Fix CMake integration of NMODL generation. (#1554)

The code for the code-generator NMODL is itself generated from Jinja
templates. This requires CMake integration to ensure it happens
automatically.

The following has been changed about the integration:

  * The CMake code needs a list of the generated files. This list is
    stored in a CMake file and included. This file must exist before
    running `code_generator.py` to generate the NMODL code, because the
    command to generate the files needs to know which file it will be
    generating. Therefore, we split the script into two phases: one to
    generate the list of generated files, and another to generate the
    files.

  * The list of generated files depends on the build flags. Therefore,
    this file (`code_generator.cmake`) can't be checked into the Git
    repo. The `code_generator.cmake` is created during the configure
    phase, and now lives in the build directory.

  * CMake code was lifted from `src/language/CMakeLists.txt` to the
    top-level `CMakeLists.txt` to avoid any scoping issues for the
    lists of generated files.

  * Removed pattern of yielding tasks while creating a list tasks in
    favour of returning the list of tasks directly.

CMakeLists.txt

@@ -230,10 +230,75 @@ if(NOT NMODL_AS_SUBPROJECT AND NMODL_ENABLE_TESTS)
 endif()
 
 # =============================================================================
-# list of autogenerated files
-# =============================================================================
-include(${PROJECT_SOURCE_DIR}/src/language/code_generator.cmake)
+# Generate NMODL code, e.g. ast & visitor base classes.
+# -----------------------------------------------------------------------------
+# clang-format is handled by the HPC coding conventions scripts, which also handle generating the
+# .clang-format configuration file. It's important that we only try to format code if formatting was
+# enabled and NMODL's .clang-format exists, otherwise clang-format will search too far up the
+# directory tree and find the wrong configuration file. This can break compilation.
+if(NMODL_CLANG_FORMAT OR NMODL_FORMATTING)
+  set(CODE_GENERATOR_OPTS -v --clang-format=${ClangFormat_EXECUTABLE})
+  foreach(clang_format_opt ${NMODL_ClangFormat_OPTIONS} --style=file)
+    list(APPEND CODE_GENERATOR_OPTS --clang-format-opts=${clang_format_opt})
+  endforeach()
+endif()
 
+if(NOT NMODL_ENABLE_PYTHON_BINDINGS)
+  list(APPEND CODE_GENERATOR_OPTS "--disable-pybind")
+endif()
+
+# -----------------------------------------------------------------------------
+# Part I: generate the list of generated files
+# -----------------------------------------------------------------------------
+execute_process(
+  COMMAND ${PYTHON_EXECUTABLE} ${CMAKE_CURRENT_SOURCE_DIR}/src/language/code_generator.py
+          ${CODE_GENERATOR_OPTS} --generate-cmake --base-dir ${PROJECT_BINARY_DIR}/src
+  WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/src/language)
+
+# Ensure that the above runs again, if its dependencies update.
+set_property(
+  DIRECTORY
+  APPEND
+  PROPERTY CMAKE_CONFIGURE_DEPENDS "${CMAKE_CURRENT_SOURCE_DIR}/src/language/code_generator.py")
+
+set_property(
+  DIRECTORY
+  APPEND
+  PROPERTY CMAKE_CONFIGURE_DEPENDS
+           ${CMAKE_CURRENT_SOURCE_DIR}/src/language/templates/code_generator.cmake)
+
+# The list should be up-to-date now.
+include(${PROJECT_BINARY_DIR}/src/code_generator.cmake)
+
+# -----------------------------------------------------------------------------
+# Part II: generate AST/Visitor classes from language definition
+# -----------------------------------------------------------------------------
+set_source_files_properties(${NMODL_GENERATED_SOURCES} PROPERTIES GENERATED TRUE)
+
+# Make the codegen options available as a dependency by storing them in a file.
+configure_file(${CMAKE_CURRENT_SOURCE_DIR}/src/language/code_generator_opts.in
+               ${CMAKE_CURRENT_BINARY_DIR}/src/language/code_generator_opts)
+
+add_custom_command(
+  OUTPUT ${NMODL_GENERATED_SOURCES}
+  COMMAND ${PYTHON_EXECUTABLE} ARGS ${CMAKE_CURRENT_SOURCE_DIR}/src/language/code_generator.py
+          ${CODE_GENERATOR_OPTS} --base-dir ${PROJECT_BINARY_DIR}/src
+  WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/src/language
+  DEPENDS ${CODE_GENERATOR_PY_FILES}
+  DEPENDS ${CODE_GENERATOR_YAML_FILES}
+  DEPENDS ${CODE_GENERATOR_JINJA_FILES}
+  DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/src/language/code_generator_opts
+  COMMENT "-- NMODL : GENERATING AST CLASSES WITH PYTHON GENERATOR! --")
+unset(CODE_GENERATOR_OPTS)
+
+# -----------------------------------------------------------------------------
+# Target to propagate dependencies properly to lexer
+# -----------------------------------------------------------------------------
+add_custom_target(pyastgen DEPENDS ${PROJECT_BINARY_DIR}/src/ast/ast.cpp)
+
+# =============================================================================
+# Deal with the hand-written code
+# =============================================================================
 add_subdirectory(src)
 
 # =============================================================================

src/language/CMakeLists.txt

@@ -1,36 +1 @@
-# =============================================================================
-# Command to generate AST/Visitor classes from language definition
-# =============================================================================
-set_source_files_properties(${NMODL_GENERATED_SOURCES} PROPERTIES GENERATED TRUE)
 
-# clang-format is handled by the HPC coding conventions scripts, which also handle generating the
-# .clang-format configuration file. It's important that we only try to format code if formatting was
-# enabled and NMODL's .clang-format exists, otherwise clang-format will search too far up the
-# directory tree and find the wrong configuration file. This can break compilation.
-if(NMODL_CLANG_FORMAT OR NMODL_FORMATTING)
-  set(CODE_GENERATOR_OPTS -v --clang-format=${ClangFormat_EXECUTABLE})
-  foreach(clang_format_opt ${NMODL_ClangFormat_OPTIONS} --style=file)
-    list(APPEND CODE_GENERATOR_OPTS --clang-format-opts=${clang_format_opt})
-  endforeach()
-endif()
-
-if(NOT NMODL_ENABLE_PYTHON_BINDINGS)
-  list(APPEND CODE_GENERATOR_OPTS "--disable-pybind")
-endif()
-
-add_custom_command(
-  OUTPUT ${NMODL_GENERATED_SOURCES}
-  COMMAND ${PYTHON_EXECUTABLE} ARGS ${CMAKE_CURRENT_SOURCE_DIR}/code_generator.py
-          ${CODE_GENERATOR_OPTS} --base-dir ${PROJECT_BINARY_DIR}/src
-  WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
-  DEPENDS ${CODE_GENERATOR_PY_FILES}
-  DEPENDS ${CODE_GENERATOR_YAML_FILES}
-  DEPENDS ${CODE_GENERATOR_JINJA_FILES}
-  DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/templates/code_generator.cmake
-  COMMENT "-- NMODL : GENERATING AST CLASSES WITH PYTHON GENERATOR! --")
-unset(CODE_GENERATOR_OPTS)
-
-# =============================================================================
-# Target to propagate dependencies properly to lexer
-# =============================================================================
-add_custom_target(pyastgen DEPENDS ${PROJECT_BINARY_DIR}/src/ast/ast.cpp)