improve naming, add comments for added misoreded implementation scenario

Author: majocha

src/Compiler/Driver/GraphChecking/DependencyResolution.fs

@@ -236,8 +236,10 @@ let mkGraph (filePairs: FilePairMap) (files: FileInProject array) : Graph<FileIn
                 | None -> Array.empty
                 | Some sigIdx -> Array.singleton sigIdx
 
-            let wrongOrderSignature =
-                match filePairs.TryGetWrongOrderSignatureToImplementationIndex file.Idx with
+            // Add a link from signature files to their implementation files, if the implementation file comes before the signature file.
+            // This allows us to emit FS0238 (implementation already given).
+            let implementationGivenBeforeSignature =
+                match filePairs.TryGetOutOfOrderImplementationIndex file.Idx with
                 | None -> Array.empty
                 | Some idx -> Array.singleton idx
 
@@ -246,7 +248,7 @@ let mkGraph (filePairs: FilePairMap) (files: FileInProject array) : Graph<FileIn
                     yield! depsResult.FoundDependencies
                     yield! ghostDependencies
                     yield! signatureDependency
-                    yield! wrongOrderSignature
+                    yield! implementationGivenBeforeSignature
                 |]
                 |> Array.distinct
 

src/Compiler/Driver/GraphChecking/Types.fs

@@ -173,13 +173,14 @@ type internal FilePairMap(files: FileInProject array) =
             |> Option.map (fun (implFile: FileInProject) -> (sigFile.Idx, implFile.Idx)))
         |> Array.choose id
 
-    let goodPairs, wrongOrderPairs =
+    let goodPairs, misorderedPairs =
         pairs |> Array.partition (fun (sigIdx, implIdx) -> sigIdx < implIdx)
 
     let sigToImpl, implToSig = buildBiDirectionalMaps goodPairs
 
-    // Pairs where the signature file comes after the implementation file in the project order. We need to track them to report such errors.
-    let wrongOrder = wrongOrderPairs |> Map.ofArray
+    // Pairs where the signature file comes after the implementation file in the project order.
+    // We need to track them to report FS0238 (implementation already given).
+    let misordered = misorderedPairs |> Map.ofArray
 
     member x.GetSignatureIndex(implementationIndex: FileIndex) = Map.find implementationIndex implToSig
     member x.GetImplementationIndex(signatureIndex: FileIndex) = Map.find signatureIndex sigToImpl
@@ -195,7 +196,8 @@ type internal FilePairMap(files: FileInProject array) =
 
     member x.IsSignature(index: FileIndex) = Map.containsKey index sigToImpl
 
-    member x.TryGetWrongOrderSignatureToImplementationIndex(index: FileIndex) = wrongOrder |> Map.tryFind index
+    member x.TryGetOutOfOrderImplementationIndex(signatureIndex: FileIndex) =
+        misordered |> Map.tryFind signatureIndex
 
 /// Callback that returns a previously calculated 'Result and updates 'State accordingly.
 type internal Finisher<'Node, 'State, 'Result> = Finisher of node: 'Node * finisher: ('State -> 'Result * 'State)

src/Compiler/Driver/GraphChecking/Types.fsi

@@ -117,7 +117,9 @@ type internal FilePairMap =
     member HasSignature: implementationIndex: FileIndex -> bool
     member TryGetSignatureIndex: implementationIndex: FileIndex -> FileIndex option
     member IsSignature: index: FileIndex -> bool
-    member TryGetWrongOrderSignatureToImplementationIndex: index: FileIndex -> FileIndex option
+    /// Covers the case where the implementation file appears before the signature file in the project.
+    /// This is needed only to correctly trigger FS0238 (implementation already given).
+    member TryGetOutOfOrderImplementationIndex: signatureIndex: FileIndex -> FileIndex option
 
 /// Callback that returns a previously calculated 'Result and updates 'State accordingly.
 type internal Finisher<'Node, 'State, 'Result> = Finisher of node: 'Node * finisher: ('State -> 'Result * 'State)