Use cmake to find a lua executable

A lua executable is now required for the build process since a lpeg-based script
is used for generating a dispatch function and metadata for the msgpack API
frontend. This removes the need for setting the LUA_BINARY environment variable.
Fixes #518.

CMakeLists.txt

@@ -68,12 +68,24 @@ endif(NOT CMAKE_USE_PTHREADS_INIT)
 
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
 
+find_program(LUA_PRG luajit)
+
+# Need a lua interpreter for running the msgapck metadata/dispatch generator
+if(NOT EXISTS ${LUA_PRG})
+  find_program(LUA_PRG lua)
+endif()
+
+if(EXISTS ${LUA_PRG})
+  message(STATUS "Using the lua interpreter ${LUA_PRG}")
+else()
+  message(FATAL_ERROR "A lua interpreter is required for building the Neovim")
+endif()
+
 add_subdirectory(config)
 add_subdirectory(src)
 add_subdirectory(test/includes)
 
 find_program(BUSTED_PRG busted)
-find_program(LUAJIT_PRG luajit)
 
 find_program(MAKE_PRG NAMES gmake make)
 if(MAKE_PRG)

src/CMakeLists.txt

@@ -1,11 +1,5 @@
 include(CheckLibraryExists)
 
-if(DEFINED ENV{LUA_BINARY})
-  set(LUA_BIN $ENV{LUA_BINARY})
-else()
-  set(LUA_BIN ${DEPS_BIN_DIR}/luajit)
-endif()
-
 set(GENERATED_DIR ${PROJECT_BINARY_DIR}/src/auto)
 set(DISPATCH_GENERATOR ${PROJECT_SOURCE_DIR}/scripts/msgpack-gen.lua)
 set(API_HEADER ${PROJECT_SOURCE_DIR}/src/api.h)
@@ -15,7 +9,7 @@ set(MSGPACK_DISPATCH ${GENERATED_DIR}/msgpack_dispatch.c)
 file(MAKE_DIRECTORY ${GENERATED_DIR})
 
 add_custom_command(OUTPUT ${MSGPACK_DISPATCH}
-  COMMAND ${LUA_BIN} ${DISPATCH_GENERATOR} ${API_HEADER} ${MSGPACK_DISPATCH}
+  COMMAND ${LUA_PRG} ${DISPATCH_GENERATOR} ${API_HEADER} ${MSGPACK_DISPATCH}
   DEPENDS
     ${API_HEADER}
     ${MSGPACK_RPC_HEADER}