New variable 'macroexp-enable-pos-preservation' (bug#79599)

* lisp/emacs-lisp/macroexp.el
(macroexp-enable-pos-preservation): New variable.
(macroexp-preserve-posification): Respect it.
* lisp/emacs-lisp/elisp-scope.el (elisp-scope-1): Use it.
* test/lisp/emacs-lisp/macroexp-tests.el
(macroexp--test-macroexp-enable-pos-preservation): New test.

lisp/emacs-lisp/elisp-scope.el

@@ -2794,6 +2794,7 @@ are analyzed."
                    (symbols-with-pos-enabled t)
                    (message-log-max nil)
                    (inhibit-message t)
+                   (macroexp-enable-pos-preservation nil)
                    (macroexpand-all-environment
                     (append (mapcar #'list elisp-scope-unsafe-macros) macroexpand-all-environment)))
                (ignore-errors (macroexpand-1 form macroexpand-all-environment)))

lisp/emacs-lisp/macroexp.el

@@ -304,6 +304,9 @@ modified FORM."
   (let ((new-form (macroexp--posify-form-1 form call-pos 10)))
     (or new-form form)))
 
+(defvar macroexp-enable-pos-preservation t
+  "Whether to attach position of a macro call to the expanded form.")
+
 (defmacro macroexp-preserve-posification (pos-form &rest body)
   "Evaluate BODY..., posifying the result with POS-FORM's position, if any.
 If the result of body happens to have a position already, we do not
@@ -316,7 +319,7 @@ change this."
                     ((symbol-with-pos-p ,pos-form)
                      (symbol-with-pos-pos ,pos-form))))
          (new-value (progn ,@body)))
-     (if (and call-pos
+     (if (and macroexp-enable-pos-preservation call-pos
               (not (or (and (consp new-value)
                             (symbol-with-pos-p (car new-value)))
                        (and (symbol-with-pos-p new-value)))))

test/lisp/emacs-lisp/macroexp-tests.el

@@ -182,4 +182,25 @@
               (user-error (error-message-string err))))))
      (should (and (stringp res) (string-match "new-replacement" res))))))
 
+(defmacro macroexp--test-with-foo (&rest body)
+  "Eagerly macro-expand BODY."
+  (macroexpand-all `(progn . ,body) macroexpand-all-environment))
+
+(ert-deftest macroexp--test-macroexp-enable-pos-preservation ()
+  (let* ((symbols-with-pos-enabled t)
+         (form (read-positioning-symbols
+                "(macroexp--test-with-foo (pop command-history))"))
+         (pop-pos (symbol-with-pos-pos (caadr form)))
+         (exp1 (macroexpand-1 form))
+         (macroexp-enable-pos-preservation nil)
+         (exp2 (macroexpand-1 form)))
+    ;; Position of `pop' preserved in EXP1.  There's no way to tell that
+    ;; the position information in EXP1 is synthetic, which may confuse
+    ;; consumers such as semantic highlighting.
+    (should (symbol-with-pos-p (caadr exp1)))
+    (should (= (symbol-with-pos-pos (caadr exp1)) pop-pos))
+    ;; Position preservation was disabled, so EXP2 is clean of synthetic
+    ;; position information.
+    (should-not (symbol-with-pos-p (caadr exp2)))))
+
 ;;; macroexp-tests.el ends here