* 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, 31 insertions, 26 deletions

diff --git a/lisp/emacs-lisp/macroexp.el b/lisp/emacs-lisp/macroexp.el
index d52aee5a4ad..4d04bfa091f 100644
--- a/lisp/emacs-lisp/macroexp.el
+++ b/lisp/emacs-lisp/macroexp.el
@@ -135,28 +135,33 @@ Other uses risk returning non-nil value that point to the wrong file."
 
 (defvar macroexp--warned (make-hash-table :test #'equal :weakness 'key))
 
-(defun macroexp--warn-and-return (msg form &optional compile-only)
+(defun macroexp--warn-wrap (msg form)
   (let ((when-compiled (lambda () (byte-compile-warn "%s" msg))))
-    (cond
-     ((null msg) form)
-     ((macroexp-compiling-p)
-      (if (and (consp form) (gethash form macroexp--warned))
-          ;; Already wrapped this exp with a warning: avoid inf-looping
-          ;; where we keep adding the same warning onto `form' because
-          ;; macroexpand-all gets right back to macroexpanding `form'.
-          form
-        (puthash form form macroexp--warned)
-        `(progn
-           (macroexp--funcall-if-compiled ',when-compiled)
-           ,form)))
-     (t
-      (unless compile-only
-        (message "%sWarning: %s"
-                 (if (stringp load-file-name)
-                     (concat (file-relative-name load-file-name) ": ")
-                   "")
-                 msg))
-      form))))
+    `(progn
+       (macroexp--funcall-if-compiled ',when-compiled)
+       ,form)))
+
+(define-obsolete-function-alias 'macroexp--warn-and-return
+  #'macroexp-warn-and-return "28.1")
+(defun macroexp-warn-and-return (msg form &optional compile-only)
+  (cond
+   ((null msg) form)
+   ((macroexp-compiling-p)
+    (if (and (consp form) (gethash form macroexp--warned))
+        ;; Already wrapped this exp with a warning: avoid inf-looping
+        ;; where we keep adding the same warning onto `form' because
+        ;; macroexpand-all gets right back to macroexpanding `form'.
+        form
+      (puthash form form macroexp--warned)
+      (macroexp--warn-wrap msg form)))
+   (t
+    (unless compile-only
+      (message "%sWarning: %s"
+               (if (stringp load-file-name)
+                   (concat (file-relative-name load-file-name) ": ")
+                 "")
+               msg))
+    form)))
 
 (defun macroexp--obsolete-warning (fun obsolescence-data type)
   (let ((instead (car obsolescence-data))
@@ -205,7 +210,7 @@ Other uses risk returning non-nil value that point to the wrong file."
                  (byte-compile-warning-enabled-p 'obsolete (car form))))
         (let* ((fun (car form))
                (obsolete (get fun 'byte-obsolete-info)))
-          (macroexp--warn-and-return
+          (macroexp-warn-and-return
            (macroexp--obsolete-warning
             fun obsolete
             (if (symbolp (symbol-function fun))
@@ -260,7 +265,7 @@ Other uses risk returning non-nil value that point to the wrong file."
                    values (cdr values))))
       (setq arglist (cdr arglist)))
     (if values
-        (macroexp--warn-and-return
+        (macroexp-warn-and-return
          (format (if (eq values 'too-few)
                      "attempt to open-code `%s' with too few arguments"
                    "attempt to open-code `%s' with too many arguments")
@@ -314,7 +319,7 @@ Assumes the caller has bound `macroexpand-all-environment'."
                        (macroexp--cons (macroexp--all-clauses bindings 1)
                                        (if (null body)
                                            (macroexp-unprogn
-                                            (macroexp--warn-and-return
+                                            (macroexp-warn-and-return
                                              (format "Empty %s body" fun)
                                              nil t))
                                          (macroexp--all-forms body))
@@ -344,13 +349,13 @@ Assumes the caller has bound `macroexpand-all-environment'."
       ;; First arg is a function:
       (`(,(and fun (or 'funcall 'apply 'mapcar 'mapatoms 'mapconcat 'mapc))
          ',(and f `(lambda . ,_)) . ,args)
-       (macroexp--warn-and-return
+       (macroexp-warn-and-return
         (format "%s quoted with ' rather than with #'"
                 (list 'lambda (nth 1 f) '...))
         (macroexp--expand-all `(,fun #',f . ,args))))
       ;; Second arg is a function:
       (`(,(and fun (or 'sort)) ,arg1 ',(and f `(lambda . ,_)) . ,args)
-       (macroexp--warn-and-return
+       (macroexp-warn-and-return
         (format "%s quoted with ' rather than with #'"
                 (list 'lambda (nth 1 f) '...))
         (macroexp--expand-all `(,fun ,arg1 #',f . ,args))))