private static string GetRelativePath(string relativeTo, string path, StringComparison comparisonType) { if (string.IsNullOrEmpty(relativeTo)) { throw new ArgumentNullException(nameof(relativeTo)); } if (string.IsNullOrWhiteSpace(path)) { throw new ArgumentNullException(nameof(path)); } Debug.Assert(comparisonType == StringComparison.Ordinal || comparisonType == StringComparison.OrdinalIgnoreCase); relativeTo = GetFullPath(relativeTo); path = GetFullPath(path); // Need to check if the roots are different- if they are we need to return the "to" path. if (!PathInternal.AreRootsEqual(relativeTo, path, comparisonType)) { return(path); } int commonLength = PathInternal.GetCommonPathLength(relativeTo, path, ignoreCase: comparisonType == StringComparison.OrdinalIgnoreCase); // If there is nothing in common they can't share the same root, return the "to" path as is. if (commonLength == 0) { return(path); } // Trailing separators aren't significant for comparison int relativeToLength = relativeTo.Length; if (PathInternal.EndsInDirectorySeparator(relativeTo)) { relativeToLength--; } bool pathEndsInSeparator = PathInternal.EndsInDirectorySeparator(path); int pathLength = path.Length; if (pathEndsInSeparator) { pathLength--; } // If we have effectively the same path, return "." if (relativeToLength == pathLength && commonLength >= relativeToLength) { return("."); } // We have the same root, we need to calculate the difference now using the // common Length and Segment count past the length. // // Some examples: // // C:\Foo C:\Bar L3, S1 -> ..\Bar // C:\Foo C:\Foo\Bar L6, S0 -> Bar // C:\Foo\Bar C:\Bar\Bar L3, S2 -> ..\..\Bar\Bar // C:\Foo\Foo C:\Foo\Bar L7, S1 -> ..\Bar StringBuilder sb = StringBuilderCache.Acquire(Math.Max(relativeTo.Length, path.Length)); // Add parent segments for segments past the common on the "from" path if (commonLength < relativeToLength) { sb.Append(PathInternal.ParentDirectoryPrefix); for (int i = commonLength; i < relativeToLength; i++) { if (PathInternal.IsDirectorySeparator(relativeTo[i])) { sb.Append(PathInternal.ParentDirectoryPrefix); } } } else if (PathInternal.IsDirectorySeparator(path[commonLength])) { // No parent segments and we need to eat the initial separator // (C:\Foo C:\Foo\Bar case) commonLength++; } // Now add the rest of the "to" path, adding back the trailing separator int count = pathLength - commonLength; if (pathEndsInSeparator) { count++; } sb.Append(path, commonLength, count); return(StringBuilderCache.GetStringAndRelease(sb)); }