Add the string-numeric-lessp function

* doc/lispref/strings.texi (Text Comparison): Document
`string-numerical-lessp'.

* src/fns.c (Fstring_numeric_lessp): New function.
(gather_number_from_string): Helper function for that function.

* test/src/fns-tests.el (fns-tests-string-numeric-lessp): Add tests.

1 files changed, 17 insertions, 0 deletions

diff --git a/test/src/fns-tests.el b/test/src/fns-tests.el
index 762f7bdd94f..0c6edb89252 100644
--- a/test/src/fns-tests.el
+++ b/test/src/fns-tests.el
@@ -191,3 +191,20 @@
               (string-collate-lessp
                a b (if (eq system-type 'windows-nt) "enu_USA" "en_US.UTF-8")))))
     '("Adrian" "Ævar" "Agustín" "Eli"))))
+
+(ert-deftest fns-tests-string-numeric-lessp ()
+  (should (string-numeric-lessp "foo2.png" "foo12.png"))
+  (should (not (string-numeric-lessp "foo12.png" "foo2.png")))
+  (should (string-numeric-lessp "foo12.png" "foo20000.png"))
+  (should (not (string-numeric-lessp "foo20000.png" "foo12.png")))
+  (should (string-numeric-lessp "foo.png" "foo2.png"))
+  (should (not (string-numeric-lessp "foo2.png" "foo.png")))
+  (should (equal (sort '("foo12.png" "foo2.png" "foo1.png")
+                       'string-numeric-lessp)
+                 '("foo1.png" "foo2.png" "foo12.png")))
+  (should (string-numeric-lessp "foo2" "foo1234"))
+  (should (not (string-numeric-lessp "foo1234" "foo2")))
+  (should (string-numeric-lessp "foo.png" "foo2"))
+  (should (string-numeric-lessp "foo1.25.5.png" "foo1.125.5"))
+  (should (string-numeric-lessp "2" "1245"))
+  (should (not (string-numeric-lessp "1245" "2"))))