Merge pull request #3218 from nojaf/fix-3135

Fix dynamic operator on qualified function call result

Author: nojaf

CHANGELOG.md

@@ -11,6 +11,7 @@
 - Multiline function type inside parentheses gets extra indentation to avoid compiler error. [#3043](https://github.com/fsprojects/fantomas/issues/3043)
 - Trivia around paren lambda with conditional compilation no longer causes merge error. [#2844](https://github.com/fsprojects/fantomas/issues/2844)
 - Type app closing angle bracket padded by previous expression length. [#3179](https://github.com/fsprojects/fantomas/issues/3179)
+- Dynamic operator on result of qualified function call causes formatting error. [#3135](https://github.com/fsprojects/fantomas/issues/3135)
 
 ## [8.0.0-alpha-002] - 2025-12-15
 

src/Fantomas.Core.Tests/DynamicOperatorTests.fs

@@ -125,3 +125,17 @@ let statusBarHeight = (window?getComputedStyle document.documentElement)?getProp
 let statusBarHeight =
     (window?getComputedStyle document.documentElement)?getPropertyValue "--statusBarHeight"
 """
+
+[<Test>]
+let ``dynamic operator on result of long ident paren arg, 3135`` () =
+    formatSourceString
+        """
+Jest.expect(json)?oMatchSnapshot ()
+"""
+        config
+    |> prepend newline
+    |> should
+        equal
+        """
+Jest.expect(json)?oMatchSnapshot ()
+"""

src/Fantomas.Core/CodePrinter.fs

@@ -57,6 +57,7 @@ let rec (|UppercaseExpr|LowercaseExpr|) (expr: Expr) =
     | Expr.DotIndexedGet node -> (|UppercaseExpr|LowercaseExpr|) node.ObjectExpr
     | Expr.TypeApp node -> (|UppercaseExpr|LowercaseExpr|) node.Identifier
     | Expr.Dynamic node -> (|UppercaseExpr|LowercaseExpr|) node.FuncExpr
+    | Expr.AppLongIdentAndSingleParenArg node -> lastFragmentInList node.FunctionName
     | Expr.AppSingleParenArg node -> (|UppercaseExpr|LowercaseExpr|) node.FunctionExpr
     | Expr.Paren node -> (|UppercaseExpr|LowercaseExpr|) node.Expr
     | Expr.App node -> (|UppercaseExpr|LowercaseExpr|) node.FunctionExpr
@@ -721,7 +722,15 @@ let genExpr (e: Expr) =
             +> genExpr node.Expr
             +> genSingleTextNode node.ClosingParen
         |> genNode node
-    | Expr.Dynamic node -> genExpr node.FuncExpr +> !-"?" +> genExpr node.ArgExpr |> genNode node
+    | Expr.Dynamic node ->
+        // Use sepNone for AppLongIdentAndSingleParenArg to preserve atomic application (no space before paren).
+        // Adding a space would change the AST from `(Jest.expect(json))?oMatchSnapshot` to `Jest.expect ((json)?oMatchSnapshot)`. See #3135.
+        let genFuncExpr =
+            match node.FuncExpr with
+            | Expr.AppLongIdentAndSingleParenArg appNode -> genAppLongIdentAndSingleParenArgExpr sepNone appNode
+            | _ -> genExpr node.FuncExpr
+
+        genFuncExpr +> !-"?" +> genExpr node.ArgExpr |> genNode node
     | Expr.PrefixApp node ->
         let genWithoutSpace = genSingleTextNode node.Operator +> genExpr node.Expr
         let genWithSpace = genSingleTextNode node.Operator +> sepSpace +> genExpr node.Expr