Allow MRI scripts as file input on cmd line

[dmikulin]

Summary

With -M option llvm-ar expects input from stdin. Change it to optionally take file name for an MRI script as input to -M.

[Bigcheese]

lgtm.

llvm/test/Object/mri5.test

-; RUN: not llvm-ar -M t < %s 2>&1 | FileCheck %s
+; RUN: not llvm-ar -M t x 2>&1 | FileCheck %s
+; RUN: not llvm-ar -M t < %s 2>&1 | FileCheck %s --check-prefix CHECK-FILE
 ; CHECK: Cannot mix -M and other options.
+; CHECK-FILE: Cannot read MRI script 't'

llvm/test/tools/llvm-ar/mri.test

+RUN: yaml2obj %S/Inputs/elf.yaml -o %t.o
+RUN: rm -f %t.ar
+
+RUN: echo "create %t.ar" > %t.mri
+RUN: echo "addmod %t.o" >> %t.mri
+RUN: echo "save" >> %t.mri
+RUN: echo "end" >> %t.mri
+
+RUN: llvm-ar -M < %t.mri
+RUN: llvm-ar tv %t.ar | FileCheck %s
+
+RUN: rm -f %t.ar
+RUN: llvm-ar -M %t.mri
+RUN: llvm-ar tv %t.ar | FileCheck %s
+
+CHECK: mri.test{{.*}}.o

llvm/tools/llvm-ar/llvm-ar.cpp

 }
 
 // Copy over remaining items in RestOfArgs to our Members vector
 static void getMembers() {
   for (auto &Arg : RestOfArgs)
     Members.push_back(Arg);
 }
 
-static void runMRIScript();
+static void runMRIScript(const MemoryBuffer &Ref);
 
 // Parse the command line options as presented and return the operation
 // specified. Process all modifiers and check to make sure that constraints on
 // modifier/operation pairs have not been violated.
 static ArchiveOperation parseCommandLine() {
   if (MRI) {
+    std::string MRIScriptName;
+    if (!RestOfArgs.empty()) {
+      MRIScriptName = RestOfArgs[0];
+      RestOfArgs.erase(RestOfArgs.begin());
+
       if (!RestOfArgs.empty())
         fail("Cannot mix -M and other options");
-    runMRIScript();
+    }
+
+    ErrorOr<std::unique_ptr<MemoryBuffer>> MemBufOrErr = MRIScriptName.empty() ?
+      MemoryBuffer::getSTDIN() : MemoryBuffer::getFile(MRIScriptName);
+
+    if (!MemBufOrErr)
+      fail("Cannot read MRI script '" + MRIScriptName + "'");
+    runMRIScript(*MemBufOrErr.get());
   }
 
   getOptions();
 
   // Keep track of number of operations. We can only specify one
   // per execution.
   unsigned NumOperations = 0;
 
if (!Create) {
       errs() << ToolName << ": creating " << ArchiveName << "\n";
     }
   }
 
   performOperation(Operation, nullptr, nullptr, NewMembers);
   return 0;
 }
 
-static void runMRIScript() {
+static void runMRIScript(const MemoryBuffer &Ref) {
   enum class MRICommand { AddLib, AddMod, Create, Save, End, Invalid };
 
-  ErrorOr<std::unique_ptr<MemoryBuffer>> Buf = MemoryBuffer::getSTDIN();
-  failIfError(Buf.getError());
-  const MemoryBuffer &Ref = *Buf.get();
   bool Saved = false;
   std::vector<NewArchiveMember> NewMembers;
   std::vector<std::unique_ptr<MemoryBuffer>> ArchiveBuffers;
   std::vector<std::unique_ptr<object::Archive>> Archives;
 
   for (line_iterator I(Ref, /*SkipBlanks*/ true, ';'), E; I != E; ++I) {
     StringRef Line = *I;
     StringRef CommandStr, Rest;