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Improve parser error recovery for underscore-dot patterns #20453

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41c8969
Improve parser error recovery for underscore-dot patterns
evgTSV Sep 4, 2026
ee2ecfe
Fix CompletionProviderTests.fs override trigger
evgTSV Sep 5, 2026
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25 changes: 18 additions & 7 deletions src/Compiler/pars.fsy
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Original file line number Diff line number Diff line change
Expand Up @@ -2258,12 +2258,25 @@ opt_typ:
let ty = SynType.FromParseError(mColon.EndRange)
Some ty }


atomicPatternLongIdent:
underscoreLongIdentPat:
| UNDERSCORE DOT pathOp
{ let underscore = ident("_", rhs parseState 1)
let mDot = rhs parseState 2
None, prependIdentInLongIdentWithTrivia (SynIdent(underscore, None)) mDot $3 }
prependIdentInLongIdentWithTrivia (SynIdent(underscore, None)) mDot $3 }
| UNDERSCORE DOT %prec prec_recover
{ let underscore = ident("_", rhs parseState 1)
let mDot = rhs parseState 2
reportParseErrorAt mDot.EndRange (FSComp.SR.parsIdentifierExpected())
SynLongIdent([underscore], [mDot], [None]) }
| UNDERSCORE DOT ends_coming_soon_or_recover
{ if not $3 then reportParseErrorAt (rhs parseState 3) (FSComp.SR.parsIdentifierExpected())
let underscore = ident("_", rhs parseState 1)
let mDot = rhs parseState 2
SynLongIdent([underscore], [mDot], [None]) }

atomicPatternLongIdent:
| underscoreLongIdentPat
{ None, $1 }

| GLOBAL DOT pathOp
{ let globalIdent = ident(MangledGlobalName, rhs parseState 1)
Expand All @@ -2273,10 +2286,8 @@ atomicPatternLongIdent:
| pathOp
{ (None, $1) }

| access UNDERSCORE DOT pathOp
{ let underscore = ident("_", rhs parseState 2)
let mDot = rhs parseState 3
Some($1), prependIdentInLongIdentWithTrivia (SynIdent(underscore, None)) mDot $4 }
| access underscoreLongIdentPat
{ Some($1), $2 }

| access pathOp
{ (Some($1), $2) }
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17 changes: 9 additions & 8 deletions tests/service/data/SyntaxTree/Member/Member 11.fs.bsl
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Expand Up @@ -32,19 +32,20 @@ ImplFile
SynValInfo
([[SynArgInfo ([], false, None)]; []],
SynArgInfo ([], false, None)), None),
FromParseError (Wild (6,10--6,10), (6,10--6,10)), None,
ArbitraryAfterError ("classDefnMember1", (6,10--6,10)),
(6,4--6,10), NoneAtInvisible,
Named (SynIdent (_, None), false, None, (6,11--6,12)),
None, ArbitraryAfterError ("memberCore2", (6,12--6,12)),
(6,11--6,12), NoneAtInvisible,
{ LeadingKeyword = Member (6,4--6,10)
InlineKeyword = None
EqualsRange = None }), (6,4--6,10))], None,
(3,5--6,10), { LeadingKeyword = Type (3,0--3,4)
EqualsRange = None }), (6,4--6,12))], None,
(3,5--6,12), { LeadingKeyword = Type (3,0--3,4)
EqualsRange = Some (3,7--3,8)
WithKeyword = None })], (3,0--6,10))],
WithKeyword = None })], (3,0--6,12))],
PreXmlDoc ((1,0), FSharp.Compiler.Xml.XmlDocCollector), [], None,
(1,0--6,10), { LeadingKeyword = Module (1,0--1,6) })], (true, true),
(1,0--6,12), { LeadingKeyword = Module (1,0--1,6) })], (true, true),
{ ConditionalDirectives = []
WarnDirectives = []
CodeComments = [] }, set []))

(7,0)-(7,0) parse error Incomplete structured construct at or before this point in member definition. Expected identifier, '(', '(*)' or other token.
(7,0)-(7,0) parse error Identifier expected
(7,0)-(7,0) parse error Expecting member body
6 changes: 3 additions & 3 deletions vsintegration/tests/FSharp.Editor.Tests/CompletionProviderTests.fs
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Expand Up @@ -1927,11 +1927,11 @@ let _ =
let fileContents =
"""
type G<'a> () =
override _.
override _.g

override x.ToString () = ""

[<AbstractClass]
[<AbstractClass>]
type A () =
abstract member A1: unit -> unit
abstract member A1: string -> unit
Expand All @@ -1953,7 +1953,7 @@ type C () =
override A1 s = ()
"""

VerifyCompletionListExactly(fileContents, "override _.", [ "Equals (obj: obj): bool"; "Finalize (): unit"; "GetHashCode (): int" ])
VerifyCompletionListExactly(fileContents, "override _.g", [ "Equals (obj: obj): bool"; "Finalize (): unit"; "GetHashCode (): int" ])

VerifyCompletionListExactly(
fileContents,
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