meson: utils: Provide environment for Python scripts

Python scripts run as part of the build process need to take a few
actions specific to the environment in which they operate. One of those
is disabling the Python bytecode cache, to avoid writing .pyc files to
the source tree. This is done manually in the IPC generate.py and
parser.py scripts.

The current implementation is not ideal because it hardcodes in the
scripts information related to the environment in which they operate. As
those scripts are part of libcamera this is more of a theoretical issue
than a practical one. A second issue is that future Python scripts will
need to duplicate similar mechanisms, resulting in a higher maintenance
burden.

Address the issue with a different approach, by creating a meson
environment for the Python scripts, and passing it to the
custom_target() functions. The environment only disables the bytecode
cache for now.

The diffstat shows an increase in code size. This is expected to be
offset by usage of the environment for more Python scripts, as well as
support of more variables in the environment.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Reviewed-by: Daniel Scally <dan.scally@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>

include/libcamera/ipa/meson.build

@@ -26,7 +26,8 @@ ipa_mojom_core = custom_target(core_mojom_file.split('.')[0] + '_mojom_module',
                                    '--output-root', meson.project_build_root(),
                                    '--input-root', meson.project_source_root(),
                                    '--mojoms', '@INPUT@'
-                               ])
+                               ],
+                               env : py_build_env)
 
 # core_ipa_interface.h
 libcamera_ipa_headers += custom_target('core_ipa_interface_h',
@@ -42,7 +43,8 @@ libcamera_ipa_headers += custom_target('core_ipa_interface_h',
                       '--libcamera_generate_core_header',
                       '--libcamera_output_path=@OUTPUT@',
                       './' +'@INPUT@'
-                  ])
+                  ],
+                  env : py_build_env)
 
 # core_ipa_serializer.h
 libcamera_ipa_headers += custom_target('core_ipa_serializer_h',
@@ -56,7 +58,8 @@ libcamera_ipa_headers += custom_target('core_ipa_serializer_h',
                       '--libcamera_generate_core_serializer',
                       '--libcamera_output_path=@OUTPUT@',
                       './' +'@INPUT@'
-                  ])
+                  ],
+                  env : py_build_env)
 
 # Mapping from pipeline handler name to mojom file
 pipeline_ipa_mojom_mapping = {
@@ -99,7 +102,8 @@ foreach pipeline, file : pipeline_ipa_mojom_mapping
                               '--output-root', meson.project_build_root(),
                               '--input-root', meson.project_source_root(),
                               '--mojoms', '@INPUT@'
-                          ])
+                          ],
+                          env : py_build_env)
 
     # {interface}_ipa_interface.h
     header = custom_target(name + '_ipa_interface_h',
@@ -115,7 +119,8 @@ foreach pipeline, file : pipeline_ipa_mojom_mapping
                                '--libcamera_generate_header',
                                '--libcamera_output_path=@OUTPUT@',
                                './' +'@INPUT@'
-                           ])
+                           ],
+                           env : py_build_env)
 
     # {interface}_ipa_serializer.h
     serializer = custom_target(name + '_ipa_serializer_h',
@@ -129,7 +134,8 @@ foreach pipeline, file : pipeline_ipa_mojom_mapping
                                    '--libcamera_generate_serializer',
                                    '--libcamera_output_path=@OUTPUT@',
                                    './' +'@INPUT@'
-                               ])
+                               ],
+                               env : py_build_env)
 
     # {interface}_ipa_proxy.h
     proxy_header = custom_target(name + '_proxy_h',
@@ -143,7 +149,8 @@ foreach pipeline, file : pipeline_ipa_mojom_mapping
                                      '--libcamera_generate_proxy_h',
                                      '--libcamera_output_path=@OUTPUT@',
                                      './' +'@INPUT@'
-                                 ])
+                                 ],
+                                 env : py_build_env)
 
     ipa_mojoms += {
         'name': name,

src/libcamera/proxy/meson.build

@@ -13,7 +13,8 @@ foreach mojom : ipa_mojoms
                               '--libcamera_generate_proxy_cpp',
                               '--libcamera_output_path=@OUTPUT@',
                               './' + '@INPUT@'
-                          ])
+                          ],
+                          env : py_build_env)
 
     libcamera_internal_sources += proxy
 endforeach

src/libcamera/proxy/worker/meson.build

@@ -15,7 +15,8 @@ foreach mojom : ipa_mojoms
                                '--libcamera_generate_proxy_worker',
                                '--libcamera_output_path=@OUTPUT@',
                                './' + '@INPUT@'
-                           ])
+                           ],
+                           env : py_build_env)
 
     proxy = executable(mojom['name'] + '_ipa_proxy', worker,
                        install : true,

test/serialization/generated_serializer/include/libcamera/ipa/meson.build

@@ -9,7 +9,8 @@ mojom = custom_target('test_mojom_module',
                           '--output-root', meson.project_build_root(),
                           '--input-root', meson.project_source_root(),
                           '--mojoms', '@INPUT@'
-                      ])
+                      ],
+                      env : py_build_env)
 
 # test_ipa_interface.h
 generated_test_header = custom_target('test_ipa_interface_h',
@@ -23,7 +24,8 @@ generated_test_header = custom_target('test_ipa_interface_h',
                            '--libcamera_generate_header',
                            '--libcamera_output_path=@OUTPUT@',
                            './' +'@INPUT@'
-                       ])
+                       ],
+                       env : py_build_env)
 
 # test_ipa_serializer.h
 generated_test_serializer = custom_target('test_ipa_serializer_h',
@@ -37,4 +39,5 @@ generated_test_serializer = custom_target('test_ipa_serializer_h',
                                '--libcamera_generate_serializer',
                                '--libcamera_output_path=@OUTPUT@',
                                './' +'@INPUT@'
-                           ])
+                           ],
+                           env : py_build_env)

utils/codegen/ipc/generate.py

@@ -9,9 +9,6 @@
 import os
 import sys
 
-# TODO set sys.pycache_prefix for >= python3.8
-sys.dont_write_bytecode = True
-
 sys.path.insert(0, f'{os.path.dirname(__file__)}/mojo/public/tools/bindings')
 
 import mojo.public.tools.bindings.mojom_bindings_generator as generator

utils/codegen/ipc/meson.build

@@ -13,6 +13,7 @@ mojom_docs_extractor = find_program('./extract-docs.py')
 mojom_templates = custom_target('mojom_templates',
                                 input : mojom_template_files,
                                 output : 'libcamera_templates.zip',
-                                command : [mojom_generator, '-o', '@OUTDIR@', 'precompile'])
+                                command : [mojom_generator, '-o', '@OUTDIR@', 'precompile'],
+                                env : py_build_env)
 
 mojom_templates_dir = meson.current_build_dir()

utils/codegen/ipc/parser.py

@@ -9,9 +9,6 @@
 import os
 import sys
 
-# TODO set sys.pycache_prefix for >= python3.8
-sys.dont_write_bytecode = True
-
 # Make sure that mojom_parser.py can import mojom
 sys.path.insert(0, f'{os.path.dirname(__file__)}/mojo/public/tools/mojom')
 

utils/codegen/meson.build

@@ -2,6 +2,10 @@
 
 ## Code generation
 
+py_build_env = environment()
+# \todo Investigate usage of PYTHONPYCACHEPREFIX for Python >= 3.8
+py_build_env.set('PYTHONDONTWRITEBYTECODE', '1')
+
 py_modules += ['jinja2', 'yaml']
 
 gen_controls = files('gen-controls.py')