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master 37d48ed: Fix merging of ambiguous nil maps
From: |
Basil L. Contovounesios |
Subject: |
master 37d48ed: Fix merging of ambiguous nil maps |
Date: |
Sat, 14 Aug 2021 06:32:56 -0400 (EDT) |
branch: master
commit 37d48edf6d406a4730caa0393f7695de2bfadfcc
Author: Basil L. Contovounesios <contovob@tcd.ie>
Commit: Basil L. Contovounesios <contovob@tcd.ie>
Fix merging of ambiguous nil maps
* lisp/emacs-lisp/map.el: Bump version to 3.1.
(map--merge): New merging subroutine that uses a hash table in place
of lists, for both efficiency and avoiding ambiguities (bug#49848).
(map-merge): Rewrite in terms of map--merge.
(map-merge-with): Ditto. This ensures that FUNCTION is called
whenever two keys are merged, even if they are not eql (which could
happen until now). It also makes map-merge-with consistent with
map-merge, thus achieving greater overall predictability.
* etc/NEWS: Announce this weakening of guarantees.
* test/lisp/emacs-lisp/map-tests.el (test-map-merge)
(test-map-merge-with): Don't depend on specific orderings. Test
that nil is correctly merged into a plist.
---
etc/NEWS | 8 ++++++
lisp/emacs-lisp/map.el | 60 ++++++++++++++++++++++++---------------
test/lisp/emacs-lisp/map-tests.el | 24 ++++++++++------
3 files changed, 61 insertions(+), 31 deletions(-)
diff --git a/etc/NEWS b/etc/NEWS
index 366ea1a..a321ffd 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1636,6 +1636,14 @@ This is a slightly deeper copy than the previous
'copy-sequence'.
---
*** The function 'map-contains-key' now supports plists.
+---
+*** More consistent duplicate key handling in 'map-merge-with'.
+Until now, 'map-merge-with' promised to call its function argument
+whenever multiple maps contained 'eql' keys. However, this did not
+always coincide with the keys that were actually merged, which could
+be 'equal' instead. The function argument is now called whenever keys
+are merged, for greater consistency with 'map-merge' and 'map-elt'.
+
** Package
---
diff --git a/lisp/emacs-lisp/map.el b/lisp/emacs-lisp/map.el
index c593428..988a62a 100644
--- a/lisp/emacs-lisp/map.el
+++ b/lisp/emacs-lisp/map.el
@@ -5,7 +5,7 @@
;; Author: Nicolas Petton <nicolas@petton.fr>
;; Maintainer: emacs-devel@gnu.org
;; Keywords: extensions, lisp
-;; Version: 3.0
+;; Version: 3.1
;; Package-Requires: ((emacs "26"))
;; This file is part of GNU Emacs.
@@ -371,37 +371,51 @@ The default implementation delegates to `map-do'."
map)
t))
+(defun map--merge (merge type &rest maps)
+ "Merge into a map of TYPE all the key/value pairs in MAPS.
+MERGE is a function that takes the target MAP, a KEY, and a
+VALUE, merges KEY and VALUE into MAP, and returns the result.
+MAP may be of a type other than TYPE."
+ ;; Use a hash table internally if `type' is a list. This avoids
+ ;; both quadratic lookup behavior and the type ambiguity of nil.
+ (let* ((tolist (memq type '(list alist plist)))
+ (result (map-into (pop maps)
+ ;; Use same testfn as `map-elt' gv setter.
+ (cond ((eq type 'plist) '(hash-table :test eq))
+ (tolist '(hash-table :test equal))
+ (type)))))
+ (dolist (map maps)
+ (map-do (lambda (key value)
+ (setq result (funcall merge result key value)))
+ map))
+ ;; Convert internal representation to desired type.
+ (if tolist (map-into result type) result)))
+
(defun map-merge (type &rest maps)
"Merge into a map of TYPE all the key/value pairs in MAPS.
See `map-into' for all supported values of TYPE."
- (let ((result (map-into (pop maps) type)))
- (while maps
- ;; FIXME: When `type' is `list', we get an O(N^2) behavior.
- ;; For small tables, this is fine, but for large tables, we
- ;; should probably use a hash-table internally which we convert
- ;; to an alist in the end.
- (map-do (lambda (key value)
- (setf (map-elt result key) value))
- (pop maps)))
- result))
+ (apply #'map--merge
+ (lambda (result key value)
+ (setf (map-elt result key) value)
+ result)
+ type maps))
(defun map-merge-with (type function &rest maps)
"Merge into a map of TYPE all the key/value pairs in MAPS.
-When two maps contain the same (`eql') key, call FUNCTION on the two
+When two maps contain the same key, call FUNCTION on the two
values and use the value returned by it.
Each of MAPS can be an alist, plist, hash-table, or array.
See `map-into' for all supported values of TYPE."
- (let ((result (map-into (pop maps) type))
- (not-found (list nil)))
- (while maps
- (map-do (lambda (key value)
- (cl-callf (lambda (old)
- (if (eql old not-found)
- value
- (funcall function old value)))
- (map-elt result key not-found)))
- (pop maps)))
- result))
+ (let ((not-found (list nil)))
+ (apply #'map--merge
+ (lambda (result key value)
+ (cl-callf (lambda (old)
+ (if (eql old not-found)
+ value
+ (funcall function old value)))
+ (map-elt result key not-found))
+ result)
+ type maps)))
(cl-defgeneric map-into (map type)
"Convert MAP into a map of TYPE.")
diff --git a/test/lisp/emacs-lisp/map-tests.el
b/test/lisp/emacs-lisp/map-tests.el
index a04c6be..658ed2e 100644
--- a/test/lisp/emacs-lisp/map-tests.el
+++ b/test/lisp/emacs-lisp/map-tests.el
@@ -446,16 +446,24 @@ Evaluate BODY for each created map."
(ert-deftest test-map-merge ()
"Test `map-merge'."
- (should (equal (map-merge 'list '(a 1) '((b . 2) (c . 3))
- #s(hash-table data (c 4)))
- '((c . 4) (b . 2) (a . 1)))))
+ (should (equal (sort (map-merge 'list '(a 1) '((b . 2) (c . 3))
+ #s(hash-table data (c 4)))
+ (lambda (x y) (string< (car x) (car y))))
+ '((a . 1) (b . 2) (c . 4))))
+ (should (equal (map-merge 'list () '(:a 1)) '((:a . 1))))
+ (should (equal (map-merge 'alist () '(:a 1)) '((:a . 1))))
+ (should (equal (map-merge 'plist () '(:a 1)) '(:a 1))))
(ert-deftest test-map-merge-with ()
- (should (equal (map-merge-with 'list #'+
- '((1 . 2))
- '((1 . 3) (2 . 4))
- '((1 . 1) (2 . 5) (3 . 0)))
- '((3 . 0) (2 . 9) (1 . 6)))))
+ (should (equal (sort (map-merge-with 'list #'+
+ '((1 . 2))
+ '((1 . 3) (2 . 4))
+ '((1 . 1) (2 . 5) (3 . 0)))
+ #'car-less-than-car)
+ '((1 . 6) (2 . 9) (3 . 0))))
+ (should (equal (map-merge-with 'list #'+ () '(:a 1)) '((:a . 1))))
+ (should (equal (map-merge-with 'alist #'+ () '(:a 1)) '((:a . 1))))
+ (should (equal (map-merge-with 'plist #'+ () '(:a 1)) '(:a 1))))
(ert-deftest test-map-merge-empty ()
"Test merging of empty maps."
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