[unix] Fix rebuilds caused by resx containing fileref with windows pa…

…th (dotnet#44)

When running on !windows, if a resx contains a fileRef like ..

```
  <data name="TextFile1" type="System.Resources.ResXFileRef, System.Windows.Forms">
	<value>..\Resources\TextFile1.txt;System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089;Windows-1252</value>
  </data>
```

.. with the path containing backslashes, then we end up treating the whole
thing as filename and thus subsequent checks for file changes etc fail. This
causes the resx to be processed every time `GenerateResource` task is run, which
can cause costly rebuilds.

Issue: mono/mono#7184

src/Tasks.UnitTests/GenerateResource_Tests.cs

@@ -3135,6 +3135,55 @@ public void ResxValueNewlines(string newline)
                 }
             }
         }
+
+        [Fact]
+        public void RebuildsInPresenceOfFileRefWithWindowsPath()
+        {
+            using (var env = TestEnvironment.Create())
+            {
+                env.SetCurrentDirectory(env.DefaultTestDirectory.FolderPath);
+
+                string fileRef = "<data name=\"TextFile1\" type=\"System.Resources.ResXFileRef, System.Windows.Forms\">" +
+                                $"<value>.\\tmp_dir\\test_file.txt;System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089;Windows-1252</value></data>";
+
+                env.CreateFile(
+                        env.CreateFolder(Path.Combine(env.DefaultTestDirectory.FolderPath, "tmp_dir")),
+                        "test_file.txt", "xyz");
+
+                string resxFile = env.CreateFile("test.resx").Path;
+                Utilities.WriteTestResX(false, null, fileRef, false, resxFile);
+
+                GenerateResource ExecuteTask()
+                {
+                    GenerateResource task = Utilities.CreateTask(_output);
+                    task.Sources = new ITaskItem[] { new TaskItem(resxFile) };
+
+                    Utilities.ExecuteTask(task);
+
+                    string outputResourceFile = task.OutputResources[0].ItemSpec;
+                    Assert.Equal(Path.GetExtension(outputResourceFile), ".resources");
+                    outputResourceFile = task.FilesWritten[0].ItemSpec;
+                    Assert.Equal(Path.GetExtension(outputResourceFile), ".resources");
+
+                    return task;
+                }
+
+                GenerateResource t = ExecuteTask();
+                string resourcesFile = t.OutputResources[0].ItemSpec;
+                DateTime initialWriteTime = File.GetLastWriteTime(resourcesFile);
+
+                // fs granularity on HFS is 1 sec!
+                System.Threading.Thread.Sleep(NativeMethodsShared.IsOSX ? 1000 : 100);
+
+                // Rebuild, it shouldn't regen .resources file since the sources
+                // haven't changed
+                t = ExecuteTask();
+                resourcesFile = t.OutputResources[0].ItemSpec;
+
+                Assert.False(Utilities.FileUpdated(resourcesFile, initialWriteTime));
+            }
+        }
+
     }
 }
 

src/Tasks/ResGenDependencies.cs

@@ -266,7 +266,7 @@ internal static string[] GetLinkedFiles(string filename, string baseLinkedFileDi
                         {
                             ResXFileRef resxFileRef = ((ResXDataNode)dictEntry.Value).FileRef;
                             if (resxFileRef != null)
-                                retVal.Add(resxFileRef.FileName);
+                                retVal.Add(FileUtilities.MaybeAdjustFilePath(resxFileRef.FileName));
                         }
                     }
                 }