CMake: Require libgnutls by default.

- Make cmake complain and abort the build process if libgnutls is not
  available.  In order to build Taskwarrior without "sync" support,
  or to build it on a system with libgnutls missing, the new cmake
  flag "-DENABLE_SYNC=OFF" can be used.

CMakeLists.txt

@@ -12,7 +12,14 @@ set (HAVE_CMAKE true)
 project (task)
 set (PROJECT_VERSION "2.4.5")
 
-OPTION(USE_GNUTLS "Build gnutls support." ON)
+OPTION (ENABLE_SYNC "Enable 'task sync' support" ON)
+
+if (ENABLE_SYNC)
+  set (USE_GNUTLS ON CACHE BOOL "Build gnutls support." FORCE)
+else (ENABLE_SYNC)
+  set (USE_GNUTLS OFF CACHE BOOL "Build gnutls support." FORCE)
+  message (WARNING "ENABLE_SYNC=OFF. Not building sync support.")
+endif (ENABLE_SYNC)
 
 message ("CMAKE_SYSTEM_NAME ${CMAKE_SYSTEM_NAME}")
 
@@ -116,6 +123,10 @@ if (USE_GNUTLS)
    endif (GNUTLS_FOUND)
 endif (USE_GNUTLS)
 
+if (ENABLE_SYNC AND NOT GNUTLS_FOUND)
+  message (FATAL_ERROR "Cannot find GnuTLS. Use -DENABLE_SYNC=OFF to build Taskwarrior without sync support. See INSTALL for more information.")
+endif (ENABLE_SYNC AND NOT GNUTLS_FOUND)
+
 check_function_exists (timegm  HAVE_TIMEGM)
 check_function_exists (get_current_dir_name HAVE_GET_CURRENT_DIR_NAME)
 check_function_exists (wordexp HAVE_WORDEXP)

ChangeLog

@@ -1,27 +1,30 @@
 2.4.5 () -
 
 - TW-32   Unable to change annotations via task edit (thanks to Peter De
-Poorter).
+          Poorter).
 - TW-50   Creation time is lost after editing (thanks to Ben Boeckel).
 - TW-148  default.command options (thanks to David Patrick).
 - TW-269  \t is not rendered correctly (thanks to Scott Kostyshak).
 - TW-283  Process rc.* items when executing config (thanks to Ben Armstrong).
 - TW-303  Ability for "import" to update existing tasks (thanks to Kosta
-Harlan).
+          Harlan).
 - TW-1285 relative dates combined with times (thanks to Adam Gibbins).
 - TW-1432 start/stop can be issued on completed tasks  (thanks to Renato Alves).
 - TW-1440 "task import" from STDIN (thanks to Renato Alves).
 - TW-1454 Redundant dependency should not stop modification  (thanks to Tomas
-Babej).
+          Babej).
 - TW-1572 Better urgency inheritance (thanks to Jens Erat).
 - Prevent potential task duplication during import for non-pending tasks.
 - Show the active context in "context list", if any is active.
 - Fix "task edit" dropping annotation text after newlines.
 - Removed obsolete script 'context'.
 - Fix "project" verbosity info not showing without "footnote" being manually
-enabled.
+  enabled.
 - Internal plumbing:  Use variadic templates for format(), reducing code bloat
-and enabling more flexible use of the function.
+  and enabling more flexible use of the function.
+- Enable "task sync" support by default.  "cmake -DENABLE_SYNC=OFF" allows
+  disabling it and building Taskwarrior without libgnutls available.
+
 
 ------ current release ---------------------------
 

INSTALL

@@ -91,6 +91,25 @@ get absolute installation directories:
   CMAKE_INSTALL_PREFIX/TASK_MAN5DIR  /usr/local/share/man/man5
 
 
+"sync" command
+--------------
+
+In order to enable the "sync" command, you will need to have GnuTLS available.
+
+cmake may fail with the following error message:
+   "Cannot find GnuTLS.  Use -DENABLE_SYNC=OFF to build Taskwarrior without
+    sync support.  See INSTALL for more information."
+
+This means that it cannot find your GnuTLS installation, and you will need to
+install GnuTLS as well as its header files.  For Debian based distributions,
+installing "libgnutls-dev" is usually sufficient.
+
+In order to build Taskwarrior without "sync" support, call cmake with the
+"-DENABLE_SYNC=OFF" flag:
+   $ cmake . -DENABLE_SYNC=OFF
+and proceed as described in "Basic Installation".
+
+
 Localizations
 -------------