Handle special parsing of new T… & inherit T… (#16239)

* Handle special parsing of `new T…` & `inherit T…`

* Ctor applications are handled differently in the parser after the
  `new` and `inherit` keywords than they are elsewhere: only a subset of
  expressions are allowed as an argument (as specified in
  `atomicExprAfterType` in pars.fsy). This means that any expression
  outside of that blessed subset must be parenthesized, even if the
  exact same ctor application would not require parentheses without
  `new` or `inherit`.

* Fantomas

* Arrays only

* Fantomas

* Clean up comments

src/Compiler/Service/ServiceAnalysis.fs

@@ -692,6 +692,22 @@ module UnnecessaryParentheses =
     module SynExpr =
         open FSharp.Compiler.SyntaxTrivia
 
+        /// See atomicExprAfterType in pars.fsy.
+        [<return: Struct>]
+        let (|AtomicExprAfterType|_|) expr =
+            match expr with
+            | SynExpr.Paren _
+            | SynExpr.Quote _
+            | SynExpr.Const _
+            | SynExpr.Tuple(isStruct = true)
+            | SynExpr.Record _
+            | SynExpr.AnonRecd _
+            | SynExpr.InterpolatedString _
+            | SynExpr.Null _
+            | SynExpr.ArrayOrList(isArray = true)
+            | SynExpr.ArrayOrListComputed(isArray = true) -> ValueSome AtomicExprAfterType
+            | _ -> ValueNone
+
         /// Matches if the given expression represents a high-precedence
         /// function application, e.g.,
         ///
@@ -1142,6 +1158,18 @@ module UnnecessaryParentheses =
             | SynExpr.Paren(expr = SynExpr.App _), SyntaxNode.SynExpr (SynExpr.App _) :: SyntaxNode.SynExpr (SynExpr.JoinIn _) :: _ ->
                 ValueNone
 
+            // Parens are not required around a few anointed expressions after inherit:
+            //
+            //     inherit T(3)
+            //     inherit T(null)
+            //     inherit T("")
+            //     …
+            | SynExpr.Paren (expr = AtomicExprAfterType; range = range), SyntaxNode.SynMemberDefn (SynMemberDefn.ImplicitInherit _) :: _ ->
+                ValueSome range
+
+            // Parens are otherwise required in inherit T(x), etc.
+            | SynExpr.Paren _, SyntaxNode.SynMemberDefn (SynMemberDefn.ImplicitInherit _) :: _ -> ValueNone
+
             // We can't remove parens when they're required for fluent calls:
             //
             //     x.M(y).N z
@@ -1284,6 +1312,14 @@ module UnnecessaryParentheses =
                 | SynExpr.AddressOf _, SynExpr.Typed _
                 | SynExpr.JoinIn _, SynExpr.Typed _ -> ValueNone
 
+                // new T(expr)
+                | SynExpr.New _, AtomicExprAfterType -> ValueSome range
+                | SynExpr.New _, _ -> ValueNone
+
+                // { inherit T(expr); … }
+                | SynExpr.Record(baseInfo = Some (_, SynExpr.Paren(expr = Is inner), _, _, _)), AtomicExprAfterType -> ValueSome range
+                | SynExpr.Record(baseInfo = Some (_, SynExpr.Paren(expr = Is inner), _, _, _)), _ -> ValueNone
+
                 | _, SynExpr.Paren _
                 | _, SynExpr.Quote _
                 | _, SynExpr.Const _

vsintegration/tests/FSharp.Editor.Tests/CodeFixes/RemoveUnnecessaryParenthesesTests.fs

@@ -127,6 +127,12 @@ let _ =
             // New
             "new exn(null)", "new exn null"
             "new exn (null)", "new exn null"
+            "new ResizeArray<int>(3)", "new ResizeArray<int> 3"
+            "let x = 3 in new ResizeArray<int>(x)", "let x = 3 in new ResizeArray<int>(x)"
+            "ResizeArray<int>([3])", "ResizeArray<int> [3]"
+            "new ResizeArray<int>([3])", "new ResizeArray<int>([3])"
+            "ResizeArray<int>([|3|])", "ResizeArray<int> [|3|]"
+            "new ResizeArray<int>([|3|])", "new ResizeArray<int> [|3|]"
 
             // ObjExpr
             "{ new System.IDisposable with member _.Dispose () = (ignore 3) }",
@@ -1091,6 +1097,50 @@ let builder = Builder ()
 let (+) _ _ = builder
 let _ = (2 + 2) { return 5 }
 "
+
+                """
+                type E (message : string) =
+                    inherit exn ($"{message}")
+                """,
+                """
+                type E (message : string) =
+                    inherit exn $"{message}"
+                """
+
+                "
+                type E (message : string) =
+                    inherit exn (message)
+                ",
+                "
+                type E (message : string) =
+                    inherit exn (message)
+                "
+
+                """
+                type E =
+                    inherit exn
+                    val Message2 : string
+                    new (str1, str2) = { inherit exn ($"{str1}"); Message2 = str2 }
+                """,
+                """
+                type E =
+                    inherit exn
+                    val Message2 : string
+                    new (str1, str2) = { inherit exn $"{str1}"; Message2 = str2 }
+                """
+
+                "
+                type E =
+                    inherit exn
+                    val Message2 : string
+                    new (str1, str2) = { inherit exn (str1); Message2 = str2 }
+                ",
+                "
+                type E =
+                    inherit exn
+                    val Message2 : string
+                    new (str1, str2) = { inherit exn (str1); Message2 = str2 }
+                "
             }
 
         [<Theory; MemberData(nameof moreComplexApps)>]