scratch/handler-bind-2 10e04044c7b 06/16: (macroexp--with-extended-form-stack): Use plain `let`

[Stefan Monnier]

branch: scratch/handler-bind-2
commit 10e04044c7b2c84d4e32b8dc4d8891d6e6047bba
Author: Stefan Monnier <monnier@iro.umontreal.ca>
Commit: Stefan Monnier <monnier@iro.umontreal.ca>

    (macroexp--with-extended-form-stack): Use plain `let`
    
    `macroexp--with-extended-form-stack` used manual push/pop so that upon
    non-local exits the "deeper" value is kept, so the error handler gets
    to know what was the deeper value, so as to be able to compute more
    precise error locations.
    Replace this with a `handler-bind` which catches that "deeper" value
    more explicitly.
    
    * lisp/emacs-lisp/bytecomp.el (bytecomp--displaying-warnings):
    Use `handler-bind` to catch the value of `byte-compile-form-stack`
    at the time of the error.  Also consolidate the duplicated code.
    
    * lisp/emacs-lisp/macroexp.el (macroexp--with-extended-form-stack):
    Use a plain dynbound let-rebinding.
---
 lisp/emacs-lisp/bytecomp.el | 41 +++++++++++++++++++++++------------------
 lisp/emacs-lisp/macroexp.el | 10 ++--------
 2 files changed, 25 insertions(+), 26 deletions(-)

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 6c5051d70c4..69f651befba 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -1874,39 +1874,44 @@ It is too wide if it has any lines longer than the 
largest of
          (setq byte-to-native-plist-environment
                overriding-plist-environment)))))
 
-(defmacro displaying-byte-compile-warnings (&rest body)
+(defmacro displaying-byte-compile-warnings (&rest body) ;FIXME: Namespace!
   (declare (debug (def-body)))
   `(bytecomp--displaying-warnings (lambda () ,@body)))
 
 (defun bytecomp--displaying-warnings (body-fn)
-  (let* ((warning-series-started
+  (let* ((wrapped-body
+         (lambda ()
+           (if byte-compile-debug
+               (funcall body-fn)
+             ;; Use a `handler-bind' to remember the `byte-compile-form-stack'
+             ;; active at the time the error is signaled, so as to
+             ;; get more precise error locations.
+             (let ((form-stack nil))
+               (condition-case error-info
+                   (handler-bind
+                       ((error (lambda (_err)
+                                 (setq form-stack byte-compile-form-stack))))
+                     (funcall body-fn))
+                 (error (let ((byte-compile-form-stack form-stack))
+                          (byte-compile-report-error error-info))))))))
+        (warning-series-started
          (and (markerp warning-series)
               (eq (marker-buffer warning-series)
                   (get-buffer byte-compile-log-buffer))))
          (byte-compile-form-stack byte-compile-form-stack))
-    (if (or (eq warning-series 'byte-compile-warning-series)
+    (if (or (eq warning-series #'byte-compile-warning-series)
            warning-series-started)
        ;; warning-series does come from compilation,
        ;; so don't bind it, but maybe do set it.
-       (let (tem)
-         ;; Log the file name.  Record position of that text.
-         (setq tem (byte-compile-log-file))
+       (let ((tem (byte-compile-log-file))) ;; Log the file name.
          (unless warning-series-started
-           (setq warning-series (or tem 'byte-compile-warning-series)))
-         (if byte-compile-debug
-             (funcall body-fn)
-           (condition-case error-info
-               (funcall body-fn)
-             (error (byte-compile-report-error error-info)))))
+           (setq warning-series (or tem #'byte-compile-warning-series)))
+         (funcall wrapped-body))
       ;; warning-series does not come from compilation, so bind it.
       (let ((warning-series
             ;; Log the file name.  Record position of that text.
-            (or (byte-compile-log-file) 'byte-compile-warning-series)))
-       (if byte-compile-debug
-           (funcall body-fn)
-         (condition-case error-info
-             (funcall body-fn)
-           (error (byte-compile-report-error error-info))))))))
+            (or (byte-compile-log-file) #'byte-compile-warning-series)))
+       (funcall wrapped-body)))))
 
 ;;;###autoload
 (defun byte-force-recompile (directory)
diff --git a/lisp/emacs-lisp/macroexp.el b/lisp/emacs-lisp/macroexp.el
index 78601c0648e..54a3ee9d66f 100644
--- a/lisp/emacs-lisp/macroexp.el
+++ b/lisp/emacs-lisp/macroexp.el
@@ -42,14 +42,8 @@ condition-case handling a signaled error.")
 (defmacro macroexp--with-extended-form-stack (expr &rest body)
   "Evaluate BODY with EXPR pushed onto `byte-compile-form-stack'."
   (declare (indent 1))
-  ;; FIXME: We really should just be using a simple dynamic let-binding here,
-  ;; but these explicit push and pop make the extended stack value visible
-  ;; to error handlers.  Remove that need for that!
-  `(progn
-     (push ,expr byte-compile-form-stack)
-     (prog1
-         (progn ,@body)
-       (pop byte-compile-form-stack))))
+  `(let ((byte-compile-form-stack (cons ,expr byte-compile-form-stack)))
+     ,@body))
 
 ;; Bound by the top-level `macroexpand-all', and modified to include any
 ;; macros defined by `defmacro'.