Auto merge of rust-lang#127147 - ChrisDenton:retry, r=<try>

Bootstrap: Retry copying/linking

May be a workaround for rust-lang#127126. But it's hard to know if this works due to the error only appearing some times.

This just adds a retry loop with a fairly long pause between retries so as to give time to whatever is locking the file to give up its lock.

try-job: x86_64-msvc-ext

Author: bors

src/bootstrap/src/lib.rs

@@ -34,7 +34,7 @@ use filetime::FileTime;
 use sha2::digest::Digest;
 use termcolor::{ColorChoice, StandardStream, WriteColor};
 use utils::channel::GitInfo;
-use utils::helpers::hex_encode;
+use utils::helpers::{hex_encode, retry};
 
 use crate::core::builder;
 use crate::core::builder::Kind;
@@ -1688,18 +1688,25 @@ impl Build {
                 return;
             }
         }
-        if let Ok(()) = fs::hard_link(&src, dst) {
-            // Attempt to "easy copy" by creating a hard link
-            // (symlinks don't work on windows), but if that fails
-            // just fall back to a slow `copy` operation.
-        } else {
-            if let Err(e) = fs::copy(&src, dst) {
-                panic!("failed to copy `{}` to `{}`: {}", src.display(), dst.display(), e)
+        // workaround for https://github.com/rust-lang/rust/issues/127126
+        // retry linking or copying up to 10 times or until success.
+        let result: io::Result<()> = retry(10, || {
+            if let Ok(()) = fs::hard_link(&src, dst) {
+                // Attempt to "easy copy" by creating a hard link
+                // (symlinks don't work on windows), but if that fails
+                // just fall back to a slow `copy` operation.
+                Ok(())
+            } else {
+                fs::copy(&src, dst)?;
+                t!(fs::set_permissions(dst, metadata.permissions()));
+                let atime = FileTime::from_last_access_time(&metadata);
+                let mtime = FileTime::from_last_modification_time(&metadata);
+                t!(filetime::set_file_times(dst, atime, mtime));
+                Ok(())
             }
-            t!(fs::set_permissions(dst, metadata.permissions()));
-            let atime = FileTime::from_last_access_time(&metadata);
-            let mtime = FileTime::from_last_modification_time(&metadata);
-            t!(filetime::set_file_times(dst, atime, mtime));
+        });
+        if let Err(e) = result {
+            panic!("failed to copy `{}` to `{}`: {}", src.display(), dst.display(), e)
         }
     }
 

src/bootstrap/src/utils/helpers.rs

@@ -517,3 +517,19 @@ pub fn git(source_dir: Option<&Path>) -> Command {
 
     git
 }
+
+/// Retry a function up to n times, returning the last call to fun.
+/// Stops early if the function returns `Ok`.
+pub fn retry<T, E>(n: usize, mut fun: impl FnMut() -> Result<T, E>) -> Result<T, E> {
+    let mut retries = 0;
+    loop {
+        retries += 1;
+
+        let result = fun();
+        if result.is_ok() || retries == n {
+            return result;
+        }
+        // wait an arbitrary length of time.
+        std::thread::sleep(std::time::Duration::from_secs(1));
+    }
+}