[tools][llvm-libtool] Emit warnings for files without symbols

[alexander-shaposhnikov]

Summary

1. Emit warnings for files without symbols.
2. Add -no_warning_for_no_symbols (consistent with cctools libtool, see https://www.manpagez.com/man/1/libtool/osx-10.11.6.php)

Test plan: make check-all

[smeenai]

Should we warn on files that would have been filtered out by -arch_only? (What does cctools libtool do?)

Should we warn on bitcode files that contain no symbols?

[alexander-shaposhnikov]

@smeenai : many thanks for the review,

1. regarding bitcode files: cctools libtool doesn't warn on them
2. regarding input files which are filtered out by -arch_only: cctools libtool doesn't warn on them either

Perhaps, it makes sense to add tests for these cases

[smeenai]

In D95843#2540709, @alexshap wrote:

@smeenai : many thanks for the review,

1. regarding bitcode files: cctools libtool doesn't warn on them
2. regarding input files which are filtered out by -arch_only: cctools libtool doesn't warn on them either

Perhaps, it makes sense to add tests for these cases

Yup, we should definitely add tests.

We're currently checking for no symbols before we do the -arch_only filtering, right? So our current behavior diverges from cctools?

[alexander-shaposhnikov]

Address comments

[smeenai]

LGTM.

A few other cases that might be good to have test cases for as well, but I'll let you judge that:

• Empty (and non-empty) archive members
• Empty (and non-empty) universal binary members, possibly with and without -arch_only

[jhenderson]

no_warning_for_no_symbols probably needs adding to the Comand Guide?

llvm/tools/llvm-libtool-darwin/llvm-libtool-darwin.cpp

94

Nit: other descriptions don't appear to end with a full stop.

263

Nit: don't end diagnostic messages with trailing full stop (as per style guide).

[alexander-shaposhnikov]

Address comments

[jhenderson]

LGTM.

llvm/test/tools/llvm-libtool-darwin/no-symbols-warning.test

+## This test verifies that the tool emits a warning for object files
+## without symbols.
+
+# RUN: yaml2obj %s -o %t-empty.o
+# RUN: yaml2obj %S/Inputs/input1.yaml -o %t-non-empty.o
+
+# RUN: llvm-libtool-darwin -static -o %t.lib %t-empty.o 2>&1 | \
+# RUN:   FileCheck --check-prefix=WARNING %s -DPREFIX=%basename_t.tmp
+
+# WARNING: warning: [[PREFIX]]-empty.o has no symbols.
+
+# RUN: llvm-libtool-darwin -no_warning_for_no_symbols -static -o %t.lib %t-empty.o 2>&1 | \
+# RUN:   FileCheck %s --allow-empty --implicit-check-not='warning:'
+
+# RUN: llvm-libtool-darwin -static -o %t.lib %t-non-empty.o 2>&1 | \
+# RUN:   FileCheck %s --allow-empty --implicit-check-not='warning:'
+
+--- !mach-o
+FileHeader:
+  magic:           0xFEEDFACF
+  cputype:         0x1000007
+  cpusubtype:      0x3
+  filetype:        0x1
+  ncmds:           0
+  sizeofcmds:      0
+  flags:           0x2000
+  reserved:        0x0
+...

llvm/tools/llvm-libtool-darwin/llvm-libtool-darwin.cpp

cl::desc(
         "L<dir> adds <dir> to the list of directories in which to search for"
         " libraries"),
     cl::ZeroOrMore, cl::Prefix, cl::cat(LibtoolCategory));
 
 static cl::opt<bool>
     VersionOption("V", cl::desc("Print the version number and exit"),
                   cl::cat(LibtoolCategory));
 
+static cl::opt<bool> NoWarningForNoSymbols(
+    "no_warning_for_no_symbols",
+    cl::desc("Do not warn about files that have no symbols."),
+    cl::cat(LibtoolCategory), cl::init(false));
+
 static const std::array<std::string, 3> StandardSearchDirs{
     "/lib",
     "/usr/lib",
     "/usr/local/lib",
 };
 
 struct Config {
   bool Deterministic = true; // Updated by 'D' and 'U' modifiers.
static Error verifyAndAddMachOObject(MembersPerArchitectureMap &Members,
 
   // Throw error if not in Mach-O format.
   if (!isa<object::MachOObjectFile>(**ObjOrErr))
     return createStringError(std::errc::invalid_argument,
                              "'%s': format not supported",
                              Member.MemberName.data());
 
   auto *O = dyn_cast<MachOObjectFile>(ObjOrErr->get());
+  if (!NoWarningForNoSymbols && O->symbols().empty())
+    WithColor::warning() << Member.MemberName + " has no symbols.\n";
+
   uint32_t FileCPUType, FileCPUSubtype;
   std::tie(FileCPUType, FileCPUSubtype) = MachO::getCPUTypeFromArchitecture(
       MachO::getArchitectureFromName(O->getArchTriple().getArchName()));
 
   // If -arch_only is specified then skip this file if it doesn't match
   // the architecture specified.
   if (!ArchType.empty() && !acceptFileArch(FileCPUType, FileCPUSubtype, C)) {
     return Error::success();
   }
 
   uint64_t FileCPUID = getCPUID(FileCPUType, FileCPUSubtype);
   Members[FileCPUID].push_back(std::move(Member));
   return Error::success();
 }
 
 static Error verifyAndAddIRObject(MembersPerArchitectureMap &Members,
                                   NewArchiveMember Member, const Config &C) {
   auto MBRef = Member.Buf->getMemBufferRef();
   Expected<std::unique_ptr<object::IRObjectFile>> IROrErr =
       object::IRObjectFile::create(MBRef, LLVMCtx);