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[Emacs-diffs] emacs-25 ca50981: Improve time zone documentation
From: |
Paul Eggert |
Subject: |
[Emacs-diffs] emacs-25 ca50981: Improve time zone documentation |
Date: |
Tue, 12 Apr 2016 15:49:24 +0000 |
branch: emacs-25
commit ca509810014726cf6bee9f7e8f69bdeaf62dc146
Author: Paul Eggert <address@hidden>
Commit: Paul Eggert <address@hidden>
Improve time zone documentation
* doc/lispref/os.texi (Time Zone Rules):
New section, mostly with material moved here from other sections.
* doc/emacs/cmdargs.texi (General Variables):
* doc/lispref/os.texi (Time Conversion, Time Parsing):
Xref new section.
* etc/NEWS, etc/PROBLEMS:
* lisp/org/org.el (org-timestamp-format):
* src/editfns.c (Fformat_time_string, Fdecode_time)
(Fencode_time, Fcurrent_time_string, Fcurrent_time_zone)
(Fset_time_zone_rule):
When documenting time zone rule strings, mention the TZ
environment variable in preference to mentioning the
sort-of-internal function set-time-zone-rule.
---
doc/emacs/cmdargs.texi | 5 ++-
doc/lispref/os.texi | 67 ++++++++++++++++++++++++++++++------------------
etc/NEWS | 10 +++---
etc/PROBLEMS | 8 +++---
lisp/org/org.el | 2 +-
src/editfns.c | 27 ++++++++++--------
6 files changed, 70 insertions(+), 49 deletions(-)
diff --git a/doc/emacs/cmdargs.texi b/doc/emacs/cmdargs.texi
index a842cb8..f0f686f 100644
--- a/doc/emacs/cmdargs.texi
+++ b/doc/emacs/cmdargs.texi
@@ -634,8 +634,9 @@ to put temporary files (@pxref{Backup}). Emacs tries to use
@env{TMP}, then @env{TEMP}, and finally @file{c:/temp}.
@item TZ
@vindex TZ, environment variable
-This specifies the current time zone and possibly also daylight
-saving time information. On MS-DOS, if @env{TZ} is not set in the
+This specifies the default time zone and possibly also daylight
+saving time information. @xref{Time Zone Rules,,, elisp, The GNU
+Emacs Lisp Reference Manual}. On MS-DOS, if @env{TZ} is not set in the
environment when Emacs starts, Emacs defines a default value as
appropriate for the country code returned by address@hidden On MS-Windows,
Emacs
does not use @env{TZ} at all.
diff --git a/doc/lispref/os.texi b/doc/lispref/os.texi
index 8839745..5f189b9 100644
--- a/doc/lispref/os.texi
+++ b/doc/lispref/os.texi
@@ -19,6 +19,7 @@ terminal and the screen.
* System Environment:: Distinguish the name and kind of system.
* User Identification:: Finding the name and user id of the user.
* Time of Day:: Getting the current time.
+* Time Zone Rules:: Rules for time zones and daylight saving time.
* Time Conversion:: Converting a time from numeric form to
calendrical data and vice versa.
* Time Parsing:: Converting a time from numeric form to text
@@ -1262,7 +1263,7 @@ information may some day be added at the end.
The argument @var{time}, if given, specifies a time to format,
instead of the current time. The optional argument @var{zone}
-defaults to the current time zone rule.
+defaults to the current time zone rule. @xref{Time Zone Rules}.
@example
@group
@@ -1299,26 +1300,9 @@ For example, if @var{time} is a number,
@code{(time-to-seconds
or rounding errors occur.
@end defun
address@hidden current-time-zone &optional time zone
address@hidden time zone, current
-This function returns a list describing the time zone that the user is
-in.
-
-The value has the form @code{(@var{offset} @var{name})}. Here
address@hidden is an integer giving the number of seconds ahead of Universal
Time
-(east of Greenwich). A negative value means west of Greenwich. The
-second element, @var{name}, is a string giving the name of the time
-zone. Both elements change when daylight saving time begins or ends;
-if the user has specified a time zone that does not use a seasonal time
-adjustment, then the value is constant through time.
-
-If the operating system doesn't supply all the information necessary to
-compute the value, the unknown elements of the list are @code{nil}.
-
-The argument @var{time}, if given, specifies a time value to
-analyze instead of the current time. The optional argument @var{zone}
-defaults to the current time zone rule.
address@hidden defun
address@hidden Time Zone Rules
address@hidden Time Zone Rules
address@hidden time zone rules
@vindex TZ, environment variable
The default time zone is determined by the @env{TZ} environment
@@ -1327,6 +1311,15 @@ to default to Universal Time with @code{(setenv "TZ"
"UTC0")}. If
@env{TZ} is not in the environment, Emacs uses system wall clock time,
which is a platform-dependent default time zone.
+The set of supported @env{TZ} strings is system-dependent. GNU and
+many other systems support the tzdata database, e.g.,
address@hidden"America/New_York"} specifies the time zone and daylight saving
+time history for locations near New York City. GNU and most other
+systems support POSIX-style @env{TZ} strings, e.g.,
address@hidden"EST+5EDT,M4.1.0/2,M10.5.0/2"} specifies the rules used in New
+York from 1987 through 2006. All systems support the string
address@hidden"UTC0"} meaning Universal Time.
+
@cindex time zone rule
Functions that convert to and from local time accept an optional
@dfn{time zone rule} argument, which specifies the conversion's time
@@ -1337,6 +1330,29 @@ If it is @code{t}, the conversion uses Universal Time.
If it is
a string, the conversion uses the time zone rule equivalent to setting
@env{TZ} to that string.
address@hidden current-time-zone &optional time zone
address@hidden time zone, current
+This function returns a list describing the time zone that the user is
+in.
+
+The value has the form @code{(@var{offset} @var{abbr})}. Here
address@hidden is an integer giving the number of seconds ahead of Universal
Time
+(east of Greenwich). A negative value means west of Greenwich. The
+second element, @var{abbr}, is a string giving an abbreviation for the
+time zone, e.g., @samp{"CST"} for China Standard Time or for
+U.S. Central Standard Time. Both elements can change when daylight
+saving time begins or ends; if the user has specified a time zone that
+does not use a seasonal time adjustment, then the value is constant
+through time.
+
+If the operating system doesn't supply all the information necessary to
+compute the value, the unknown elements of the list are @code{nil}.
+
+The argument @var{time}, if given, specifies a time value to
+analyze instead of the current time. The optional argument @var{zone}
+defaults to the current time zone rule.
address@hidden defun
+
@node Time Conversion
@section Time Conversion
@cindex calendrical information
@@ -1361,8 +1377,8 @@ as traditional Gregorian years do; for example, the year
number
@defun decode-time &optional time zone
This function converts a time value into calendrical information. If
you don't specify @var{time}, it decodes the current time, and similarly
address@hidden defaults to the current time zone rule. The return
-value is a list of nine elements, as follows:
address@hidden defaults to the current time zone rule. @xref{Time Zone Rules}.
+The return value is a list of nine elements, as follows:
@example
(@var{seconds} @var{minutes} @var{hour} @var{day} @var{month} @var{year}
@var{dow} @var{dst} @var{utcoff})
@@ -1409,6 +1425,7 @@ to stand for years above 1900, or years above 2000, you
must alter them
yourself before you call @code{encode-time}.
The optional argument @var{zone} defaults to the current time zone rule.
address@hidden Zone Rules}.
In addition to the usual time zone rule values, it can also be a list
(as you would get from @code{current-time-zone}) or an integer (as
from @code{decode-time}), applied without any further alteration for
@@ -1452,8 +1469,8 @@ corresponding time value.
This function converts @var{time} (or the current time, if
@var{time} is omitted) to a string according to
address@hidden The conversion uses the time zone rule @var{zone}
-(or the current time zone rule, if omitted). The argument
address@hidden The conversion uses the time zone rule @var{zone}, which
+defaults to the current time zone rule. @xref{Time Zone Rules}. The argument
@var{format-string} may contain @samp{%}-sequences which say to
substitute parts of the time. Here is a table of what the
@samp{%}-sequences mean:
diff --git a/etc/NEWS b/etc/NEWS
index fe7df96..bae42af 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1778,11 +1778,11 @@ quotation marks.
*** Time conversion functions now accept an optional ZONE argument
that specifies the time zone rules for conversion. ZONE is omitted or
nil for Emacs local time, t for Universal Time, 'wall' for system wall
-clock time, or a string as in 'set-time-zone-rule' for a time zone
-rule. The affected functions are 'current-time-string',
-'current-time-zone', 'decode-time', and 'format-time-string'. The
-function 'encode-time', which already accepted a simple time zone rule
-argument, has been extended to accept all the new forms.
+clock time, or a string as in the TZ environment variable. The
+affected functions are 'current-time-string', 'current-time-zone',
+'decode-time', and 'format-time-string'. The function 'encode-time',
+which already accepted a simple time zone rule argument, has been
+extended to accept all the new forms.
*** Incompatible change in the third argument of 'format-time-string'.
Previously, any non-nil argument was interpreted as specifying Universal Time.
diff --git a/etc/PROBLEMS b/etc/PROBLEMS
index b0c21ee..be9400b 100644
--- a/etc/PROBLEMS
+++ b/etc/PROBLEMS
@@ -2220,11 +2220,11 @@ month names with consistent widths for some locales on
some versions
of Windows. This is caused by a deficiency in the underlying system
library function.
-** Problems with set-time-zone-rule function
+** Non-US time zones.
-The function set-time-zone-rule gives incorrect results for many
-non-US timezones. This is due to over-simplistic handling of
-daylight savings switchovers by the Windows libraries.
+Many non-US time zones are implemented incorrectly. This is due to
+over-simplistic handling of daylight savings switchovers by the
+Windows libraries.
** Files larger than 4GB report wrong size in a 32-bit Windows build
diff --git a/lisp/org/org.el b/lisp/org/org.el
index d2b48a6..231daa9 100644
--- a/lisp/org/org.el
+++ b/lisp/org/org.el
@@ -22674,7 +22674,7 @@ time-range, if possible.
The optional ZONE is omitted or nil for Emacs local time, t for
Universal Time, `wall' for system wall clock time, or a string as in
-`set-time-zone-rule' for a time zone rule."
+the TZ environment variable."
(format-time-string
format
(apply 'encode-time
diff --git a/src/editfns.c b/src/editfns.c
index 2ac0537..94b9495 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -1969,10 +1969,10 @@ DEFUN ("format-time-string", Fformat_time_string,
Sformat_time_string, 1, 3, 0,
doc: /* Use FORMAT-STRING to format the time TIME, or now if omitted.
TIME is specified as (HIGH LOW USEC PSEC), as returned by
`current-time' or `file-attributes'. The obsolete form (HIGH . LOW)
-is also still accepted.
-The optional ZONE is omitted or nil for Emacs local time, t for
-Universal Time, `wall' for system wall clock time, or a string as in
-`set-time-zone-rule' for a time zone rule.
+is also still accepted. The optional ZONE is omitted or nil for Emacs
+local time, t for Universal Time, `wall' for system wall clock time,
+or a string as in the TZ environment variable.
+
The value is a copy of FORMAT-STRING, but with certain constructs replaced
by text that describes the specified date and time in TIME:
@@ -2086,7 +2086,7 @@ as from `current-time' and `file-attributes', or nil to
use the
current time. The obsolete form (HIGH . LOW) is also still accepted.
The optional ZONE is omitted or nil for Emacs local time, t for
Universal Time, `wall' for system wall clock time, or a string as in
-`set-time-zone-rule' for a time zone rule.
+the TZ environment variable.
The list has the following nine members: SEC is an integer between 0
and 60; SEC is 60 for a leap second, which only some operating systems
@@ -2151,9 +2151,9 @@ DEFUN ("encode-time", Fencode_time, Sencode_time, 6,
MANY, 0,
This is the reverse operation of `decode-time', which see.
The optional ZONE is omitted or nil for Emacs local time, t for
Universal Time, `wall' for system wall clock time, or a string as in
-`set-time-zone-rule' for a time zone rule. It can also be a list (as
-from `current-time-zone') or an integer (as from `decode-time')
-applied without consideration for daylight saving time.
+the TZ environment variable. It can also be a list (as from
+`current-time-zone') or an integer (as from `decode-time') applied
+without consideration for daylight saving time.
You can pass more than 7 arguments; then the first six arguments
are used as SECOND through YEAR, and the *last* argument is used as ZONE.
@@ -2213,7 +2213,7 @@ but this is considered obsolete.
The optional ZONE is omitted or nil for Emacs local time, t for
Universal Time, `wall' for system wall clock time, or a string as in
-`set-time-zone-rule' for a time zone rule. */)
+the TZ environment variable. */)
(Lisp_Object specified_time, Lisp_Object zone)
{
time_t value = lisp_seconds_argument (specified_time);
@@ -2290,7 +2290,7 @@ instead of using the current time. The argument should
have the form
`current-time' and from `file-attributes'. SPECIFIED-TIME can also
have the form (HIGH . LOW), but this is considered obsolete.
Optional second arg ZONE is omitted or nil for the local time zone, or
-a string as in `set-time-zone-rule'.
+a string as in the TZ environment variable.
Some operating systems cannot provide all this information to Emacs;
in this case, `current-time-zone' returns a list containing nil for
@@ -2331,8 +2331,11 @@ the data it can't find. */)
DEFUN ("set-time-zone-rule", Fset_time_zone_rule, Sset_time_zone_rule, 1, 1, 0,
doc: /* Set the Emacs local time zone using TZ, a string specifying a
time zone rule.
-If TZ is nil or `wall', use system wall clock time. If TZ is t, use
-Universal Time. If TZ is an integer, treat it as in `encode-time'.
+
+If TZ is nil or `wall', use system wall clock time; this differs from
+the usual Emacs convention where nil means current local time. If TZ
+is t, use Universal Time. If TZ is an integer, treat it as in
+`encode-time'.
Instead of calling this function, you typically want something else.
To temporarily use a different time zone rule for just one invocation
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