Fix record completions in patterns (#15945)

Author: kerams

src/Compiler/Checking/CheckExpressions.fs

@@ -1812,8 +1812,6 @@ let BuildFieldMap (cenv: cenv) env isPartial ty (flds: ((Ident list * Ident) * '
     let g = cenv.g
     let ad = env.eAccessRights
 
-    if isNil flds then invalidArg "flds" "BuildFieldMap"
-
     let allFields = flds |> List.map (fun ((_, ident), _) -> ident)
     if allFields.Length > 1 then
         // In the case of nested record fields on the same level in record copy-and-update.

src/Compiler/Service/ServiceParsedInputOps.fs

@@ -1313,7 +1313,7 @@ module ParsedInput =
             | _ ->
                 pats
                 |> List.tryPick (fun pat -> TryGetCompletionContextInPattern false pat None pos)
-        | SynPat.Record (fieldPats = pats) ->
+        | SynPat.Record (fieldPats = pats; range = m) when rangeContainsPos m pos ->
             pats
             |> List.tryPick (fun ((_, fieldId), _, pat) ->
                 if rangeContainsPos fieldId.idRange pos then
@@ -1328,15 +1328,16 @@ module ParsedInput =
                 // That is, pos is after the last field and still within braces
                 if
                     pats
-                    |> List.forall (fun (_, m, _) ->
-                        match m with
-                        | Some m -> rangeBeforePos m pos
-                        | None -> false)
+                    |> List.forall (fun (_, mEquals, pat) ->
+                        match mEquals, pat with
+                        | Some mEquals, SynPat.Wild mPat -> rangeBeforePos mEquals pos && mPat.StartColumn <> mPat.EndColumn
+                        | Some mEquals, _ -> rangeBeforePos mEquals pos
+                        | _ -> false)
                 then
                     let referencedFields = pats |> List.map (fun ((_, x), _, _) -> x.idText, x.idRange)
                     Some(CompletionContext.Pattern(PatternContext.RecordFieldIdentifier referencedFields))
                 else
-                    None)
+                    Some(CompletionContext.Pattern PatternContext.Other))
         | SynPat.Ands (pats = pats)
         | SynPat.ArrayOrList (elementPats = pats) ->
             pats

vsintegration/tests/FSharp.Editor.Tests/CompletionProviderTests.fs

@@ -1935,7 +1935,14 @@ type R1 = { A: int; B: int }
 type R2 = { C: int; D: int }
 
 match [] with
-| [ { A = 2; l = 2 } ]
+| [ { A = 2; l = 2 } ] -> ()
+
+match { A = 1; B = 2 } with
+| { A = 1;  } -> ()
+| { A = 2; s } -> ()
+| { B = } -> ()
+| { X = ; A = 3 } -> ()
+| {   } -> ()
 """
 
         VerifyCompletionList(
@@ -1945,6 +1952,16 @@ match [] with
             [ "A"; "C"; "D"; "DU"; "X"; "log"; "let"; "Lazy" ]
         )
 
+        VerifyCompletionList(fileContents, "| { A = 1; ", [ "B"; "R1"; "R2" ], [ "C"; "D" ])
+        VerifyCompletionList(fileContents, "| { A = 2; s", [ "B"; "R1"; "R2" ], [ "C"; "D" ])
+        VerifyCompletionList(fileContents, "| { B =", [ "R1"; "R2"; "Some"; "None"; "System"; "DU" ], [ "A"; "B"; "C"; "D" ])
+        VerifyCompletionList(fileContents, "| { B = ", [ "R1"; "R2"; "Some"; "None"; "System"; "DU" ], [ "A"; "B"; "C"; "D" ])
+        VerifyCompletionList(fileContents, "| { X =", [ "R1"; "R2"; "Some"; "None"; "System"; "DU" ], [ "A"; "B"; "C"; "D" ])
+        VerifyCompletionList(fileContents, "| { X = ", [ "R1"; "R2"; "Some"; "None"; "System"; "DU" ], [ "A"; "B"; "C"; "D" ])
+
+        // Ideally C and D should not be present here, but right now we're not able to filter fields in an empty record pattern stub
+        VerifyCompletionList(fileContents, "| {  ", [ "A"; "B"; "C"; "D"; "R1"; "R2" ], [])
+
     [<Fact>]
     let ``Completion list for record field identifier in a pattern contains fields of all records in scope when the record type is not known yet``
         ()