bug#69108: false-positive warning "variable ‘_’ not left unused" in if-let* and if-let

[Michael Heerdegen via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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Eli Zaretskii <eliz@gnu.org> writes:

> > [...] repeating a test.  Is this what you prefer?
>
> Yes, I think so.  And you could perhaps avoid repetition of
> (cdr binding) by saving the result of (null (cdr binding)) in
> a local variable.

I went with a separate `cond' branch added instead, I think this is even
simpler.  Ok?


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From 83d42089a77bc0fa4745f708ca73b5e7cddd1829 Mon Sep 17 00:00:00 2001
From: Michael Heerdegen <michael_heerdegen@web.de>
Date: Fri, 16 Feb 2024 22:07:18 +0100
Subject: [PATCH 1/2] Don't warn about _ not left unused in if-let and alike

The macro expansions did not leave a variable _ unused; this triggered
an irritating compiler warning (bug#69108).

* lisp/subr.el (internal--build-binding): Handle bindings of the form
(_ EXPR) separately.
---
 lisp/subr.el | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/lisp/subr.el b/lisp/subr.el
index c317d558e24..afbe6845d7a 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -2580,6 +2580,8 @@ internal--build-binding
           (list binding binding))
          ((null (cdr binding))
           (list (make-symbol "s") (car binding)))
+         ((eq '_ (car binding))
+          (list (make-symbol "s") (cadr binding)))
          (t binding)))
   (when (> (length binding) 2)
     (signal 'error
--
2.39.2


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> > {My unsuccessful doc tweaks}
>
> [...] I'd prefer to separate it.

Done.  Feel free to tune it to your likes.  Or send me an "ok", then
I'll just commit this version.


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From 117a82505c3fe9ec1148cb2a7b870cb8e2eb2b6d Mon Sep 17 00:00:00 2001
From: Michael Heerdegen <michael_heerdegen@web.de>
Date: Sun, 18 Feb 2024 02:27:56 +0100
Subject: [PATCH 2/2] WIP: ; * lisp/subr.el (if-let, and-let*): Tweak doc

---
 lisp/subr.el | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/lisp/subr.el b/lisp/subr.el
index afbe6845d7a..62600ff49bf 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -2622,7 +2622,7 @@ when-let*
 (defmacro and-let* (varlist &rest body)
   "Bind variables according to VARLIST and conditionally evaluate BODY.
 Like `when-let*', except if BODY is empty and all the bindings
-are non-nil, then the result is non-nil."
+are non-nil, then the result is the value of the last binding."
   (declare (indent 1) (debug if-let*))
   (let (res)
     (if varlist
@@ -2635,7 +2635,8 @@ if-let
   "Bind variables according to SPEC and evaluate THEN or ELSE.
 Evaluate each binding in turn, as in `let*', stopping if a
 binding value is nil.  If all are non-nil return the value of
-THEN, otherwise the last form in ELSE.
+THEN, otherwise the value of the last form in ELSE, or nil if
+there are none.

 Each element of SPEC is a list (SYMBOL VALUEFORM) that binds
 SYMBOL to the value of VALUEFORM.  An element can additionally be
--
2.39.2


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>   https://en.wikipedia.org/wiki/Construct_state

Thanks.  Did not expect that my change could be interpreted involving
genitive...


Michael.