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

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

[Felipe Contreras]

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

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

[Oliver Kiddle]

Felipe Contreras wrote:
> readline uses \001 (start of header) and \002 (start of text) as markers

So the literal ASCII Ctrl-A and Ctrl-B characters and not the \001 etc
strings, right?

The main concern I have with this is whether there definitely is no use
of those two characters anywhere by any terminal for some other purpose
such that some user somewhere has them already in their prompt? And do
we know they won't form part of some other future terminal sequence? We
can find a special way to generate the literal characters but that only
helps with future uses, not backward compatibility.

I can understand the motivation to be able to support the lack of
prompt_percent and perhaps both bash and zsh in some plugin or other.
That aside, it is somewhat frustrating that zsh doesn't have full
control of terminal attributes in the prompt and I would advise anyone
to use prompt_percent. And in a plugin to add bash and zsh special case
code, even if this is added. Do we really want to encourage the use of
literal escapes?

> +	} else if(*bv->fm == 0x01) { // start non-visible characters

For now, we've not, to my knowledge, bumped our requirements to cover
C99, C17 etc so stick with old-style C comments in the code.*

Oliver

*Except I notice exceptions have crept into Src/Modules/curses.c
If we want to consider this, it should be a separate discussion.

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

[Felipe Contreras]

On Tue, Feb 28, 2023 at 10:29 AM Oliver Kiddle <opk@zsh.org> wrote:
>
> Felipe Contreras wrote:
> > readline uses \001 (start of header) and \002 (start of text) as markers
>
> So the literal ASCII Ctrl-A and Ctrl-B characters and not the \001 etc
> strings, right?

Yes.

> The main concern I have with this is whether there definitely is no use
> of those two characters anywhere by any terminal for some other purpose
> such that some user somewhere has them already in their prompt?

If that was an issue, wouldn't bash users have already experienced it
in the years this code has been active? (or possibly decades)

Moreover, can we agree that it's at least extremely unlikely for this
to be an actual issue?

> And do we know they won't form part of some other future terminal
> sequence?

Once again, can we agree that's unlikely? (especially since bash
already uses these)

> We can find a special way to generate the literal characters but that
> only helps with future uses, not backward compatibility.

Like what? A setopt flag?

> I can understand the motivation to be able to support the lack of
> prompt_percent and perhaps both bash and zsh in some plugin or other.

I personally don't care about the prompt_percent stuff, somebody else
mentioned it. The usefulness of sharing prompts between bash and zsh
is what I'm interested in.

> > +     } else if(*bv->fm == 0x01) { // start non-visible characters
>
> For now, we've not, to my knowledge, bumped our requirements to cover
> C99, C17 etc so stick with old-style C comments in the code.*

OK. Will fix in the next version.

-- 
Felipe Contreras

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

[Bart Schaefer]

Previous discussion of this starts at workers/50469

[PATCH v4] prompt: support generic non-visible regions

[Felipe Contreras]

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>
---
Interdiff against v3:
  diff --git a/Src/prompt.c b/Src/prompt.c
  index 8d7a38089..2ed90ebe1 100644
  --- a/Src/prompt.c
  +++ b/Src/prompt.c
  @@ -877,12 +877,12 @@ putpromptchar(int doprint, int endchar)
   		    bv->bp += strlen(bv->bp);
   		}
   	    }
  -	} else if(*bv->fm == 0x01) { // start non-visible characters
  +	} 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
  +	} else if(*bv->fm == 0x02) { /* end non-visible characters */
   	    if (bv->dontcount && !--bv->dontcount) {
   		addbufspc(1);
   		*bv->bp++ = Outpar;

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

diff --git a/Src/prompt.c b/Src/prompt.c
index 39fcf5eb7..2ed90ebe1 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