Unify dylib loading between proc macros and codegen backends

As bonus this makes the errors when failing to load a proc macro more
informative to match the backend loading errors. In addition it makes it
slightly easier to patch rustc to work on platforms that don't support
dynamic linking like wasm.

2 files changed, 11 insertions, 23 deletions

diff --git a/compiler/rustc_interface/src/lib.rs b/compiler/rustc_interface/src/lib.rs
index 24c2e290534..d0ce23dacb5 100644
--- a/compiler/rustc_interface/src/lib.rs
+++ b/compiler/rustc_interface/src/lib.rs
@@ -1,5 +1,4 @@
 #![feature(decl_macro)]
-#![feature(error_iter)]
 #![feature(generic_nonzero)]
 #![feature(lazy_cell)]
 #![feature(let_chains)]
diff --git a/compiler/rustc_interface/src/util.rs b/compiler/rustc_interface/src/util.rs
index 087c43075f1..823614e1f06 100644
--- a/compiler/rustc_interface/src/util.rs
+++ b/compiler/rustc_interface/src/util.rs
@@ -1,10 +1,10 @@
 use crate::errors;
 use info;
-use libloading::Library;
 use rustc_ast as ast;
 use rustc_codegen_ssa::traits::CodegenBackend;
 #[cfg(parallel_compiler)]
 use rustc_data_structures::sync;
+use rustc_metadata::{load_symbol_from_dylib, DylibError};
 use rustc_parse::validate_attr;
 use rustc_session as session;
 use rustc_session::config::{self, Cfg, CrateType, OutFileName, OutputFilenames, OutputTypes};
@@ -17,7 +17,6 @@ use rustc_span::symbol::{sym, Symbol};
 use session::EarlyDiagCtxt;
 use std::env;
 use std::env::consts::{DLL_PREFIX, DLL_SUFFIX};
-use std::mem;
 use std::path::{Path, PathBuf};
 use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::OnceLock;
@@ -162,29 +161,19 @@ pub(crate) fn run_in_thread_pool_with_globals<F: FnOnce() -> R + Send, R: Send>(
 }
 
 fn load_backend_from_dylib(early_dcx: &EarlyDiagCtxt, path: &Path) -> MakeBackendFn {
-    fn format_err(e: &(dyn std::error::Error + 'static)) -> String {
-        e.sources().map(|e| format!(": {e}")).collect()
-    }
-    let lib = unsafe { Library::new(path) }.unwrap_or_else(|err| {
-        let err = format!("couldn't load codegen backend {path:?}{}", format_err(&err));
-        early_dcx.early_fatal(err);
-    });
-
-    let backend_sym = unsafe { lib.get::<MakeBackendFn>(b"__rustc_codegen_backend") }
-        .unwrap_or_else(|e| {
+    match unsafe { load_symbol_from_dylib::<MakeBackendFn>(path, "__rustc_codegen_backend") } {
+        Ok(backend_sym) => backend_sym,
+        Err(DylibError::DlOpen(path, err)) => {
+            let err = format!("couldn't load codegen backend {path}{err}");
+            early_dcx.early_fatal(err);
+        }
+        Err(DylibError::DlSym(_path, err)) => {
             let e = format!(
-                "`__rustc_codegen_backend` symbol lookup in the codegen backend failed{}",
-                format_err(&e)
+                "`__rustc_codegen_backend` symbol lookup in the codegen backend failed{err}",
             );
             early_dcx.early_fatal(e);
-        });
-
-    // Intentionally leak the dynamic library. We can't ever unload it
-    // since the library can make things that will live arbitrarily long.
-    let backend_sym = unsafe { backend_sym.into_raw() };
-    mem::forget(lib);
-
-    *backend_sym
+        }
+    }
 }
 
 /// Get the codegen backend based on the name and specified sysroot.