* Makefile, date.1, newctime.3, newtzset.3, theory.html: Don’t say settings like TZ='EST5EDT' are “nonstandard and obsolete”, as draft POSIX says they use implementation-defined DST rules. Clarify and strengthen the wording of the description of the now-obsolete POSIXRULES macro and posixrules file, the latter of which is still commonly installed even though it does not work. Improve doc for TZDEFRULESTRING. Give Morocco instead of Iran as an example of unusual DST, as Iran no longer observes DST. --- Makefile | 21 +++++++++------------ date.1 | 3 ++- newctime.3 | 3 ++- newtzset.3 | 3 ++- theory.html | 13 +++++++------ zic.8 | 13 ++++++++----- 6 files changed, 30 insertions(+), 26 deletions(-) diff --git a/Makefile b/Makefile index 5ebd5d2e..95b54487 100644 --- a/Makefile +++ b/Makefile @@ -35,22 +35,14 @@ DATAFORM= main LOCALTIME= Factory -# The POSIXRULES macro controls interpretation of nonstandard and obsolete -# POSIX-like TZ settings like TZ='EET-2EEST' that lack DST transition rules. -# Such a setting uses the rules in a template file to determine -# "spring forward" and "fall back" days and times; the environment -# variable itself specifies UT offsets of standard and daylight saving time. -# +# The POSIXRULES macro controls interpretation of POSIX-like TZ +# settings like TZ='EET-2EEST' that lack DST transition rules. # If POSIXRULES is '-', no template is installed; this is the default. -# # Any other value for POSIXRULES is obsolete and should not be relied on, as: # * It does not work correctly in popular implementations such as GNU/Linux. # * It does not work even in tzcode, except for historical timestamps # that precede the last explicit transition in the POSIXRULES file. # Hence it typically does not work for current and future timestamps. -# In short, software should avoid ruleless settings like TZ='EET-2EEST' -# and so should not depend on the value of POSIXRULES. -# # If, despite the above, you want a template for handling these settings, # you can change the line below (after finding the timezone you want in the # one of the $(TDATA) source files, or adding it to a source file). @@ -63,7 +55,7 @@ LOCALTIME= Factory POSIXRULES= - # Also see TZDEFRULESTRING below, which takes effect only -# if the time zone files cannot be accessed. +# if POSIXRULES is '-' or if the template file cannot be accessed. # Installation locations. @@ -258,7 +250,12 @@ LDLIBS= # -DTZ_DOMAINDIR=\"/path\" to use "/path" for gettext directory; # the default is system-supplied, typically "/usr/lib/locale" # -DTZDEFRULESTRING=\",date/time,date/time\" to default to the specified -# DST transitions if the time zone files cannot be accessed +# DST transitions for POSIX-style TZ strings lacking them, +# in the usual case where POSIXRULES is '-'. If not specified, +# TZDEFRULESTRING defaults to US rules for future DST transitions. +# This mishandles some past timestamps, as US DST rules have changed. +# It also mishandles settings like TZ='EET-2EEST' for eastern Europe, +# as Europe and US DST rules differ. # -DUNINIT_TRAP if reading uninitialized storage can cause problems # other than simply getting garbage data # -DUSE_LTZ=0 to build zdump with the system time zone library diff --git a/date.1 b/date.1 index 043e5681..8670ff10 100644 --- a/date.1 +++ b/date.1 @@ -156,7 +156,8 @@ hexadecimal (leading 0x), preceded by an optional sign. .br /usr/share/zoneinfo timezone information directory .br -/usr/share/zoneinfo/posixrules used with POSIX-style TZ's +/usr/share/zoneinfo/posixrules default DST rules (obsolete, + and can cause bugs if present) .br /usr/share/zoneinfo/GMT for UTC leap seconds .sp diff --git a/newctime.3 b/newctime.3 index 2790c810..08601514 100644 --- a/newctime.3 +++ b/newctime.3 @@ -296,7 +296,8 @@ continue to exist in this form in future releases of this code. .br /usr/share/zoneinfo/localtime local timezone file .br -/usr/share/zoneinfo/posixrules used with POSIX-style TZ's +/usr/share/zoneinfo/posixrules default DST rules (obsolete, + and can cause bugs if present) .br /usr/share/zoneinfo/GMT for UTC leap seconds .sp diff --git a/newtzset.3 b/newtzset.3 index 1e75acf0..086152ac 100644 --- a/newtzset.3 +++ b/newtzset.3 @@ -333,7 +333,8 @@ from the rest of the specification. .br /usr/share/zoneinfo/localtime local timezone file .br -/usr/share/zoneinfo/posixrules used with POSIX-style TZ +/usr/share/zoneinfo/posixrules default DST rules (obsolete, + and can cause bugs if present) .br /usr/share/zoneinfo/GMT for UTC leap seconds .sp diff --git a/theory.html b/theory.html index 04706009..7870a919 100644 --- a/theory.html +++ b/theory.html @@ -878,7 +878,7 @@ an older <code>zic</code>. is error-prone in practice. Also, POSIX <code>TZ</code> strings cannot deal with daylight saving time rules not based on the Gregorian calendar (as in - Iran), or with situations where more than two time zone + Morocco), or with situations where more than two time zone abbreviations or <abbr>UT</abbr> offsets are used in an area. </p> @@ -914,8 +914,8 @@ an older <code>zic</code>. <dt><var>date</var>[<code>/</code><var>time</var>]<code>,</code><var>date</var>[<code>/</code><var>time</var>]</dt><dd> specifies the beginning and end of <abbr>DST</abbr>. If this is absent, the system supplies its own ruleset - for <abbr>DST</abbr>, and its rules can differ from year to year; - typically <abbr>US</abbr> <abbr>DST</abbr> rules are used. + for <abbr>DST</abbr>, typically current <abbr>US</abbr> + <abbr>DST</abbr> rules. </dd> <dt><var>time</var></dt><dd> takes the form @@ -975,10 +975,11 @@ an older <code>zic</code>. Traditionally the current <abbr>US</abbr> <abbr>DST</abbr> rules were used to interpret such values, but this meant that the <abbr>US</abbr> <abbr>DST</abbr> rules were compiled into each - program that did time conversion. This meant that when + time conversion package, and when <abbr>US</abbr> time conversion rules changed (as in the United - States in 1987), all programs that did time conversion had to be - recompiled to ensure proper results. + States in 1987 and again in 2007), all packages that + interpreted <code>TZ</code> values had to be updated + to ensure proper results. </li> <li> The <code>TZ</code> environment variable is process-global, which diff --git a/zic.8 b/zic.8 index 019a289c..06cf07bc 100644 --- a/zic.8 +++ b/zic.8 @@ -121,7 +121,10 @@ will act as if the input contained a link line of the form .ti +.5i Link \fItimezone\fP posixrules .sp -This feature is obsolete and poorly supported. +Unless +.I timezone is +.q "\*-" , +this option is obsolete and poorly supported. Among other things it should not be used for timestamps after the year 2037, and it should not be combined with .B "\*-b slim" @@ -242,10 +245,10 @@ for .PP The output file does not contain all the information about the long-term future of a timezone, because the future cannot be summarized as -an extended POSIX TZ string. For example, as of 2019 this problem -occurs for Iran's daylight-saving rules for the predicted future, as -these rules are based on the Iranian calendar, which cannot be -represented. +an extended POSIX TZ string. For example, as of 2023 this problem +occurs for Morocco's daylight-saving rules, as these rules are based +on predictions for when Ramadan will be observed, something that +an extended POSIX TZ string cannot represent. .PP The output contains data that may not be handled properly by client code designed for older -- 2.37.2