[lld-macho] Don't double emit reexported libraries

When a library is specified with both `-l` and
`-reexport_libraries`, lld will emit two load commands
for it, in contrast with ld64. In an upcoming version
of macOS, this fails dyld validation; see
https://crbug.com/404905688

Co-authored-by: Mark Rowe <[email protected]>>

Author: speednoisemovement

lld/MachO/Writer.cpp

@@ -938,17 +938,19 @@ template <class LP> void Writer::createLoadCommands() {
     }
 
     ordinal = dylibFile->ordinal = dylibOrdinal++;
-    LoadCommandType lcType =
-        dylibFile->forceWeakImport || dylibFile->refState == RefState::Weak
-            ? LC_LOAD_WEAK_DYLIB
-            : LC_LOAD_DYLIB;
+    LoadCommandType lcType = LC_LOAD_DYLIB;
+    if (dylibFile->reexport) {
+      if (dylibFile->forceWeakImport)
+        warn(path::filename(dylibFile->getName()) + " is re-exported so cannot be weak-linked");
+
+      lcType = LC_REEXPORT_DYLIB;
+    } else if (dylibFile->forceWeakImport || dylibFile->refState == RefState::Weak) {
+      lcType = LC_LOAD_WEAK_DYLIB;
+    }
     in.header->addLoadCommand(make<LCDylib>(lcType, dylibFile->installName,
-                                            dylibFile->compatibilityVersion,
-                                            dylibFile->currentVersion));
+                                        dylibFile->compatibilityVersion,
+                                        dylibFile->currentVersion));
 
-    if (dylibFile->reexport)
-      in.header->addLoadCommand(
-          make<LCDylib>(LC_REEXPORT_DYLIB, dylibFile->installName));
   }
 
   for (const auto &dyldEnv : config->dyldEnvs)

lld/test/MachO/sub-library.s

@@ -42,6 +42,17 @@
 # REEXPORT-HEADERS-NOT: Load command
 # REEXPORT-HEADERS:     name    [[PATH]]
 
+## Check that specifying a library both with `l` and `reexport_library`
+## doesn't emit two load commands.
+# RUN: %lld -dylib -reexport_library %t/libgoodbye.dylib \
+# RUN:   -L%t -lgoodbye %t/libsuper.o -o %t/libsuper.dylib
+# RUN: llvm-otool -L %t/libsuper.dylib | FileCheck %s \
+# RUN:   --check-prefix=REEXPORT-DOUBLE -DPATH=%t/libgoodbye.dylib
+
+# REEXPORT-DOUBLE: [[PATH]]
+# REEXPORT-DOUBLE-SAME: reexport
+# REEXPORT-DOUBLE-NOT: [[PATH]]
+
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/sub-library.o
 # RUN: %lld -o %t/sub-library -L%t -lsuper %t/sub-library.o