From 5a42da2585671c6b27ebeefe01e8fa32c4074e39 Mon Sep 17 00:00:00 2001
From: ijanus <emekamicro@gmail.com>
Date: Thu, 10 Mar 2022 11:39:19 +0800
Subject: [PATCH] Avoid vanity alignment in multiline match clause

Fixes https://github.com/fsharp/fslang-design/issues/646
---
 src/Fantomas.Tests/PatternMatchingTests.fs | 43 ++++++++++++++++++++++
 src/Fantomas/CodePrinter.fs                | 19 ++++++----
 2 files changed, 55 insertions(+), 7 deletions(-)

diff --git a/src/Fantomas.Tests/PatternMatchingTests.fs b/src/Fantomas.Tests/PatternMatchingTests.fs
index 89f4923d5e..4ca3e674af 100644
--- a/src/Fantomas.Tests/PatternMatchingTests.fs
+++ b/src/Fantomas.Tests/PatternMatchingTests.fs
@@ -2152,6 +2152,49 @@ match! // foo
 | B b -> ()
 """
 
+[<Test>]
+let ``vanity alignment removed from multiline match expression`` () =
+    formatSourceString
+        false
+        """
+match directoryRouter.GetIdentity()
+      |> self.ServerDescriptors.TryFind with
+| None -> CircuitNodeDetail.FastCreate
+| Some serverDescriptor ->
+    self.ConvertToCircuitNodeDetail serverDescriptor
+"""
+        config
+    |> prepend newline
+    |> should
+        equal
+        """
+match
+    directoryRouter.GetIdentity()
+    |> self.ServerDescriptors.TryFind
+    with
+| None -> CircuitNodeDetail.FastCreate
+| Some serverDescriptor -> self.ConvertToCircuitNodeDetail serverDescriptor
+"""
+
+[<Test>]
+let ``match expression covering one line`` () =
+    formatSourceString
+        false
+        """
+match directoryRouter.GetIdentity() with
+| None -> CircuitNodeDetail.FastCreate
+| Some serverDescriptor ->
+    self.ConvertToCircuitNodeDetail serverDescriptor"""
+        config
+    |> prepend newline
+    |> should
+        equal
+        """
+match directoryRouter.GetIdentity() with
+| None -> CircuitNodeDetail.FastCreate
+| Some serverDescriptor -> self.ConvertToCircuitNodeDetail serverDescriptor
+"""
+
 [<Test>]
 let ``comment after with keyword in match bang`` () =
     formatSourceString
diff --git a/src/Fantomas/CodePrinter.fs b/src/Fantomas/CodePrinter.fs
index de8cddcea9..aa7648e6ea 100644
--- a/src/Fantomas/CodePrinter.fs
+++ b/src/Fantomas/CodePrinter.fs
@@ -1605,7 +1605,7 @@ and genExpr astContext synExpr ctx =
                     expressionFitsOnRestOfLine
                         (genExpr astContext e
                          +> genWithAfterMatch SynExpr_Match_With withRange)
-                        (genExprInIfOrMatch astContext e
+                        (genExprInIfOrMatch astContext e true
                          +> (sepNlnUnlessLastEventIsNewline
                              +> (genWithAfterMatch SynExpr_Match_With withRange)))
                 )
@@ -1618,7 +1618,7 @@ and genExpr astContext synExpr ctx =
                     expressionFitsOnRestOfLine
                         (genExpr astContext e
                          +> genWithAfterMatch SynExpr_MatchBang_With withRange)
-                        (genExprInIfOrMatch astContext e
+                        (genExprInIfOrMatch astContext e true
                          +> (sepNlnUnlessLastEventIsNewline
                              +> (genWithAfterMatch SynExpr_MatchBang_With withRange)))
                 )
@@ -2309,7 +2309,7 @@ and genExpr astContext synExpr ctx =
                 optSingle genElse elseKw
                 +> sepNlnWhenWriteBeforeNewlineNotEmpty sepSpace
                 +> genIf ifKw isElif
-                +> autoIndentAndNlnWhenWriteBeforeNewlineNotEmpty (genExprInIfOrMatch astContext e1)
+                +> autoIndentAndNlnWhenWriteBeforeNewlineNotEmpty (genExprInIfOrMatch astContext e1 false)
                 +> sepNlnWhenWriteBeforeNewlineNotEmpty sepSpace
                 +> genThen thenKw
                 +> indent
@@ -2344,7 +2344,7 @@ and genExpr astContext synExpr ctx =
                 //           x
                 // bool expr x should be indented
                 +> autoIndentAndNlnWhenWriteBeforeNewlineNotEmpty (
-                    genExprInIfOrMatch astContext e1
+                    genExprInIfOrMatch astContext e1 false
                     +> sepNlnWhenWriteBeforeNewlineNotEmpty sepSpace
                 )
                 +> genThen thenKw
@@ -3415,7 +3415,7 @@ and genAppWithSingleParenthesisArgument (e, lpr, a, rpr, _pr) astContext =
     +> (genExpr astContext a)
     +> sepCloseTFor rpr
 
-and genExprInIfOrMatch astContext (e: SynExpr) (ctx: Context) : Context =
+and genExprInIfOrMatch astContext (e: SynExpr) (shouldBeSplitToNextLine: bool) (ctx: Context) : Context =
     let short =
         sepNlnWhenWriteBeforeNewlineNotEmpty sepSpace
         +> genExpr astContext e
@@ -3435,6 +3435,11 @@ and genExprInIfOrMatch astContext (e: SynExpr) (ctx: Context) : Context =
         let fallback =
             if hasCommentBeforeExpr e then
                 genExpr astContext e |> indentNlnUnindentNln
+            elif shouldBeSplitToNextLine then
+                indent
+                +> sepNln
+                +> genExpr astContext e
+                +> unindent
             else
                 sepNlnWhenWriteBeforeNewlineNotEmpty sepNone
                 +> genExpr astContext e
@@ -5528,7 +5533,7 @@ and genKeepIndentMatch
         (genTriviaFor SynExpr_MatchBang_Match matchKeyword !- "match! ")
         (genTriviaFor SynExpr_Match_Match matchKeyword !- "match ")
     +> autoIndentAndNlnWhenWriteBeforeNewlineNotEmpty (
-        genExprInIfOrMatch astContext e
+        genExprInIfOrMatch astContext e false
         +> genWithAfterMatch
             (if isMatchBang then
                  SynExpr_MatchBang_With
@@ -5588,7 +5593,7 @@ and genKeepIdentIf
 
             let long =
                 genKeywordStart
-                +> genExprInIfOrMatch astContext ifExpr
+                +> genExprInIfOrMatch astContext ifExpr false
                 +> sepSpace
                 +> !- "then"