[Fix] Allow missing solution file

src/ProjectDiff.Core/Entrypoints/SolutionProjectGraphEntryPointProvider.cs

@@ -26,8 +26,8 @@ CancellationToken cancellationToken
     {
         if (!fs.FileExists(_solution.FullName))
         {
-            _logger.LogError("Could not find the solution file {SolutionFile} in the file system", _solution.FullName);
-            throw new FileNotFoundException("Could not find the solution file in the file system", _solution.FullName);
+            _logger.LogWarning("Could not find the solution file {SolutionFile} in the file system, assuming empty", _solution.FullName);
+            return [];
         }
 
         await using var stream = fs.GetFileStream(

src/dotnet-proj-diff/ProjectDiffCommand.cs

@@ -35,10 +35,6 @@ public sealed class ProjectDiffCommand : RootCommand
                 {
                     x.AddError("{x.Argument.Name} must be specified");
                 }
-                else if (!f.Exists)
-                {
-                    x.AddError($"File '{f.FullName}' does not exist.");
-                }
                 else if (f.Extension is not (".sln" or ".slnx"))
                 {
                     x.AddError($"File '{f.FullName}' is not a valid sln file.");

test/ProjectDiff.Tests/Tool/ProjectDiffTests.NewSolutionMarksProjectAsAdded.verified.txt

@@ -0,0 +1,7 @@
+[
+  {
+    path: Sample/Sample.csproj,
+    name: Sample,
+    status: Added
+  }
+]

test/ProjectDiff.Tests/Tool/ProjectDiffTests.cs

@@ -337,6 +337,24 @@ public async Task DetectsAddedProjectsWithDirectoryScan()
         await VerifyJson(output);
     }
 
+    [Fact]
+    public async Task NewSolutionMarksProjectAsAdded()
+    {
+
+        using var repo = await TestRepository.SetupAsync(static async r =>
+            {
+                r.CreateDirectory("Sample");
+                r.CreateProject("Sample/Sample.csproj");
+                await r.WriteAllTextAsync("Sample/MyClass.cs", "// Some content");
+            }
+        );
+
+        var sln = await repo.CreateSolutionAsync("Sample.sln", sln => sln.AddProject("Sample/Sample.csproj"));
+
+        var output = await ExecuteAndReadStdout(repo, $"--solution={sln}");
+        await VerifyJson(output);
+    }
+
     private static async Task<string> ExecuteAndReadStdout(
         TestRepository repository,
         params string[] args