From 5d7a37958b9103cde6c31129e45ed26bf0b58693 Mon Sep 17 00:00:00 2001
From: Florian Verdonck <florian.verdonck@outlook.com>
Date: Thu, 12 Dec 2024 11:07:31 +0100
Subject: [PATCH] Add active pattern for empty computation expression (#3141)

* Add active pattern for empty computation expression

* Comment out lex.fsi

* Add changelog entry
---
 CHANGELOG.md                                  |  5 +++++
 .../ComputationExpressionTests.fs             | 14 ++++++++++++++
 src/Fantomas.Core/ASTTransformer.fs           | 19 +++++++++++++++++++
 src/Fantomas.FCS/Fantomas.FCS.fsproj          |  6 +++---
 4 files changed, 41 insertions(+), 3 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index c5c2b31b7..af5acb1f1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,10 @@
 # Changelog
 
+## 7.0.0-alpha-004 - 2024-12-12
+
+### Fixed
+* (Empty/NoEmpty)-bodied named computation expression produces inconsistent formatting. [#3140](https://github.com/fsprojects/fantomas/issues/3140)
+
 ## 7.0.0-alpha-003 - 2024-11-29
 
 ### Removed
diff --git a/src/Fantomas.Core.Tests/ComputationExpressionTests.fs b/src/Fantomas.Core.Tests/ComputationExpressionTests.fs
index 31c1a96c7..1b7912be9 100644
--- a/src/Fantomas.Core.Tests/ComputationExpressionTests.fs
+++ b/src/Fantomas.Core.Tests/ComputationExpressionTests.fs
@@ -2453,3 +2453,17 @@ let zero =
     async { () } // foo
     |> ignore
 """
+
+[<Test>]
+let ``empty computation expression with application`` () =
+    formatSourceString
+        """
+A() {}
+"""
+        config
+    |> prepend newline
+    |> should
+        equal
+        """
+A() { }
+"""
diff --git a/src/Fantomas.Core/ASTTransformer.fs b/src/Fantomas.Core/ASTTransformer.fs
index 93240f743..f1c4d9784 100644
--- a/src/Fantomas.Core/ASTTransformer.fs
+++ b/src/Fantomas.Core/ASTTransformer.fs
@@ -455,6 +455,15 @@ let (|IndexWithoutDot|_|) expr =
         Some(identifierExpr, indexExpr)
     | _ -> None
 
+let (|EmptyComputationExpr|_|) expr =
+    match expr with
+    | SynExpr.App(ExprAtomicFlag.NonAtomic,
+                  false,
+                  funcExpr,
+                  SynExpr.Record(recordFields = []; range = StartEndRange 1 (mOpen, _, mClose)),
+                  range) -> Some(funcExpr, mOpen, mClose, range)
+    | _ -> None
+
 let (|MultipleConsInfixApps|_|) expr =
     let rec visit expr (headAndLastOperator: (SynExpr * SingleTextNode) option) (xs: Queue<SingleTextNode * SynExpr>) =
         match expr with
@@ -1252,6 +1261,16 @@ let mkExpr (creationAide: CreationAide) (e: SynExpr) : Expr =
         ExprIndexWithoutDotNode(mkExpr creationAide identifierExpr, mkExpr creationAide indexExpr, exprRange)
         |> Expr.IndexWithoutDot
 
+    | EmptyComputationExpr(expr, mOpen, mClose, m) ->
+        ExprNamedComputationNode(
+            mkExpr creationAide expr,
+            stn "{" mOpen,
+            Expr.Ident(stn "" Range.Zero),
+            stn "}" mClose,
+            m
+        )
+        |> Expr.NamedComputation
+
     | ChainExpr links ->
         let chainLinks =
             links
diff --git a/src/Fantomas.FCS/Fantomas.FCS.fsproj b/src/Fantomas.FCS/Fantomas.FCS.fsproj
index db012a03f..dc2b8f3d4 100644
--- a/src/Fantomas.FCS/Fantomas.FCS.fsproj
+++ b/src/Fantomas.FCS/Fantomas.FCS.fsproj
@@ -303,9 +303,9 @@
     <Compile Include="$(FsYaccOutputFolder)pplex.fs">
       <Link>SyntaxTree\FsLexOutput\pplex.fs</Link>
     </Compile>
-    <Compile Include="$(FsYaccOutputFolder)\lex.fsi">
-      <Link>SyntaxTree\FsLexOutput\lex.fsi</Link>
-    </Compile>
+<!--    <Compile Include="$(FsYaccOutputFolder)\lex.fsi">-->
+<!--      <Link>SyntaxTree\FsLexOutput\lex.fsi</Link>-->
+<!--    </Compile>-->
     <Compile Include="$(FsYaccOutputFolder)\lex.fs">
       <Link>SyntaxTree\FsLexOutput\lex.fs</Link>
     </Compile>