Fix parser recovery, name resolution, and code completion for unfinished enum patterns (#19708)

* Code completion/patterns: fix enum member completion

* Release notes

Author: auduchinok

docs/release-notes/.FSharp.Compiler.Service/11.0.100.md

@@ -51,6 +51,7 @@
 * Fix signature generation: type params with special characters missing backtick escaping. ([Issue #19595](https://github.com/dotnet/fsharp/issues/19595), [PR #19609](https://github.com/dotnet/fsharp/pull/19609))
 * Fix internal error when using custom attribute with `[<Optional>]` value type parameter and no `[<DefaultParameterValue>]`. ([Issue #8353](https://github.com/dotnet/fsharp/issues/8353), [PR #19484](https://github.com/dotnet/fsharp/pull/19484))
 * Fix parallel compilation of scripts ([PR #19649](https://github.com/dotnet/fsharp/pull/19649))
+* Fix parser recovery, name resolution, and code completion for unfinished enum patterns ([PR #19708](https://github.com/dotnet/fsharp/pull/19708))
 * Parser: fix unexpected diagnostics in debug builds, improve error messages ([PR #19730](https://github.com/dotnet/fsharp/pull/19730))
 
 ### Added

src/Compiler/Checking/NameResolution.fs

@@ -3531,7 +3531,7 @@ let rec ResolvePatternLongIdentPrim sink (ncenv: NameResolver) fullyQualified wa
                 match extraDotAtTheEnd with
                 | ExtraDotAfterIdentifier.Yes ->
                     match LookupTypeNameInEnvNoArity fullyQualified id.idText nenv with
-                    | tcref :: _ when tcref.IsUnionTycon ->
+                    | tcref :: _ when tcref.IsUnionTycon || tcref.IsEnumTycon ->
                         let res = ResolutionInfo.Empty.AddEntity (id.idRange, tcref)
                         ResolutionInfo.SendEntityPathToSink (sink, ncenv, nenv, ItemOccurrence.Pattern, ad, res, ResultTyparChecker(fun () -> true))
                         Item.Types (id.idText, [ mkWoNullAppTy tcref [] ])

src/Compiler/Service/FSharpCheckerResults.fs

@@ -904,6 +904,7 @@ type internal TypeCheckInfo
     /// Is the item suitable for completion in a pattern
     let IsPatternCandidate (item: CompletionItem) =
         match item.Item with
+        | Item.RecdField f -> f.Tycon.IsEnumTycon
         | Item.Value v -> v.LiteralValue.IsSome
         | Item.ILField field -> field.LiteralValue.IsSome
         | Item.ActivePatternCase _

src/Compiler/pars.fsy

@@ -241,6 +241,7 @@ let parse_error_rich = Some(fun (ctxt: ParseErrorContext<_>) ->
 
 /* start with lowest */
 
+%nonassoc prec_atompat_pathop_error
 %nonassoc prec_args_error            /* less than RPAREN */
 %nonassoc prec_atomexpr_lparen_error /* less than RPAREN */
 
@@ -6934,6 +6935,11 @@ pathOp:
      { let ident, trivia = $1
        SynLongIdent([ident], [], [Some trivia]) }
 
+  | ident DOT %prec prec_atompat_pathop_error
+     { let mDot = rhs parseState 2
+       reportParseErrorAt mDot.EndRange (FSComp.SR.parsIdentifierExpected())
+       SynLongIdent([$1], [mDot], [None]) }
+
   | ident DOT pathOp
      { prependIdentInLongIdentWithTrivia (SynIdent($1, None)) (rhs parseState 2) $3 }
 

tests/FSharp.Compiler.Service.Tests/CompletionTests.fs

@@ -369,6 +369,45 @@ module Module =
 """
     assertHasNoItemsWithNames ["E"] info
 
+[<Fact>]
+let ``Pattern - Enum 01`` () =
+    let info =
+        Checker.getCompletionInfo """
+namespace Ns1
+type E =
+    | A = 1
+    | B = 2
+
+namespace Ns2
+
+open Ns1
+
+module M =
+    match E.A with
+    | E.{caret}
+"""
+    assertHasItemWithNames ["A"] info
+
+[<Fact>]
+let ``Pattern - Enum 02`` () =
+    let info =
+        Checker.getCompletionInfo """
+namespace Ns1
+type E =
+    | A = 1
+    | B = 2
+
+namespace Ns2
+
+open Ns1
+
+module M =
+    match E.A with
+    | E.{caret}
+    | E.B -> ()
+"""
+    assertHasItemWithNames ["A"] info
+
 #if NETCOREAPP
 [<Fact>]
 let ``Span appears in completion and is not marked obsolete`` () =

tests/FSharp.Compiler.Service.Tests/SyntaxTreeTests.fs

@@ -124,6 +124,7 @@ let private sanitizeAST (sourceDirectoryValue: string) (ast: ParsedInput) : Pars
 
 let parseSourceCode (name: string, code: string) =
     let location = Path.Combine(RootDirectory, name).Replace("\\", "/")
+    Range.setTestSource location code
 
     let parseResults =
         checker.ParseFile(
@@ -188,7 +189,10 @@ let ParseFile fileName =
     let equals = expected = actual
     let testUpdateBSLEnv = System.Environment.GetEnvironmentVariable("TEST_UPDATE_BSL")
 
-    if not (isNull testUpdateBSLEnv) && testUpdateBSLEnv.Trim() = "1" && not equals then
+    let shouldUpdateBaseline =
+        (not (isNull testUpdateBSLEnv) && testUpdateBSLEnv.Trim() = "1" && not equals)
+
+    if shouldUpdateBaseline then
         File.WriteAllText(bslPath, actual)
     elif not equals then
         File.WriteAllText(actualPath, actual)

tests/FSharp.Compiler.Service.Tests/TypeChecker/TypeCheckerRecoveryTests.fs

@@ -119,3 +119,76 @@ let o: obj = null
 if true then
     o.GetHashCode{caret}
 """
+
+module Patterns =
+    [<Fact>]
+    let ``Enum - Type 01`` () =
+        assertHasSymbolUsageAtCaret "E" """
+type E =
+    | A = 1
+
+match E.A with
+| E{caret}.A -> ()
+"""
+
+    [<Fact>]
+    let ``Enum - Type 02`` () =
+        assertHasSymbolUsageAtCaret "E" """
+type E =
+    | A = 1
+
+match E.A with
+| E{caret} -> ()
+"""
+
+    [<Fact>]
+    let ``Enum - Type 03`` () =
+        assertHasSymbolUsageAtCaret "E" """
+type E =
+    | A = 1
+
+match E.A with
+| E{caret}
+"""
+
+    [<Fact>]
+    let ``Enum - Type 04`` () =
+        assertHasSymbolUsageAtCaret "E" """
+type E =
+    | A = 1
+
+match E.A with
+| E{caret}.
+"""
+        
+    [<Fact>]
+    let ``Enum - Type 05`` () =
+        assertHasSymbolUsageAtCaret "E" """
+type E =
+    | A = 1
+
+match E.A with
+| E{caret}. -> ()
+"""
+
+    [<Fact(Skip = "Improve name resolution recovery")>]
+    let ``Enum - Type 06`` () =
+        assertHasSymbolUsageAtCaret "E" """
+type E =
+    | A = 1
+
+match E.A with
+| E{caret}.B
+"""
+
+    [<Fact>]
+    let ``Enum - Type 07`` () =
+        assertHasSymbolUsageAtCaret "E" """
+type E =
+    | A = 1
+
+match E.A with
+| E{caret}.
+
+()
+"""

tests/service/data/SyntaxTree/Expression/Object - Class 13.fs.bsl

@@ -58,5 +58,5 @@ ImplFile
         WarnDirectives = []
         CodeComments = [] }, set []))
 
-(4,18)-(5,5) parse error Incomplete structured construct at or before this point in object expression
+(4,17)-(4,17) parse error Identifier expected
 (4,18)-(5,5) parse error Expecting member body

tests/service/data/SyntaxTree/Member/Member 03.fs.bsl

@@ -110,5 +110,5 @@ ImplFile
         WarnDirectives = []
         CodeComments = [] }, set []))
 
-(5,23)-(6,4) parse error Incomplete structured construct at or before this point in member definition
+(5,22)-(5,22) parse error Identifier expected
 (5,23)-(6,4) parse error Expecting member body

tests/service/data/SyntaxTree/Member/Member 07.fs.bsl

@@ -109,4 +109,4 @@ ImplFile
         WarnDirectives = []
         CodeComments = [] }, set []))
 
-(5,23)-(5,24) parse error Unexpected symbol '=' in member definition
+(5,22)-(5,22) parse error Identifier expected