fix: copy the string returned by getenv (#3264)

src/builtin.c

@@ -1474,8 +1474,10 @@ static time_t my_mktime(struct tm *tm) {
   if (tz != NULL)
     setenv("TZ", "", 1);
   time_t t = mktime(tm);
-  if (tz != NULL)
+  if (tz != NULL) {
     setenv("TZ", tz, 1);
+    free(tz);
+  }
   return t;
 #endif
 }
@@ -1762,13 +1764,14 @@ static jv f_strftime(jq_state *jq, jv a, jv b) {
   /* Apple Libc (as of version 1669.40.2) contains a bug which causes it to
    * ignore the `tm.tm_gmtoff` in favor of the global timezone. To print the
    * proper timezone offset we temporarily switch the TZ to UTC. */
-  char *tz = getenv("TZ");
+  char *tz = (tz = getenv("TZ")) != NULL ? strdup(tz) : NULL;
   setenv("TZ", "UTC", 1);
 #endif
   size_t n = strftime(buf, alloced, fmt, &tm);
 #ifdef __APPLE__
   if (tz) {
     setenv("TZ", tz, 1);
+    free(tz);
   } else {
     unsetenv("TZ");
   }

tests/shtest

@@ -728,6 +728,14 @@ if ! $msys && ! $mingw; then
     echo "Incorrectly formatted universal time"
     exit 1
   fi
+ 
+  if ! r=$(TZ=Etc/GMT+7 $JQ -nc '1731627341 | .,. | [strftime("%FT%T"),strflocaltime("%FT%T%z")]'
+) \
+    || [ "$r" != '["2024-11-14T23:35:41","2024-11-14T16:35:41-0700"]
+["2024-11-14T23:35:41","2024-11-14T16:35:41-0700"]' ]; then
+    echo "strftime or strftimelocal are not pure functions"
+    exit 1
+  fi
 fi
 
 exit 0