Fix issue where a Windows path is being used

Make private ExtractToTempFile method accept Git path.

Author: jcansdale

src/GitHub.App/Services/PullRequestService.cs

@@ -62,7 +62,7 @@ public class PullRequestService : IPullRequestService, IStaticReviewFileMap
         readonly IUsageTracker usageTracker;
 
         readonly IDictionary<string, (string commitId, string repoPath)> tempFileMappings;
-   
+
         [ImportingConstructor]
         public PullRequestService(
             IGitClient gitClient,
@@ -751,20 +751,20 @@ public async Task<string> ExtractToTempFile(
             Encoding encoding)
         {
             var tempFilePath = CalculateTempFileName(relativePath, commitSha, encoding);
+            var gitPath = relativePath.TrimStart('/').Replace('\\', '/');
 
             if (!File.Exists(tempFilePath))
             {
                 using (var repo = gitService.GetRepository(repository.LocalPath))
                 {
                     var remote = await gitClient.GetHttpRemote(repo, "origin");
-                    await ExtractToTempFile(repo, pullRequest.Number, commitSha, relativePath, encoding, tempFilePath);
+                    await ExtractToTempFile(repo, pullRequest.Number, commitSha, gitPath, encoding, tempFilePath);
                 }
             }
 
-            lock (this.tempFileMappings)
+            lock (tempFileMappings)
             {
-                string gitRelativePath = relativePath.TrimStart('/').Replace('\\', '/');
-                this.tempFileMappings[CanonicalizeLocalFilePath(tempFilePath)] = (commitSha, gitRelativePath);
+                tempFileMappings[CanonicalizeLocalFilePath(tempFilePath)] = (commitSha, gitPath);
             }
 
             return tempFilePath;
@@ -894,22 +894,24 @@ async Task ExtractToTempFile(
             IRepository repo,
             int pullRequestNumber,
             string commitSha,
-            string relativePath,
+            string path,
             Encoding encoding,
             string tempFilePath)
         {
+            Guard.ArgumentIsGitPath(path, nameof(path));
+
             string contents;
 
             try
             {
-                contents = await gitClient.ExtractFile(repo, commitSha, relativePath) ?? string.Empty;
+                contents = await gitClient.ExtractFile(repo, commitSha, path) ?? string.Empty;
             }
             catch (FileNotFoundException)
             {
                 var pullHeadRef = $"refs/pull/{pullRequestNumber}/head";
                 var remote = await gitClient.GetHttpRemote(repo, "origin");
                 await gitClient.Fetch(repo, remote.Name, commitSha, pullHeadRef);
-                contents = await gitClient.ExtractFile(repo, commitSha, relativePath) ?? string.Empty;
+                contents = await gitClient.ExtractFile(repo, commitSha, path) ?? string.Empty;
             }
 
             Directory.CreateDirectory(Path.GetDirectoryName(tempFilePath));