Add a code fix for adding missing seq before {…}

src/FsAutoComplete/CodeFixes/AddMissingSeq.fs

@@ -0,0 +1,96 @@
+module FsAutoComplete.CodeFix.AddMissingSeq
+
+open FSharp.Compiler.Symbols
+open FSharp.Compiler.Syntax
+open FSharp.Compiler.Text
+open FsToolkit.ErrorHandling
+open Ionide.LanguageServerProtocol.Types
+open FsAutoComplete.CodeFix.Types
+open FsAutoComplete
+open FsAutoComplete.LspHelpers
+
+let title = "Add missing 'seq'"
+
+let fix
+  (getParseResultsForFile: GetParseResultsForFile)
+  : CodeFix =
+  Run.ifDiagnosticByCode (Set.ofList [ "3873"; "740" ]) (fun _ codeActionParams ->
+    asyncResult {
+      // Most code fixes have some general setup.
+      // We initially want to detect the state of the current code and whether we can propose any text edits to the user.
+
+      let fileName = codeActionParams.TextDocument.GetFilePath() |> Utils.normalizePath
+      // The converted LSP start position to an FCS start position.
+      let fcsPos = protocolPosToPos codeActionParams.Range.Start
+      // The syntax tree and typed tree, current line and sourceText of the current file.
+      let! (parseAndCheckResults:ParseAndCheckResults, _line:string, sourceText:IFSACSourceText) =
+        getParseResultsForFile fileName fcsPos
+
+      // The syntax tree can be an intimidating set of types to work with.
+      // It is a tree structure but it consists out of many different types.
+      // See https://fsharp.github.io/fsharp-compiler-docs/reference/fsharp-compiler-syntax.html
+      // It can be useful to inspect a syntax tree via a code sample using https://fsprojects.github.io/fantomas-tools/#/ast
+      // For example `let a b c = ()` in
+      // https://fsprojects.github.io/fantomas-tools/#/ast?data=N4KABGBEAmCmBmBLAdrAzpAXFSAacUiaAYmolmPAIYA2as%2BEkAxgPZwWQ2wAuYVYAEZhmYALxgAFAEo8BSLAAeAByrJoFHgCcArrBABfIA
+      // Let's say we want to find the (FCS) range for identifier `a` if the user's cursor is inside the function name.
+      // We will query the syntax tree to verify this is the case.
+      let maybeCERange =
+        (fcsPos, parseAndCheckResults.GetParseResults.ParseTree)
+        ||> ParsedInput.tryPick (fun _path node ->
+          match node with
+          // We know that `a` will be part of a `SynPat.LongIdent`
+          // This was visible in the online tool.
+          | SyntaxNode.SynExpr(SynExpr.ComputationExpr _) as e when
+            // When our code fix operates on the user's code there is no way of knowing what will be inside the syntax tree.
+            // So we need to be careful and verify that the pattern is indeed matching the position of the cursor.
+            Range.rangeContainsPos e.Range fcsPos
+            ->
+            Some  e.Range
+          | _ -> None)
+
+      match maybeCERange with
+      | None ->
+        // The cursor is not in a position we are interested in.
+        // This code fix should not trigger any suggestions so we return an empty list.
+        return []
+      | Some ceExprRange ->
+        // It turns out we are inside a let binding and we have the range of the function name.
+        // Just for fun, we want to detect if there is a matching typed tree symbol present for the current name.
+        // We could have passed the function name from the syntax visitor, instead will we grab it from the source text.
+        let! sourceText = sourceText.GetText ceExprRange
+        // FSharpSymbolUse is reflecting the typed tree.
+        // See https://fsharp.github.io/fsharp-compiler-docs/fcs/symbols.html
+        // let symbolUse: FSharp.Compiler.CodeAnalysis.FSharpSymbolUse option =
+        //   parseAndCheckResults.GetCheckResults.GetSymbolUseAtLocation(ceExprRange.EndLine, ceExprRange.EndColumn, line, [ functionName ])
+
+        // let hasCEExprDefinitionSymbol =
+        //   match symbolUse with
+        //   | None -> false
+        //   | Some symbolUse ->
+        //     // We want to verify the found symbol is indeed a definition of a function
+        //     match symbolUse.Symbol with
+        //     | :? FSharpMemberOrFunctionOrValue -> true
+        //     | _ -> false
+
+        // if not hasCEExprDefinitionSymbol then
+        //   return []
+        // else
+          // Return a list of Fix records for when the code fix is applicable.
+        return [
+            {
+                  SourceDiagnostic = None
+                  Title = title
+                  File = codeActionParams.TextDocument
+                  // Based on conditional logic, you typically want to suggest a text edit to the user.
+                  Edits = [|
+                    {
+                      // When dealing with FCS, we typically want to use the FCS flavour of range.
+                      // However, to interact correctly with the LSP protocol, we need to return an LSP range.
+                      Range = fcsRangeToLsp ceExprRange
+                      NewText = $"seq { sourceText }"
+                     }
+                  |]
+                  Kind = FixKind.Fix
+            }
+          ]
+    })

src/FsAutoComplete/CodeFixes/AddMissingSeq.fsi

@@ -0,0 +1,6 @@
+module FsAutoComplete.CodeFix.AddMissingSeq
+
+open FsAutoComplete.CodeFix.Types
+
+val title: string
+val fix: getParseResultsForFile: GetParseResultsForFile -> CodeFix

src/FsAutoComplete/LspServers/AdaptiveServerState.fs

@@ -2194,7 +2194,8 @@ type AdaptiveState
          AddBindingToSignatureFile.fix forceGetFSharpProjectOptions tryGetParseAndCheckResultsForFile
          ReplaceLambdaWithDotLambda.fix getLanguageVersion tryGetParseAndCheckResultsForFile
          IgnoreExpression.fix tryGetParseAndCheckResultsForFile
-         ExprTypeMismatch.fix tryGetParseAndCheckResultsForFile |])
+         ExprTypeMismatch.fix tryGetParseAndCheckResultsForFile
+         AddMissingSeq.fix tryGetParseAndCheckResultsForFile |])
 
   let forgetDocument (uri: DocumentUri) =
     async {
@@ -2541,4 +2542,4 @@ type AdaptiveState
     member this.Dispose() =
 
       traceNotifications |> Option.iter (dispose)
-      disposables.Dispose()
+      disposables.Dispose()

test/FsAutoComplete.Tests.Lsp/CodeFixTests/AddMissingSeqTests.fs

@@ -0,0 +1,60 @@
+module private FsAutoComplete.Tests.CodeFixTests.AddMissingSeqTests
+
+open Expecto
+open Helpers
+open Utils.ServerTests
+open Utils.CursorbasedTests
+open FsAutoComplete.CodeFix
+
+let tests state =
+  serverTestList (nameof AddMissingSeq) state defaultConfigDto None (fun server ->
+    [ let selectCodeFix = CodeFix.withTitle AddMissingSeq.title
+
+      testCaseAsync "FS3873 — Adds missing seq before { start..step..finish } top level"
+      <| CodeFix.check
+        server
+        "$0{ 1..10..20 }"
+        Diagnostics.acceptAll
+        selectCodeFix
+        "seq { 1..10..20 }"
+
+      testCaseAsync "FS3873 — Adds missing seq before { start..step..finish } binding"
+      <| CodeFix.check
+        server
+        "let xs = $0{ 1..10..20 }"
+        Diagnostics.acceptAll
+        selectCodeFix
+        "let xs = seq { 1..10..20 }"
+
+      testCaseAsync "FS3873 — Adds missing seq before { start..finish } top level"
+      <| CodeFix.check
+        server
+        "$0{ 1..10 }"
+        Diagnostics.acceptAll
+        selectCodeFix
+        "seq { 1..10 }"
+
+      testCaseAsync "FS3873 — Adds missing seq before { start..finish } binding"
+      <| CodeFix.check
+        server
+        "let xs = $0{ 1..10 }"
+        Diagnostics.acceptAll
+        selectCodeFix
+        "let xs = seq { 1..10 }"
+
+      testCaseAsync "FS0740 — Adds missing seq before { x; y } top level"
+      <| CodeFix.check
+        server
+        "$0{ 1;10 }"
+        Diagnostics.acceptAll
+        selectCodeFix
+        "seq { 1;10 }"
+
+      testCaseAsync "FS0740 — Adds missing seq before { x; y } binding"
+      <| CodeFix.check
+        server
+        "let xs = $0{ 1;10 }"
+        Diagnostics.acceptAll
+        selectCodeFix
+        "let xs = seq { 1;10 }"
+    ])

test/FsAutoComplete.Tests.Lsp/CodeFixTests/Tests.fs

@@ -3605,4 +3605,5 @@ let tests textFactory state =
       AddBindingToSignatureFileTests.tests state
       ReplaceLambdaWithDotLambdaTests.tests state
       IgnoreExpressionTests.tests state
-      ExprTypeMismatchTests.tests state ]
+      ExprTypeMismatchTests.tests state
+      AddMissingSeqTests.tests state ]