Fix -each-while on improper lists

* NEWS.md (2.19.2): Announce regression fix.
* dash.el (--each-while): Evaluate predicate before continuing list
traversal.
* dev/examples.el (-take, -drop, -take-while, -drop-while)
(-each-while): Extend tests.

Fixes #393.

NEWS.md

@@ -6,6 +6,13 @@ See the end of the file for license conditions.
 
 ## Change log
 
+### From 2.19.1 to 2.19.2
+
+#### Fixes
+
+- Fixed a regression from `2.18` in `-take` that caused it to
+  prematurely signal an error on improper lists (#393).
+
 ### From 2.19.0 to 2.19.1
 
 #### Fixes

dash.el

@@ -112,8 +112,8 @@ This is the anaphoric counterpart to `-each-while'."
            (,i 0)
            ,elt it it-index)
        (ignore it it-index)
-       (while (and ,l (setq ,elt (pop ,l) it ,elt it-index ,i) ,pred)
-         (setq it ,elt it-index ,i ,i (1+ ,i))
+       (while (and ,l (setq ,elt (car-safe ,l) it ,elt it-index ,i) ,pred)
+         (setq it ,elt it-index ,i ,i (1+ ,i) ,l (cdr ,l))
          ,@body))))
 
 (defun -each-while (list pred fn)

dev/examples.el

@@ -277,10 +277,15 @@ new list."
     (-take 3 '(1 2 3 4 5)) => '(1 2 3)
     (-take 17 '(1 2 3 4 5)) => '(1 2 3 4 5)
     (-take 0 '(1 2 3 4 5)) => '()
-    (-take 0 ()) => ()
     (-take -1 ()) => ()
-    (-take -1 '(1)) => ()
+    (-take 0 ()) => ()
     (-take 1 ()) => ()
+    (-take -1 '(1)) => ()
+    (-take 0 '(1)) => ()
+    (-take 1 '(1)) => '(1)
+    (-take -1 '(1 . 2)) => ()
+    (-take 0 '(1 . 2)) => ()
+    (-take 1 '(1 . 2)) => '(1)
     (let ((l (list 1 2))) (eq (-take 3 l) l)) => nil)
 
   (defexamples -take-last
@@ -298,10 +303,15 @@ new list."
     (-drop 3 '(1 2 3 4 5)) => '(4 5)
     (-drop 17 '(1 2 3 4 5)) => '()
     (-drop 0 '(1 2 3 4 5)) => '(1 2 3 4 5)
-    (-drop 0 ()) => ()
     (-drop -1 ()) => ()
-    (-drop -1 '(1)) => '(1)
+    (-drop 0 ()) => ()
     (-drop 1 ()) => ()
+    (-drop -1 '(1)) => '(1)
+    (-drop 0 '(1)) => '(1)
+    (-drop 1 '(1)) => ()
+    (-drop -1 '(1 . 2)) => '(1 . 2)
+    (-drop 0 '(1 . 2)) => '(1 . 2)
+    (-drop 1 '(1 . 2)) => 2
     (let ((l (list 1 2))) (setcar (-drop 1 l) 0) l) => '(1 0)
     (let ((l (list 1 2))) (eq (-drop 0 l) l)) => t)
 
@@ -323,8 +333,11 @@ new list."
     (--take-while t ()) => ()
     (--take-while nil ()) => ()
     (--take-while nil '(1)) => ()
+    (--take-while nil '(1 . 2)) => ()
     (--take-while t '(1)) => '(1)
     (--take-while t '(1 2)) => '(1 2)
+    (--take-while (< it-index 0) '(1 . 2)) => ()
+    (--take-while (< it-index 1) '(1 . 2)) => '(1)
     (let ((l (list 1 2))) (eq (--take-while t l) l)) => nil)
 
   (defexamples -drop-while
@@ -335,8 +348,11 @@ new list."
     (--drop-while nil ()) => ()
     (--drop-while nil '(1)) => '(1)
     (--drop-while nil '(1 2)) => '(1 2)
+    (--drop-while nil '(1 . 2)) => '(1 . 2)
     (--drop-while t '(1)) => ()
     (--drop-while t '(1 2)) => ()
+    (--drop-while (< it-index 0) '(1 . 2)) => '(1 . 2)
+    (--drop-while (< it-index 1) '(1 . 2)) => 2
     (let ((l (list t 2))) (setcar (-drop-while #'booleanp l) 0) l) => '(t 0)
     (let ((l (list 1 2))) (eq (--drop-while nil l) l)) => t)
 
@@ -1748,6 +1764,9 @@ or readability."
     (let (s) (--each-while '(1) t (setq s it)) s) => 1
     (let (s) (--each-while '(1) nil (setq s it)) s) => nil
     (let (s) (--each-while '(1) (setq it t) (setq s it)) s) => 1
+    (let (s) (--each-while '(1 . 2) nil (setq s it)) s) => nil
+    (let (s) (--each-while '(1 . 2) (< it-index 0) (setq s it)) s) => nil
+    (let (s) (--each-while '(1 . 2) (< it-index 1) (setq s it)) s) => 1
     (--each-while '(1) t t) => nil)
 
   (defexamples -each-indexed