Add some `pure` and `side-effect-free` declarations

* lisp/subr.el (string-to-list, string-to-vector, string-or-null-p)
(booleanp, special-form-p, plistp, macrop, compiled-function-p)
(flatten-tree):
* lisp/emacs-lisp/subr-x.el (string-join, string-truncate-left)
(string-blank-p, string-remove-prefix, string-remove-suffix)
(string-pad, string-chop-newline):
Declare functions pure, side-effect-free, and/or error-free.

1 files changed, 9 insertions, 0 deletions

diff --git a/lisp/subr.el b/lisp/subr.el
index 898ecb6e358..a5fc566cc74 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -4124,15 +4124,18 @@ system's shell."
 
 (defsubst string-to-list (string)
   "Return a list of characters in STRING."
+  (declare (side-effect-free t))
   (append string nil))
 
 (defsubst string-to-vector (string)
   "Return a vector of characters in STRING."
+  (declare (side-effect-free t))
   (vconcat string))
 
 (defun string-or-null-p (object)
   "Return t if OBJECT is a string or nil.
 Otherwise, return nil."
+  (declare (pure t) (side-effect-free error-free))
   (or (stringp object) (null object)))
 
 (defun list-of-strings-p (object)
@@ -4145,21 +4148,25 @@ Otherwise, return nil."
 (defun booleanp (object)
   "Return t if OBJECT is one of the two canonical boolean values: t or nil.
 Otherwise, return nil."
+  (declare (pure t) (side-effect-free error-free))
   (and (memq object '(nil t)) t))
 
 (defun special-form-p (object)
   "Non-nil if and only if OBJECT is a special form."
+  (declare (side-effect-free error-free))
   (if (and (symbolp object) (fboundp object))
       (setq object (indirect-function object)))
   (and (subrp object) (eq (cdr (subr-arity object)) 'unevalled)))
 
 (defun plistp (object)
   "Non-nil if and only if OBJECT is a valid plist."
+  (declare (pure t) (side-effect-free error-free))
   (let ((len (proper-list-p object)))
     (and len (zerop (% len 2)))))
 
 (defun macrop (object)
   "Non-nil if and only if OBJECT is a macro."
+  (declare (side-effect-free t))
   (let ((def (indirect-function object)))
     (when (consp def)
       (or (eq 'macro (car def))
@@ -4169,6 +4176,7 @@ Otherwise, return nil."
   "Return non-nil if OBJECT is a function that has been compiled.
 Does not distinguish between functions implemented in machine code
 or byte-code."
+  (declare (side-effect-free error-free))
   (or (subrp object) (byte-code-function-p object)))
 
 (defun field-at-pos (pos)
@@ -6843,6 +6851,7 @@ returned list are in the same order as in TREE.
 
 \(flatten-tree \\='(1 (2 . 3) nil (4 5 (6)) 7))
 => (1 2 3 4 5 6 7)"
+  (declare (side-effect-free error-free))
   (let (elems)
     (while (consp tree)
       (let ((elem (pop tree)))