Fix off-by-one errors by also handling attributes in top-level modules

Co-authored-by: T-Gro <46543583+T-Gro@users.noreply.github.com>

Author: Copilot

src/Compiler/Service/ServiceParsedInputOps.fs

@@ -2428,7 +2428,7 @@ module ParsedInput =
             List.iter (walkSynModuleOrNamespace []) file.Contents
 
         and walkSynModuleOrNamespace (parent: LongIdent) modul =
-            let (SynModuleOrNamespace(longId = ident; kind = kind; decls = decls; range = range)) =
+            let (SynModuleOrNamespace(longId = ident; kind = kind; decls = decls; range = range; trivia = trivia)) =
                 modul
 
             if range.EndLine >= currentLine then
@@ -2444,7 +2444,14 @@ module ParsedInput =
 
                 let fullIdent = parent @ ident
 
-                let startLine = if isModule then range.StartLine else range.StartLine - 1
+                // Use trivia to get the actual module/namespace keyword line, which excludes attributes
+                let startLine =
+                    match trivia.LeadingKeyword with
+                    | SynModuleOrNamespaceLeadingKeyword.Module moduleRange
+                    | SynModuleOrNamespaceLeadingKeyword.Namespace moduleRange -> moduleRange.StartLine
+                    | SynModuleOrNamespaceLeadingKeyword.None ->
+                        // No keyword (implicit module), use range.StartLine
+                        if isModule then range.StartLine else range.StartLine - 1
 
                 let scopeKind =
                     match isModule, parent with

vsintegration/src/FSharp.Editor/CodeFixes/AddOpenCodeFixProvider.fs

@@ -31,15 +31,27 @@ type internal AddOpenCodeFixProvider [<ImportingConstructor>] (assemblyContentPr
         }
 
     // With the fix in ServiceParsedInputOps, the InsertionContext now correctly
-    // points to the line after the module keyword (or namespace), so we can trust it.
+    // points to the line after the module/namespace keyword (excluding attributes).
+    // However, we still need to handle implicit top-level modules and nested modules.
     let getOpenDeclaration (sourceText: SourceText) (ctx: InsertionContext) (ns: string) =
         // insertion context counts from 2, make the world sane
         let insertionLineNumber = ctx.Pos.Line - 2
         let margin = String(' ', ctx.Pos.Column)
 
         let startLineNumber, openDeclaration =
             match ctx.ScopeKind with
-            | ScopeKind.TopModule -> insertionLineNumber + 2, $"{margin}open {ns}{br}{br}"
+            | ScopeKind.TopModule ->
+                match sourceText.Lines[insertionLineNumber].ToString().Trim() with
+
+                // explicit top level module
+                | line when line.StartsWith "module" && not (line.EndsWith "=") -> insertionLineNumber + 2, $"{margin}open {ns}{br}{br}"
+
+                // nested module, shouldn't be here
+                | line when line.StartsWith "module" -> insertionLineNumber, $"{margin}open {ns}{br}{br}"
+
+                // implicit top level module
+                | _ -> insertionLineNumber, $"{margin}open {ns}{br}{br}"
+
             | ScopeKind.Namespace -> insertionLineNumber + 3, $"{margin}open {ns}{br}{br}"
             | ScopeKind.NestedModule -> insertionLineNumber + 2, $"{margin}open {ns}{br}{br}"
             | ScopeKind.OpenDeclaration -> insertionLineNumber + 1, $"{margin}open {ns}{br}"