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