[LLD][COFF] Make /wholearchive thin-archive member identifiers consistent

A thin archive is an archive/library format where the archive itself
contains only references to member object files on disk, rather than
embedding the file contents.

For the non-/wholearchive case, we use the path to the archive member
as the identifier for thin-archive members (see comments in
`enqueueArchiveMember`). This patch modifies the /wholearchive path to
behave the same way.

Apart from consistency, my motivation for fixing this is DTLTO
(#126654), where having the
member identifier be the path on disk allows distribution of bitcode
members during ThinLTO.

Author: bd1976bris

lld/COFF/Driver.cpp

@@ -275,7 +275,12 @@ void LinkerDriver::addBuffer(std::unique_ptr<MemoryBuffer> mb,
 
       int memberIndex = 0;
       for (MemoryBufferRef m : getArchiveMembers(ctx, archive))
-        addArchiveBuffer(m, "<whole-archive>", filename, memberIndex++);
+        if (!archive->isThin())
+          addArchiveBuffer(m, "<whole-archive>", filename, memberIndex++);
+        else
+          // Pass empty string as archive name so that the original filename is
+          // used as the buffer identifier.
+          addArchiveBuffer(m, "<whole-archive>", "", /*OffsetInArchive=*/0);
       return;
     }
     addFile(make<ArchiveFile>(ctx, mbref));

lld/test/COFF/thin-archive.s

@@ -22,23 +22,34 @@
 # SYMTAB:        ?f@@YAHXZ in
 # NO-SYMTAB-NOT: ?f@@YAHXZ in
 
-# RUN: lld-link /entry:main %t.main.obj %t.lib /out:%t.exe 2>&1 | \
-# RUN:     FileCheck --allow-empty %s
-# RUN: lld-link /entry:main %t.main.obj %t_thin.lib /out:%t.exe 2>&1 | \
-# RUN:     FileCheck --allow-empty %s
-# RUN: lld-link /entry:main %t.main.obj /wholearchive:%t_thin.lib /out:%t.exe 2>&1 | \
-# RUN:     FileCheck --allow-empty %s
+# RUN: echo /entry:main %t.main.obj /out:%t.exe > %t.rsp
+
+# RUN: lld-link @%t.rsp %t.lib /verbose 2>&1 | \
+# RUN:     FileCheck %s --check-prefix=LOAD_NON_THIN
+# RUN: lld-link @%t.rsp %t_thin.lib /verbose 2>&1 | \
+# RUN:     FileCheck %s --check-prefix=LOAD_THIN_SYM
+# RUN: lld-link @%t.rsp /wholearchive:%t_thin.lib /verbose 2>&1 | \
+# RUN:     FileCheck %s --check-prefix=LOAD_THIN_WHOLE
+# RUN: lld-link @%t.rsp /wholearchive %t_thin.lib /verbose 2>&1 | \
+# RUN:     FileCheck %s --check-prefix=LOAD_THIN_WHOLE
+
+# LOAD_NON_THIN:   Loaded {{.*}}.lib({{.*}}.obj) for int __cdecl f(void)
+# LOAD_THIN_SYM:   Loaded {{.*}}.obj for int __cdecl f(void)
+# LOAD_THIN_WHOLE: Loaded {{.*}}.obj for <whole-archive>
 
 # RUN: rm %t.lib.obj
-# RUN: lld-link /entry:main %t.main.obj %t.lib /out:%t.exe 2>&1 | \
-# RUN:     FileCheck --allow-empty %s
-# RUN: env LLD_IN_TEST=1 not lld-link /entry:main %t.main.obj %t_thin.lib \
-# RUN:     /out:%t.exe 2>&1 | FileCheck --check-prefix=NOOBJ %s
-# RUN: env LLD_IN_TEST=1 not lld-link /entry:main %t.main.obj %t_thin.lib /out:%t.exe \
-# RUN:     /demangle:no 2>&1 | FileCheck --check-prefix=NOOBJNODEMANGLE %s
-
-# CHECK-NOT: error: could not get the buffer for the member defining
+# RUN: lld-link @%t.rsp %t.lib /out:%t.exe 2>&1 | \
+# RUN:     FileCheck --check-prefix=ERR --allow-empty  %s
+# RUN: env LLD_IN_TEST=1 not lld-link @%t.rsp %t_thin.lib 2>&1 | \
+# RUN:     FileCheck --check-prefix=NOOBJ %s
+# RUN: env LLD_IN_TEST=1 not lld-link @%t.rsp /wholearchive:%t_thin.lib 2>&1 | \
+# RUN:     FileCheck --check-prefix=NOOBJWHOLE %s
+# RUN: env LLD_IN_TEST=1 not lld-link @%t.rsp %t_thin.lib /demangle:no 2>&1 | \
+# RUN:     FileCheck --check-prefix=NOOBJNODEMANGLE %s
+
+# ERR-NOT: error: could not get the buffer for the member defining
 # NOOBJ: error: could not get the buffer for the member defining symbol int __cdecl f(void): {{.*}}.lib({{.*}}.lib.obj):
+# NOOBJWHOLE: error: {{.*}}.lib: could not get the buffer for a child of the archive: '{{.*}}.obj': no such file or directory
 # NOOBJNODEMANGLE: error: could not get the buffer for the member defining symbol ?f@@YAHXZ: {{.*}}.lib({{.*}}.lib.obj):
 
 	.text