Linux time zones: modernize libical support

libical v2 introduces a new API for generating system time zones
in a more interoperable format, with rules for summer and winter time (same
as in libical before v1) instead of just the transition dates (as in
libical v1). We should use that whenever possible.

We can drop support for libical embedded in libecal, that's really ancient.

Binary compatibility is now enabled with a dedicated configure parameter
(cleaner that piggy-backing on the parameter used by SyncEvolution). To make
this work for the libical v1/v2 ABI break (icalarray changed its types),
we must wrap some calls.

3 files changed, 71 insertions, 37 deletions

diff --git a/configure.in b/configure.in
index 173628b..bfea2da 100644
--- a/configure.in
+++ b/configure.in
@@ -100,21 +100,20 @@ AC_ARG_ENABLE(libical,
               [enable_libical="yes"])
 if test "$enable_libical" == "yes"; then
    PKG_CHECK_MODULES(LIBICAL, libical,
-                     [AC_DEFINE(HAVE_LIBICAL, 1, "libical available")],
-                     [PKG_CHECK_MODULES(LIBECAL, libecal-1.2,
-                                        [AC_DEFINE(HAVE_LIBICAL, 1, "libical available")
-                                         AC_DEFINE(HAVE_LIBECAL, 1, "libecal available")],
-                                         [true])])
+                     [AC_DEFINE(HAVE_LIBICAL, 1, "libical available")
+                      PKG_CHECK_MODULES(LIBICAL2, libical >= 2,
+                                        [AC_DEFINE(USE_ICALTZUTIL_SET_EXACT_VTIMEZONES_SUPPORT, 1, "Use icaltzutil_set_exact_vtimezones_support() to enable interoperable timezone definitions.")],
+                                        [true])],
+                     [AC_ERROR([libical not found, required for --enable-libical])])
 fi
 
-AC_ARG_ENABLE(evolution-compatibility,
-              AS_HELP_STRING([--enable-evolution-compatibility],
-                             [build executables which only call Evolution via dlopen/dlsym: this avoids all hard dependencies on EDS shared objects, but might lead to crashes when their ABI changes]),
-              enable_evolution_compatibility="$enableval", enable_evolution_compatibility="no")
-if test "$enable_evolution_compatibility" == "yes"; then
-   AC_DEFINE(EVOLUTION_COMPATIBILITY, 1, [avoid hard dependency on Evolution shared objects])
+AC_ARG_ENABLE(ical-compatibility,
+              AS_HELP_STRING([--enable-ical-compatibility],
+                             [build executables which only call libical via dlopen/dlsym: this avoids a hard dependency on a specific libical.so version]),
+              enable_ical_compatibility="$enableval", enable_ical_compatibility="no")
+if test "$enable_ical_compatibility" == "yes"; then
+   AC_DEFINE(ICAL_COMPATIBILITY, 1, [avoid hard dependency on libical shared object])
    LIBICAL_LIBS=
-   LIBECAL_LIBS=
 fi
 
 AC_ARG_WITH(xmltok,
diff --git a/src/Makefile.am.in b/src/Makefile.am.in
index 347dbe3..18a5c63 100644
--- a/src/Makefile.am.in
+++ b/src/Makefile.am.in
@@ -76,10 +76,9 @@ libsynthesis_la_CFLAGS = \
 	$(ZLIB_CFLAGS) \
 	$(XMLPARSE_CFLAGS) \
 	$(XMLPARSE_CFLAGS_BUILTIN) \
-	$(LIBICAL_CFLAGS) \
-	$(LIBECAL_CFLAGS)
+	$(LIBICAL_CFLAGS)
 libsynthesis_la_CXXFLAGS = $(libsynthesis_la_CFLAGS)
-libsynthesis_la_LIBADD = $(PCRE_LIBS) $(DLT_LIBS) $(SQLITE3_LIBS) $(XMLPARSE_LIBS) $(LIBICAL_LIBS) $(LIBECAL_LIBS) libsmltk.la -lz -ldl -lpthread
+libsynthesis_la_LIBADD = $(PCRE_LIBS) $(DLT_LIBS) $(SQLITE3_LIBS) $(XMLPARSE_LIBS) $(LIBICAL_LIBS) libsmltk.la -lz -ldl -lpthread
 libsynthesis_la_LDFLAGS = -version-info $(ENGINE_CURRENT):$(ENGINE_REVISION):$(ENGINE_AGE) \
 	-Wl,--version-script=$(srcdir)/synthesis-linker.map
 libsynthesis_la_DEPENDENCIES = $(srcdir)/synthesis-linker.map libsmltk.la
@@ -187,4 +186,4 @@ clean-doxygen:
 if COND_DOXYGEN
 all: doxygen
 clean-local: clean-doxygen
-endif
\ No newline at end of file
+endif
diff --git a/src/platform_adapters/linux/platform_timezones.cpp b/src/platform_adapters/linux/platform_timezones.cpp
index 83cba58..ac9dcde 100644
--- a/src/platform_adapters/linux/platform_timezones.cpp
+++ b/src/platform_adapters/linux/platform_timezones.cpp
@@ -19,7 +19,7 @@
 # include <config.h>
 #endif
 
-#if defined(HAVE_LIBICAL) && defined(EVOLUTION_COMPATIBILITY)
+#if defined(HAVE_LIBICAL) && defined(ICAL_COMPATIBILITY)
 # ifndef _GNU_SOURCE
 #  define _GNU_SOURCE 1
 # endif
@@ -45,7 +45,7 @@
   extern int   daylight;
 #endif
 
-#ifdef EVOLUTION_COMPATIBILITY
+#ifdef ICAL_COMPATIBILITY
 // Avoid calling libical directly. This way libsynthesis does not
 // depend on a specific version of libecal (which changed its soname
 // frequently, without affecting libical much!) or libical. The user
@@ -58,6 +58,7 @@ static struct {
   void *(* icalarray_element_at_p)(icalarray *array, unsigned index);
   icalcomponent *(* icaltimezone_get_component_p)(icaltimezone *zone);
   char *(* icalcomponent_as_ical_string_p)(icalcomponent *comp);
+  void (* icaltzutil_set_exact_vtimezones_support)(int on);
   bool must_free_strings;
 } icalcontext;
 
@@ -86,6 +87,8 @@ static icalarray *ICALTIMEZONE_GET_BUILTIN_TIMEZONES()
       (typeof(icalcontext.icalcomponent_as_ical_string_p))dlsym(RTLD_DEFAULT, "icalcomponent_as_ical_string");
     icalcontext.must_free_strings = dlsym(RTLD_DEFAULT, "ical_memfixes") != NULL;
   }
+  icalcontext.icaltzutil_set_exact_vtimezones_support =
+    (typeof(icalcontext.icaltzutil_set_exact_vtimezones_support))dlsym(RTLD_DEFAULT, "icaltzutil_set_exact_vtimezones_support");
 
   return icalcontext.icaltimezone_get_builtin_timezones_p ?
     icalcontext.icaltimezone_get_builtin_timezones_p() :
@@ -99,6 +102,31 @@ static void *ICALARRAY_ELEMENT_AT(icalarray *array, unsigned index)
     NULL;
 }
 
+static size_t ICALARRAY_NUM_ELEMENTS(icalarray *array)
+{
+  struct icalarray_traditional {
+    unsigned int         element_size;
+    unsigned int         increment_size;
+    unsigned int         num_elements;
+    unsigned int         space_allocated;
+    void                *data;
+  };
+  // libical v2 changed to size_t
+  struct icalarray_v2 {
+    size_t         element_size;
+    size_t         increment_size;
+    size_t         num_elements;
+    size_t         space_allocated;
+    void **chunks;
+  };
+  // distinguish between v2 and older based on
+  // icaltzutil_set_exact_vtimezones_support, which was introduced in
+  // v2
+  return icalcontext.icaltzutil_set_exact_vtimezones_support ?
+    reinterpret_cast<icalarray_v2 *>(array)->num_elements :
+    reinterpret_cast<icalarray_traditional *>(array)->num_elements;
+}
+
 static icalcomponent *ICALTIMEZONE_GET_COMPONENT(icaltimezone *zone)
 {
   return icalcontext.icaltimezone_get_component_p ?
@@ -119,26 +147,22 @@ static void ICAL_FREE(char *str)
     free(str);
 }
 
+static void ICALTZUTIL_SET_EXACT_VTIMEZONES_SUPPORT(int on)
+{
+  if (icalcontext.icaltzutil_set_exact_vtimezones_support)
+    icalcontext.icaltzutil_set_exact_vtimezones_support(on);
+}
+
 #else
 // call functions directly
 # define ICALTIMEZONE_GET_BUILTIN_TIMEZONES icaltimezone_get_builtin_timezones
 # define ICALARRAY_ELEMENT_AT icalarray_element_at
+# define ICALARRAY_NUM_ELEMENTS(_array) (size_t)((_array)->num_elements)
 # define ICALTIMEZONE_GET_COMPONENT icaltimezone_get_component
 
-# if defined(HAVE_LIBICAL) && !defined(HAVE_LIBECAL)
-#  // new-style libical _r version which requires freeing the string
-#  define ICALCOMPONENT_AS_ICAL_STRING icalcomponent_as_ical_string_r
-#  define ICAL_FREE(_x) free(_x)
-# else
-#  define ICALCOMPONENT_AS_ICAL_STRING icalcomponent_as_ical_string
-#  ifdef LIBICAL_MEMFIXES
-   // new-style Evolution libical: memory must be freed by caller
-#   define ICAL_FREE(_x) free(_x)
-#  else
-    // old-style libical: memory is stored in buffers owned by libical
-#   define ICAL_FREE(_x)
-#  endif
-# endif
+// not-so-new-style libical _r version which requires freeing the string
+# define ICALCOMPONENT_AS_ICAL_STRING icalcomponent_as_ical_string_r
+# define ICAL_FREE(_x) free(_x)
 #endif
 
 
@@ -167,10 +191,22 @@ void finalizeSystemZoneDefinitions(GZones* aGZones)
 #ifdef HAVE_LIBICAL
   PLOGDEBUGBLOCKDESCCOLL(aGZones->getDbgLogger, "loadSystemZoneDefinitions", "Linux system time zones");
   icalarray *builtin = ICALTIMEZONE_GET_BUILTIN_TIMEZONES();
-#ifdef EVOLUTION_COMPATIBILITY
+#ifdef ICAL_COMPATIBILITY
   PLOGDEBUGPRINTFX(aGZones->getDbgLogger, DBG_PARSE+DBG_EXOTIC,
-                   ("runtime check: libical %s",
-                    icalcontext.icaltimezone_get_builtin_timezones_p ? "available" : "unavailable"))
+                   ("runtime check: libical %s, %s icaltzutil_set_exact_vtimezones_support",
+                    icalcontext.icaltimezone_get_builtin_timezones_p ? "available" : "unavailable",
+                    icalcontext.icaltzutil_set_exact_vtimezones_support ? "with" : "without"));
+  // If we end up using the libical code (and not some replacement
+  // provided by SyncEvolution, which is the solution for distros with
+  // a libical that doesn't have the API), then enable timezones in the
+  // format more useful for us.
+  //
+  // We want interoperable timezones with one entry for summer time and one for winter time.
+  // That's what libsynthesis and other devices can handle, and not the exact definitions
+  // with the full set of transitions.
+  ICALTZUTIL_SET_EXACT_VTIMEZONES_SUPPORT(0);
+#elif defined(USE_ICALTZUTIL_SET_EXACT_VTIMEZONES_SUPPORT)
+  icaltzutil_set_exact_vtimezones_support(0);
 #endif
   if (!builtin) {
     PLOGDEBUGPUTSX(aGZones->getDbgLogger, DBG_PARSE+DBG_ERROR,
@@ -178,8 +214,8 @@ void finalizeSystemZoneDefinitions(GZones* aGZones)
     return;
   }
   PLOGDEBUGPRINTFX(aGZones->getDbgLogger, DBG_PARSE+DBG_EXOTIC,
-                   ("%d time zones from libical", builtin->num_elements));
-  for (unsigned i = 0; builtin && i < builtin->num_elements; i++) {
+                   ("%lu time zones from libical", (unsigned long)ICALARRAY_NUM_ELEMENTS(builtin)));
+  for (size_t i = 0; builtin && i < ICALARRAY_NUM_ELEMENTS(builtin); i++) {
     icaltimezone *zone = (icaltimezone *)ICALARRAY_ELEMENT_AT(builtin, i);
     if (!zone)
       continue;