Add code fix for adding missing seq before {…}

Author: brianrourkeboll

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

@@ -0,0 +1,79 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace Microsoft.VisualStudio.FSharp.Editor
+
+open System.Collections.Immutable
+open System.Composition
+open FSharp.Compiler.Syntax
+open FSharp.Compiler.Text
+open Microsoft.CodeAnalysis.CodeFixes
+open Microsoft.CodeAnalysis.Text
+open CancellableTasks
+
+[<Sealed>]
+[<ExportCodeFixProvider(FSharpConstants.FSharpLanguageName, Name = CodeFix.ChangeToUpcast); Shared>]
+type internal AddMissingSeqCodeFixProvider() =
+    inherit CodeFixProvider()
+
+    static let title = SR.AddMissingSeq()
+    static let fixableDiagnosticIds = ImmutableArray.Create("FS3873", "FS0740")
+
+    override _.FixableDiagnosticIds = fixableDiagnosticIds
+
+    override this.RegisterCodeFixesAsync context = context.RegisterFsharpFix this
+
+    override this.GetFixAllProvider() = this.RegisterFsharpFixAll()
+
+    interface IFSharpCodeFixProvider with
+        member _.GetCodeFixIfAppliesAsync context =
+            cancellableTask {
+                let! sourceText = context.GetSourceTextAsync()
+                let! parseFileResults = context.Document.GetFSharpParseResultsAsync(nameof AddMissingSeqCodeFixProvider)
+
+                let getSourceLineStr line =
+                    sourceText.Lines[Line.toZ line].ToString()
+
+                let range =
+                    RoslynHelpers.TextSpanToFSharpRange(context.Document.FilePath, context.Span, sourceText)
+
+                let needsParens =
+                    (range.Start, parseFileResults.ParseTree)
+                    ||> ParsedInput.exists (fun path node ->
+                        match path, node with
+                        | SyntaxNode.SynExpr outer :: _, SyntaxNode.SynExpr(expr & SynExpr.ComputationExpr _) when
+                            expr.Range |> Range.equals range
+                            ->
+                            let seqRange =
+                                range
+                                |> Range.withEnd (Position.mkPos range.Start.Line (range.Start.Column + 3))
+
+                            let inner =
+                                SynExpr.App(
+                                    ExprAtomicFlag.NonAtomic,
+                                    false,
+                                    SynExpr.Ident(Ident(nameof seq, seqRange)),
+                                    expr,
+                                    Range.unionRanges seqRange expr.Range
+                                )
+
+                            let outer =
+                                match outer with
+                                | SynExpr.App(flag, isInfix, funcExpr, _, outerAppRange) ->
+                                    SynExpr.App(flag, isInfix, funcExpr, inner, outerAppRange)
+                                | outer -> outer
+
+                            inner
+                            |> SynExpr.shouldBeParenthesizedInContext getSourceLineStr (SyntaxNode.SynExpr outer :: path)
+                        | _ -> false)
+
+                let text = sourceText.ToString(TextSpan(context.Span.Start, context.Span.Length))
+                let newText = if needsParens then $"(seq {text})" else $"seq {text}"
+
+                return
+                    ValueSome
+                        {
+                            Name = CodeFix.AddMissingSeq
+                            Message = title
+                            Changes = [ TextChange(context.Span, newText) ]
+                        }
+            }

vsintegration/src/FSharp.Editor/Common/Constants.fs

@@ -208,3 +208,6 @@ module internal CodeFix =
 
     [<Literal>]
     let RemoveUnnecessaryParentheses = "RemoveUnnecessaryParentheses"
+
+    [<Literal>]
+    let AddMissingSeq = "AddMissingSeq"

vsintegration/src/FSharp.Editor/FSharp.Editor.fsproj

@@ -141,6 +141,7 @@
     <Compile Include="CodeFixes\RenameParamToMatchSignature.fs" />
     <Compile Include="CodeFixes\UseTripleQuotedInterpolation.fs" />
     <Compile Include="CodeFixes\RemoveUnnecessaryParentheses.fs" />
+    <Compile Include="CodeFixes\AddMissingSeq.fs" />
     <Compile Include="Build\SetGlobalPropertiesForSdkProjects.fs" />
     <Compile Include="AutomaticCompletion\BraceCompletionSessionProvider.fsi" />
     <Compile Include="AutomaticCompletion\BraceCompletionSessionProvider.fs" />

vsintegration/src/FSharp.Editor/FSharp.Editor.resx

@@ -359,6 +359,9 @@ Use live (unsaved) buffers for analysis</value>
   <data name="RemoveUnnecessaryParentheses" xml:space="preserve">
     <value>Remove unnecessary parentheses</value>
   </data>
+  <data name="AddMissingSeq" xml:space="preserve">
+    <value>Add missing 'seq'</value>
+  </data>
   <data name="RemarksHeader" xml:space="preserve">
     <value>Remarks:</value>
   </data>