* lisp/emacs-lisp/cconv.el: Improve line-nb info of unused var warnings

Instead of warning about unused vars during the analysis phase of
closure conversion, do it in the actual closure conversion by
annotating the code with "unused" warnings, so that the warnings
get emitted later by the bytecomp phase, like all other warnings,
at which point the line-number info is a bit less imprecise.

Take advantage of this change to wrap the expressions of unused
let-bound vars inside (ignore ...) so the byte-compiler can better
optimize them away.

Finally, promote `macroexp--warn-and-return` to "official" status
by removing its "--" marker.

(cconv-captured+mutated, cconv-lambda-candidates): Remove vars.
(cconv-var-classification): New var to replace them.
(cconv-warnings-only): Delete function.
(cconv--warn-unused-msg, cconv--var-classification): New functions.
(cconv--convert-funcbody): Add warnings for unused args.
(cconv-convert): Add warnings for unused vars in `let` and `condition-case`.
(cconv--analyze-use): Don't emit an "unused var" warning any more,
but instead remember the fact in `cconv-var-classification`.

* lisp/emacs-lisp/bytecomp.el (byte-compile-force-lexical-warnings):
Remove variable.
(byte-compile-preprocess): Remove corresponding case.

* lisp/emacs-lisp/pcase.el (pcase--if): Don't throw away `test` effects.
(\`):
* lisp/emacs-lisp/cl-macs.el (cl--do-arglist): Use `car-safe` instead
of `car`, so it can more easily be removed by the optimizer if the
result is not used.

* lisp/emacs-lisp/macroexp.el (macroexp--warn-wrap): New function.
(macroexp-warn-and-return): Rename from `macroexp--warn-and-return`.

1 files changed, 7 insertions, 5 deletions

diff --git a/lisp/emacs-lisp/pcase.el b/lisp/emacs-lisp/pcase.el
index c7288b7fa2a..95e5dd3ba01 100644
--- a/lisp/emacs-lisp/pcase.el
+++ b/lisp/emacs-lisp/pcase.el
@@ -469,8 +469,10 @@ for the result of evaluating EXP (first arg to `pcase').
 ;; the depth of the generated tree.
 (defun pcase--if (test then else)
   (cond
-   ((eq else :pcase--dontcare) then)
-   ((eq then :pcase--dontcare) (debug) else) ;Can/should this ever happen?
+   ((eq else :pcase--dontcare) `(progn (ignore ,test) ,then))
+   ;; This happens very rarely.  Known case:
+   ;;     (pcase EXP ((and 1 pcase--dontcare) FOO))
+   ((eq then :pcase--dontcare) `(progn (ignore ,test) ,else))
    (t (macroexp-if test then else))))
 
 ;; Note about MATCH:
@@ -845,7 +847,7 @@ Otherwise, it defers to REST which is a list of branches of the form
        ((memq upat '(t _))
         (let ((code (pcase--u1 matches code vars rest)))
           (if (eq upat '_) code
-            (macroexp--warn-and-return
+            (macroexp-warn-and-return
              "Pattern t is deprecated.  Use `_' instead"
              code))))
        ((eq upat 'pcase--dontcare) :pcase--dontcare)
@@ -971,8 +973,8 @@ The predicate is the logical-AND of:
               (nreverse upats))))
    ((consp qpat)
     `(and (pred consp)
-          (app car ,(list '\` (car qpat)))
-          (app cdr ,(list '\` (cdr qpat)))))
+          (app car-safe ,(list '\` (car qpat)))
+          (app cdr-safe ,(list '\` (cdr qpat)))))
    ((or (stringp qpat) (numberp qpat) (symbolp qpat)) `',qpat)
    ;; In all other cases just raise an error so we can't break
    ;; backward compatibility when adding \` support for other