Fix generated build.zig to defer resolving pydust src (#11)

build.zig

@@ -41,7 +41,9 @@ pub fn build(b: *std.Build) void {
     }
 }
 
-fn getPythonIncludePath(allocator: std.mem.Allocator) ![]const u8 {
+fn getPythonIncludePath(
+    allocator: std.mem.Allocator,
+) ![]const u8 {
     const includeResult = try std.process.Child.exec(.{
         .allocator = allocator,
         .argv = &.{ "python", "-c", "import sysconfig; print(sysconfig.get_path('include'), end='')" },

pydust/buildzig.py

@@ -1,18 +1,12 @@
 import contextlib
-import os
 import subprocess
 import sys
 import sysconfig
 import textwrap
 from typing import TextIO
 
-import pydust
 from pydust import config
 
-# We ship the PyDust Zig library inside our Python package to make it easier
-# for us to auto-configure user projects.
-PYDUST_ROOT = os.path.join(os.path.dirname(pydust.__file__), "src", "pydust.zig")
-
 PYVER_MINOR = ".".join(str(v) for v in sys.version_info[:2])
 PYVER_HEX = f"{sys.hexversion:#010x}"
 PYINC = sysconfig.get_path("include")
@@ -45,13 +39,46 @@ def generate_build_zig(build_zig_file):
         b.writeln('const std = @import("std");')
         b.writeln()
 
+        # We choose to ship Pydust source code inside our PyPi package. This means the that once the PyPi package has
+        # been downloaded there are no further requests out to the internet.
+        #
+        # As a result of this though, we need some way to locate the source code. We can't use a reference to the
+        # currently running pydust, since that could be inside a temporary build env which won't exist later when the
+        # user is developing locally. Therefore, we defer resolving the path until the build.zig is invoked by shelling
+        # out to Python.
+        #
+        # We also want to avoid creating a pydust module (and instead prefer anonymous modules) so that we can populate
+        # a separate pyconf options object for each Python extension module.
+        b.write(
+            """
+            fn getPydustRootPath(allocator: std.mem.Allocator) ![]const u8 {
+                const includeResult = try std.process.Child.exec(.{
+                    .allocator = allocator,
+                    .argv = &.{
+                        "python",
+                        "-c",
+                        \\\\import os
+                        \\\\import pydust
+                        \\\\print(os.path.join(os.path.dirname(pydust.__file__), 'src', 'pydust.zig'), end='')
+                        \\\\
+                    },
+                });
+                allocator.free(includeResult.stderr);
+                return includeResult.stdout;
+            }
+            """
+        )
+        b.writeln()
+
         with b.block("pub fn build(b: *std.Build) void"):
             b.write(
                 """
                 const target = b.standardTargetOptions(.{});
                 const optimize = b.standardOptimizeOption(.{});
 
                 const test_step = b.step("test", "Run library tests");
+
+                const pydust = getPydustRootPath(b.allocator) catch @panic("Failed to locate Pydust source code");
                 """
             )
 
@@ -76,7 +103,7 @@ def generate_build_zig(build_zig_file):
                             .target = target,
                             .optimize = optimize,
                         }});
-                        configurePythonInclude(lib{ext_module.libname}, pyconf);
+                        configurePythonInclude(pydust, lib{ext_module.libname}, pyconf);
 
                         // Install the shared library within the source tree
                         const install{ext_module.libname} = b.addInstallFileWithDir(
@@ -92,7 +119,7 @@ def generate_build_zig(build_zig_file):
                             .target = target,
                             .optimize = optimize,
                         }});
-                        configurePythonRuntime(test{ext_module.libname}, pyconf);
+                        configurePythonRuntime(pydust, test{ext_module.libname}, pyconf);
 
                         const run_test{ext_module.libname} = b.addRunArtifact(test{ext_module.libname});
                         test_step.dependOn(&run_test{ext_module.libname}.step);
@@ -119,7 +146,7 @@ def generate_build_zig(build_zig_file):
                         .target = target,
                         .optimize = optimize,
                     }});
-                    configurePythonRuntime(testdebug, pyconf);
+                    configurePythonRuntime(pydust, testdebug, pyconf);
 
                     const debugBin = b.addInstallBinFile(testdebug.getEmittedBin(), "debug.bin");
                     b.getInstallStep().dependOn(&debugBin.step);
@@ -129,18 +156,22 @@ def generate_build_zig(build_zig_file):
 
         b.write(
             f"""
-            fn configurePythonInclude(compile: *std.Build.CompileStep, pyconf: *std.Build.Step.Options) void {{
+            fn configurePythonInclude(
+                pydust: []const u8, compile: *std.Build.CompileStep, pyconf: *std.Build.Step.Options,
+            ) void {{
                 compile.addAnonymousModule("pydust", .{{
-                    .source_file = .{{ .path = "{PYDUST_ROOT}" }},
+                    .source_file = .{{ .path = pydust }},
                     .dependencies = &.{{.{{ .name = "pyconf", .module = pyconf.createModule() }}}},
                 }});
                 compile.addIncludePath(.{{ .path = "{PYINC}" }});
                 compile.linkLibC();
                 compile.linker_allow_shlib_undefined = true;
             }}
 
-            fn configurePythonRuntime(compile: *std.Build.CompileStep, pyconf: *std.Build.Step.Options) void {{
-                configurePythonInclude(compile, pyconf);
+            fn configurePythonRuntime(
+                pydust: []const u8, compile: *std.Build.CompileStep, pyconf: *std.Build.Step.Options
+            ) void {{
+                configurePythonInclude(pydust, compile, pyconf);
                 compile.linkSystemLibrary("python{PYVER_MINOR}");
                 compile.addLibraryPath(.{{ .path =  "{PYLIB}" }});
             }}
@@ -180,4 +211,4 @@ def writeln(self, text: str = ""):
 
 
 if __name__ == "__main__":
-    generate_build_zig()
+    generate_build_zig("test.build.zig")