Avoid fingerprint busting during builds (#4244)

* Avoid fingerprint busting during builds

* delete `.fingerprint/package-hash` instead of modifying source code

---------

Co-authored-by: Jonathan Kelley <jkelleyrtp@gmail.com>

packages/cli/src/rustcwrapper.rs

@@ -54,13 +54,23 @@ pub async fn run_rustc() {
         link_args: Default::default(),
     };
 
-    std::fs::create_dir_all(var_file.parent().expect("Failed to get parent dir"))
-        .expect("Failed to create parent dir");
-    std::fs::write(
-        &var_file,
-        serde_json::to_string(&rustc_args).expect("Failed to serialize rustc args"),
-    )
-    .expect("Failed to write rustc args to file");
+    // Another terrible hack to avoid caching non-sensical args when
+    // a build is completely fresh (rustc is invoked with --crate-name ___)
+    if rustc_args
+        .args
+        .iter()
+        .skip_while(|arg| *arg != "--crate-name")
+        .nth(1)
+        .is_some_and(|name| name != "___")
+    {
+        std::fs::create_dir_all(var_file.parent().expect("Failed to get parent dir"))
+            .expect("Failed to create parent dir");
+        std::fs::write(
+            &var_file,
+            serde_json::to_string(&rustc_args).expect("Failed to serialize rustc args"),
+        )
+        .expect("Failed to write rustc args to file");
+    }
 
     // Run the actual rustc command
     // We want all stdout/stderr to be inherited, so the running process can see the output