CMake: Extend TIMESTAMP sub-commands with new unix time format specifier

The new `%s` format specifier is substituted by file()/string()
`TIMESTAMP` sub-commands with the number of seconds since unix-epoch
(1970-01-01 00:00:00 UTC).

Co-Author: Nils Gladitz <nilsgladitz@gmail.com>

2 files changed, 28 insertions, 0 deletions

diff --git a/Tests/CMakeTests/String-TIMESTAMP-UnixTime.cmake b/Tests/CMakeTests/String-TIMESTAMP-UnixTime.cmake
new file mode 100644
index 0000000..a93e7f5
--- /dev/null
+++ b/Tests/CMakeTests/String-TIMESTAMP-UnixTime.cmake
@@ -0,0 +1,22 @@
+string(TIMESTAMP timestamp "[%Y-%m-%d %H:%M:%S] %s" UTC)
+
+string(TIMESTAMP unix_time "%s")
+
+string(TIMESTAMP year "%Y" UTC)
+string(TIMESTAMP days "%j" UTC)
+
+# Doing proper date calculations here to verify unix timestamps
+# could be error prone.
+# At the very least use some safe lower and upper bounds to
+# see if we are somewhere in the right region.
+
+math(EXPR years_since_epoch "${year} - 1970")
+math(EXPR lower_bound "((${years_since_epoch} * 365) + ${days}) * 86400")
+math(EXPR upper_bound "((${years_since_epoch} * 366) + ${days}) * 86400")
+
+
+if(unix_time GREATER lower_bound AND unix_time LESS upper_bound)
+  message("~${unix_time}~")
+else()
+  message(FATAL_ERROR "${timestamp} unix time not in expected range [${lower_bound}, ${upper_bound}]")
+endif()
diff --git a/Tests/CMakeTests/StringTest.cmake.in b/Tests/CMakeTests/StringTest.cmake.in
index 92e70c3..aba35fe 100644
--- a/Tests/CMakeTests/StringTest.cmake.in
+++ b/Tests/CMakeTests/StringTest.cmake.in
@@ -36,6 +36,8 @@ set(TIMESTAMP-IncompleteSpecifier-RESULT 0)
 set(TIMESTAMP-IncompleteSpecifier-STDERR "~foobar%~")
 set(TIMESTAMP-AllSpecifiers-RESULT 0)
 set(TIMESTAMP-AllSpecifiers-STDERR "~[0-9]+(;[0-9]+)*~")
+set(TIMESTAMP-UnixTime-RESULT 0)
+set(TIMESTAMP-UnixTime-STDERR "~[1-9][0-9]+~")
 
 include("@CMAKE_CURRENT_SOURCE_DIR@/CheckCMakeTest.cmake")
 check_cmake_test(String
@@ -58,6 +60,7 @@ check_cmake_test(String
   TIMESTAMP-UnknownSpecifier
   TIMESTAMP-IncompleteSpecifier
   TIMESTAMP-AllSpecifiers
+  TIMESTAMP-UnixTime
   )
 
 # Execute each test listed in StringTestScript.cmake:
@@ -68,9 +71,12 @@ set(number_of_tests_expected 70)
 include("@CMAKE_CURRENT_SOURCE_DIR@/ExecuteScriptTests.cmake")
 execute_all_script_tests(${scriptname} number_of_tests_executed)
 
+string(TIMESTAMP timestamp "[%Y-%m-%d %H:%M:%S] UTC %s" UTC)
+
 # And verify that number_of_tests_executed is at least as many as we know
 # about as of this writing...
 #
+message(STATUS "timestamp='${timestamp}'")
 message(STATUS "scriptname='${scriptname}'")
 message(STATUS "number_of_tests_executed='${number_of_tests_executed}'")
 message(STATUS "number_of_tests_expected='${number_of_tests_expected}'")