Fix compilation of closures with nontrivial doc strings

* lisp/emacs-lisp/bytecomp.el (byte-compile-make-closure):
Use the supplied doc string if it's a literal; fall back to the old
slow way of building a closure otherwise.

lisp/emacs-lisp/bytecomp.el

@@ -3818,20 +3818,37 @@ discarding."
 		     docstring-exp))	;Otherwise, we don't need a closure.
       (cl-assert (byte-code-function-p fun))
       (byte-compile-form
-       ;; Use symbols V0, V1 ... as placeholders for closure variables:
-       ;; they should be short (to save space in the .elc file), yet
-       ;; distinct when disassembled.
-       (let* ((dummy-vars (mapcar (lambda (i) (intern (format "V%d" i)))
-                                  (number-sequence 0 (1- (length env)))))
-              (proto-fun
-               (apply #'make-byte-code
-                      (aref fun 0) (aref fun 1)
-                      ;; Prepend dummy cells to the constant vector,
-                      ;; to get the indices right when disassembling.
-                      (vconcat dummy-vars (aref fun 2))
-                      (mapcar (lambda (i) (aref fun i))
-                              (number-sequence 3 (1- (length fun)))))))
-         `(make-closure ,proto-fun ,@env))))))
+       (if (or (not docstring-exp) (stringp docstring-exp))
+           ;; Use symbols V0, V1 ... as placeholders for closure variables:
+           ;; they should be short (to save space in the .elc file), yet
+           ;; distinct when disassembled.
+           (let* ((dummy-vars (mapcar (lambda (i) (intern (format "V%d" i)))
+                                      (number-sequence 0 (1- (length env)))))
+                  (opt-args (mapcar (lambda (i) (aref fun i))
+                                    (number-sequence 4 (1- (length fun)))))
+                  (proto-fun
+                   (apply #'make-byte-code
+                          (aref fun 0) (aref fun 1)
+                          ;; Prepend dummy cells to the constant vector,
+                          ;; to get the indices right when disassembling.
+                          (vconcat dummy-vars (aref fun 2))
+                          (aref fun 3)
+                          (if docstring-exp
+                              (cons docstring-exp (cdr opt-args))
+                            opt-args))))
+             `(make-closure ,proto-fun ,@env))
+         ;; Nontrivial doc string expression: create a bytecode object
+         ;; from small pieces at run time.
+         `(make-byte-code
+           ',(aref fun 0) ',(aref fun 1)
+           (vconcat (vector . ,env) ',(aref fun 2))
+           ,@(let ((rest (nthcdr 3 (mapcar (lambda (x) `',x) fun))))
+               (if docstring-exp
+                   `(,(car rest)
+                     ,docstring-exp
+                     ,@(cddr rest))
+                 rest))))
+         ))))
 
 (defun byte-compile-get-closed-var (form)
   "Byte-compile the special `internal-get-closed-var' form."