[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.

260

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

[alexander-shaposhnikov]

Address comments

[jhenderson]

LGTM.

llvm/docs/CommandGuide/llvm-libtool-darwin.rst

 
 .. option:: -L <dir>
 
   Adds `<dir>` to the list of directories in which to search for libraries. The
   directories are searched in the order in which they are specified with
   :option:`-L` and before the default search path. The default search path
   includes directories `/lib`, `/usr/lib` and `/usr/local/lib`.
 
+.. option:: -no_warning_for_no_symbols
+
+   Do not warn about files that have no symbols.
+
 .. option:: -o <filename>
 
   Specify the output file name. Must be specified exactly once.
 
 .. option:: -static
 
   Produces a static library from the input files.
 

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 --docnum=1 %s -o %t-x86_64-empty.o
+# RUN: yaml2obj --docnum=2 %s -o %t-armv7-empty.o
+# RUN: echo 'target triple = "arm64-apple-ios8.0.0"' | llvm-as -o %t-empty.bc
+# RUN: yaml2obj %S/Inputs/input1.yaml -o %t-non-empty.o
+
+# RUN: llvm-libtool-darwin -static -o %t.lib %t-x86_64-empty.o 2>&1 | \
+# RUN:   FileCheck --check-prefix=WARNING %s -DPREFIX=%basename_t.tmp
+
+# WARNING: warning: [[PREFIX]]-x86_64-empty.o has no symbols
+
+# RUN: llvm-libtool-darwin -no_warning_for_no_symbols -static -o %t.lib \
+# RUN:   %t-x86_64-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:'
+
+# RUN: llvm-libtool-darwin -arch_only x86_64 -static -o %t.lib \
+# RUN:   %t-non-empty.o %t-armv7-empty.o 2>&1 | \
+# RUN:   FileCheck %s --allow-empty --implicit-check-not='warning:'
+
+# RUN: llvm-libtool-darwin -static -o %t.lib %t-empty.bc 2>&1 | \
+# RUN:   FileCheck %s --allow-empty --implicit-check-not='warning:'
+
+## x86_64
+--- !mach-o
+FileHeader:
+  magic:           0xFEEDFACF
+  cputype:         0x1000007
+  cpusubtype:      0x3
+  filetype:        0x1
+  ncmds:           0
+  sizeofcmds:      0
+  flags:           0x2000
+  reserved:        0x0
+...
+
+## armv7
+--- !mach-o
+FileHeader:
+  magic:           0xFEEDFACE
+  cputype:         0x0000000C
+  cpusubtype:      0x00000009
+  filetype:        0x00000001
+  ncmds:           0
+  sizeofcmds:      0
+  flags:           0x00002000

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.
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();
   }
 
+  if (!NoWarningForNoSymbols && O->symbols().empty())
+    WithColor::warning() << Member.MemberName + " has no symbols\n";
+
   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();