refactor(coprocessor): simplify solc retry helper

Author: Eikix

coprocessor/fhevm-engine/build-utils/solc_retry.rs

@@ -2,30 +2,34 @@ use foundry_compilers::{error::SolcError, solc::Solc};
 use semver::Version;
 use std::{thread, time::Duration};
 
-const SOLC_INSTALL_RETRY_ATTEMPTS: usize = 5;
+const SOLC_INSTALL_RETRY_ATTEMPTS: u64 = 5;
+const SOLC_INSTALL_RETRY_BASE_BACKOFF_MS: u64 = 200;
 
 fn is_etxtbsy(err: &SolcError) -> bool {
     matches!(err, SolcError::Io(io_err) if io_err.source().kind() == std::io::ErrorKind::ExecutableFileBusy || io_err.source().raw_os_error() == Some(26))
 }
 
+fn backoff_ms(attempt: u64) -> u64 {
+    attempt * SOLC_INSTALL_RETRY_BASE_BACKOFF_MS
+}
+
 pub(crate) fn find_or_install_solc(version: &Version) -> Solc {
-    for attempt in 1..=SOLC_INSTALL_RETRY_ATTEMPTS {
+    let mut attempt = 1_u64;
+    loop {
         match Solc::find_or_install(version) {
             Ok(solc) => return solc,
             Err(err) => {
                 if is_etxtbsy(&err) && attempt < SOLC_INSTALL_RETRY_ATTEMPTS {
-                    let backoff = Duration::from_millis((attempt as u64) * 200);
+                    let backoff_ms = backoff_ms(attempt);
                     println!(
-                        "cargo:warning=solc install race (ETXTBSY), retrying attempt {attempt}/{SOLC_INSTALL_RETRY_ATTEMPTS} after {:?}",
-                        backoff
+                        "cargo:warning=solc install race (ETXTBSY), retrying attempt {attempt}/{SOLC_INSTALL_RETRY_ATTEMPTS} after {backoff_ms}ms"
                     );
-                    thread::sleep(backoff);
+                    thread::sleep(Duration::from_millis(backoff_ms));
+                    attempt += 1;
                 } else {
                     panic!("Failed to find or install solc {version}: {err:?}");
                 }
             }
         }
     }
-
-    unreachable!("solc install retry loop exited unexpectedly")
 }