[PATCH] Fix multiple minor tzset glitches [BZ #24004]

[Paul Eggert <eggert at cs dot ucla dot edu>]

Avoid polling if TZ is unset.
Consistently ignore leading ":" in TZ as per documentation.
Treat TZ="" as Universal Time without leap seconds,
for consistency with upstream.
* time/tzset.c (tzset_internal): Check for null TZ first.
Do not substitute "Universal" for ""; this is __tzfile_read’s
job and we were doing it incorrectly as we treated TZ=""
differently from TZ=":".
* time/tzfile.c (__tzfile_read): Simplify, as FILE cannot be null.
---
 ChangeLog     | 13 +++++++++++++
 NEWS          |  7 +++++++
 time/tzfile.c |  5 +----
 time/tzset.c  | 15 ++++++---------
 4 files changed, 27 insertions(+), 13 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 6f1d967f62..831d89ba8f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,16 @@
+2019-02-11  Paul Eggert  <eggert@cs.ucla.edu>
+
+	Fix multiple minor tzset glitches [BZ #24004]
+	Avoid polling if TZ is unset.
+	Consistently ignore leading ":" in TZ as per documentation.
+	Treat TZ="" as Universal Time without leap seconds,
+	for consistency with upstream.
+	* time/tzset.c (tzset_internal): Check for null TZ first.
+	Do not substitute "Universal" for ""; this is __tzfile_read’s
+	job and we were doing it incorrectly as we treated TZ=""
+	differently from TZ=":".
+	* time/tzfile.c (__tzfile_read): Simplify, as FILE cannot be null.
+
 2019-02-11  Paul A. Clarke  <pc@us.ibm.com>
 
 	* sysdeps/powerpc/fpu/e_sqrt.c (__slow_ieee754_sqrtf):
diff --git a/NEWS b/NEWS
index 0a3b6c7a5a..87de5030c1 100644
--- a/NEWS
+++ b/NEWS
@@ -22,6 +22,13 @@ Deprecated and removed features, and other changes affecting compatibility:
   definitions in libc will be used automatically, which have been available
   since glibc 2.17.
 
+* If the TZ environment variable is unset, functions like localtime no
+  longer stat the file /etc/localtime if the file has already been
+  consulted.  Instead, they reuse the cached timezone info, just as they
+  would with TZ="/etc/localtime".  If TZ="", these functions now omit leap
+  seconds even on unusual installations where TZ="Universal" identifies a
+  TZif file with leap seconds; this is for consistency with tzcode and BSD.
+
 Changes to build and runtime requirements:
 
 * GCC 6.2 or later is required to build the GNU C Library.
diff --git a/time/tzfile.c b/time/tzfile.c
index 7229ed93b7..db66f22a4e 100644
--- a/time/tzfile.c
+++ b/time/tzfile.c
@@ -115,10 +115,7 @@ __tzfile_read (const char *file, size_t extra, char **extrap)
 
   __use_tzfile = 0;
 
-  if (file == NULL)
-    /* No user specification; use the site-wide default.  */
-    file = TZDEFAULT;
-  else if (*file == '\0')
+  if (*file == '\0')
     /* User specified the empty string; use UTC with no leap seconds.  */
     goto ret_free_transitions;
   else
diff --git a/time/tzset.c b/time/tzset.c
index 307eb651ad..1903ef864d 100644
--- a/time/tzset.c
+++ b/time/tzset.c
@@ -375,25 +375,22 @@ tzset_internal (int always)
 
   /* Examine the TZ environment variable.  */
   tz = getenv ("TZ");
-  if (tz && *tz == '\0')
-    /* User specified the empty string; use UTC explicitly.  */
-    tz = "Universal";
+
+  if (tz == NULL)
+    /* No user specification; use the site-wide default.  */
+    tz = TZDEFAULT;
 
   /* A leading colon means "implementation defined syntax".
      We ignore the colon and always use the same algorithm:
      try a data file, and if none exists parse the 1003.1 syntax.  */
-  if (tz && *tz == ':')
+  if (*tz == ':')
     ++tz;
 
   /* Check whether the value changed since the last run.  */
-  if (old_tz != NULL && tz != NULL && strcmp (tz, old_tz) == 0)
+  if (old_tz != NULL && strcmp (tz, old_tz) == 0)
     /* No change, simply return.  */
     return;
 
-  if (tz == NULL)
-    /* No user specification; use the site-wide default.  */
-    tz = TZDEFAULT;
-
   tz_rules[0].name = NULL;
   tz_rules[1].name = NULL;
 
-- 
2.20.1