Auto merge of rust-lang#123436 - amyspark:allow-msvc-to-use-meson-and…

…-mingw-import-libraries, r=petrochenkov

linker: Allow MSVC to use import libraries following the Meson/MinGW convention

Hi all,

This PR implements support for `MsvcLinker` to use import libraries following Meson and the MinGW toolchain's naming convention. Meson [follows the `libfoo.dll.a` naming convention](https://mesonbuild.com/FAQ.html#why-does-building-my-project-with-msvc-output-static-libraries-called-libfooa) to disambiguate between static and import libraries.

This support already existed for static libraries (see rust-lang#100101), but not for dynamic libraries. The latter case was added by duplicating the logic in `native_libs::find_native_static_library`, but a separate case was added in `link_dylib_by_name` for the Windows CRT libraries which must be handled by the linker itself.

See for prerequisites rust-lang#129366, rust-lang#126094, and rust-lang#128370.

All feedback is appreciated!

Fixes rust-lang#122455

cc `@sdroege` `@nirbheek`

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -7,7 +7,9 @@ use std::{env, iter, mem, str};
 
 use cc::windows_registry;
 use rustc_hir::def_id::{CrateNum, LOCAL_CRATE};
-use rustc_metadata::{find_native_static_library, try_find_native_static_library};
+use rustc_metadata::{
+    find_native_static_library, try_find_native_dynamic_library, try_find_native_static_library,
+};
 use rustc_middle::bug;
 use rustc_middle::middle::dependency_format::Linkage;
 use rustc_middle::middle::exported_symbols;
@@ -876,7 +878,13 @@ impl<'a> Linker for MsvcLinker<'a> {
     }
 
     fn link_dylib_by_name(&mut self, name: &str, verbatim: bool, _as_needed: bool) {
-        self.link_arg(format!("{}{}", name, if verbatim { "" } else { ".lib" }));
+        // On MSVC-like targets rustc supports import libraries using alternative naming
+        // scheme (`libfoo.a`) unsupported by linker, search for such libraries manually.
+        if let Some(path) = try_find_native_dynamic_library(self.sess, name, verbatim) {
+            self.link_arg(path);
+        } else {
+            self.link_arg(format!("{}{}", name, if verbatim { "" } else { ".lib" }));
+        }
     }
 
     fn link_dylib_by_path(&mut self, path: &Path, _as_needed: bool) {

compiler/rustc_metadata/src/lib.rs

@@ -37,7 +37,8 @@ pub mod locator;
 pub use creader::{load_symbol_from_dylib, DylibError};
 pub use fs::{emit_wrapper_file, METADATA_FILENAME};
 pub use native_libs::{
-    find_native_static_library, try_find_native_static_library, walk_native_lib_search_dirs,
+    find_native_static_library, try_find_native_dynamic_library, try_find_native_static_library,
+    walk_native_lib_search_dirs,
 };
 pub use rmeta::{encode_metadata, rendered_const, EncodedMetadata, METADATA_HEADER};
 

compiler/rustc_metadata/src/native_libs.rs

@@ -109,6 +109,44 @@ pub fn try_find_native_static_library(
     .break_value()
 }
 
+pub fn try_find_native_dynamic_library(
+    sess: &Session,
+    name: &str,
+    verbatim: bool,
+) -> Option<PathBuf> {
+    let formats = if verbatim {
+        vec![("".into(), "".into())]
+    } else {
+        // While the official naming convention for MSVC import libraries
+        // is foo.lib...
+        let os = (sess.target.staticlib_prefix.clone(), sess.target.staticlib_suffix.clone());
+        // ... Meson follows the libfoo.dll.a convention to
+        // disambiguate .a for static libraries
+        let meson = ("lib".into(), ".dll.a".into());
+        // and MinGW uses .a altogether
+        let mingw = ("lib".into(), ".a".into());
+        vec![os, meson, mingw]
+    };
+
+    walk_native_lib_search_dirs(
+        sess,
+        LinkSelfContainedComponents::empty(),
+        None,
+        |dir, is_framework| {
+            if !is_framework {
+                for (prefix, suffix) in &formats {
+                    let test = dir.join(format!("{prefix}{name}{suffix}"));
+                    if test.exists() {
+                        return ControlFlow::Break(test);
+                    }
+                }
+            }
+            ControlFlow::Continue(())
+        },
+    )
+    .break_value()
+}
+
 pub fn find_native_static_library(name: &str, verbatim: bool, sess: &Session) -> PathBuf {
     try_find_native_static_library(sess, name, verbatim)
         .unwrap_or_else(|| sess.dcx().emit_fatal(errors::MissingNativeLibrary::new(name, verbatim)))