[lld] Do not implicitly link non "public" libraries (#97639)

The LC_SUB_CLIENT Mach-O command and the `allowable-clients` TBD entry
specify that the given framework (or library?) can only be linked
directly from the specified names, even if it is sitting in `/usr/lib`
or `/System/Library/Frameworks`.

Add a check for those conditions before checking if a library should be
implicitly linked, and link against their umbrella if they have
allowable clients. The code needs to be in both the binary libraries and
the interface libraries.

Add a test that reproduces the scenario in which a framework reexports a
private framework that sits in `/System/Library/Frameworks`, and check
for the symbols of the reexported framework to be associated with the
public framework, and not the private one.

lld/MachO/InputFiles.cpp

@@ -1725,7 +1725,10 @@ DylibFile::DylibFile(MemoryBufferRef mb, DylibFile *umbrella,
   }
 
   // Initialize symbols.
-  exportingFile = isImplicitlyLinked(installName) ? this : this->umbrella;
+  bool canBeImplicitlyLinked = findCommand(hdr, LC_SUB_CLIENT) == nullptr;
+  exportingFile = (canBeImplicitlyLinked && isImplicitlyLinked(installName))
+                      ? this
+                      : this->umbrella;
 
   const auto *dyldInfo = findCommand<dyld_info_command>(hdr, LC_DYLD_INFO_ONLY);
   const auto *exportsTrie =
@@ -1884,7 +1887,10 @@ DylibFile::DylibFile(const InterfaceFile &interface, DylibFile *umbrella,
 
   checkAppExtensionSafety(interface.isApplicationExtensionSafe());
 
-  exportingFile = isImplicitlyLinked(installName) ? this : umbrella;
+  bool canBeImplicitlyLinked = interface.allowableClients().size() == 0;
+  exportingFile = (canBeImplicitlyLinked && isImplicitlyLinked(installName))
+                      ? this
+                      : umbrella;
   auto addSymbol = [&](const llvm::MachO::Symbol &symbol,
                        const Twine &name) -> void {
     StringRef savedName = saver().save(name);

lld/test/MachO/implicit-and-allowable-clients.test

@@ -0,0 +1,49 @@
+# REQUIRES: arm
+# RUN: rm -rf %t; split-file %s %t
+# RUN: ln -s Versions/A/FrameworkPublic.tbd %t/System/Library/Frameworks/FrameworkPublic.framework/
+# RUN: ln -s Versions/A/FrameworkPrivate.tbd %t/System/Library/Frameworks/FrameworkPrivate.framework/
+# RUN: llvm-mc -filetype obj -triple arm64-apple-macos11.0 %t/test.s -o %t/test.o
+# RUN: %lld -arch arm64 -platform_version macos 11.0 11.0 -o %t/test -syslibroot %t -framework FrameworkPublic %t/test.o
+
+# RUN: llvm-objdump --bind --no-show-raw-insn -d %t/test | FileCheck %s
+# CHECK:     Bind table:
+# CHECK-DAG: __DATA __data {{.*}} pointer 0 FrameworkPublic   _funcPublic
+# CHECK-DAG: __DATA __data {{.*}} pointer 0 FrameworkPublic   _funcPrivate
+
+#--- System/Library/Frameworks/FrameworkPublic.framework/Versions/A/FrameworkPublic.tbd
+--- !tapi-tbd
+tbd-version: 4
+targets: [ arm64-macos ]
+install-name: '/System/Library/Frameworks/FrameworkPublic.framework/Versions/A/FrameworkPublic'
+current-version: 1.0.0
+reexported-libraries:
+  - targets: [ arm64-macos ]
+    libraries: [ '/System/Library/Frameworks/FrameworkPrivate.framework/Versions/A/FrameworkPrivate' ]
+exports:
+  - targets: [ arm64-macos ]
+    symbols: [ '_funcPublic' ]
+...
+#--- System/Library/Frameworks/FrameworkPrivate.framework/Versions/A/FrameworkPrivate.tbd
+--- !tapi-tbd
+tbd-version: 4
+targets: [ arm64-macos ]
+install-name: '/System/Library/Frameworks/FrameworkPrivate.framework/Versions/A/FrameworkPrivate'
+current-version: 1.0.0
+allowable-clients:
+  - targets: [ arm64-macos ]
+    clients: [ FrameworkPublic ]
+exports:
+  - targets: [ arm64-macos ]
+    symbols: [ '_funcPrivate' ]
+...
+#--- test.s
+.text
+.globl _main
+
+_main:
+  ret
+
+.data
+  .quad _funcPublic
+  .quad _funcPrivate
+