fix(man): Add correct date and version to manpage

The previous approach relied on manually updating the version and date
using a Makefile

This approach dynamically gathers the correct version from git and uses
the date of the latest commit in the branch

.gitignore

@@ -1,6 +1,7 @@
 /build*
 /doc/config
 /include/settings.hpp
+/man/polybar.1
 /polybar
 /polybar-msg
 /tags

include/CMakeLists.txt

@@ -38,4 +38,5 @@ configure_file(
   ${CMAKE_CURRENT_LIST_DIR}/settings.hpp
   ESCAPE_QUOTES @ONLY)
 
+set(APP_VERSION ${APP_VERSION} PARENT_SCOPE)
 set(dirs ${dirs} PARENT_SCOPE)

man/CMakeLists.txt

@@ -1,4 +1,16 @@
+# Gets the date of the latest commit in the form YYYY-MM-DD
+# This date is used in the man page
+execute_process(COMMAND git log -1 --date=format:%Y-%m-%d --format=%cd
+  WORKING_DIRECTORY ${PROJECT_SOURCE_DIR}
+  OUTPUT_VARIABLE LAST_COMMIT_DATE
+  OUTPUT_STRIP_TRAILING_WHITESPACE)
+
 set(MAN_PAGES_1 polybar.1)
+configure_file(
+  ${CMAKE_CURRENT_LIST_DIR}/${MAN_PAGES_1}.cmake
+  ${CMAKE_CURRENT_LIST_DIR}/${MAN_PAGES_1}
+  ESCAPE_QUOTES @ONLY)
+
 INSTALL(FILES ${MAN_PAGES_1}
   DESTINATION ${CMAKE_INSTALL_PREFIX}/share/man/man1
   COMPONENT doc)

man/polybar.1 → man/polybar.1.cmake

@@ -1,4 +1,4 @@
-.TH polybar 1 2017-01-26 "polybar 3.0.2" "User Manual"
+.TH polybar 1 @LAST_COMMIT_DATE@ "polybar @APP_VERSION@" "User Manual"
 .SH NAME
 polybar \- A fast and easy-to-use tool status bar
 .SH SYNOPSIS