[PATCH] strftime: respect empty TZ

[dana <dana@xxxxxxx>]

i recently noticed this with zsh/datetime's strftime:

  % ( unset TZ; strftime '%a %F %T %z' 1234567890 )
  Sat 2009-02-14 06:31:30 +0700
  % ( unset TZ; TZ= strftime '%a %F %T %z' 1234567890 )
  Sat 2009-02-14 06:31:30 +0700

what i expected:

  % ( unset TZ; date -jf%s 1234567890 '+%a %F %T %z' )
  Sat 2009-02-14 06:31:30 +0700
  % ( unset TZ; TZ= date -jf%s 1234567890 '+%a %F %T %z' )
  Fri 2009-02-13 23:31:30 +0000

this apparently isn't prescribed by posix but it's the documented
behaviour on most platforms. e.g. from glibc's tzset(3):

> If the TZ variable does appear in the environment, but its value is
> empty, ... then Coordinated Universal Time (UTC) is used.

was it a conscious choice not to pass through empty TZ? workers/34596
doesn't explicitly say

if not, is there any issue with changing it (whether now or after 5.10)?
attached patch does that + fixes a typo in the documentation

dana


diff --git a/Doc/Zsh/mod_datetime.yo b/Doc/Zsh/mod_datetime.yo
index 5475bd6cc..84f49086d 100644
--- a/Doc/Zsh/mod_datetime.yo
+++ b/Doc/Zsh/mod_datetime.yo
@@ -33,7 +33,7 @@ function tt(strptime); see manref(strptime)(3).  This means that zsh
 format extensions are not available, but for reverse lookup they are not
 required.
 
-In most implementations of tt(strftime) any timezone in the
+In most implementations of tt(strptime) any timezone in the
 var(timestring) is ignored and the local timezone declared by the tt(TZ)
 environment variable is used; other parameters are set to zero if not
 present.

diff --git a/Src/Modules/datetime.c b/Src/Modules/datetime.c
index 085e4cc26..eb6b9e65f 100644
--- a/Src/Modules/datetime.c
+++ b/Src/Modules/datetime.c
@@ -190,7 +190,7 @@ bin_strftime(char *nam, char **argv, Options ops, int func)
     char *tz = getsparam("TZ");
 
     startparamscope();
-    if (tz && *tz) {
+    if (tz) {
 	Param pm = createparam("TZ", PM_LOCAL|PM_SCALAR|PM_EXPORTED);
 	if (pm)
 	    pm->level = locallevel; /* because createparam() doesn't */

diff --git a/Test/V09datetime.ztst b/Test/V09datetime.ztst
index 622bdf6ed..0eae31687 100644
--- a/Test/V09datetime.ztst
+++ b/Test/V09datetime.ztst
@@ -134,3 +134,13 @@
   strftime -n 'one line%n' 2> /dev/null
 0:-n option
 >one line
+
+# most platforms treat a set-but-empty TZ as UTC. however, it's not actually
+# required by POSIX, so we'll only test on systems we can be fairly sure about
+  if [[ $OSTYPE != (darwin|freebsd|netbsd|openbsd|linux-gnu)* ]]; then
+    ZTST_skip='unsure of empty-TZ behaviour'
+  else
+    ( unset TZ; TZ= strftime '%F %T' 1234567890 )
+  fi
+0:empty TZ respected
+>2009-02-13 23:31:30