[PATCH v3 try2] prompt: support generic non-visible regions

[Felipe Contreras <felipe.contreras@gmail.com>]

readline uses \001 (start of header) and \002 (start of text) as markers
to delimit a non-visible character zone, which are necessary to
calculate the width of a prompt.

In zsh we do this with %{ and %}, but we could support
\001 and \002 as well, so that a function which generates output for
the prompt can use colors in a way that works for both bash and zsh.

This additionally has the benefit of allowing prompts without
PROMPT_PERCENT to use colors correctly.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
---

No change since the previous try.

This is how I tested the nesting:

  $' %{\e[31m\x01\e[31m\x01\e[31m\x02\e[31m\x02\e[31m%}master%{\e[m\x01\e[m\x01\e[m\x02\e[m\x02\e[m%}'

And for the \001 and \002 reference:

https://git.savannah.gnu.org/cgit/readline.git/tree/display.c#n340

 Src/prompt.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Src/prompt.c b/Src/prompt.c
index 39fcf5eb7..8d7a38089 100644
--- a/Src/prompt.c
+++ b/Src/prompt.c
@@ -877,6 +877,16 @@ putpromptchar(int doprint, int endchar)
 		    bv->bp += strlen(bv->bp);
 		}
 	    }
+	} else if(*bv->fm == 0x01) { // start non-visible characters
+	    if (!bv->dontcount++) {
+		addbufspc(1);
+		*bv->bp++ = Inpar;
+	    }
+	} else if(*bv->fm == 0x02) { // end non-visible characters
+	    if (bv->dontcount && !--bv->dontcount) {
+		addbufspc(1);
+		*bv->bp++ = Outpar;
+	    }
 	} else {
 	    char c = *bv->fm == Meta ? *++bv->fm ^ 32 : *bv->fm;
 
-- 
2.39.2