Remember user choices

There are 2 things we ask for input for:

- input variables
- exception breakpoints

It's irritating to have to repeat yourself when going through the
edit/debug loop.

Howver, cacheing has some quirks and disadvantages - they key one being
when to clear the cache. To resolve this we take two slightly different
approaches:

1. For input variables, we remember the choice of the user, but present
that only as the default, so they can just hit enter to accept it. We
already rememeber the choices for the length of the debug session (i.e.
across 'restart' calls).

2. For exception breakpoints, we remember the choices for as long as the
current session is running.

This allows users to hit the 'restart' button without being prompted at
all.

Meanwhile, we also remove the (broken) support for exception breakpoint
matchers and state the server default for exception breakpoint filters.

python3/vimspector/utils.py

@@ -261,10 +261,16 @@ def SelectFromList( prompt, options ):
       return None
 
 
-def AskForInput( prompt ):
+def AskForInput( prompt, default_value = None ):
+  if default_value is None:
+    default_option = ''
+  else:
+    default_option = ", '{}'".format( Escape( default_value ) )
+
   with InputSave():
     try:
-      return vim.eval( "input( '{0}' )".format( Escape( prompt ) ) )
+      return vim.eval( "input( '{}' {} )".format( Escape( prompt ),
+                                                  default_option ) )
     except KeyboardInterrupt:
       return ''
 
@@ -306,7 +312,7 @@ def IsCurrent( window, buf ):
 
 # TODO: Should we just run the substitution on the whole JSON string instead?
 # That woul dallow expansion in bool and number values, such as ports etc. ?
-def ExpandReferencesInDict( obj, mapping, **kwargs ):
+def ExpandReferencesInDict( obj, mapping, user_choices ):
   def expand_refs_in_string( orig_s ):
     s = os.path.expanduser( orig_s )
     s = os.path.expandvars( s )
@@ -318,13 +324,16 @@ def ExpandReferencesInDict( obj, mapping, **kwargs ):
       ++bug_catcher
 
       try:
-        s = string.Template( s ).substitute( mapping, **kwargs )
+        s = string.Template( s ).substitute( mapping )
         break
       except KeyError as e:
         # HACK: This is seemingly the only way to get the key. str( e ) returns
         # the key surrounded by '' for unknowable reasons.
         key = e.args[ 0 ]
-        mapping[ key ] = AskForInput( 'Enter value for {}: '.format( key ) )
+        default_value = user_choices.get( key, None )
+        mapping[ key ] = AskForInput( 'Enter value for {}: '.format( key ),
+                                      default_value )
+        user_choices[ key ] = mapping[ key ]
         _logger.debug( "Value for %s not set in %s (from %s): set to %s",
                        key,
                        s,
@@ -339,7 +348,7 @@ def ExpandReferencesInDict( obj, mapping, **kwargs ):
 
   def expand_refs_in_object( obj ):
     if isinstance( obj, dict ):
-      ExpandReferencesInDict( obj, mapping, **kwargs )
+      ExpandReferencesInDict( obj, mapping, user_choices )
     elif isinstance( obj, list ):
       for i, _ in enumerate( obj ):
         # FIXME: We are assuming that it is a list of string, but could be a
@@ -354,7 +363,7 @@ def ExpandReferencesInDict( obj, mapping, **kwargs ):
     obj[ k ] = expand_refs_in_object( obj[ k ] )
 
 
-def ParseVariables( variables_list, mapping, **kwargs ):
+def ParseVariables( variables_list, mapping, user_choices ):
   new_variables = {}
   new_mapping = mapping.copy()
 
@@ -371,7 +380,7 @@ def ParseVariables( variables_list, mapping, **kwargs ):
 
           new_v = v.copy()
           # Bit of a hack. Allows environment variables to be used.
-          ExpandReferencesInDict( new_v, new_mapping, **kwargs )
+          ExpandReferencesInDict( new_v, new_mapping, user_choices )
 
           env = os.environ.copy()
           env.update( new_v.get( 'env' ) or {} )