C++ Target grammars in subdirectory

[mcmikecreations]

Hey everyone! I have a small question for my usage of Antlr4 with the C++ target. I'm using version 4.13.0 on wsl/ubuntu 22.04.2 with OpenJDK 11.0.20.

My directory structure is as follows:

myproject/
  |- src/main.cpp
  |- grammar/TLexer.g4
  |- grammar/TParser.g4
  |- CMakeLists.txt

Initial setup

The CMakeLists is as follows from the example in the official repo:

cmake_minimum_required(VERSION 3.7 FATAL_ERROR)
list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake)
set(CMAKE_CXX_STANDARD 17)
add_definitions(-DANTLR4CPP_STATIC)
set(ANTLR4_WITH_STATIC_CRT OFF)
include(ExternalAntlr4Cpp)
include_directories(${ANTLR4_INCLUDE_DIRS})
set(ANTLR_EXECUTABLE somepath)
find_package(ANTLR REQUIRED)

antlr_target(SampleGrammarLexer grammar/TLexer.g4 LEXER
             PACKAGE antlrcpptest)
antlr_target(SampleGrammarParser grammar/TParser.g4 PARSER
             PACKAGE antlrcpptest
             DEPENDS_ANTLR SampleGrammarLexer
             COMPILE_FLAGS -lib ${ANTLR_SampleGrammarLexer_OUTPUT_DIR})

include_directories(${ANTLR_SampleGrammarLexer_OUTPUT_DIR})
include_directories(${ANTLR_SampleGrammarParser_OUTPUT_DIR})
add_executable(myproject src/main.cpp
               ${ANTLR_SampleGrammarLexer_CXX_OUTPUTS}
               ${ANTLR_SampleGrammarParser_CXX_OUTPUTS})
target_link_libraries(myproject antlr4_static)

The issue I get is:

error(114): TParser.g4:4:14: cannot find tokens file grammar/TLexer.tokens

Updating path

I observed that in FindANTLR.cmake on line 40 you can specify the output directory more clearly. According to the docs, the default is ${CMAKE_CURRENT_BINARY_DIR}, so I set it manually. TParser still kept searching in build/myproject/TLexer.tokens, so I changed -lib too. Updated CMakeLists lines:

antlr_target(SampleGrammarLexer grammar/TLexer.g4 LEXER
             OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
             PACKAGE antlrcpptest)
antlr_target(SampleGrammarParser grammar/TParser.g4 PARSER
             OUTPUT_DIRECTORY ${CMAKE_CURRENT_BINARY_DIR}
             PACKAGE antlrcpptest
             DEPENDS_ANTLR SampleGrammarLexer
             COMPILE_FLAGS -lib ${ANTLR_SampleGrammarLexer_OUTPUT_DIR}/grammar)

Now the generation works, but during the build process in add_executable I get:

cc1plus: fatal error: .../build/myproject/TLexer.cpp: No such file or directory

If I check the content of ${ANTLR_SampleGrammarLexer_CXX_OUTPUTS} I see indeed the incorrect path. Further investigating the FindANTLR.cmake file, I found that:

1. On line 38 we get only the file name, so TLexer without grammar/
2. On line 51 we append that path to the list also without grammar/
3. As a result the ${ANTLR_SampleGrammarLexer_CXX_OUTPUTS} variable contains the incorrect path.

Question

What is the correct way to overcome this? Maybe by adding an additional CMakeLists.txt file in the grammar/ subdirectory?