[lld/COFF] Support thin archives in /reproduce: files (#121512)

This already worked without /wholearchive; now it works with it too.
(Only for thin archives containing relative file names, matching the ELF
and Mach-O ports.)

Author: nico

lld/COFF/InputFiles.cpp

@@ -149,11 +149,19 @@ std::vector<MemoryBufferRef>
 lld::coff::getArchiveMembers(COFFLinkerContext &ctx, Archive *file) {
   std::vector<MemoryBufferRef> v;
   Error err = Error::success();
+
+  // Thin archives refer to .o files, so --reproduces needs the .o files too.
+  bool addToTar = file->isThin() && ctx.driver.tar;
+
   for (const Archive::Child &c : file->children(err)) {
     MemoryBufferRef mbref =
         CHECK(c.getMemoryBufferRef(),
               file->getFileName() +
                   ": could not get the buffer for a child of the archive");
+    if (addToTar) {
+      ctx.driver.tar->append(relativeToRoot(check(c.getFullName())),
+                             mbref.getBuffer());
+    }
     v.push_back(mbref);
   }
   if (err)

lld/test/COFF/linkrepro-thin-archives.s

@@ -0,0 +1,23 @@
+# REQUIRES: x86
+
+# RUN: rm -rf %t.dir; split-file %s %t.dir
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-windows %t.dir/foo.s -o %t.dir/foo.obj
+# RUN: cd %t.dir
+# RUN: llvm-ar rcsT foo.lib foo.obj
+
+# RUN: lld-link foo.lib /out:/dev/null /reproduce:repro.tar \
+# RUN:     /subsystem:console /machine:x64
+# RUN: tar tf repro.tar | FileCheck -DPATH='repro/%:t.dir' %s
+
+# RUN: lld-link /wholearchive foo.lib /out:/dev/null /reproduce:repro2.tar \
+# RUN:     /subsystem:console /machine:x64
+# RUN: tar tf repro2.tar | FileCheck -DPATH='repro2/%:t.dir' %s
+
+# CHECK-DAG: [[PATH]]/foo.lib
+# CHECK-DAG: [[PATH]]/foo.obj
+
+#--- foo.s
+.globl mainCRTStartup
+mainCRTStartup:
+  nop