Test wholearchive on rust staticlib

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

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+// This page is intentionally left blank

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

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+LIBRARY dll
+EXPORTS
+        hello
+        number

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

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+//! 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

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