bug#26163: time-difference doesn't detect error of differing time types

bug#26163: time-difference doesn't detect error of differing time types

[Zefram]

scheme@(guile-user)> (use-modules (srfi srfi-19))
scheme@(guile-user)> (time-difference (make-time time-tai 0 1) (make-time time-utc 0 1))
$1 = #<time type: time-duration nanosecond: 0 second: 0>

SRFI-19 is explicit that it "is an error" if the arguments to
time-difference are of different time types, and correspondingly the
Guile documentation says the arguments "must be" of the same type.
It would be very easy for time-difference to detect and signal this error.
It's not absolutely a bug that it currently doesn't, but it would be a
useful improvement if it did.

-zefram

bug#26163: time-difference doesn't detect error of differing time types

[Zefram]

[-- Attachment #1: Type: text/plain, Size: 25 bytes --]

Patch attached.

-zefram

[-- Attachment #2: 0001-signal-error-of-time-difference-on-differing-types.patch --]
[-- Type: text/x-diff, Size: 1462 bytes --]

From 6f9d9b355233b578eb3ce13549c8fdc9d7fb8364 Mon Sep 17 00:00:00 2001
From: Zefram <zefram@fysh.org>
Date: Wed, 19 Apr 2017 19:02:13 +0100
Subject: [PATCH] signal error of time-difference on differing types

It is an error to apply SRFI-19's time-difference to time structures of
differing time types.  Detect and signal the error.
---
 module/srfi/srfi-19.scm | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/module/srfi/srfi-19.scm b/module/srfi/srfi-19.scm
index c6a55a2..8da711f 100644
--- a/module/srfi/srfi-19.scm
+++ b/module/srfi/srfi-19.scm
@@ -413,12 +413,14 @@
 ;; -- Time arithmetic
 
 (define (time-difference! time1 time2)
-  (let ((sec-diff (- (time-second time1) (time-second time2)))
-        (nsec-diff (- (time-nanosecond time1) (time-nanosecond time2))))
-    (set-time-type! time1 time-duration)
-    (set-time-second! time1 sec-diff)
-    (set-time-nanosecond! time1 nsec-diff)
-    (time-normalize! time1)))
+  (if (not (eq? (time-type time1) (time-type time2)))
+      (time-error 'time-difference 'incompatible-time-types time2)
+      (let ((sec-diff (- (time-second time1) (time-second time2)))
+	    (nsec-diff (- (time-nanosecond time1) (time-nanosecond time2))))
+	(set-time-type! time1 time-duration)
+	(set-time-second! time1 sec-diff)
+	(set-time-nanosecond! time1 nsec-diff)
+	(time-normalize! time1))))
 
 (define (time-difference time1 time2)
   (let ((result (copy-time time1)))
-- 
2.1.4

bug#26163: time-difference doesn't detect error of differing time types

[Mark H Weaver]

Zefram <zefram@fysh.org> writes:

> scheme@(guile-user)> (use-modules (srfi srfi-19))
> scheme@(guile-user)> (time-difference (make-time time-tai 0 1) (make-time time-utc 0 1))
> $1 = #<time type: time-duration nanosecond: 0 second: 0>
>
> SRFI-19 is explicit that it "is an error" if the arguments to
> time-difference are of different time types, and correspondingly the
> Guile documentation says the arguments "must be" of the same type.
> It would be very easy for time-difference to detect and signal this error.
> It's not absolutely a bug that it currently doesn't, but it would be a
> useful improvement if it did.

Agreed.  Fixed in commit c9d903b6e4f8cc1d8382b20a2f0502c4ce8ffe0a on the
stable-2.2 branch.  I'm closing this bug, but feel free to reopen if
appropriate.

     Thanks!
       Mark