Allow rust staticlib to work with MSVC's /WHOLEARCHIVE

Cargo.lock

@@ -205,9 +205,9 @@ dependencies = [
 
 [[package]]
 name = "ar_archive_writer"
-version = "0.4.0"
+version = "0.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "de11a9d32db3327f981143bdf699ade4d637c6887b13b97e6e91a9154666963c"
+checksum = "01667f6f40216b9a0b2945e05fed5f1ad0ab6470e69cb9378001e37b1c0668e4"
 dependencies = [
  "object 0.36.2",
 ]

compiler/rustc_codegen_ssa/Cargo.toml

@@ -5,7 +5,7 @@ edition = "2021"
 
 [dependencies]
 # tidy-alphabetical-start
-ar_archive_writer = "0.4.0"
+ar_archive_writer = "0.4.2"
 arrayvec = { version = "0.7", default-features = false }
 bitflags = "2.4.1"
 cc = "1.0.90"

compiler/rustc_codegen_ssa/src/back/archive.rs

@@ -108,7 +108,11 @@ pub trait ArchiveBuilderBuilder {
                 &exports,
                 machine,
                 !sess.target.is_like_msvc,
-                /*comdat=*/ false,
+                // Enable compatibility with MSVC's `/WHOLEARCHIVE` flag.
+                // Without this flag a duplicate symbol error would be emitted
+                // when linking a rust staticlib using `/WHOLEARCHIVE`.
+                // See #129020
+                true,
             ) {
                 sess.dcx()
                     .emit_fatal(ErrorCreatingImportLibrary { lib_name, error: error.to_string() });

tests/run-make/msvc-wholearchive/c.c

@@ -0,0 +1 @@
+// This page is intentionally left blank

tests/run-make/msvc-wholearchive/dll.def

@@ -0,0 +1,4 @@
+LIBRARY dll
+EXPORTS
+        hello
+        number

tests/run-make/msvc-wholearchive/rmake.rs

@@ -0,0 +1,52 @@
+//! This is a regression test for #129020
+//! It ensures we can use `/WHOLEARCHIVE` to link a rust staticlib into DLL
+//! using the MSVC linker
+
+//@ only-msvc
+// Reason: this is testing the MSVC linker
+
+use std::path::PathBuf;
+
+use run_make_support::{cc, cmd, env_var, extra_c_flags, rustc};
+
+fn main() {
+    // Build the staticlib
+    rustc().crate_type("staticlib").input("static.rs").output("static.lib").run();
+    // Build an empty object to pass to the linker.
+    cc().input("c.c").output("c.obj").args(["-c"]).run();
+
+    // Find the C toolchain's linker.
+    let mut linker = PathBuf::from(env_var("CC"));
+    let linker_flavour = if linker.file_stem().is_some_and(|s| s == "cl") {
+        linker.set_file_name("link.exe");
+        "msvc"
+    } else if linker.file_stem().is_some_and(|s| s == "clang-cl") {
+        linker.set_file_name("lld-link.exe");
+        "llvm"
+    } else {
+        panic!("unknown C toolchain");
+    };
+
+    // As a sanity check, make sure this works without /WHOLEARCHIVE.
+    // Otherwise the actual test failure may be caused by something else.
+    cmd(&linker)
+        .args(["c.obj", "./static.lib", "-dll", "-def:dll.def", "-out:dll.dll"])
+        .args(extra_c_flags())
+        .run();
+
+    // FIXME(@ChrisDenton): this doesn't currently work with llvm's lld-link for other reasons.
+    // May need LLVM patches.
+    if linker_flavour == "msvc" {
+        // Link in the staticlib using `/WHOLEARCHIVE` and produce a DLL.
+        cmd(&linker)
+            .args([
+                "c.obj",
+                "-WHOLEARCHIVE:./static.lib",
+                "-dll",
+                "-def:dll.def",
+                "-out:dll_whole_archive.dll",
+            ])
+            .args(extra_c_flags())
+            .run();
+    }
+}

tests/run-make/msvc-wholearchive/static.rs

@@ -0,0 +1,9 @@
+#[no_mangle]
+pub extern "C" fn hello() {
+    println!("Hello world!");
+}
+
+#[no_mangle]
+pub extern "C" fn number() -> u32 {
+    42
+}