[llvm-rc] Support absolute filenames in manifests

[phosek]

Summary

CMake generate manifests that contain absolute filenames and these
currently result in assertion error. This change ensures that we
handle these correctly.

[mstorsjo]

Looks ok to me.

Is it possible to construct a test for this somehow? We don't know the absolute paths on the system running the tests, but can we e.g. do something like echo "INCLUDE %p/Inputs/somefile" > %t.rc in order to exercise it?

[phosek]

Test added.

[mstorsjo]

LGTM

llvm/test/tools/llvm-rc/absolute.test

5

The negative check for assertion might be a bit overkill, as a failed assert would make the llvm-rc command itself fail (a plain ; RUN: llvm-rc %t.rc to see that it can successfully compile that file would be enough), but I don't mind this either.

llvm/test/tools/llvm-rc/absolute.test

+; RUN: touch %t.manifest
+; RUN: echo "1 24 \"%t.manifest\"" > %t.rc
+; RUN: llvm-rc %t.rc 2>&1 | FileCheck %s --allow-empty
+
+; CHECK-NOT: Assertion `!path::is_absolute(FileName)' failed.

llvm/tools/llvm-rc/ResourceFileWriter.cpp

 }
 
 Expected<std::unique_ptr<MemoryBuffer>>
 ResourceFileWriter::loadFile(StringRef File) const {
   SmallString<128> Path;
   SmallString<128> Cwd;
   std::unique_ptr<MemoryBuffer> Result;
 
+  // 0. The file path is absolute and the file exists.
+  if (sys::path::is_absolute(File))
+    return errorOrToExpected(MemoryBuffer::getFile(File, -1, false));
+
   // 1. The current working directory.
   sys::fs::current_path(Cwd);
   Path.assign(Cwd.begin(), Cwd.end());
   sys::path::append(Path, File);
   if (sys::fs::exists(Path))
     return errorOrToExpected(MemoryBuffer::getFile(Path, -1, false));
 
   // 2. The directory of the input resource file, if it is different from the
-  // current
-  //    working directory.
+  // current working directory.
   StringRef InputFileDir = sys::path::parent_path(Params.InputFilePath);
   Path.assign(InputFileDir.begin(), InputFileDir.end());
   sys::path::append(Path, File);
   if (sys::fs::exists(Path))
     return errorOrToExpected(MemoryBuffer::getFile(Path, -1, false));
 
   // 3. All of the include directories specified on the command line.
   for (StringRef ForceInclude : Params.Include) {