ui: fix escape sequences in in readline prompts (issue6930)

Text that is meant to represent zero-width output in a readline
prompt, such as terminal escape sequences, is supposed to be
delimited by \001 ... \002:

> Applications may indicate that the prompt contains characters that
> take up no physical screen space when displayed by bracketing a
> sequence of such characters with the special markers
> RL_PROMPT_START_IGNORE and RL_PROMPT_END_IGNORE (declared in
> readline.h `\001' and `\002', respectively).  This may be used to
> embed terminal-specific escape sequences in prompts.

https://tiswww.cwru.edu/php/chet/readline/readline.html#index-rl_005fexpand_005fprompt

When formatting a readline prompt in ui._readline, arrange to do this
in the color.py labelling routines.  Keeping mutable dynamically
scoped state like this isn't great but threading it as a parameter
through all the subroutines seems like much more trouble.

(This doesn't address the missing line break -- that's a separate bug
in libedit.)

https://bz.mercurial-scm.org/show_bug.cgi?id=6930

mercurial/color.py

@@ -386,6 +386,9 def _render_effects(ui, text, effects):
         ]
         start = b'\033[' + b';'.join(start) + b'm'
         stop = b'\033[' + pycompat.bytestr(activeeffects[b'none']) + b'm'
+        if ui._readlineprompt:
+            start = b'\001' + start + b'\001'
+            stop = b'\002' + stop + b'\002'
     return _mergeeffects(text, start, stop)
 
 
@@ -518,7 +521,8 if pycompat.iswindows:
         else:
             origattr = csbi.wAttributes
             ansire = re.compile(
-                br'\033\[([^m]*)m([^\033]*)(.*)', re.MULTILINE | re.DOTALL
+                br'\001?\033\[([^m]*)m\002?([^\033]*)(.*)',
+                re.MULTILINE | re.DOTALL,
             )
 
     def win32print(ui, writefunc, text, **opts):

mercurial/ui.py

@@ -265,6 +265,8 class ui:
         self.logblockedtimes = False
         # color mode: see mercurial/color.py for possible value
         self._colormode = None
+        # readline prompt: is this currently for a readline prompt?
+        self._readlineprompt = False
         self._terminfoparams = {}
         self._styles = {}
         self._uninterruptible = False
@@ -1745,7 +1747,12 class ui:
             self.flush()
             prompt = b' '
         else:
-            prompt = self.label(prompt, b'ui.prompt') + b' '
+            wasreadlineprompt = self._readlineprompt
+            try:
+                self._readlineprompt = True
+                prompt = self.label(prompt, b'ui.prompt') + b' '
+            finally:
+                self._readlineprompt = wasreadlineprompt
 
         # prompt ' ' must exist; otherwise readline may delete entire line
         # - http://bugs.python.org/issue12833