Improve support for arbitrary machine architectures

- Prevent running on 32bit Windows or 32bit Python on 64bit Windows
- Support building an AppImage for i386; verify LinuxDeploy for all Commands
- Support building Linux System packages on i386
- Support installing JDK for armv7/8
- Let users know when Android SDK must be manually installed
- Derive the Linux system target distro architecture from the build environment
- Download a 32bit JDK and 32bit standalone Python when host Python is 32bit
- Ensure `makepkg` creates a `.pkg.tar.zst` distributable

src/briefcase/commands/create.py

@@ -344,6 +344,7 @@ def _download_support_package(self, app: AppConfig):
                             python_version_tag=self.python_version_tag,
                             platform=self.platform,
                             host_arch=self.tools.host_arch,
+                            is_32bit=self.tools.is_32bit_python,
                         )
 
                 support_package_url = self.support_package_url(support_revision)
@@ -384,6 +385,7 @@ def _download_support_package(self, app: AppConfig):
                     python_version_tag=self.python_version_tag,
                     platform=self.platform,
                     host_arch=self.tools.host_arch,
+                    is_32bit=self.tools.is_32bit_python,
                 ) from e
 
     def _write_requirements_file(

src/briefcase/exceptions.py

@@ -103,6 +103,18 @@ def __init__(self, tool):
         super().__init__(msg=f"Unable to locate {tool!r}. Has it been installed?")
 
 
+class IncompatibleToolError(BriefcaseCommandError):
+    def __init__(self, tool: str, env_var: str):
+        self.tool = tool
+        super().__init__(
+            msg=f"""\
+Briefcase cannot install {tool} on this machine.
+
+Install {tool} manually and specify the installation directory in the {env_var} environment variable.
+            """
+        )
+
+
 class NonManagedToolError(BriefcaseCommandError):
     def __init__(self, tool):
         self.tool = tool
@@ -153,16 +165,16 @@ def __init__(self, app_bundle_path):
 
 
 class MissingSupportPackage(BriefcaseCommandError):
-    def __init__(self, python_version_tag, platform, host_arch):
+    def __init__(self, python_version_tag, platform, host_arch, is_32bit):
         self.python_version_tag = python_version_tag
-        self.platform = platform
+        self.platform = f"{'32 bit ' if is_32bit else ''}{platform}"
         self.host_arch = host_arch
         super().__init__(
             f"""\
 Unable to download {self.platform} support package for Python {self.python_version_tag} on {self.host_arch}.
 
-This is likely because either Python {self.python_version_tag} and/or {self.host_arch}
-is not yet supported on {self.platform}. You will need to:
+This is likely because either Python {self.python_version_tag} and/or {self.host_arch} is not yet
+supported on {self.platform}. You will need to:
     * Use an older version of Python; or
     * Compile your own custom support package.
 """

src/briefcase/integrations/android_sdk.py

@@ -15,6 +15,7 @@
 from briefcase.console import InputDisabled, select_option
 from briefcase.exceptions import (
     BriefcaseCommandError,
+    IncompatibleToolError,
     InvalidDeviceError,
     MissingToolError,
 )
@@ -57,15 +58,35 @@ def __init__(self, tools: ToolCache, root_path: Path):
 
     @property
     def cmdline_tools_url(self) -> str:
-        """The Android SDK Command-Line Tools URL appropriate to the current operating
-        system."""
-        platform_name = self.tools.host_os.lower()
-        if self.tools.host_os.lower() == "darwin":
-            platform_name = "mac"
-        elif self.tools.host_os.lower() == "windows":  # pragma: no branch
-            platform_name = "win"
-
-        return f"https://dl.google.com/android/repository/commandlinetools-{platform_name}-{self.cmdline_tools_version}_latest.zip"  # noqa: E501
+        """The Android SDK Command-Line Tools URL appropriate for the current machine.
+
+        The SDK largely only supports typical development environments; if a machine is
+        using an unsupported architecture, `sdkmanager` will error while installing the
+        emulator as a dependency of the build-tools. However, for some of the platforms
+        that are unsupported by sdkmanager, users can set up their own SDK install.
+        """
+        try:
+            platform_name = {
+                "Darwin": {
+                    "arm64": "mac",
+                    "x86_64": "mac",
+                },
+                "Linux": {
+                    "x86_64": "linux",
+                },
+                "Windows": {
+                    "AMD64": "win",
+                },
+            }[self.tools.host_os][self.tools.host_arch]
+        except KeyError as e:
+            raise IncompatibleToolError(
+                tool=self.full_name, env_var="ANDROID_HOME"
+            ) from e
+
+        return (
+            f"https://dl.google.com/android/repository/commandlinetools-"
+            f"{platform_name}-{self.cmdline_tools_version}_latest.zip"
+        )
 
     @property
     def cmdline_tools_path(self) -> Path:

src/briefcase/integrations/base.py

@@ -195,6 +195,8 @@ def __init__(
 
         self.host_arch = self.platform.machine()
         self.host_os = self.platform.system()
+        # Python is 32bit if its pointers can only address with 32 bits or fewer
+        self.is_32bit_python = self.sys.maxsize <= 2**32
 
         self.app_tools: DefaultDict[AppConfig, ToolCache] = defaultdict(
             lambda: ToolCache(

src/briefcase/integrations/java.py

@@ -5,7 +5,11 @@
 import subprocess
 from pathlib import Path
 
-from briefcase.exceptions import BriefcaseCommandError, MissingToolError
+from briefcase.exceptions import (
+    BriefcaseCommandError,
+    IncompatibleToolError,
+    MissingToolError,
+)
 from briefcase.integrations.base import ManagedTool, ToolCache
 
 
@@ -26,28 +30,40 @@ def __init__(self, tools: ToolCache, java_home: Path):
 
     @property
     def OpenJDK_download_url(self):
-        arch = {
-            "x86_64": "x64",  # Linux\macOS x86-64
-            "aarch64": "aarch64",  # Linux arm64
-            "armv6l": "arm",  # Linux arm
-            "arm64": "aarch64",  # macOS arm64
-            "AMD64": "x64",  # Windows x86-64
-        }.get(self.tools.host_arch)
-
-        platform = {
-            "Darwin": "mac",
-            "Windows": "windows",
-            "Linux": "linux",
-        }.get(self.tools.host_os)
-
-        extension = {
-            "Windows": "zip",
-        }.get(self.tools.host_os, "tar.gz")
+        """The OpenJDK download URL appropriate for the current machine."""
+        system_arch = self.tools.host_arch
+        # use a 32bit JDK if using 32bit Python on 64bit hardware
+        if self.tools.is_32bit_python and self.tools.host_arch == "aarch64":
+            system_arch = "armv7l"
+
+        try:
+            jdk_download_arch = {
+                "armv7l": "arm",  # Linux armv7
+                "armv8l": "arm",  # Linux armv8
+                "aarch64": "aarch64",  # Linux arm64
+                "arm64": "aarch64",  # macOS arm64
+                "x86_64": "x64",  # Linux/macOS x86-64
+                "AMD64": "x64",  # Windows x86-64
+            }[system_arch]
+
+            platform = {
+                "Darwin": "mac",
+                "Windows": "windows",
+                "Linux": "linux",
+            }[self.tools.host_os]
+
+            extension = {
+                "Darwin": "tar.gz",
+                "Linux": "tar.gz",
+                "Windows": "zip",
+            }[self.tools.host_os]
+        except KeyError as e:
+            raise IncompatibleToolError(tool=self.full_name, env_var="JAVA_HOME") from e
 
         return (
             f"https://github.com/adoptium/temurin{self.JDK_MAJOR_VER}-binaries/"
             f"releases/download/jdk-{self.JDK_RELEASE}+{self.JDK_BUILD}/"
-            f"OpenJDK{self.JDK_MAJOR_VER}U-jdk_{arch}_{platform}_hotspot_"
+            f"OpenJDK{self.JDK_MAJOR_VER}U-jdk_{jdk_download_arch}_{platform}_hotspot_"
             f"{self.JDK_RELEASE}_{self.JDK_BUILD}.{extension}"
         )
 

src/briefcase/integrations/linuxdeploy.py

@@ -11,6 +11,7 @@
     BriefcaseCommandError,
     CorruptToolError,
     MissingToolError,
+    UnsupportedHostError,
 )
 from briefcase.integrations.base import ManagedTool, Tool, ToolCache
 
@@ -48,6 +49,21 @@ def download_url(self) -> str:
     def file_path(self) -> Path:
         """The folder on the local filesystem that contains the file_name."""
 
+    @classmethod
+    def arch(cls, host_os: str, host_arch: str) -> str:
+        # always use the x86-64 arch on macOS since Docker
+        # containers are always run in an x86-64 VM
+        arch = host_arch if host_os != "Darwin" else "x86_64"
+        try:
+            return {
+                "x86_64": "x86_64",
+                "i686": "i386",
+            }[arch]
+        except KeyError as e:
+            raise UnsupportedHostError(
+                f"Linux AppImages cannot be built on {host_arch}."
+            ) from e
+
     def exists(self) -> bool:
         return (self.file_path / self.file_name).is_file()
 
@@ -208,7 +224,7 @@ class LinuxDeployQtPlugin(LinuxDeployPluginBase, ManagedTool):
 
     @property
     def file_name(self) -> str:
-        return f"linuxdeploy-plugin-qt-{self.tools.host_arch}.AppImage"
+        return f"linuxdeploy-plugin-qt-{self.arch(self.tools.host_os, self.tools.host_arch)}.AppImage"
 
     @property
     def download_url(self) -> str:
@@ -319,7 +335,7 @@ def file_path(self) -> Path:
 
     @property
     def file_name(self) -> str:
-        return f"linuxdeploy-{self.tools.host_arch}.AppImage"
+        return f"linuxdeploy-{self.arch(self.tools.host_os, self.tools.host_arch)}.AppImage"
 
     @property
     def download_url(self) -> str:

src/briefcase/platforms/linux/__init__.py

@@ -66,10 +66,17 @@ def support_package_url(self, support_revision):
         System packages don't use a support package; this is defined by
         the template, so this method won't be invoked
         """
+        python_download_arch = self.tools.host_arch
+        # use a 32bit Python if using 32bit Python on 64bit hardware
+        if self.tools.is_32bit_python and self.tools.host_arch == "aarch64":
+            python_download_arch = "armv7"
+        elif self.tools.is_32bit_python and self.tools.host_arch == "x86_64":
+            python_download_arch = "i686"
+
         version, datestamp = support_revision.split("+")
         return (
             "https://github.com/indygreg/python-build-standalone/releases/download/"
-            f"{datestamp}/cpython-{support_revision}-{self.tools.host_arch}-unknown-linux-gnu-install_only.tar.gz"
+            f"{datestamp}/cpython-{support_revision}-{python_download_arch}-unknown-linux-gnu-install_only.tar.gz"
         )
 
     def vendor_details(self, freedesktop_info):

src/briefcase/platforms/linux/appimage.py

@@ -44,14 +44,20 @@ def project_path(self, app):
 
     def binary_name(self, app):
         safe_name = app.formal_name.replace(" ", "_")
-        return f"{safe_name}-{app.version}-{self.tools.host_arch}.AppImage"
+        arch = LinuxDeploy.arch(self.tools.host_os, self.tools.host_arch)
+        return f"{safe_name}-{app.version}-{arch}.AppImage"
 
     def binary_path(self, app):
         return self.bundle_path(app) / self.binary_name(app)
 
     def distribution_path(self, app):
         return self.dist_path / self.binary_name(app)
 
+    def verify_tools(self):
+        """Verify the AppImage LinuxDeploy tool and its plugins exist."""
+        super().verify_tools()
+        LinuxDeploy.verify(tools=self.tools)
+
     def add_options(self, parser):
         super().add_options(parser)
         parser.add_argument(
@@ -213,11 +219,6 @@ class LinuxAppImageOpenCommand(LinuxAppImageMostlyPassiveMixin, DockerOpenComman
 class LinuxAppImageBuildCommand(LinuxAppImageMixin, BuildCommand):
     description = "Build a Linux AppImage."
 
-    def verify_tools(self):
-        """Verify the AppImage linuxdeploy tool and plugins exist."""
-        super().verify_tools()
-        LinuxDeploy.verify(tools=self.tools)
-
     def build_app(self, app: AppConfig, **kwargs):  # pragma: no-cover-if-is-windows
         """Build an application.