Read iOS/macOS minimum versions from the framework, where possible.

changes/2443.bugfix.rst

@@ -0,0 +1 @@
+iOS and macOS apps now read the minimum supported OS version from the Python framework's metadata, rather than requiring a ``VERSIONS`` file as part of the support package.

changes/2443.feature.rst

@@ -0,0 +1 @@
+If an iOS or macOS app doesn't specify a minimum OS version, the minimum OS version is now derived from the support package, rather than being hard coded.

src/briefcase/platforms/iOS/xcode.py

@@ -322,27 +322,47 @@ def _install_app_requirements(
         app_packages_path: Path,
         **kwargs,
     ):
-        # Determine the min iOS version from the VERSIONS file in the support package.
-        versions = dict(
-            [part.strip() for part in line.split(": ", 1)]
-            for line in (
-                (self.support_path(app) / "VERSIONS")
-                .read_text(encoding="UTF-8")
-                .split("\n")
+        try:
+            # Determine the min iOS version from the framework metadata
+            # of the ios-arm64 slice of the XCframework
+            plist_file = (
+                self.support_path(app)
+                / "Python.xcframework/ios-arm64/Python.framework/Info.plist"
             )
-            if ": " in line
-        )
-        support_min_version = Version(versions.get("Min iOS version", "13.0"))
+            with plist_file.open("rb") as f:
+                info_plist = plistlib.load(f)
+
+            support_min_version = info_plist["MinimumOSVersion"]
+        except KeyError:
+            raise BriefcaseCommandError(
+                "Your iOS XCframework doesn't specify a minimum iOS version."
+            )
+        except FileNotFoundError:
+            # If a plist file couldn't be found, it's an old-style support package;
+            # Determine the min iOS version from the VERSIONS file in the support package.
+            versions = dict(
+                [part.strip() for part in line.split(": ", 1)]
+                for line in (
+                    (self.support_path(app) / "VERSIONS")
+                    .read_text(encoding="UTF-8")
+                    .split("\n")
+                )
+                if ": " in line
+            )
+            support_min_version = versions.get("Min iOS version", "13.0")
+
+        # Check that the app's definition is compatible with the support package.
+        # If the app doesn't specify a minimum version, use the support package
+        # minimum version as a default.
+        ios_min_version = getattr(app, "min_os_version", support_min_version)
 
-        # Check that the app's definition is compatible with the support package
-        ios_min_version = Version(getattr(app, "min_os_version", "13.0"))
-        if ios_min_version < support_min_version:
+        if Version(ios_min_version) < Version(support_min_version):
             raise BriefcaseCommandError(
                 f"Your iOS app specifies a minimum iOS version of {ios_min_version}, "
                 f"but the support package only supports {support_min_version}"
             )
 
-        ios_min_tag = str(ios_min_version).replace(".", "_")
+        ios_min_tag = ios_min_version.replace(".", "_")
 
         # Feb 2025: The platform-site was moved into the xcframework as
         # `platform-config`. Look for the new location; fall back to the old location.

src/briefcase/platforms/macOS/__init__.py

@@ -184,27 +184,44 @@ def _install_app_requirements(
         app_packages_path: Path,
         **kwargs,
     ):
-        # Determine the min macOS version from the VERSIONS file in the support package.
-        versions = dict(
-            [part.strip() for part in line.split(": ", 1)]
-            for line in (
-                (self.support_path(app) / "VERSIONS")
-                .read_text(encoding="UTF-8")
-                .split("\n")
+        try:
+            # Determine the min macOS version from the framework metadata
+            # of the macos-arm64_x86_64 slice of the XCframework
+            plist_file = (
+                self.support_path(app)
+                / "Python.xcframework/macos-arm64_x86_64"
+                / "Python.framework/Resources/Info.plist"
             )
-            if ": " in line
-        )
-        support_min_version = Version(versions.get("Min macOS version", "11.0"))
+            with plist_file.open("rb") as f:
+                info_plist = plistlib.load(f)
+
+            support_min_version = info_plist.get("MinimumOSVersion", "11.0")
+        except FileNotFoundError:
+            # If a plist file couldn't be found, it's an old-style support package;
+            # Determine the min macOS version from the VERSIONS file in the support package.
+            versions = dict(
+                [part.strip() for part in line.split(": ", 1)]
+                for line in (
+                    (self.support_path(app) / "VERSIONS")
+                    .read_text(encoding="UTF-8")
+                    .split("\n")
+                )
+                if ": " in line
+            )
+            support_min_version = versions.get("Min macOS version", "11.0")
 
         # Check that the app's definition is compatible with the support package
-        macOS_min_version = Version(getattr(app, "min_os_version", "11.0"))
-        if macOS_min_version < support_min_version:
+        # If the app doesn't specify a minimum version, use the support package
+        # minimum version as a default.
+        macOS_min_version = getattr(app, "min_os_version", support_min_version)
+
+        if Version(macOS_min_version) < Version(support_min_version):
             raise BriefcaseCommandError(
                 f"Your macOS app specifies a minimum macOS version of {macOS_min_version}, "
                 f"but the support package only supports {support_min_version}"
             )
 
-        macOS_min_tag = str(macOS_min_version).replace(".", "_")
+        macOS_min_tag = macOS_min_version.replace(".", "_")
 
         if getattr(app, "universal_build", True):
             # Perform the initial install targeting the current platform

tests/platforms/iOS/xcode/conftest.py

@@ -32,30 +32,24 @@ def first_app_generated(first_app_config, tmp_path):
         },
     )
 
-    # Create the support package VERSIONS file
-    # with a deliberately weird min iOS version
-    create_file(
-        tmp_path / "base_path/build/first-app/ios/xcode/Support/VERSIONS",
-        "\n".join(
-            [
-                "Python version: 3.10.15",
-                "Build: b11",
-                "Min iOS version: 12.0",
-                "---------------------",
-                "BZip2: 1.0.8-1",
-                "libFFI: 3.4.6-1",
-                "OpenSSL: 3.0.15-1",
-                "XZ: 5.6.2-1",
-                "",
-            ]
-        ),
-    )
     # Create the package-config folders for each platform.
     # We don't need anything in them; they just need to exist.
     xcframework_path = (
         tmp_path / "base_path/build/first-app/ios/xcode/Support/Python.xcframework"
     )
+
+    # Create the XCframeworks's ios-arm64 Info.plist file
+    # with a deliberately weird min iOS version
+    create_plist_file(
+        xcframework_path / "ios-arm64/Python.framework/Info.plist",
+        {
+            "CFBundleSupportedPlatforms": "iPhoneOS",
+            "CFBundleVersion": "3.10.15",
+            "MinimumOSVersion": "12.0",
+        },
+    )
     (xcframework_path / "ios-arm64/platform-config/arm64-iphoneos").mkdir(parents=True)
+
     (
         xcframework_path
         / "ios-arm64_x86_64-simulator/platform-config/arm64-iphonesimulator"