        # documentation is available locally.  See the corresponding code in
+        # src/bin/sage-notebook.
 
-        if url:
+        from sage.env import SAGE_DOC_SERVER_URL
+        from sage.features.sagemath import sagemath_doc_html
+
+        if SAGE_DOC_SERVER_URL:
             def doc_url(path):
-                return '{}/{}'.format(url, path)
-        else:
+                return f'{SAGE_DOC_SERVER_URL}/{path}'
+        elif sagemath_doc_html().is_present():
             from sage.env import SAGE_DOC_LOCAL_PORT as port
 
             def doc_url(path):
-                return 'http://localhost:{}/{}'.format(port, path)
+                return f'http://localhost:{port}/{path}'
+        else:
+            def doc_url(path):
+                return f'https://doc.sagemath.org/{path}'
 
         return [
             {