CC Mode: Don't bind max-specpdl-size when it doesn't exist or is obsolete

This is part of the changes for bug #57911.

* lisp/progmodes/cc-defs.el (c-let*-maybe-max-specpdl-size): New macro.
(c-get-lang-constant): Use the new macro in place of let*.

1 files changed, 30 insertions, 15 deletions

diff --git a/lisp/progmodes/cc-defs.el b/lisp/progmodes/cc-defs.el
index f867625480c..59927f0f2ca 100644
--- a/lisp/progmodes/cc-defs.el
+++ b/lisp/progmodes/cc-defs.el
@@ -2629,6 +2629,20 @@ fallback definition for all modes, to break the cycle).")
 
 (defconst c-lang--novalue "novalue")
 
+(defmacro c-let*-maybe-max-specpdl-size (varlist &rest body)
+  ;; Like let*, but doesn't bind `max-specpdl-size' if that variable
+  ;; is in the bindings list and either doesn't exist or is obsolete.
+  (declare (debug let*) (indent 1))
+  (let ((-varlist- varlist) msp-binding)
+    (if (or (not (boundp 'max-specpdl-size))
+	    (get 'max-specpdl-size 'byte-obsolete-variable))
+	(cond
+	 ((memq 'max-specpdl-size -varlist-)
+	  (setq -varlist- (delq 'max-specpdl-size -varlist-)))
+	 ((setq msp-binding (assq 'max-specpdl-size -varlist-))
+	  (setq -varlist- (delq msp-binding -varlist-)))))
+    `(let* ,varlist ,@body)))
+
 (defun c-get-lang-constant (name &optional source-files mode)
   ;; Used by `c-lang-const'.
 
@@ -2669,21 +2683,22 @@ fallback definition for all modes, to break the cycle).")
       ;; In that case we just continue with the "assignment" before
       ;; the one currently being evaluated, thereby creating the
       ;; illusion if a `setq'-like sequence of assignments.
-      (let* ((c-buffer-is-cc-mode mode)
-	     (source-pos
-	      (or (assq sym c-lang-constants-under-evaluation)
-		  (cons sym (vector source nil))))
-	     ;; Append `c-lang-constants-under-evaluation' even if an
-	     ;; earlier entry is found.  It's only necessary to get
-	     ;; the recording of dependencies above correct.
-	     (c-lang-constants-under-evaluation
-	      (cons source-pos c-lang-constants-under-evaluation))
-	     (fallback (get mode 'c-fallback-mode))
-	     value
-	     ;; Make sure the recursion limits aren't very low
-	     ;; since the `c-lang-const' dependencies can go deep.
-	     (max-specpdl-size (max max-specpdl-size 3000))
-	     (max-lisp-eval-depth (max max-lisp-eval-depth 1000)))
+      (c-let*-maybe-max-specpdl-size
+	  ((c-buffer-is-cc-mode mode)
+	   (source-pos
+	    (or (assq sym c-lang-constants-under-evaluation)
+		(cons sym (vector source nil))))
+	   ;; Append `c-lang-constants-under-evaluation' even if an
+	   ;; earlier entry is found.  It's only necessary to get
+	   ;; the recording of dependencies above correct.
+	   (c-lang-constants-under-evaluation
+	    (cons source-pos c-lang-constants-under-evaluation))
+	   (fallback (get mode 'c-fallback-mode))
+	   value
+	   ;; Make sure the recursion limits aren't very low
+	   ;; since the `c-lang-const' dependencies can go deep.
+	   (max-specpdl-size (max max-specpdl-size 3000))
+	   (max-lisp-eval-depth (max max-lisp-eval-depth 1000)))
 
 	(if (if fallback
 		(let ((backup-source-pos (copy-sequence (cdr source-pos))))