File type check on macosx (if file is "dylib") (#4206)

* added file type check on macosx (if file is "dylib" AKA has "dylib" extension)

* Added unit test and fixes for empty path

* refactored to test Path and suffix ("extension") GetExtension throws

* inclusively covering all PE extensions (not excluding dylib only)

* fixing tests accoring new logic (reverting to old)

* style fixes

* Update src/Cake.Core/IO/FileExtensions.cs

Co-authored-by: Mattias Karlsson <mattias@devlead.se>

* Add `.` to extensions

Co-authored-by: Mattias Karlsson <mattias@devlead.se>

---------

Co-authored-by: Mattias Karlsson <mattias@devlead.se>

Author: moljac

src/Cake.Core.Tests/Unit/IO/FileExtensionsTests.cs

@@ -297,6 +297,21 @@ public void Should_Return_False_When_File_Is_Not_A_Valid_PE()
                 // Then
                 Assert.False(FileExtensions.IsClrAssembly(file));
             }
+
+            [Fact]
+            public void Should_Return_False_When_File_Is_MacOS_MachO_dylib()
+            {
+                // Given
+                var file = Substitute.For<IFile>();
+
+                // When
+                file.Exists.Returns(true);
+                file.Path.Returns(new string("fullname.dylib"));
+                file.Length.Returns(_invalidPeBytes.Length);
+
+                // Then
+                Assert.False(FileExtensions.IsClrAssembly(file));
+            }
         }
     }
 }

src/Cake.Core/IO/FileExtensions.cs

@@ -116,6 +116,28 @@ public static bool IsClrAssembly(this IFile file)
                 return false;
             }
 
+            // Is known extension?
+            switch (file.Path?.GetExtension().ToLowerInvariant())
+            {
+                case ".dll":
+                case ".exe":
+                case ".sys":
+                case ".tsp":
+                case ".acm":
+                case ".ax":
+                case ".cpl":
+                case ".drv":
+                case ".efi":
+                case ".mui":
+                case ".ocx":
+                case ".scr":
+                case null:
+                    break;
+
+                default:
+                    return false;
+            }
+
             using (var fs = file.OpenRead())
             {
                 using (var reader = new System.IO.BinaryReader(fs))