Only run once codegen.pl and git-describe.cmake with make

ninja has a single build file which avoided issues if multiple targets
depend on same files. But Unix Makefiles generator user recursive make
which requires each ADD_CUSTOM_COMMAND to have only one target depending
on them.

Then makefile generator also has stupid rule that it touches all
secundary output files if primary file has been updated.

It was surprising hard to find a version that actually works correctly
for both issues. Solution is using BYPRODUCTS and refactoring command
and target dependencies.

As a bonus this change now allows build to work from source tarball if
the tarball includes git-describe.h.

library/CMakeLists.txt

@@ -258,20 +258,19 @@ LIST(APPEND PROJECT_SOURCES ${GENERATED_HDRS})
 FILE(GLOB GENERATE_INPUT_SCRIPTS ${dfapi_SOURCE_DIR}/xml/*.pm ${dfapi_SOURCE_DIR}/xml/*.xslt)
 FILE(GLOB GENERATE_INPUT_XMLS ${dfapi_SOURCE_DIR}/xml/df.*.xml)
 
-STRING(REPLACE ":" " " GEN_HDRS_STR "${GENERATED_HDRS}")
-
 ADD_CUSTOM_COMMAND(
-    OUTPUT ${dfapi_SOURCE_DIR}/include/df/codegen.out.xml ${GEN_HDRS_STR}
+    OUTPUT ${dfapi_SOURCE_DIR}/include/df/codegen.out.xml
     COMMAND ${PERL_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/xml/codegen.pl
         ${CMAKE_CURRENT_SOURCE_DIR}/xml
         ${CMAKE_CURRENT_SOURCE_DIR}/include/df
     MAIN_DEPENDENCY ${dfapi_SOURCE_DIR}/xml/codegen.pl
+    BYPRODUCTS ${GENERATED_HDRS}
     COMMENT "Generating codegen.out.xml and df/headers"
     DEPENDS ${GENERATE_INPUT_XMLS} ${GENERATE_INPUT_SCRIPTS}
 )
 
 ADD_CUSTOM_TARGET(generate_headers
-  DEPENDS ${dfapi_SOURCE_DIR}/include/df/codegen.out.xml ${GEN_HDRS_STR})
+    DEPENDS ${dfapi_SOURCE_DIR}/include/df/codegen.out.xml)
 
 IF(REMOVE_SYMBOLS_FROM_DF_STUBS)
   IF(UNIX)
@@ -325,24 +324,29 @@ ENDIF()
 
 # always re-run git-describe if cmake is re-run (e.g. if build ID or version changes)
 EXECUTE_PROCESS(COMMAND ${CMAKE_COMMAND} -E touch ${CMAKE_CURRENT_SOURCE_DIR}/git-describe.cmake)
-ADD_CUSTOM_COMMAND(OUTPUT always_rebuild
-  COMMAND ${CMAKE_COMMAND} -E echo)
-
-ADD_CUSTOM_COMMAND(OUTPUT ${CMAKE_CURRENT_SOURCE_DIR}/include/git-describe.h
+if (EXISTS ${CMAKE_SOURCE_DIR}/.git/index AND EXISTS ${CMAKE_SOURCE_DIR}/.git/modules/library/xml/index)
+    ADD_CUSTOM_COMMAND(OUTPUT ${CMAKE_CURRENT_BINARY_DIR}/git-describe.h
       COMMAND ${CMAKE_COMMAND}
           -D dfhack_SOURCE_DIR:STRING=${dfhack_SOURCE_DIR}
-        -D git_describe_h:STRING=${CMAKE_CURRENT_SOURCE_DIR}/include/git-describe.h
           -D git_describe_tmp_h:STRING=${CMAKE_CURRENT_BINARY_DIR}/git-describe.h
           -D GIT_EXECUTABLE:STRING=${GIT_EXECUTABLE}
           -D DFHACK_BUILD_ID:STRING=${DFHACK_BUILD_ID}
           -P ${CMAKE_CURRENT_SOURCE_DIR}/git-describe.cmake
       COMMENT "Obtaining git commit information"
-    DEPENDS ${GIT_EXECUTABLE} always_rebuild
-    VERBATIM
-)
+      DEPENDS ${CMAKE_SOURCE_DIR}/.git/index
+          ${CMAKE_SOURCE_DIR}/.git/modules/library/xml/index
+          ${CMAKE_CURRENT_SOURCE_DIR}/git-describe.cmake
+    )
+    ADD_CUSTOM_COMMAND(OUTPUT ${CMAKE_CURRENT_SOURCE_DIR}/include/git-describe.h
+        DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/git-describe.h
+        COMMAND ${CMAKE_COMMAND} -E copy_if_different ${CMAKE_CURRENT_BINARY_DIR}/git-describe.h ${CMAKE_CURRENT_SOURCE_DIR}/include/git-describe.h
+        COMMENT "Copy include/git-describe.h"
+    )
+endif ()
 
 ADD_LIBRARY(dfhack SHARED ${PROJECT_SOURCES})
 ADD_DEPENDENCIES(dfhack generate_proto_core)
+ADD_DEPENDENCIES(dfhack generate_headers)
 
 ADD_LIBRARY(dfhack-client SHARED RemoteClient.cpp ColorText.cpp MiscUtils.cpp Error.cpp ${PROJECT_PROTO_SRCS})
 ADD_DEPENDENCIES(dfhack-client dfhack)

library/git-describe.cmake

@@ -1,14 +1,3 @@
-if(NOT EXISTS ${dfhack_SOURCE_DIR}/.git/index OR NOT EXISTS ${dfhack_SOURCE_DIR}/.git/modules/library/xml/index)
-    MESSAGE(FATAL_ERROR "Could not find git index file(s)")
-endif()
-
-if(EXISTS ${git_describe_tmp_h} AND EXISTS ${git_describe_h} AND
-        NOT(${dfhack_SOURCE_DIR}/.git/index IS_NEWER_THAN ${git_describe_tmp_h}) AND
-        NOT(${dfhack_SOURCE_DIR}/.git/modules/library/xml/index IS_NEWER_THAN ${git_describe_tmp_h}) AND
-        NOT(${dfhack_SOURCE_DIR}/library/git-describe.cmake IS_NEWER_THAN ${git_describe_tmp_h}))
-    return()
-endif()
-
 execute_process(COMMAND ${GIT_EXECUTABLE} describe --tags --abbrev=8 --long
     WORKING_DIRECTORY "${dfhack_SOURCE_DIR}"
     OUTPUT_VARIABLE DFHACK_GIT_DESCRIPTION)
@@ -46,5 +35,3 @@ endif()
 if(${DFHACK_GIT_XML_COMMIT} STREQUAL ${DFHACK_GIT_XML_EXPECTED_COMMIT})
     file(APPEND ${git_describe_tmp_h} "#define DFHACK_GIT_XML_MATCH\n")
 endif()
-execute_process(COMMAND ${CMAKE_COMMAND} -E copy_if_different
-    ${git_describe_tmp_h} ${git_describe_h})