From 9b2e9d093c0596baa7a42328314af9799f863c83 Mon Sep 17 00:00:00 2001
From: Carl Lundin <clundin@google.com>
Date: Thu, 20 Feb 2025 12:52:44 -0800
Subject: [PATCH] Fix caliptra-sw cold build

[Commit](https://github.com/chipsalliance/caliptra-dpe/commit/387034197f091694610c09548b2513731101ea54) improves the DPE build
by checking if arbitrary_handles.rs has changed.

Caliptra-sw fails to compile after this change if the build is cold,
since the arbitrary_handles.rs file is never written to if it does not
yet exist.
---
 dpe/build.rs | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/dpe/build.rs b/dpe/build.rs
index 53c244da..69062feb 100644
--- a/dpe/build.rs
+++ b/dpe/build.rs
@@ -20,10 +20,16 @@ fn main() {
     let max_handles_str = format!("pub const MAX_HANDLES: usize = {};", arbitrary_max_handles);
 
     let dest_path = PathBuf::from(&dest_path);
-    if dest_path.exists()
-        && std::fs::read_to_string(&dest_path).unwrap_or_default() != max_handles_str
-    {
-        std::fs::write(&dest_path, max_handles_str).unwrap();
+    match std::fs::read_to_string(&dest_path) {
+        // arbitrary_max_handles.rs changed so overwrite it's contents.
+        Ok(handles) if handles != max_handles_str => {
+            std::fs::write(&dest_path, max_handles_str).unwrap();
+        }
+        // arbitrary_max_handles.rs does not exist.
+        Err(_) => {
+            std::fs::write(&dest_path, max_handles_str).unwrap();
+        }
+        _ => (),
     }
     println!("cargo:rerun-if-changed={}", dest_path.display());
 }