[MachO LLD] Respect -all_load with --start-lib --end-lib style archives (#93993)

The -all_load flag is intended to force the linker to load all lazy members, but doesn't do so if the archive is specified with --start-lib, --end-lib flags. The `-all_load` flag is global, that is it can be placed anywhere in the linker invocation, and it affects the load behavior of all conventional archives listed. Unlike ELF's --whole-archive, the user need not necessarily have access to the entire linker invocation to reasonably make use of the flag. The user can supply `-all_load` to a build system without inspecting the rest of the linker invocation.

To make the behavior of `--start-lib` style archives consistent with regular archives, this patch makes it so that -all_load also applies in this case.

Author: NuriAmari

lld/MachO/Driver.cpp

@@ -1162,6 +1162,8 @@ static void createFiles(const InputArgList &args) {
   // This loop should be reserved for options whose exact ordering matters.
   // Other options should be handled via filtered() and/or getLastArg().
   bool isLazy = false;
+  // If we've processed an opening --start-lib, without a matching --end-lib
+  bool inLib = false;
   for (const Arg *arg : args) {
     const Option &opt = arg->getOption();
     warnIfDeprecatedOption(opt);
@@ -1219,13 +1221,16 @@ static void createFiles(const InputArgList &args) {
                    LoadType::CommandLine);
       break;
     case OPT_start_lib:
-      if (isLazy)
+      if (inLib)
         error("nested --start-lib");
-      isLazy = true;
+      inLib = true;
+      if (!config->allLoad)
+        isLazy = true;
       break;
     case OPT_end_lib:
-      if (!isLazy)
+      if (!inLib)
         error("stray --end-lib");
+      inLib = false;
       isLazy = false;
       break;
     default:

lld/test/MachO/start-lib.s

@@ -86,6 +86,11 @@
 # RUN: not %lld --end-lib 2>&1 | FileCheck %s --check-prefix=STRAY
 # STRAY: error: stray --end-lib
 
+# RUN: %lld -dylib --start-lib %t/1.bc %t/2.o --end-lib -all_load -o %t/out
+# RUN: llvm-readobj -s %t/out | FileCheck --check-prefix=ALL-LOAD %s
+# ALL-LOAD-DAG: _foo
+# ALL-LOAD-DAG: _bar
+
 #--- main.s
 .globl _main
 _main: