Correct indentation of clause body if when condition is multiline.

src/Fantomas.Tests/PatternMatchingTests.fs

@@ -1089,7 +1089,42 @@ module Foo =
             // Ordinary functions or values
             | false, _, _, name when
                 not (hasAttribute<RequireQualifiedAccessAttribute> v.ApparentEnclosingEntity.Attributes) ->
-                  name + " " + parArgs
+                name + " " + parArgs
             // Ordinary static members or things (?) that require fully qualified access
             | _, _, _, name -> name + parArgs
 """
+
+[<Test>]
+let ``maintain indent if when condition is multiline`` () =
+    formatSourceString
+        false
+        """
+    match foo with
+    | headToken :: rest when (isOperatorOrKeyword headToken && List.exists (fun k -> headToken.TokenInfo.TokenName = k) keywordTrivia) ->
+          let range =
+              getRangeBetween "keyword" headToken headToken
+
+          let info =
+              Trivia.Create(Keyword(headToken)) range
+              |> List.prependItem foundTrivia
+
+          getTriviaFromTokensThemSelves allTokens rest info
+"""
+        config
+    |> prepend newline
+    |> should
+        equal
+        """
+match foo with
+| headToken :: rest when
+    (isOperatorOrKeyword headToken
+     && List.exists (fun k -> headToken.TokenInfo.TokenName = k) keywordTrivia) ->
+    let range =
+        getRangeBetween "keyword" headToken headToken
+
+    let info =
+        Trivia.Create(Keyword(headToken)) range
+        |> List.prependItem foundTrivia
+
+    getTriviaFromTokensThemSelves allTokens rest info
+"""

src/Fantomas/CodePrinter.fs

@@ -4229,21 +4229,21 @@ and genClause astContext hasBar (Clause (p, e, eo)) =
     let arrowRange =
         mkRange "arrowRange" p.Range.End e.Range.Start
 
-    let body =
-        optPre
+    let body = clauseBody e
+
+    let astCtx =
+        { astContext with
+              IsInsideMatchClausePattern = true }
+
+    let pat =
+        genPat astCtx p
+        +> optPre
             (!- " when")
             sepNone
             eo
             (fun e -> sepSpaceOrIndentAndNlnIfExpressionExceedsPageWidth (genExpr astContext e))
         +> sepArrow
         +> leaveNodeTokenByName arrowRange RARROW
-        +> clauseBody e
-
-    let astCtx =
-        { astContext with
-              IsInsideMatchClausePattern = true }
-
-    let pat = genPat astCtx p
 
     genTriviaBeforeClausePipe p.Range
     +> ifElse hasBar (sepBar +> atCurrentColumnWithPrepend pat body) (pat +> body)