Fix editable installation with custom build backend and configuration options

.github/workflows/wheels.yml

@@ -5,6 +5,7 @@ on:
     paths:
       - ".ci/requirements-cibw.txt"
       - ".github/workflows/wheel*"
+      - "setup.py"
       - "wheels/*"
       - "winbuild/build_prepare.py"
       - "winbuild/fribidi.cmake"
@@ -14,6 +15,7 @@ on:
     paths:
       - ".ci/requirements-cibw.txt"
       - ".github/workflows/wheel*"
+      - "setup.py"
       - "wheels/*"
       - "winbuild/build_prepare.py"
       - "winbuild/fribidi.cmake"

_custom_build/backend.py

@@ -11,41 +11,14 @@
 class _CustomBuildMetaBackend(backend_class):
     def run_setup(self, setup_script="setup.py"):
         if self.config_settings:
-
-            def config_has(key, value):
-                settings = self.config_settings.get(key)
-                if settings:
-                    if not isinstance(settings, list):
-                        settings = [settings]
-                    return value in settings
-
-            flags = []
-            for dependency in (
-                "zlib",
-                "jpeg",
-                "tiff",
-                "freetype",
-                "raqm",
-                "lcms",
-                "webp",
-                "webpmux",
-                "jpeg2000",
-                "imagequant",
-                "xcb",
-            ):
-                if config_has(dependency, "enable"):
-                    flags.append("--enable-" + dependency)
-                elif config_has(dependency, "disable"):
-                    flags.append("--disable-" + dependency)
-            for dependency in ("raqm", "fribidi"):
-                if config_has(dependency, "vendor"):
-                    flags.append("--vendor-" + dependency)
-            if self.config_settings.get("platform-guessing") == "disable":
-                flags.append("--disable-platform-guessing")
-            if self.config_settings.get("debug") == "true":
-                flags.append("--debug")
-            if flags:
-                sys.argv = sys.argv[:1] + ["build_ext"] + flags + sys.argv[1:]
+            params = []
+            for key, values in self.config_settings.items():
+                if not isinstance(values, list):
+                    values = [values]
+                for value in values:
+                    params.append(f"--pillow-configuration={key}={value}")
+
+            sys.argv = sys.argv[:1] + params + sys.argv[1:]
         return super().run_setup(setup_script)
 
     def build_wheel(
@@ -54,5 +27,15 @@ def build_wheel(
         self.config_settings = config_settings
         return super().build_wheel(wheel_directory, config_settings, metadata_directory)
 
+    def build_editable(
+        self, wheel_directory, config_settings=None, metadata_directory=None
+    ):
+        self.config_settings = config_settings
+        return super().build_editable(
+            wheel_directory, config_settings, metadata_directory
+        )
+
 
-build_wheel = _CustomBuildMetaBackend().build_wheel
+_backend = _CustomBuildMetaBackend()
+build_wheel = _backend.build_wheel
+build_editable = _backend.build_editable

docs/installation/building-from-source.rst

@@ -266,9 +266,10 @@ After navigating to the Pillow directory, run::
 Build Options
 ^^^^^^^^^^^^^
 
-* Environment variable: ``MAX_CONCURRENCY=n``. Pillow can use
-  multiprocessing to build the extension. Setting ``MAX_CONCURRENCY``
-  sets the number of CPUs to use, or can disable parallel building by
+* Config setting: ``-C parallel=n``. Can also be given
+  with environment variable: ``MAX_CONCURRENCY=n``. Pillow can use
+  multiprocessing to build the extension. Setting ``-C parallel=n``
+  sets the number of CPUs to use to ``n``, or can disable parallel building by
   using a setting of 1. By default, it uses 4 CPUs, or if 4 are not
   available, as many as are present.
 
@@ -293,14 +294,13 @@ Build Options
   used to compile the standard Pillow wheels. Compiling libraqm requires
   a C99-compliant compiler.
 
-* Build flag: ``-C platform-guessing=disable``. Skips all of the
+* Config setting: ``-C platform-guessing=disable``. Skips all of the
   platform dependent guessing of include and library directories for
   automated build systems that configure the proper paths in the
   environment variables (e.g. Buildroot).
 
-* Build flag: ``-C debug=true``. Adds a debugging flag to the include and
-  library search process to dump all paths searched for and found to
-  stdout.
+* Config setting: ``-C debug=true``. Adds a debugging flag to the include and
+  library search process to dump all paths searched for and found to stdout.
 
 
 Sample usage::

setup.py

@@ -27,6 +27,9 @@ def get_version():
     return locals()["__version__"]
 
 
+configuration = {}
+
+
 PILLOW_VERSION = get_version()
 FREETYPE_ROOT = None
 HARFBUZZ_ROOT = None
@@ -333,15 +336,24 @@ def __iter__(self):
         + [("add-imaging-libs=", None, "Add libs to _imaging build")]
     )
 
+    @staticmethod
+    def check_configuration(option, value):
+        return True if value in configuration.get(option, []) else None
+
     def initialize_options(self):
-        self.disable_platform_guessing = None
+        self.disable_platform_guessing = self.check_configuration(
+            "platform-guessing", "disable"
+        )
         self.add_imaging_libs = ""
         build_ext.initialize_options(self)
         for x in self.feature:
-            setattr(self, f"disable_{x}", None)
-            setattr(self, f"enable_{x}", None)
+            setattr(self, f"disable_{x}", self.check_configuration(x, "disable"))
+            setattr(self, f"enable_{x}", self.check_configuration(x, "enable"))
         for x in ("raqm", "fribidi"):
-            setattr(self, f"vendor_{x}", None)
+            setattr(self, f"vendor_{x}", self.check_configuration(x, "vendor"))
+        if self.check_configuration("debug", "true"):
+            self.debug = True
+        self.parallel = configuration.get("parallel", [None])[-1]
 
     def finalize_options(self):
         build_ext.finalize_options(self)
@@ -984,6 +996,13 @@ def debug_build():
     Extension("PIL._imagingmorph", ["src/_imagingmorph.c"]),
 ]
 
+
+# parse configuration from _custom_build/backend.py
+while len(sys.argv[1]) >= 2 and sys.argv[1].startswith("--pillow-configuration="):
+    _, key, value = sys.argv[1].split("=", 2)
+    configuration.setdefault(key, []).append(value)
+    del sys.argv[1]
+
 try:
     setup(
         cmdclass={"build_ext": pil_build_ext},

winbuild/build.rst

@@ -87,11 +87,18 @@ are set by running ``winbuild\build\build_env.cmd`` and install Pillow with pip:
     winbuild\build\build_env.cmd
     python.exe -m pip install -v -C raqm=vendor -C fribidi=vendor .
 
-To build a wheel instead, run::
+You can also install Pillow in `editable mode`_::
+
+    winbuild\build\build_env.cmd
+    python.exe -m pip install -v -C raqm=vendor -C fribidi=vendor -e .
+
+To build a binary wheel instead, run::
 
     winbuild\build\build_env.cmd
     python.exe -m pip wheel -v -C raqm=vendor -C fribidi=vendor .
 
+.. _editable mode: https://setuptools.pypa.io/en/stable/userguide/development_mode.html
+
 Testing Pillow
 --------------