Add a default implementation for CodegenBackend::link

As a side effect this should add raw-dylib support to cg_gcc as the
default ArchiveBuilderBuilder that is used implements
create_dll_import_lib. I haven't tested if the raw-dylib support
actually works however.

compiler/rustc_codegen_cranelift/src/archive.rs

@@ -1,12 +0,0 @@
-use rustc_codegen_ssa::back::archive::{
-    ArArchiveBuilder, ArchiveBuilder, ArchiveBuilderBuilder, DEFAULT_OBJECT_READER,
-};
-use rustc_session::Session;
-
-pub(crate) struct ArArchiveBuilderBuilder;
-
-impl ArchiveBuilderBuilder for ArArchiveBuilderBuilder {
-    fn new_archive_builder<'a>(&self, sess: &'a Session) -> Box<dyn ArchiveBuilder + 'a> {
-        Box::new(ArArchiveBuilder::new(sess, &DEFAULT_OBJECT_READER))
-    }
-}

compiler/rustc_codegen_cranelift/src/lib.rs

@@ -43,7 +43,6 @@ use rustc_codegen_ssa::CodegenResults;
 use rustc_codegen_ssa::back::versioned_llvm_target;
 use rustc_codegen_ssa::traits::CodegenBackend;
 use rustc_data_structures::profiling::SelfProfilerRef;
-use rustc_errors::ErrorGuaranteed;
 use rustc_metadata::EncodedMetadata;
 use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
 use rustc_session::Session;
@@ -56,7 +55,6 @@ use crate::prelude::*;
 mod abi;
 mod allocator;
 mod analyze;
-mod archive;
 mod base;
 mod cast;
 mod codegen_i128;
@@ -249,17 +247,6 @@ impl CodegenBackend for CraneliftCodegenBackend {
             self.config.borrow().as_ref().unwrap(),
         )
     }
-
-    fn link(
-        &self,
-        sess: &Session,
-        codegen_results: CodegenResults,
-        outputs: &OutputFilenames,
-    ) -> Result<(), ErrorGuaranteed> {
-        use rustc_codegen_ssa::back::link::link_binary;
-
-        link_binary(sess, &crate::archive::ArArchiveBuilderBuilder, &codegen_results, outputs)
-    }
 }
 
 fn target_triple(sess: &Session) -> target_lexicon::Triple {

compiler/rustc_codegen_gcc/src/archive.rs

@@ -1,25 +0,0 @@
-use std::path::Path;
-
-use rustc_codegen_ssa::back::archive::{
-    ArArchiveBuilder, ArchiveBuilder, ArchiveBuilderBuilder, DEFAULT_OBJECT_READER,
-    ImportLibraryItem,
-};
-use rustc_session::Session;
-
-pub(crate) struct ArArchiveBuilderBuilder;
-
-impl ArchiveBuilderBuilder for ArArchiveBuilderBuilder {
-    fn new_archive_builder<'a>(&self, sess: &'a Session) -> Box<dyn ArchiveBuilder + 'a> {
-        Box::new(ArArchiveBuilder::new(sess, &DEFAULT_OBJECT_READER))
-    }
-
-    fn create_dll_import_lib(
-        &self,
-        _sess: &Session,
-        _lib_name: &str,
-        _items: Vec<ImportLibraryItem>,
-        _output_path: &Path,
-    ) {
-        unimplemented!("creating dll imports is not yet supported");
-    }
-}

compiler/rustc_codegen_gcc/src/lib.rs

@@ -58,7 +58,6 @@ extern crate rustc_driver;
 
 mod abi;
 mod allocator;
-mod archive;
 mod asm;
 mod attributes;
 mod back;
@@ -103,7 +102,7 @@ use rustc_codegen_ssa::traits::{CodegenBackend, ExtraBackendMethods, WriteBacken
 use rustc_codegen_ssa::{CodegenResults, CompiledModule, ModuleCodegen};
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_data_structures::sync::IntoDynSyncSend;
-use rustc_errors::{DiagCtxtHandle, ErrorGuaranteed};
+use rustc_errors::DiagCtxtHandle;
 use rustc_metadata::EncodedMetadata;
 use rustc_middle::dep_graph::{WorkProduct, WorkProductId};
 use rustc_middle::ty::TyCtxt;
@@ -261,17 +260,6 @@ impl CodegenBackend for GccCodegenBackend {
             .join(sess)
     }
 
-    fn link(
-        &self,
-        sess: &Session,
-        codegen_results: CodegenResults,
-        outputs: &OutputFilenames,
-    ) -> Result<(), ErrorGuaranteed> {
-        use rustc_codegen_ssa::back::link::link_binary;
-
-        link_binary(sess, &crate::archive::ArArchiveBuilderBuilder, &codegen_results, outputs)
-    }
-
     fn target_features(&self, sess: &Session, allow_unstable: bool) -> Vec<Symbol> {
         target_features(sess, allow_unstable, &self.target_info)
     }

compiler/rustc_codegen_ssa/src/back/archive.rs

@@ -304,6 +304,14 @@ pub trait ArchiveBuilder {
     fn build(self: Box<Self>, output: &Path) -> bool;
 }
 
+pub struct ArArchiveBuilderBuilder;
+
+impl ArchiveBuilderBuilder for ArArchiveBuilderBuilder {
+    fn new_archive_builder<'a>(&self, sess: &'a Session) -> Box<dyn ArchiveBuilder + 'a> {
+        Box::new(ArArchiveBuilder::new(sess, &DEFAULT_OBJECT_READER))
+    }
+}
+
 #[must_use = "must call build() to finish building the archive"]
 pub struct ArArchiveBuilder<'a> {
     sess: &'a Session,

compiler/rustc_codegen_ssa/src/traits/backend.rs

@@ -16,6 +16,8 @@ use rustc_span::symbol::Symbol;
 
 use super::CodegenObject;
 use super::write::WriteBackendMethods;
+use crate::back::archive::ArArchiveBuilderBuilder;
+use crate::back::link::link_binary;
 use crate::back::write::TargetMachineFactoryFn;
 use crate::{CodegenResults, ModuleCodegen};
 
@@ -87,7 +89,9 @@ pub trait CodegenBackend {
         sess: &Session,
         codegen_results: CodegenResults,
         outputs: &OutputFilenames,
-    ) -> Result<(), ErrorGuaranteed>;
+    ) -> Result<(), ErrorGuaranteed> {
+        link_binary(sess, &ArArchiveBuilderBuilder, &codegen_results, outputs)
+    }
 
     /// Returns `true` if this backend can be safely called from multiple threads.
     ///