Add a baseDirectory argument for LooksLikeUnixFilePath and ..

.. MaybeAdjustFilePath. The former checks if the first segment of the
path might be the name of an existent directory. This depends on the
CWD, but in some cases we might need to check this in a different
directory.

For example, project A initiates a build of project B, and while B is
being evaluated the CWD may not have been updated, but the paths in B's
project file are relative to B. So, the checks should be done in B's
directory.

This will be useful in an upcoming fix.

src/Shared/FileUtilities.cs

@@ -401,8 +401,10 @@ internal static string FixFilePath(string path)
         /// first segment exists and is a directory.
         /// Use a native shared method to massage file path. If the file is adjusted,
         /// that qualifies is as a path.
+        ///
+        /// @baseDirectory is just passed to LooksLikeUnixFilePath, to help with the check
         /// </summary>
-        internal static string MaybeAdjustFilePath(string value)
+        internal static string MaybeAdjustFilePath(string value, string baseDirectory="")
         {
             // Don't bother with arrays or properties or network paths, or those that
             // have no slashes.
@@ -436,15 +438,18 @@ internal static string MaybeAdjustFilePath(string value)
                 }
             }
 
-            return LooksLikeUnixFilePath(checkValue) ? newValue : value;
+            return LooksLikeUnixFilePath(checkValue, baseDirectory) ? newValue : value;
         }
 
         /// <summary>
         /// If on Unix, check if the string looks like a file path.
         /// The heuristic is if something resembles paths (contains slashes) check if the
         /// first segment exists and is a directory.
+        ///
+        /// If @baseDirectory is not null, then look for the first segment exists under
+        /// that
         /// </summary>
-        internal static bool LooksLikeUnixFilePath(string value)
+        internal static bool LooksLikeUnixFilePath(string value, string baseDirectory="")
         {
             if (!NativeMethodsShared.IsUnixLike)
             {
@@ -459,7 +464,7 @@ internal static bool LooksLikeUnixFilePath(string value)
                 firstSlash = value.Substring(1).IndexOf('/') + 1;
             }
 
-            if (firstSlash > 0 && Directory.Exists(value.Substring(0, firstSlash)))
+            if (firstSlash > 0 && Directory.Exists(Path.Combine(baseDirectory, value.Substring(0, firstSlash))))
             {
                 return true;
             }

src/Shared/UnitTests/FileUtilities_Tests.cs

@@ -849,6 +849,69 @@ public void PathDoesNotLookLikeUnixPathOnWindows()
             Assert.False(FileUtilities.LooksLikeUnixFilePath("/root"));
         }
 
+        [Fact]
+        [PlatformSpecific(Xunit.PlatformID.AnyUnix)]
+        public void RelativePathLooksLikeUnixPathOnUnixWithBaseDirectory()
+        {
+            string filePath = ObjectModelHelpers.CreateFileInTempProjectDirectory("first/second/file.txt", String.Empty);
+            string oldCWD = Directory.GetCurrentDirectory();
+
+            try
+            {
+                // <tmp_dir>/first
+                string firstDirectory = Path.GetDirectoryName(Path.GetDirectoryName(filePath));
+                string tmpDirectory = Path.GetDirectoryName(Path.GetDirectoryName(Path.GetDirectoryName(filePath)));
+
+                Directory.SetCurrentDirectory(tmpDirectory);
+
+                // We are in <tmp_dir> and second is not under that, so this will be false
+                Assert.False(FileUtilities.LooksLikeUnixFilePath("second/file.txt"));
+
+                // .. but if we have baseDirectory:firstDirectory, then it will be true
+                Assert.True(FileUtilities.LooksLikeUnixFilePath("second/file.txt", firstDirectory));
+            }
+            finally
+            {
+                if (filePath != null)
+                {
+                    File.Delete(filePath);
+                }
+                Directory.SetCurrentDirectory(oldCWD);
+            }
+        }
+
+        [Fact]
+        [PlatformSpecific(Xunit.PlatformID.AnyUnix)]
+        public void RelativePathMaybeAdjustFilePathWithBaseDirectory()
+        {
+            // <tmp_dir>/first/second/file.txt
+            string filePath = ObjectModelHelpers.CreateFileInTempProjectDirectory("first/second/file.txt", String.Empty);
+            string oldCWD = Directory.GetCurrentDirectory();
+
+            try
+            {
+                // <tmp_dir>/first
+                string firstDirectory = Path.GetDirectoryName(Path.GetDirectoryName(filePath));
+                string tmpDirectory = Path.GetDirectoryName(Path.GetDirectoryName(Path.GetDirectoryName(filePath)));
+
+                Directory.SetCurrentDirectory(tmpDirectory);
+
+                // We are in <tmp_dir> and second is not under that, so this won't convert
+                Assert.Equal("second\\file.txt", FileUtilities.MaybeAdjustFilePath("second\\file.txt"));
+
+                // .. but if we have baseDirectory:firstDirectory, then it will
+                Assert.Equal("second/file.txt", FileUtilities.MaybeAdjustFilePath("second\\file.txt", firstDirectory));
+            }
+            finally
+            {
+                if (filePath != null)
+                {
+                    File.Delete(filePath);
+                }
+                Directory.SetCurrentDirectory(oldCWD);
+            }
+        }
+
         private static string SystemSpecificAbsolutePath => FileUtilities.ExecutingAssemblyPath;