(format "%d" F) now truncates floating F

Problem reported by Paul Pogonyshev (Bug#31938).
* src/editfns.c: Include math.h, for trunc.
(styled_format): For %d, truncate floating-point numbers and
convert -0 to 0, going back to how Emacs 26 did things.
* doc/lispref/strings.texi (Formatting Strings):
Document behavior of %o, %d, %x, %X on floating-point numbers.
* src/floatfns.c (trunc) [!HAVE_TRUNC]: Rename from emacs_trunc
and make it an extern function, so that editfns.c can use it.
All callers changed.
* test/src/editfns-tests.el (format-%d-float): New test.

1 files changed, 8 insertions, 0 deletions

diff --git a/test/src/editfns-tests.el b/test/src/editfns-tests.el
index 1ed0bd5bbaf..c828000bb4f 100644
--- a/test/src/editfns-tests.el
+++ b/test/src/editfns-tests.el
@@ -176,6 +176,14 @@
   (should-error (format "%o" -1e-37)
                 :type 'overflow-error))
 
+;; Bug#31938
+(ert-deftest format-%d-float ()
+  (should (string-equal (format "%d" -1.1) "-1"))
+  (should (string-equal (format "%d" -0.9) "0"))
+  (should (string-equal (format "%d" -0.0) "0"))
+  (should (string-equal (format "%d" 0.0) "0"))
+  (should (string-equal (format "%d" 0.9) "0"))
+  (should (string-equal (format "%d" 1.1) "1")))
 
 ;;; Check format-time-string with various TZ settings.
 ;;; Use only POSIX-compatible TZ values, since the tests should work