Rebase absolute URIs relative to the closest enclosing repo root.

src/Sarif/ExternalProcess.cs

@@ -17,7 +17,7 @@ public class ExternalProcess
 
         public ExternalProcess(
             string workingDirectory,
-            string fileName,
+            string exePath,
             string arguments,
             IConsoleCapture stdOut = null,
             int[] acceptableReturnCodes = null)
@@ -26,7 +26,7 @@ public ExternalProcess(
 
             ProcessStartInfo psi = new ProcessStartInfo();
 
-            psi.FileName = fileName;
+            psi.FileName = exePath;
             psi.Arguments = arguments;
             psi.WorkingDirectory = workingDirectory;
 

src/Sarif/GitHelper.cs

@@ -0,0 +1,192 @@
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Threading;
+
+namespace Microsoft.CodeAnalysis.Sarif
+{
+    public class GitHelper : IDisposable
+    {
+        public static readonly GitHelper Default = new GitHelper();
+
+        public delegate string ProcessRunner(string workingDirectory, string exePath, string arguments);
+
+        private static readonly ProcessRunner DefaultProcessRunner =
+            (string workingDirectory, string exePath, string arguments)
+                => new ExternalProcess(workingDirectory, exePath, arguments, stdOut: null, acceptableReturnCodes: null).StdOut.Text;
+
+        private readonly IFileSystem fileSystem;
+        private readonly ProcessRunner processRunner;
+        private readonly ReaderWriterLockSlim cacheLock = new ReaderWriterLockSlim();
+
+        internal static readonly string s_expectedGitExePath = Environment.ExpandEnvironmentVariables(@"%ProgramFiles%\Git\cmd\git.exe");
+
+        // A cache that maps directory names to the root directory of the repository, if any, that
+        // contains them.
+        //
+        // The case-insensitive key comparison is correct on Windows systems and wrong on Linux/MacOS.
+        // This is a general problem in the SDK. See /~https://github.com/microsoft/sarif-sdk/issues/1736,
+        // "File path comparisons are not file-system-appropriate".
+        //
+        // The cache is internal rather than private so that tests can verify that the cache is
+        // being populated appropriately. It's not so easy to verify that it's being _used_
+        // appropriately.
+        internal readonly Dictionary<string, string> directoryToRepoRootPathDictionary = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
+
+        public bool IsRepositoryRoot(string repositoryPath) => this.fileSystem.DirectoryExists(Path.Combine(repositoryPath, ".git"));
+
+        public GitHelper(IFileSystem fileSystem = null, ProcessRunner processRunner = null)
+        {
+            this.fileSystem = fileSystem ?? new FileSystem();
+            this.processRunner = processRunner ?? DefaultProcessRunner;
+
+            GitExePath = GetGitExePath();
+        }
+
+        public string GitExePath { get; }
+
+        public Uri GetRemoteUri(string repoPath)
+        {
+            string uriText = GetSimpleGitCommandOutput(
+                    repoPath,
+                    args: $"remote get-url origin");
+
+            return uriText == null
+                ? null
+                : new Uri(uriText, UriKind.Absolute);
+        }
+
+        public string GetCurrentCommit(string repoPath)
+        {
+            return GetSimpleGitCommandOutput(
+                repoPath,
+                args: "rev-parse --verify HEAD");
+        }
+
+        public void Checkout(string repoPath, string commitSha)
+        {
+            GetSimpleGitCommandOutput(
+                repoPath,
+                args: $"checkout {commitSha}");
+        }
+
+        private string GetGitExePath()
+            => this.fileSystem.FileExists(s_expectedGitExePath) ? s_expectedGitExePath : null;
+
+        public string GetCurrentBranch(string repoPath)
+        {
+            return GetSimpleGitCommandOutput(
+                repoPath,
+                args: "rev-parse --abbrev-ref HEAD");
+        }
+
+        private string GetSimpleGitCommandOutput(string repositoryPath, string args)
+        {
+            string gitPath = this.GitExePath;
+
+            if (gitPath == null || !IsRepositoryRoot(repositoryPath))
+            {
+                return null;
+            }
+
+            string stdOut = this.processRunner(
+                workingDirectory: repositoryPath,
+                exePath: gitPath,
+                arguments: args);
+
+            return TrimNewlines(stdOut);
+        }
+
+        private static string TrimNewlines(string text) => text
+                .Replace("\r", string.Empty)
+                .Replace("\n", string.Empty);
+
+        public string GetRepositoryRoot(string path, bool useCache = true)
+        {
+            // The "default" instance won't let you use the cache, to prevent independent users
+            // from interfering with each other.
+            if (useCache && object.ReferenceEquals(this, Default))
+            {
+                throw new ArgumentException(SdkResources.GitHelperDefaultInstanceDoesNotPermitCaching, nameof(useCache));
+            }
+
+            if (this.fileSystem.FileExists(path))
+            {
+                path = Path.GetDirectoryName(path);
+            }
+
+            string repoRootPath;
+            if (useCache)
+            {
+                cacheLock.EnterReadLock();
+                try
+                {
+                    if (directoryToRepoRootPathDictionary.TryGetValue(path, out repoRootPath))
+                    {
+                        return repoRootPath;
+                    }
+                }
+                finally
+                {
+                    cacheLock.ExitReadLock();
+                }
+            }
+
+            repoRootPath = path;
+            while (!string.IsNullOrEmpty(repoRootPath) && !IsRepositoryRoot(repoRootPath))
+            {
+                repoRootPath = Path.GetDirectoryName(repoRootPath);
+            }
+
+            // It's important to terminate with a slash because the value returned from this method
+            // will be used to create an absolute URI on which MakeUriRelative will be called. For
+            // example, suppose this method returns @"C:\\dev\sarif-sdk\". The caller will use it
+            // to create an absolute URI (call it repoRootUri) "file:///C:/dev/sarif-sdk/". The
+            // caller will use this URI to "rebase" another URI (call it artifactUri) such as
+            // "file:///C:/dev/sarif-sdk/src/Sarif". The caller will do that by calling
+            // repoRootUri.MakeRelativeUri(artifactUri). It turns out that unless repoRootUri
+            // ends with a slash, this call will return "sarif-sdk/src/Sarif" rather than the
+            // expected (at least for me) "src/Sarif".
+            if (repoRootPath != null && !repoRootPath.EndsWith(@"\")) { repoRootPath += @"\"; }
+
+            if (useCache)
+            {
+                cacheLock.EnterWriteLock();
+                try
+                {
+                    // Add whatever we found to the cache, even if it was null (in which case we now know
+                    // that this path isn't under source control).
+                    directoryToRepoRootPathDictionary.Add(path, repoRootPath);
+                }
+                finally
+                {
+                    cacheLock.ExitWriteLock();
+                }
+            }
+
+            return repoRootPath;
+        }
+
+        /// <summary>
+        /// Dispose pattern as required by style
+        /// </summary>
+        /// <param name="disposing">Set to true to actually dispose</param>
+        protected virtual void Dispose(bool disposing)
+        {
+            if (disposing)
+            {
+                cacheLock.Dispose();
+            }
+        }
+
+        /// <inheritdoc/>
+        public void Dispose()
+        {
+            Dispose(true);
+            GC.SuppressFinalize(this);
+        }
+    }
+}