Preserve the order files are added to archives

rust.metadata.bin could have been at the start of an .rlib file confusing ld

example/alloc_example.rs

@@ -1,4 +1,4 @@
-#![feature(start, box_syntax, alloc_system, core_intrinsics, alloc, alloc_prelude, alloc_error_handler)]
+#![feature(start, box_syntax, alloc_system, core_intrinsics, alloc_prelude, alloc_error_handler)]
 #![no_std]
 
 extern crate alloc;

src/archive.rs

@@ -1,4 +1,3 @@
-use std::collections::HashMap;
 use std::fs::File;
 use std::path::{Path, PathBuf};
 
@@ -24,7 +23,9 @@ enum ArchiveEntry {
 pub struct ArArchiveBuilder<'a> {
     config: ArchiveConfig<'a>,
     src_archives: Vec<ar::Archive<File>>,
-    entries: HashMap<String, ArchiveEntry>,
+    // Don't use `HashMap` here, as the order is important. `rust.metadata.bin` must always be at
+    // the end of an archive for linkers to not get confused.
+    entries: Vec<(String, ArchiveEntry)>,
     update_symbols: bool,
 }
 
@@ -42,21 +43,21 @@ fn new(sess: &'a Session, output: &Path, input: Option<&Path>) -> Self {
 
         let (src_archives, entries) = if let Some(src) = &config.src {
             let mut archive = ar::Archive::new(File::open(src).unwrap());
-            let mut entries = HashMap::new();
+            let mut entries = Vec::new();
 
             let mut i = 0;
             while let Some(entry) = archive.next_entry() {
                 let entry = entry.unwrap();
-                entries.insert(
+                entries.push((
                     String::from_utf8(entry.header().identifier().to_vec()).unwrap(),
                     ArchiveEntry::FromArchive { archive_index: 0, entry_index: i },
-                );
+                ));
                 i += 1;
             }
 
             (vec![archive], entries)
         } else {
-            (vec![], HashMap::new())
+            (vec![], Vec::new())
         };
 
         ArArchiveBuilder {
@@ -68,22 +69,22 @@ fn new(sess: &'a Session, output: &Path, input: Option<&Path>) -> Self {
     }
 
     fn src_files(&mut self) -> Vec<String> {
-        self.entries.keys().cloned().collect()
+        self.entries.iter().map(|(name, _)| name.clone()).collect()
     }
 
     fn remove_file(&mut self, name: &str) {
-        let file = self.entries.remove(name);
-        assert!(
-            file.is_some(),
-            "Tried to remove file not existing in src archive",
-        );
+        let index = self.entries
+            .iter()
+            .position(|(entry_name, _)| entry_name == name)
+            .expect("Tried to remove file not existing in src archive");
+        self.entries.remove(index);
     }
 
     fn add_file(&mut self, file: &Path) {
-        self.entries.insert(
+        self.entries.push((
             file.file_name().unwrap().to_str().unwrap().to_string(),
             ArchiveEntry::File(File::open(file).unwrap()),
-        );
+        ));
     }
 
     fn add_native_library(&mut self, name: &str) {
@@ -132,7 +133,7 @@ enum BuilderKind {
         let mut builder = if self.config.use_gnu_style_archive {
             BuilderKind::Gnu(ar::GnuBuilder::new(
                 archive_file,
-                self.entries.keys().map(|key| key.as_bytes().to_vec()).collect(),
+                self.entries.iter().map(|(name, _)| name.as_bytes().to_vec()).collect(),
             ))
         } else {
             BuilderKind::Bsd(ar::Builder::new(archive_file))
@@ -193,10 +194,10 @@ fn add_archive<F>(&mut self, archive: &Path, mut skip: F) -> std::io::Result<()>
             let entry = entry.unwrap();
             let file_name = String::from_utf8(entry.header().identifier().to_vec()).unwrap();
             if !skip(&file_name) {
-                self.entries.insert(
+                self.entries.push((
                     file_name,
                     ArchiveEntry::FromArchive { archive_index, entry_index: i },
-                );
+                ));
             }
             i += 1;
         }