Remove use of setup.py by using a proxied build backend.

android/builder.py

@@ -0,0 +1,8 @@
+# PEP517 doesn't allow ".." in a build backend's `backend-path` setting.
+# To avoid duplicating the backend's code, insert ".." into sys.path,
+# then import the toga_builder.
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.dirname(__file__))))
+from toga_builder import *  # noqa: F401,E402,F403

android/pyproject.toml

@@ -1,6 +1,7 @@
 [build-system]
 requires = ["setuptools==66.1.1", "setuptools_scm[toml]==7.0.5"]
-build-backend = "setuptools.build_meta"
+build-backend = "builder"
+backend-path = ["."]
 
 [tool.coverage.run]
 parallel = true
@@ -16,3 +17,6 @@ source = [
     "src/toga_android",
     "**/toga_android",
 ]
+
+[tool.setuptools_scm]
+root = ".."

android/setup.cfg

@@ -46,6 +46,9 @@ package_dir =
 python_requires = >= 3.8
 zip_safe = False
 
+# Build backend will inject a dependency on toga-core==VERSION
+# install_requires =
+
 [options.entry_points]
 toga.backends =
     android = toga_android

cocoa/builder.py

@@ -0,0 +1,8 @@
+# PEP517 doesn't allow ".." in a build backend's `backend-path` setting.
+# To avoid duplicating the backend's code, insert ".." into sys.path,
+# then import the toga_builder.
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.dirname(__file__))))
+from toga_builder import *  # noqa: F401,E402,F403

cocoa/pyproject.toml

@@ -1,6 +1,7 @@
 [build-system]
 requires = ["setuptools==66.1.1", "setuptools_scm[toml]==7.0.5"]
-build-backend = "setuptools.build_meta"
+build-backend = "builder"
+backend-path = ["."]
 
 [tool.coverage.run]
 parallel = true
@@ -16,3 +17,6 @@ source = [
     "src/toga_cocoa",
     "**/toga_cocoa",
 ]
+
+[tool.setuptools_scm]
+root = ".."

cocoa/setup.cfg

@@ -47,6 +47,11 @@ package_dir =
 python_requires = >= 3.8
 zip_safe = False
 
+# Build backend will inject a dependency on toga-core==VERSION
+install_requires =
+    fonttools >= 4.42.1, < 5.0.0
+    rubicon-objc >= 0.4.7, < 0.5.0
+
 [options.entry_points]
 toga.backends =
     macOS = toga_cocoa

demo/builder.py

@@ -0,0 +1,23 @@
+# A wrapper around setuptools that injects a dynamic dependency on toga.
+# It presents as a PEP517 build backend with the same interface as
+# setuptools.build_meta, but dynamically injects a modification to
+# `parse_config_files` that injects the extra dependency, using the version
+# number computed at runtime.
+from setuptools import dist
+from setuptools.build_meta import *  # noqa: F401,F403
+from setuptools_scm import get_version
+
+TOGA_VERSION = get_version(root="..")
+
+
+orig_parse_config_files = dist.Distribution.parse_config_files
+
+
+def parse_config_files(self, filenames=None, ignore_option_errors=False):
+    orig_parse_config_files(self, filenames=None, ignore_option_errors=False)
+
+    # Insert a dependency on toga at the same version as the repo.
+    self.install_requires.insert(0, f"toga=={TOGA_VERSION}")
+
+
+dist.Distribution.parse_config_files = parse_config_files

demo/pyproject.toml

@@ -1,6 +1,7 @@
 [build-system]
 requires = ["setuptools==66.1.1", "setuptools_scm[toml]==7.0.5"]
-build-backend = "setuptools.build_meta"
+build-backend = "builder"
+backend-path = ["."]
 
 [tool.briefcase]
 project_name = "Toga Demo"
@@ -42,3 +43,6 @@ requires = [
 requires = [
     "../android",
 ]
+
+[tool.setuptools_scm]
+root = ".."

demo/setup.cfg

@@ -52,6 +52,9 @@ packages = find:
 python_requires = >= 3.7
 zip_safe = False
 
+# Build backend will inject a dependency on toga==VERSION
+# install_requires =
+
 [options.entry_points]
 console_scripts =
     toga-demo = toga_demo.__main__:run

dummy/builder.py

@@ -0,0 +1,8 @@
+# PEP517 doesn't allow ".." in a build backend's `backend-path` setting.
+# To avoid duplicating the backend's code, insert ".." into sys.path,
+# then import the toga_builder.
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.dirname(__file__))))
+from toga_builder import *  # noqa: F401,E402,F403

dummy/pyproject.toml

@@ -1,3 +1,7 @@
 [build-system]
 requires = ["setuptools==66.1.1", "setuptools_scm[toml]==7.0.5"]
-build-backend = "setuptools.build_meta"
+build-backend = "builder"
+backend-path = ["."]
+
+[tool.setuptools_scm]
+root = ".."

dummy/setup.cfg

@@ -45,6 +45,9 @@ package_dir =
 python_requires = >= 3.8
 zip_safe = False
 
+# Build backend will inject a dependency on toga==VERSION
+# install_requires =
+
 [options.entry_points]
 toga.backends =
     dummy = toga_dummy

gtk/builder.py

@@ -0,0 +1,8 @@
+# PEP517 doesn't allow ".." in a build backend's `backend-path` setting.
+# To avoid duplicating the backend's code, insert ".." into sys.path,
+# then import the toga_builder.
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.dirname(__file__))))
+from toga_builder import *  # noqa: F401,E402,F403

gtk/pyproject.toml

@@ -1,6 +1,7 @@
 [build-system]
 requires = ["setuptools==66.1.1", "setuptools_scm[toml]==7.0.5"]
-build-backend = "setuptools.build_meta"
+build-backend = "builder"
+backend-path = ["."]
 
 [tool.coverage.run]
 parallel = true
@@ -16,3 +17,6 @@ source = [
     "src/toga_gtk",
     "**/toga_gtk",
 ]
+
+[tool.setuptools_scm]
+root = ".."

gtk/setup.cfg

@@ -48,6 +48,12 @@ package_dir =
 python_requires = >= 3.8
 zip_safe = False
 
+# Build backend will inject a dependency on toga-core==VERSION
+install_requires =
+    gbulb >= 0.5.3
+    pycairo >= 1.17.0
+    pygobject >= 3.46.0
+
 [options.entry_points]
 toga.backends =
     linux = toga_gtk

iOS/builder.py

@@ -0,0 +1,8 @@
+# PEP517 doesn't allow ".." in a build backend's `backend-path` setting.
+# To avoid duplicating the backend's code, insert ".." into sys.path,
+# then import the toga_builder.
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.dirname(__file__))))
+from toga_builder import *  # noqa: F401,E402,F403

iOS/pyproject.toml

@@ -1,6 +1,7 @@
 [build-system]
 requires = ["setuptools==66.1.1", "setuptools_scm[toml]==7.0.5"]
-build-backend = "setuptools.build_meta"
+build-backend = "builder"
+backend-path = ["."]
 
 [tool.coverage.run]
 parallel = true
@@ -16,3 +17,6 @@ source = [
     "src/toga_iOS",
     "**/toga_iOS",
 ]
+
+[tool.setuptools_scm]
+root = ".."

iOS/setup.cfg

@@ -46,6 +46,11 @@ package_dir =
 python_requires = >= 3.8
 zip_safe = False
 
+# Build backend will inject a dependency on toga-core==VERSION
+install_requires =
+    fonttools >= 4.42.1, < 5.0.0
+    rubicon-objc >= 0.4.7, < 0.5.0
+
 [options.entry_points]
 toga.backends =
     iOS = toga_iOS

textual/builder.py

@@ -0,0 +1,8 @@
+# PEP517 doesn't allow ".." in a build backend's `backend-path` setting.
+# To avoid duplicating the backend's code, insert ".." into sys.path,
+# then import the toga_builder.
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(os.path.dirname(__file__))))
+from toga_builder import *  # noqa: F401,E402,F403

textual/pyproject.toml

@@ -1,6 +1,7 @@
 [build-system]
 requires = ["setuptools==66.1.1", "setuptools_scm[toml]==7.0.5"]
-build-backend = "setuptools.build_meta"
+build-backend = "builder"
+backend-path = ["."]
 
 [tool.coverage.run]
 parallel = true
@@ -16,3 +17,6 @@ source = [
     "src/toga_textual",
     "**/toga_textual",
 ]
+
+[tool.setuptools_scm]
+root = ".."

textual/setup.cfg

@@ -47,6 +47,10 @@ package_dir =
 python_requires = >= 3.8
 zip_safe = False
 
+# Build backend will inject a dependency on toga-core==VERSION
+install_requires =
+    textual
+
 [options.entry_points]
 toga.backends =
     # The textual backend is a candidate for use on every platform.

toga/builder.py

@@ -0,0 +1,29 @@
+# A wrapper around setuptools that injects a dynamic dependency on toga.
+#
+# It presents as a PEP517 build backend with the same interface as
+# setuptools.build_meta, but dynamically injects a modification to
+# `parse_config_files` that injects the extra dependencies, using the
+# version number computed at runtime.
+from setuptools import dist
+from setuptools.build_meta import *  # noqa: F401,F403
+from setuptools_scm import get_version
+
+TOGA_VERSION = get_version(root="..")
+
+
+orig_parse_config_files = dist.Distribution.parse_config_files
+
+
+def parse_config_files(self, filenames=None, ignore_option_errors=False):
+    orig_parse_config_files(self, filenames=None, ignore_option_errors=False)
+
+    # Insert the per-platform extra dependencies with the same version as the
+    self.extras_require = {
+        ':sys_platform=="win32"': [f"toga-winforms=={TOGA_VERSION}"],
+        ':sys_platform=="linux"': [f"toga-gtk=={TOGA_VERSION}"],
+        ':"freebsd" in sys_platform': [f"toga-gtk=={TOGA_VERSION}"],
+        ':sys_platform=="darwin"': [f"toga-cocoa=={TOGA_VERSION}"],
+    }
+
+
+dist.Distribution.parse_config_files = parse_config_files

toga/pyproject.toml

@@ -1,3 +1,7 @@
 [build-system]
 requires = ["setuptools==66.1.1", "setuptools_scm[toml]==7.0.5"]
-build-backend = "setuptools.build_meta"
+build-backend = "builder"
+backend-path = ["."]
+
+[tool.setuptools_scm]
+root = ".."