bifrucate the service_model module based pre-packaging

build.zig

@@ -114,12 +114,41 @@ pub fn build(b: *Builder) !void {
 
     cg.dependOn(&cg_cmd.step);
 
-    exe.step.dependOn(cg);
+    // Each module will need access to the generated AWS modules. These
+    // are all imported by service_manifest.zig, which is a generated list
+    // of services created by the codegen process.
+    //
+    // First, we need to check if pre-generated models exist, which only happens
+    // for packaged distribution.
+    //
+    // The idea here is that if we have a packaged distibution (tarball with
+    // models available, we are pre-generated, do not need the codegen step
+    // (and in fact do not have that available), and our service_manifest
+    // module needs to be the pre-packaged file.
+    //
+    // If we do not have a packaged distribution, the file will not exist,
+    // because it is generated by codegen and will live in the zig cache directory,
+    // so we depend on the codegen step and the service_manifest module will
+    // be based on the codegen output itself.
+    //
+    // Most of this complication comes from the fact that we want to enable
+    // consuming build.zig files to be able to use the SDK at build time for
+    // things like code deployments, e.g. https://git.lerch.org/lobo/lambda-zig
+    const has_pre_generated =
+        if (b.build_root.handle.access("src/models/service_manifest.zig", .{})) true else |_| false;
+
+    // Only depend on codegen if we don't have pre-generated models
+    if (!has_pre_generated)
+        exe.step.dependOn(cg);
+
+    // Use pre-generated models if available, otherwise use codegen output
+    const service_manifest_source: std.Build.LazyPath = if (has_pre_generated)
+        b.path("src/models/service_manifest.zig")
+    else
+        cg_output_dir.path(b, "service_manifest.zig");
 
-    // This allows us to have each module depend on the
-    // generated service manifest.
     const service_manifest_module = b.createModule(.{
-        .root_source_file = cg_output_dir.path(b, "service_manifest.zig"),
+        .root_source_file = service_manifest_source,
         .target = target,
         .optimize = optimize,
     });
@@ -179,7 +208,8 @@ pub fn build(b: *Builder) !void {
             .filters = test_filters,
         });
 
-        unit_tests.step.dependOn(cg);
+        if (!has_pre_generated)
+            unit_tests.step.dependOn(cg);
         unit_tests.use_llvm = !no_llvm;
 
         const run_unit_tests = b.addRunArtifact(unit_tests);
@@ -202,7 +232,8 @@ pub fn build(b: *Builder) !void {
         .filters = test_filters,
     });
     smoke_test.use_llvm = !no_llvm;
-    smoke_test.step.dependOn(cg);
+    if (!has_pre_generated)
+        smoke_test.step.dependOn(cg);
 
     const run_smoke_test = b.addRunArtifact(smoke_test);