Add polyfill for Emacs 26+ alist-get

core/core-lib.el

@@ -12,7 +12,27 @@
     ;; if-let and when-let were moved to (if|when)-let* in Emacs 26+ so we alias
     ;; them for 25 users.
     (defalias 'if-let* #'if-let)
-    (defalias 'when-let* #'when-let)))
+    (defalias 'when-let* #'when-let)
+
+    (defun alist-get (key alist &optional default remove testfn)
+      "Return the value associated with KEY in ALIST.
+If KEY is not found in ALIST, return DEFAULT.
+Use TESTFN to lookup in the alist if non-nil.  Otherwise, use `assq'.
+
+This is a generalized variable suitable for use with `setf'.
+When using it to set a value, optional argument REMOVE non-nil
+means to remove KEY from ALIST if the new value is `eql' to DEFAULT."
+      (ignore remove) ;;Silence byte-compiler.
+      (let ((x (if (not testfn)
+                   (assq key alist)
+                 ;; In Emacs<26, `assoc' has no testfn arg, so we have to
+                 ;; implement it ourselves
+                 (if testfn
+                     (cl-loop for entry in alist
+                              if (funcall testfn key entry)
+                              return entry)
+                   (assoc key alist)))))
+        (if x (cdr x) default)))))
 
 
 ;;