DotLambda: add parser recovery

src/Compiler/pars.fsy

@@ -4885,6 +4885,28 @@ atomicExpr:
         let trivia: SynExprDotLambdaTrivia = { UnderscoreRange = mUnderscore ; DotRange = mDot  }
         SynExpr.DotLambda(expr, unionRanges mUnderscore  expr.Range, trivia), false }
 
+
+  | UNDERSCORE DOT recover %prec dot_lambda
+      { let mUnderscore = rhs parseState 1
+        let mDot = rhs parseState 2
+        let mWhole = unionRanges mUnderscore mDot
+        parseState.LexBuffer.CheckLanguageFeatureAndRecover LanguageFeature.AccessorFunctionShorthand mWhole
+
+        let mExpr = mDot.EndRange
+        if not $3 then reportParseErrorAt mDot (FSComp.SR.parsUnexpectedEndOfFileExpression())
+
+        let expr = arbExpr ("dotLambda1", mExpr)
+        let trivia: SynExprDotLambdaTrivia = { UnderscoreRange = mUnderscore ; DotRange = mDot  }
+        SynExpr.DotLambda(expr, mWhole, trivia), false }
+
+  | UNDERSCORE recover %prec dot_lambda
+      { let mUnderscore = rhs parseState 1
+
+        if not $2 then reportParseErrorAt mUnderscore (FSComp.SR.parsUnexpectedEndOfFileExpression())
+
+        let expr = SynExpr.Ident(Ident("_", mUnderscore))
+        SynExpr.FromParseError(expr, mUnderscore), false }
+
   | atomicExpr HIGH_PRECEDENCE_BRACK_APP atomicExpr
       { let arg1, _ = $1
         let arg2, hpa = $3

tests/FSharp.Compiler.ComponentTests/Language/DotLambdaTests.fs

@@ -173,9 +173,7 @@ let c = ( _ :> obj) """
     |> withDiagnostics [
         Error 10, Line 2, Col 20, Line 2, Col 21, "Unexpected symbol ')' in expression. Expected '.' or other token."
         Error 10, Line 3, Col 13, Line 3, Col 15, "Unexpected symbol ':>' in expression. Expected '.' or other token."
-        Error 583, Line 3, Col 9, Line 3, Col 10, "Unmatched '('"
-        Error 10, Line 4, Col 13, Line 4, Col 15, "Unexpected symbol ':>' in expression. Expected '.' or other token."
-        Error 583, Line 4, Col 9, Line 4, Col 10, "Unmatched '('"]
+        Error 10, Line 4, Col 13, Line 4, Col 15, "Unexpected symbol ':>' in expression. Expected '.' or other token."]
 
 [<Fact>]
 let ``ToString with F# 7`` () =

tests/service/data/SyntaxTree/Expression/DotLambda - _ Recovery - Casts.fsx

@@ -0,0 +1,3 @@
+let a = ( upcast _ ) : obj
+let b = ( _ :> _ ) : obj
+let c = ( _ :> obj)

tests/service/data/SyntaxTree/Expression/DotLambda - _ Recovery - Casts.fsx.bsl

@@ -0,0 +1,70 @@
+ImplFile
+  (ParsedImplFileInput
+     ("/root/Expression/DotLambda - _ Recovery - Casts.fsx", true,
+      QualifiedNameOfFile DotLambda - _ Recovery - Casts$fsx, [], [],
+      [SynModuleOrNamespace
+         ([DotLambda - _ Recovery - Casts], false, AnonModule,
+          [Let
+             (false,
+              [SynBinding
+                 (None, Normal, false, false, [],
+                  PreXmlDoc ((1,0), FSharp.Compiler.Xml.XmlDocCollector),
+                  SynValData
+                    (None, SynValInfo ([], SynArgInfo ([], false, None)), None,
+                     None), Named (SynIdent (a, None), false, None, (1,4--1,5)),
+                  None,
+                  Typed
+                    (Paren
+                       (InferredUpcast
+                          (FromParseError (Ident _, (1,17--1,18)), (1,10--1,18)),
+                        (1,8--1,9), Some (1,19--1,20), (1,8--1,20)),
+                     LongIdent (SynLongIdent ([obj], [], [None])), (1,8--1,26)),
+                  (1,4--1,5), Yes (1,0--1,26), { LeadingKeyword = Let (1,0--1,3)
+                                                 InlineKeyword = None
+                                                 EqualsRange = Some (1,6--1,7) })],
+              (1,0--1,26));
+           Let
+             (false,
+              [SynBinding
+                 (None, Normal, false, false, [],
+                  PreXmlDoc ((2,0), FSharp.Compiler.Xml.XmlDocCollector),
+                  SynValData
+                    (None, SynValInfo ([], SynArgInfo ([], false, None)), None,
+                     None), Named (SynIdent (b, None), false, None, (2,4--2,5)),
+                  None,
+                  Typed
+                    (Paren
+                       (Upcast
+                          (FromParseError (Ident _, (2,10--2,11)),
+                           Anon (2,15--2,16), (2,10--2,16)), (2,8--2,9),
+                        Some (2,17--2,18), (2,8--2,18)),
+                     LongIdent (SynLongIdent ([obj], [], [None])), (2,8--2,24)),
+                  (2,4--2,5), Yes (2,0--2,24), { LeadingKeyword = Let (2,0--2,3)
+                                                 InlineKeyword = None
+                                                 EqualsRange = Some (2,6--2,7) })],
+              (2,0--2,24));
+           Let
+             (false,
+              [SynBinding
+                 (None, Normal, false, false, [],
+                  PreXmlDoc ((3,0), FSharp.Compiler.Xml.XmlDocCollector),
+                  SynValData
+                    (None, SynValInfo ([], SynArgInfo ([], false, None)), None,
+                     None), Named (SynIdent (c, None), false, None, (3,4--3,5)),
+                  None,
+                  Paren
+                    (Upcast
+                       (FromParseError (Ident _, (3,10--3,11)),
+                        LongIdent (SynLongIdent ([obj], [], [None])),
+                        (3,10--3,18)), (3,8--3,9), Some (3,18--3,19),
+                     (3,8--3,19)), (3,4--3,5), Yes (3,0--3,19),
+                  { LeadingKeyword = Let (3,0--3,3)
+                    InlineKeyword = None
+                    EqualsRange = Some (3,6--3,7) })], (3,0--3,19))],
+          PreXmlDocEmpty, [], None, (1,0--4,0), { LeadingKeyword = None })],
+      (true, true), { ConditionalDirectives = []
+                      CodeComments = [] }, set []))
+
+(1,19)-(1,20) parse error Unexpected symbol ')' in expression. Expected '.' or other token.
+(2,12)-(2,14) parse error Unexpected symbol ':>' in expression. Expected '.' or other token.
+(3,12)-(3,14) parse error Unexpected symbol ':>' in expression. Expected '.' or other token.

tests/service/data/SyntaxTree/Expression/DotLambda - _ Recovery - Eof.fsx

@@ -0,0 +1 @@
+1 |> _

tests/service/data/SyntaxTree/Expression/DotLambda - _ Recovery - Eof.fsx.bsl

@@ -0,0 +1,23 @@
+ImplFile
+  (ParsedImplFileInput
+     ("/root/Expression/DotLambda - _ Recovery - Eof.fsx", true,
+      QualifiedNameOfFile DotLambda - _ Recovery - Eof$fsx, [], [],
+      [SynModuleOrNamespace
+         ([DotLambda - _ Recovery - Eof], false, AnonModule,
+          [Expr
+             (App
+                (NonAtomic, false,
+                 App
+                   (NonAtomic, true,
+                    LongIdent
+                      (false,
+                       SynLongIdent
+                         ([op_PipeRight], [], [Some (OriginalNotation "|>")]),
+                       None, (1,2--1,4)), Const (Int32 1, (1,0--1,1)),
+                    (1,0--1,4)), FromParseError (Ident _, (1,5--1,6)),
+                 (1,0--1,6)), (1,0--1,6))], PreXmlDocEmpty, [], None, (1,0--1,6),
+          { LeadingKeyword = None })], (true, true),
+      { ConditionalDirectives = []
+        CodeComments = [] }, set []))
+
+(1,5)-(1,6) parse error Unexpected end of input in expression

tests/service/data/SyntaxTree/Expression/DotLambda - _ Recovery.fsx

@@ -0,0 +1 @@
+(_)

tests/service/data/SyntaxTree/Expression/DotLambda - _ Recovery.fsx.bsl

@@ -0,0 +1,15 @@
+ImplFile
+  (ParsedImplFileInput
+     ("/root/Expression/DotLambda - _ Recovery.fsx", true,
+      QualifiedNameOfFile DotLambda - _ Recovery$fsx, [], [],
+      [SynModuleOrNamespace
+         ([DotLambda - _ Recovery], false, AnonModule,
+          [Expr
+             (Paren
+                (FromParseError (Ident _, (1,1--1,2)), (1,0--1,1),
+                 Some (1,2--1,3), (1,0--1,3)), (1,0--1,3))], PreXmlDocEmpty, [],
+          None, (1,0--1,3), { LeadingKeyword = None })], (true, true),
+      { ConditionalDirectives = []
+        CodeComments = [] }, set []))
+
+(1,2)-(1,3) parse error Unexpected symbol ')' in expression. Expected '.' or other token.

tests/service/data/SyntaxTree/Expression/DotLambda - _. Recovery - Eof.fsx

@@ -0,0 +1 @@
+1 |> _.

tests/service/data/SyntaxTree/Expression/DotLambda - _. Recovery - Eof.fsx.bsl

@@ -0,0 +1,26 @@
+ImplFile
+  (ParsedImplFileInput
+     ("/root/Expression/DotLambda - _. Recovery - Eof.fsx", true,
+      QualifiedNameOfFile DotLambda - _. Recovery - Eof$fsx, [], [],
+      [SynModuleOrNamespace
+         ([DotLambda - _;  Recovery - Eof], false, AnonModule,
+          [Expr
+             (App
+                (NonAtomic, false,
+                 App
+                   (NonAtomic, true,
+                    LongIdent
+                      (false,
+                       SynLongIdent
+                         ([op_PipeRight], [], [Some (OriginalNotation "|>")]),
+                       None, (1,2--1,4)), Const (Int32 1, (1,0--1,1)),
+                    (1,0--1,4)),
+                 DotLambda
+                   (ArbitraryAfterError ("dotLambda1", (1,7--1,7)), (1,5--1,7),
+                    { UnderscoreRange = (1,5--1,6)
+                      DotRange = (1,6--1,7) }), (1,0--1,7)), (1,0--1,7))],
+          PreXmlDocEmpty, [], None, (1,0--1,7), { LeadingKeyword = None })],
+      (true, true), { ConditionalDirectives = []
+                      CodeComments = [] }, set []))
+
+(1,6)-(1,7) parse error Unexpected end of input in expression

tests/service/data/SyntaxTree/Expression/DotLambda - _. Recovery.fsx

@@ -0,0 +1 @@
+(_.)

tests/service/data/SyntaxTree/Expression/DotLambda - _. Recovery.fsx.bsl

@@ -0,0 +1,18 @@
+ImplFile
+  (ParsedImplFileInput
+     ("/root/Expression/DotLambda - _. Recovery.fsx", true,
+      QualifiedNameOfFile DotLambda - _. Recovery$fsx, [], [],
+      [SynModuleOrNamespace
+         ([DotLambda - _;  Recovery], false, AnonModule,
+          [Expr
+             (Paren
+                (DotLambda
+                   (ArbitraryAfterError ("dotLambda1", (1,3--1,3)), (1,1--1,3),
+                    { UnderscoreRange = (1,1--1,2)
+                      DotRange = (1,2--1,3) }), (1,0--1,1), Some (1,3--1,4),
+                 (1,0--1,4)), (1,0--1,4))], PreXmlDocEmpty, [], None, (1,0--1,4),
+          { LeadingKeyword = None })], (true, true),
+      { ConditionalDirectives = []
+        CodeComments = [] }, set []))
+
+(1,3)-(1,4) parse error Unexpected symbol ')' in expression