Re: Invisible PROMPT2

On Tue, Nov 19, 2019 at 12:09 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> You should follow the logic in pg_wcswidth: compute PQmblen() first,
> and bail out if it's more than the remaining string length, otherwise
> it's ok to apply PQdsplen().

Got it. I was worried that it wasn't safe to call even PQmblen(),
because I didn't know a fact about all encodings: as described in the
comment of pg_gb18030_mblen(), all implementations read only the first
byte to determine the length, except for GB18030 which reads the
second byte too, and that's OK because there's always a null
terminator.

> It might be a good idea to explicitly initialize last_prompt1_width to
> zero, for clarity.
>
> Should the user docs explicitly say "of the same width as the most recent
> output of PROMPT1", as you have in the comments? That seems a more
> precise specification, and it will eliminate some questions people will
> otherwise ask.
>
> LGTM otherwise.

Done, and pushed. I also skipped negative results from PQdsplen like
pg_wcswidth() does (that oversight explained why a non-readline build
showed the correct alignment for PROMPT1 '%[%033[1m%]%M
%n(at)%/%R%[%033[0m%]%# ' by strange concindence).

Thanks all for the feedback. I think the new bikeshed colour looks good.