Parser: recover on missing interface members

Author: auduchinok

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

@@ -129,6 +129,7 @@
 * Fix dot-completion after indexed expressions (`a.[0].Data.`, `a[0].Data.`, `[1;2].Length.`) returning unrelated global completions instead of expression-typings members. ([Issue #4966](https://github.com/dotnet/fsharp/issues/4966), [PR #19934](https://github.com/dotnet/fsharp/pull/19934))
 * Quotations of `match s with "" -> _` no longer leak the `s <> null && s.Length = 0` lowering; the empty-string optimization moved from pattern-match compilation to the optimizer so quoted expressions keep `op_Equality(s, "")`. ([Issue #19873](https://github.com/dotnet/fsharp/issues/19873))
 * Fix #5795: Allow attributes defined in a `module rec` / `namespace rec` scope to be used on union cases, record fields, and generic type parameters of types in the same recursive scope. ([Issue #5795](https://github.com/dotnet/fsharp/issues/5795), [PR #19744](https://github.com/dotnet/fsharp/pull/19744))
+* Parser: recover on missing interface members ([PR #20105](https://github.com/dotnet/fsharp/pull/20105))
 
 ### Added
 

src/Compiler/pars.fsy

@@ -2313,6 +2313,10 @@ opt_interfaceImplDefn:
      { let mWithKwd = rhs parseState 1
        Some(mWithKwd, [], mWithKwd) }
 
+  | OWITH recover
+     { let mWithKwd = rhs parseState 1
+       Some(mWithKwd, [], mWithKwd) }
+
   | /* EMPTY */
      { None }
 

tests/service/data/SyntaxTree/Member/Interface 11.fs

@@ -0,0 +1,6 @@
+module Module
+
+type T =
+    interface I with [<Attr>]
+
+let f () = ()

tests/service/data/SyntaxTree/Member/Interface 11.fs.bsl

@@ -0,0 +1,42 @@
+ImplFile
+  (ParsedImplFileInput
+     ("/root/Member/Interface 11.fs", false, QualifiedNameOfFile Module, [],
+      [SynModuleOrNamespace
+         ([Module], false, NamedModule,
+          [Types
+             ([SynTypeDefn
+                 (SynComponentInfo
+                    ([], None, [], [T],
+                     PreXmlDoc ((3,0), FSharp.Compiler.Xml.XmlDocCollector),
+                     false, None, (3,5--3,6)),
+                  ObjectModel
+                    (Unspecified,
+                     [Interface
+                        (LongIdent (SynLongIdent ([I], [], [None])),
+                         Some (4,16--4,20), Some [], (4,4--4,20))], (4,4--4,20)),
+                  [], None, (3,5--4,20), { LeadingKeyword = Type (3,0--3,4)
+                                           EqualsRange = Some (3,7--3,8)
+                                           WithKeyword = None })], (3,0--4,20));
+           Let
+             (false,
+              [SynBinding
+                 (None, Normal, false, false, [],
+                  PreXmlDoc ((6,0), FSharp.Compiler.Xml.XmlDocCollector),
+                  SynValData
+                    (None, SynValInfo ([[]], SynArgInfo ([], false, None)), None),
+                  LongIdent
+                    (SynLongIdent ([f], [], [None]), None, None,
+                     Pats [Paren (Const (Unit, (6,6--6,8)), (6,6--6,8))], None,
+                     (6,4--6,8)), None, Const (Unit, (6,11--6,13)), (6,4--6,8),
+                  NoneAtLet, { LeadingKeyword = Let (6,0--6,3)
+                               InlineKeyword = None
+                               EqualsRange = Some (6,9--6,10) })], (6,0--6,13),
+              { InKeyword = None })],
+          PreXmlDoc ((1,0), FSharp.Compiler.Xml.XmlDocCollector), [], None,
+          (1,0--6,13), { LeadingKeyword = Module (1,0--1,6) })], (true, true),
+      { ConditionalDirectives = []
+        WarnDirectives = []
+        CodeComments = [] }, set []))
+
+(4,21)-(4,23) parse error Unexpected symbol '[<' in member definition
+(6,0)-(6,3) parse error Incomplete structured construct at or before this point in member definition