1 files changed, 50 insertions, 0 deletions
diff --git a/web/atward/build.rs b/web/atward/build.rs
new file mode 100644
index 000000000000..5dadba3bf352
--- /dev/null
+++ b/web/atward/build.rs
@@ -0,0 +1,50 @@
+//! Build script that can be used outside of Nix builds to inject the
+//! ATWARD_INDEX_HTML variable when building in development mode.
+//!
+//! Note that this script assumes that atward is in a checkout of the
+//! TVL depot.
+
+use std::process::Command;
+
+static ATWARD_INDEX_HTML: &str = "ATWARD_INDEX_HTML";
+static ERROR_MESSAGE: &str = r#"Failed to build index page.
+
+When building during development, atward expects to be in a checkout
+of the TVL depot. This is required to automatically build the index
+page that is needed at compile time.
+
+As atward can not automatically detect the location of the page,
+you must set the `ATWARD_INDEX_HTML` environment variable to the
+right path.
+
+The expected page is build using the files in //web/atward/indexHtml
+in the depot."#;
+
+fn main() {
+    // Do nothing if the variable is already set (e.g. via Nix)
+    if let Ok(_) = std::env::var(ATWARD_INDEX_HTML) {
+        return;
+    }
+
+    // Otherwise ask Nix to build it and inject the result.
+    let output = Command::new("nix-build")
+        .arg("-A").arg("web.atward.indexHtml")
+        // ... assuming atward is at //web/atward ...
+        .arg("../..")
+        .output()
+        .expect(ERROR_MESSAGE);
+
+    if !output.status.success() {
+        eprintln!("{}\nNix output: {}", ERROR_MESSAGE, String::from_utf8_lossy(&output.stderr));
+        return;
+    }
+
+    let out_path = String::from_utf8(output.stdout)
+        .expect("Nix returned invalid output after building index page");
+
+    // Return an instruction to Cargo that will set the environment
+    // variable during rustc calls.
+    //
+    // https://doc.rust-lang.org/cargo/reference/build-scripts.html#cargorustc-envvarvalue
+    println!("cargo:rustc-env={}={}", ATWARD_INDEX_HTML, out_path.trim());
+}