Missing reference in Transparent Compiler

src/Compiler/Driver/ParseAndCheckInputs.fs

@@ -1488,6 +1488,7 @@ let CheckOneInputWithCallback
     : Cancellable<Finisher<NodeToTypeCheck, TcState, PartialResult>> =
     cancellable {
         try
+            printfn "About to type-check %A" node
             CheckSimulateException tcConfig
 
             let m = input.Range

tests/FSharp.Compiler.Service.Tests/FSharp.Compiler.Service.Tests.fsproj

@@ -98,6 +98,7 @@
       <Link>PrettyNaming.fs</Link>
     </Compile>
     <Compile Include="TooltipTests.fs" />
+    <Compile Include="TransparentTests.fs" />
     <Compile Include="..\service\Program.fs">
       <Link>Program.fs</Link>
     </Compile>

tests/FSharp.Compiler.Service.Tests/TransparentTests.fs

@@ -0,0 +1,99 @@
+module FSharp.Compiler.Service.Tests.TransparentTests
+
+open FSharp.Compiler.CodeAnalysis
+open FSharp.Compiler.Text
+open NUnit.Framework
+
+// The goal of this test is to raise awareness of how the Transparent Compiler should be behave when only the dependent files are being type-checked.
+
+[<Test>]
+let ``Establish link`` () =
+    let checker = FSharpChecker.Create(useTransparentCompiler = true)
+
+    let args = mkProjectCommandLineArgsSilent ("Project.dll", Array.empty)
+
+    // In the sample project we have two files who are not linked to each other initially.
+    let options =
+        { checker.GetProjectOptionsFromCommandLineArgs("Project.fsproj", args) with
+            SourceFiles = [| "A.fs"; "B.fs" |] }
+
+    let content_Of_A =
+        """
+module Project.A
+
+type X =
+    {
+        Y : int
+    }
+"""
+
+    let content_Of_B_V1 =
+        """
+module Project.B
+
+let meh _ = ()
+"""
+
+    // We start to edit the second file and hope to use a type from the first file.
+    let content_Of_B_V2 =
+        """
+module Project.B
+
+let meh _ : X = ()
+"""
+
+    let getFileSnapShot useV1 _ fileName =
+        async {
+            return
+                { FileName = fileName
+                  Version = if useV1 || fileName <> "B.fs" then "1" else "2"
+                  GetSource =
+                    fun () ->
+                        task {
+                            match fileName with
+                            | "A.fs" -> return SourceText.ofString content_Of_A
+                            | "B.fs" -> return SourceText.ofString (if useV1 then content_Of_B_V1 else content_Of_B_V2)
+                            | _ -> return failwithf $"No source for %s{fileName}"
+                        } }
+        }
+
+    let projectSnapShot_Initial =
+        FSharpProjectSnapshot.FromOptions(options, getFileSnapShot true)
+        |> Async.RunImmediate
+
+    let unwrapCheckResult (_, checkResult) =
+        match checkResult with
+        | FSharpCheckFileAnswer.Aborted -> failwith "aborted"
+        | FSharpCheckFileAnswer.Succeeded checkFileResults -> checkFileResults
+
+    let initialCheckResult =
+        checker.ParseAndCheckFileInProject("B.fs", projectSnapShot_Initial)
+        |> Async.RunImmediate
+        |> unwrapCheckResult
+
+    Assert.True(Array.isEmpty initialCheckResult.Diagnostics)
+
+    // Now we start to edit the second file and introduce an unresolved type
+
+    let projectSnapShot_Subsequent =
+        FSharpProjectSnapshot.FromOptions(options, getFileSnapShot false)
+        |> Async.RunImmediate
+
+    let subsequentCheckResult =
+        checker.ParseAndCheckFileInProject("B.fs", projectSnapShot_Subsequent)
+        |> Async.RunImmediate
+        |> unwrapCheckResult
+
+    // After the second checker.ParseAndCheckFileInProject
+    // CheckOneInputWithCallback will still not have been called for A.fs
+    // This is understandable, as no link was established via the AST in both cases.
+
+    // This leads to `  B.fs(3, 13): [FS0039] The type 'X' is not defined.`
+    // And my main question is how editor will resolve the missing 'X' via an editor light bulb-like action?
+    // I don't know how the different editors deal with this today, but there might be a chance that they rely on all the files being type-checked.
+    // If this is the case, we should discuss this with the community.
+    let diagnostic =
+        subsequentCheckResult.Diagnostics
+        |> Array.find (fun diag -> diag.ErrorNumber = 39)
+
+    ()