snaplist: improve hack to display double stars instead of ✓

We used to rely on the narrow non-breakable space to be displayed as a
star in basic mode. This is not great and could impact other screens.

We now make use of two check-marks (each replaced by a star in basic
mode) and mask one of them in rich mode using display attributes.

Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>

subiquity/ui/views/snaplist.py

@@ -16,6 +16,7 @@
 import asyncio
 import datetime
 import logging
+from typing import Tuple
 
 import yaml
 
@@ -104,6 +105,20 @@ def format_datetime(d):
     return _("{amount:2} {unit} ago").format(amount=amount, unit=unit)
 
 
+def check_mark() -> Tuple[Tuple[str, str], ...]:
+    """ Return a tuple that can be passed to a urwid.Text() """
+
+    # We want a single check-mark "✓" in rich-mode but a double star "**" in
+    # basic mode.  Because we have a 1:1 mapping between a given unicode
+    # character and its ASCII substitute, we use two check-marks and make one
+    # invisible in rich-mode. In basic mode, they both get substituted with a
+    # star.
+    return (
+        ('verified', '\N{check mark}'),
+        ('verified invisible', '\N{check mark}'),
+    )
+
+
 class SnapInfoView(WidgetWrap):
 
     # This is mostly like a Pile but it tries to be a bit smart about
@@ -182,9 +197,8 @@ class SnapInfoView(WidgetWrap):
 
         publisher = [('info_minor', _("by: ")), snap.publisher]
         if snap.verified:
-            # Check extend_dec_special_charmap for the meaning of the
-            # narrow non-breakable space here.
-            publisher.append(('verified', ' \N{check mark}\N{NNBSP}'))
+            publisher.append(" ")
+            publisher.extend(check_mark())
         elif snap.starred:
             publisher.append(' \N{circled white star}')
 
@@ -439,9 +453,7 @@ class SnapListView(BaseView):
                 self, snap, snap.name in self.selections_by_name)
             publisher = [snap.publisher]
             if snap.verified:
-                # Check extend_dec_special_charmap for the meaning of the
-                # narrow non-breakable space here.
-                publisher.append(('verified', '\N{check mark}\N{NNBSP}'))
+                publisher.extend(check_mark())
             elif snap.starred:
                 publisher.append('\N{circled white star}')
             row = [
@@ -453,7 +465,11 @@ class SnapListView(BaseView):
             body.append(AttrMap(
                 TableRow(row),
                 'menu_button',
-                {None: 'menu_button focus', 'verified': 'verified focus'},
+                {
+                    None: 'menu_button focus',
+                    'verified': 'verified focus',
+                    'verified invisible': 'verified inv focus'
+                },
                 ))
         table = NoTabCyclingTableListBox(
             body,

subiquitycore/palette.py

@@ -66,6 +66,8 @@ PALETTE_COLOR = [
 
     ('verified',            'good',    'bg'),
     ('verified focus',      'good',    'gray'),
+    ('verified invisible',  'bg',      'bg'),
+    ('verified inv focus',  'gray',    'gray'),
 ]
 
 PALETTE_MONO = [
@@ -100,6 +102,8 @@ PALETTE_MONO = [
 
     ('verified',            'white',   'black'),
     ('verified focus',      'black',   'white'),
+    ('verified invisible',  'white',   'black'),
+    ('verified inv focus',  'black',   'white'),
 ]
 
 urwid_8_names = (

subiquitycore/tui.py

@@ -53,11 +53,6 @@ def extend_dec_special_charmap():
         ord('\N{upper half block}'): '=',
         ord('\N{FULL BLOCK}'): urwid.escape.DEC_SPECIAL_CHARMAP[
             ord('\N{BOX DRAWINGS LIGHT VERTICAL}')],
-        # XXX: Hack to show the verified snap publishers with two stars when
-        # unicode is not supported. In rich mode, we display ✪ followed by a
-        # mostly invisible character (i.e., NNBSP). In basic mode,
-        # both characters get translated to a star, resulting in two stars.
-        ord('\N{NNBSP}'): '*',
     })