fix: reproducibility of generate_vm_config

rs/ic_os/config/BUILD.bazel

@@ -1,9 +1,17 @@
+load("@rules_rust//cargo:defs.bzl", "cargo_build_script")
 load("@rules_rust//rust:defs.bzl", "rust_binary", "rust_library", "rust_test")
 
 package(default_visibility = ["//rs:ic-os-pkg"])
 
+cargo_build_script(
+    name = "build_script",
+    srcs = ["build.rs"],
+    data = ["templates/guestos_vm_template.xml"],
+)
+
 DEPENDENCIES = [
     # Keep sorted.
+    ":build_script",
     "//rs/ic_os/config_types",
     "//rs/ic_os/deterministic_ips",
     "//rs/ic_os/metrics_tool",
@@ -79,7 +87,6 @@ rust_binary(
     name = "config",
     srcs = BIN_SOURCES,
     aliases = ALIASES,
-    compile_data = ["templates/guestos_vm_template.xml"],
     crate_name = "config",
     proc_macro_deps = MACRO_DEPENDENCIES,
     deps = [
@@ -91,7 +98,6 @@ rust_binary(
     name = "config_dev",
     srcs = BIN_SOURCES,
     aliases = ALIASES,
-    compile_data = ["templates/guestos_vm_template.xml"],
     crate_name = "config",
     proc_macro_deps = MACRO_DEPENDENCIES,
     deps = [

rs/ic_os/config/build.rs

@@ -0,0 +1,37 @@
+use std::fs::File;
+use std::io::Write;
+use std::path::PathBuf;
+
+// Build reproducibility. askama adds a include_bytes! call when it's generating
+// a template impl so that rustc will recompile the module when the file changes
+// on disk. See https://github.com/djc/askama/blob/180696053833147a61b3348646a953e7d92ae582/askama_shared/src/generator.rs#L141
+// The stringified output of every proc-macro is added to the metadata hash for
+// a crate. That output includes the full filepath to include_bytes!. It may be
+// different on two machines, if they use different tempdir paths for the build.
+// However, if we include the html source directly in the output, no
+// inconsistency is introduced.
+fn main() {
+    println!("cargo:rerun-if-changed=templates/guestos_vm_template.xml");
+    let mut f = File::create(
+        PathBuf::from(std::env::var("OUT_DIR").unwrap()).join("guestos_vm_template.rs"),
+    )
+    .unwrap();
+    f.write_all(
+        format!(
+            r#"
+#[derive(Template)]
+#[template(escape = "xml", source = {:?}, ext = "xml")]
+pub struct GuestOSTemplateProps<'a> {{
+    pub cpu_domain: &'a str,
+    pub vm_memory: u32,
+    pub nr_of_vcpus: u32,
+    pub mac_address: MacAddr6,
+    pub config_media: &'a str,
+}}
+    "#,
+            std::fs::read_to_string("templates/guestos_vm_template.xml").unwrap()
+        )
+        .as_bytes(),
+    )
+    .unwrap();
+}

rs/ic_os/config/src/guest_vm_config.rs

@@ -14,6 +14,9 @@ use std::io::Write;
 use std::path::{Path, PathBuf};
 use std::process::Command;
 
+// See build.rs
+include!(concat!(env!("OUT_DIR"), "/guestos_vm_template.rs"));
+
 /// Generate the GuestOS VM configuration
 #[derive(Parser, Debug)]
 #[command(author, version, about, long_about = None)]
@@ -194,18 +197,6 @@ fn make_bootstrap_options(
     Ok(bootstrap_options)
 }
 
-// If you get a compile error pointing at #[derive(Template)], there is likely a syntax error in
-// the template.
-#[derive(Template)]
-#[template(path = "guestos_vm_template.xml")]
-pub struct GuestOSTemplateProps<'a> {
-    pub cpu_domain: &'a str,
-    pub vm_memory: u32,
-    pub nr_of_vcpus: u32,
-    pub mac_address: MacAddr6,
-    pub config_media: &'a str,
-}
-
 /// Generate the GuestOS VM libvirt XML configuration and return it as String.
 fn generate_vm_config(config: &HostOSConfig, media_path: &Path) -> Result<String> {
     let mac_address = calculate_deterministic_mac(