Trac #29291: Check for required extension module "ssl" in python3 build and spkg-configure

Follow up from #27705.

As openssl has been a standard package since Sage 9.3, there is no more
point in accepting system python3 without ssl support or ignoring errors
in building the ssl module when building the python3 spkg.

As SSL issues are no longer a likely diagnosis for failures with
launching the notebook, we change the corresponding code in `src/bin
/sage-notebook`. (Prompted by https://groups.google.com/g/sage-
devel/c/IXypXTbVkDM/m/CsWl8HbZAwAJ)

URL: https://trac.sagemath.org/29291
Reported by: mkoeppe
Ticket author(s): Matthias Koeppe
Reviewer(s): John Palmieri

Author: Release Manager

build/pkgs/python3/spkg-build.in

@@ -107,7 +107,7 @@ fi
 echo "Testing importing of various modules..."
 import_errors=false
 # Trac #31160: We no longer check for readline here.
-test_modules="ctypes math hashlib crypt socket zlib sqlite3"
+test_modules="ctypes math hashlib crypt socket zlib sqlite3 ssl"
 if [ "$UNAME" = "Darwin" ]; then
     test_modules="$test_modules _scproxy"
 fi

build/pkgs/python3/spkg-configure.m4

@@ -23,7 +23,7 @@ SAGE_SPKG_CONFIGURE([python3], [
       dnl Check if we can do venv with a system python3
       dnl instead of building our own copy.
       dnl  Trac #31160: We no longer check for readline here.
-      check_modules="sqlite3, ctypes, math, hashlib, crypt, socket, zlib, distutils.core"
+      check_modules="sqlite3, ctypes, math, hashlib, crypt, socket, zlib, distutils.core, ssl"
       AC_CACHE_CHECK([for python3 >= ]MIN_VERSION[, < ]LT_VERSION[ with modules $check_modules], [ac_cv_path_PYTHON3], [
         AS_IF([test x"$ac_path_PYTHON3" != x], [dnl checking explicitly specified $with_python
            AC_MSG_RESULT([])

src/bin/sage-notebook

@@ -13,13 +13,10 @@ logger = logging.getLogger()
 from sage.misc.banner import banner
 
 
-class NotebookJupyter(object):
+_system_jupyter_url = "https://doc.sagemath.org/html/en/installation/launching.html#setting-up-sagemath-as-a-jupyter-kernel-in-an-existing-jupyter-notebook-or-jupyterlab-installation"
+
 
-    PREREQUISITE_ERROR = textwrap.dedent("""
-    The Jupyter notebook requires ssl, even if you do not use
-    https. Install the openssl development packages in your system and
-    then rebuild Python (sage -f python3).
-    """)
+class NotebookJupyter(object):
 
     def print_banner(self):
         banner()
@@ -31,11 +28,18 @@ class NotebookJupyter(object):
 
     def __init__(self, argv):
         self.print_banner()
-        from sage.repl.ipython_kernel.install import have_prerequisites
-        if not have_prerequisites():
-            print(self.PREREQUISITE_ERROR)
+        try:
+            from notebook.notebookapp import main
+        except ImportError:
+            import traceback
+            traceback.print_exc()
+            print("The Jupyter notebook is not installed (at least not in this Sage installation).")
+            print("You can install it by running")
+            print("  sage -i notebook")
+            print("Alternatively, you can follow the instructions at")
+            print("  " + _system_jupyter_url)
+            print("to use Sage with an existing Jupyter notebook installation.")
             raise SystemExit(1)
-        from notebook.notebookapp import main
         main(argv)
 
 
@@ -52,12 +56,17 @@ class NotebookJupyterlab(object):
         try:
             from jupyterlab.labapp import main
         except ImportError:
+            import traceback
+            traceback.print_exc()
             print("Jupyterlab is not installed (at least not in this Sage installation).")
             print("You can install it by running")
             print("  sage -i jupyterlab_widgets")
             print("which includes support for interacts and the ability to download and")
             print("install other Jupyterlab extensions. For a minimal installation, run")
             print("  sage -i jupyterlab")
+            print("Alternatively, you can follow the instructions at")
+            print("  " + _system_jupyter_url)
+            print("to use Sage with an existing Jupyterlab installation.")
             raise SystemExit(1)
         self.print_banner()
         main(argv)