Try to use Homebrew's Bison and Flex in macOS

CMakeLists.txt

@@ -18,7 +18,35 @@ else()
     MONAA_VERSION="${VERSION_MAJOR}.${VERSION_MINOR}.${VERSION_PATCH}")
 endif()
 
-find_package(BISON REQUIRED)
+# Mostly taken from the following but
+# https://stackoverflow.com/questions/53877344/cannot-configure-cmake-to-look-for-homebrew-installed-version-of-bison
+# On macOS, search Homebrew for keg-only versions of Bison and Flex. Xcode does
+# not provide new enough versions for us to use.
+if (CMAKE_HOST_SYSTEM_NAME MATCHES "Darwin")
+    execute_process(
+        COMMAND brew --prefix bison
+        RESULT_VARIABLE BREW_BISON
+        OUTPUT_VARIABLE BREW_BISON_PREFIX
+        OUTPUT_STRIP_TRAILING_WHITESPACE
+    )
+    if (BREW_BISON EQUAL 0 AND EXISTS "${BREW_BISON_PREFIX}")
+        message(STATUS "Found Bison keg installed by Homebrew at ${BREW_BISON_PREFIX}")
+        set(CMAKE_FIND_ROOT_PATH "${BREW_BISON_PREFIX};${CMAKE_FIND_ROOT_PATH}")
+    endif()
+
+    execute_process(
+        COMMAND brew --prefix flex
+        RESULT_VARIABLE BREW_FLEX
+        OUTPUT_VARIABLE BREW_FLEX_PREFIX
+        OUTPUT_STRIP_TRAILING_WHITESPACE
+    )
+    if (BREW_FLEX EQUAL 0 AND EXISTS "${BREW_FLEX_PREFIX}")
+        message(STATUS "Found Flex keg installed by Homebrew at ${BREW_FLEX_PREFIX}")
+        set(CMAKE_FIND_ROOT_PATH "${BREW_FLEX_PREFIX};${CMAKE_FIND_ROOT_PATH}")
+    endif()
+endif()
+
+find_package(BISON 3.0 REQUIRED)
 find_package(FLEX REQUIRED)
 find_package(Boost REQUIRED COMPONENTS
   program_options unit_test_framework iostreams graph)
@@ -27,6 +55,8 @@ find_package(Eigen3 REQUIRED)
 include_directories(
   monaa/
   libmonaa/
+  ${BISON_INCLUDE_DIRS}
+  ${FLEX_INCLUDE_DIRS}
   ${PROJECT_BINARY_DIR}
   ${Boost_INCLUDE_DIRS}
   ${EIGEN3_INCLUDE_DIRS})

README.md

@@ -44,7 +44,7 @@ MONAA is tested on Arch Linux, Ubuntu (18.04 and 20.04), and macOS 10.15 Catalin
 * Boost (>= 1.59)
 * Eigen
 * CMake
-* Bison
+* Bison (>= 3.0)
 * Flex
 
 ### Instructions