traceutils: add traceutils

The implementation of TRACE2 tracing will require truncation of long file
names just as TRACE does. To prepare for this, move this logic out of the
TRACE class and into its own method in a new static TraceUtils class.
Additionally, add a unit test to validate this logic.

Author: Lessley Dennington

src/shared/Core.Tests/TraceUtilsTests.cs

@@ -0,0 +1,18 @@
+using System;
+using System.IO;
+using System.Text;
+using Xunit;
+
+namespace GitCredentialManager.Tests;
+
+public class TraceUtilsTests
+{
+    [Theory]
+    [InlineData("/foo/bar/baz/boo", 10, "...baz/boo")]
+    [InlineData("thisfileshouldbetruncated", 12, "...truncated")]
+    public void FormatSource_ReturnsExpectedSourceValues(string path, int sourceColumnMaxWidth, string expectedSource)
+    {
+        string actualSource = TraceUtils.FormatSource(path, sourceColumnMaxWidth);
+        Assert.Equal(actualSource, expectedSource);
+    }
+}

src/shared/Core/Trace.cs

@@ -307,22 +307,7 @@ private static string FormatText(string message, string filePath, int lineNumber
 
             if (source.Length > sourceColumnMaxWidth)
             {
-                int idx = 0;
-                int maxlen = sourceColumnMaxWidth - 3;
-                int srclen = source.Length;
-
-                while (idx >= 0 && (srclen - idx) > maxlen)
-                {
-                    idx = source.IndexOf('\\', idx + 1);
-                }
-
-                // If we cannot find a path separator which allows the path to be long enough, just truncate the file name
-                if (idx < 0)
-                {
-                    idx = srclen - maxlen;
-                }
-
-                source = "..." + source.Substring(idx);
+                source = TraceUtils.FormatSource(source, sourceColumnMaxWidth);
             }
 
             // Git's trace format is "{timestamp,-15} {source,-23} trace: {details}"

src/shared/Core/TraceUtils.cs

@@ -0,0 +1,24 @@
+namespace GitCredentialManager;
+
+public static class TraceUtils
+{
+    public static string FormatSource(string source, int sourceColumnMaxWidth)
+    {
+        int idx = 0;
+        int maxlen = sourceColumnMaxWidth - 3;
+        int srclen = source.Length;
+
+        while (idx >= 0 && (srclen - idx) > maxlen)
+        {
+            idx = source.IndexOf('\\', idx + 1);
+        }
+
+        // If we cannot find a path separator which allows the path to be long enough, just truncate the file name
+        if (idx < 0)
+        {
+            idx = srclen - maxlen;
+        }
+
+        return "..." + source.Substring(idx);
+    }
+}