[lldb] Improve error message for modules with dots or dashes

LLDB does not like to import Python files with dashes or dots in their
name. While the former are technically allowed, it is discouraged. Dots
are allowed for subpackages but not in module names. This patch improves
the user experience by printing a useful error.

Before this patch:

  error: module importing failed: SyntaxError('invalid syntax',
  ('<string>', 1, 11, 'import foo-bar\n'))

After this patch:

  error: module importing failed: Python discourages dashes in module
  names: foo-bar

rdar://74263511

[1] https://www.python.org/dev/peps/pep-0008/#package-and-module-names

Differential revision: https://reviews.llvm.org/D96833

lldb/source/Plugins/ScriptInterpreter/Python/ScriptInterpreterPython.cpp

@@ -2781,6 +2781,7 @@ bool ScriptInterpreterPythonImpl::LoadScriptingModule(
   };
 
   std::string module_name(pathname);
+  bool possible_package = false;
 
   if (extra_search_dir) {
     if (llvm::Error e = ExtendSysPath(extra_search_dir.GetPath())) {
@@ -2805,6 +2806,7 @@ bool ScriptInterpreterPythonImpl::LoadScriptingModule(
         return false;
       }
       // Not a filename, probably a package of some sort, let it go through.
+      possible_package = true;
     } else if (is_directory(st) || is_regular_file(st)) {
       if (module_file.GetDirectory().IsEmpty()) {
         error.SetErrorString("invalid directory name");
@@ -2831,6 +2833,18 @@ bool ScriptInterpreterPythonImpl::LoadScriptingModule(
       module_name.resize(module_name.length() - 4);
   }
 
+  if (!possible_package && module_name.find('.') != llvm::StringRef::npos) {
+    error.SetErrorStringWithFormat(
+        "Python does not allow dots in module names: %s", module_name.c_str());
+    return false;
+  }
+
+  if (module_name.find('-') != llvm::StringRef::npos) {
+    error.SetErrorStringWithFormat(
+        "Python discourages dashes in module names: %s", module_name.c_str());
+    return false;
+  }
+
   // check if the module is already import-ed
   StreamString command_stream;
   command_stream.Clear();