Just: drop the separator check, keep the single read of the variable

The check rejected a `JUST_CMD_RULE` that was not a shell comment. That is a
real failure mode, but not one worth code: setting the variable at all means
being able to run commands already, so the check only defended whoever set it
from themselves, and nothing sets it. The requirement is documented where the
value is read, which is where someone about to set it is looking.

`_given_rule` stays. Naming the value was about not spelling
`env('JUST_CMD_RULE', '')` twice, which stands whether or not it is checked.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: redsun82

misc/just/README.md

@@ -162,9 +162,8 @@ for itself, and the count is one per `mod` reached, however deeply nested, plus
 the file itself. That is cheap, and modules agree anyway since they share a terminal,
 but it is worth knowing before counting measurements. Presetting `JUST_CMD_RULE` skips
 all of them, and is also how to fix the width in CI or in a recording — it is the whole
-separator and ends up in a shell script, so it has to be a single line starting with
-`#`. Anything else is rejected rather than documented against, because otherwise it
-runs, silently and once per place the separator appears.
+separator and ends up in a shell script, so every line of it has to be a comment, or it
+runs.
 
 With no terminal to ask — a pipe, a log, a shell without `stty` — it falls back to a
 fixed 57 columns, so logs and CI output are the same width every time. That is one

misc/just/defs.just

@@ -29,10 +29,8 @@ error := f'{{ style("error") }}error{{ NORMAL }}: '
 # That is a branch, not a platform test: just runs `sh` everywhere.
 #
 # `JUST_CMD_RULE` is the whole separator and lands in a shell script, so a hand-set value
-# that is not a shell comment gets run -- silently, with a zero exit, once per place the
-# separator appears. Hence the check rather than a warning in prose: a rule is one line by
-# construction, so demanding one line starting with `#` rejects every value that would
-# run, without having to describe what running looks like.
+# has to be a shell comment, every line of it, or it runs. Left unchecked: setting it at
+# all means being able to run commands already, so there is nothing to defend.
 #
 # Exported and preferred over measuring: `shell()` runs on every parse, so a forwarded
 # verb would otherwise re-measure in every child it spawns, and `if` is lazy in its
@@ -44,7 +42,7 @@ _rule := if _given_rule == '' { shell('''
     w=$(stty size 2>/dev/null | cut -d" " -f2)
     case "$w" in '' | *[!0-9]*) w=57 ;; esac
     printf "%*s" $w "" | tr " " '#'
-''') } else if _given_rule =~ '^#[^\n]*$' { _given_rule } else { error('JUST_CMD_RULE must be a single line starting with `#`') }
+''') } else { _given_rule }
 
 export JUST_CMD_RULE := _rule