Parser: recover on unfinished isConst patterns

docs/release-notes/.FSharp.Compiler.Service/9.0.100.md

@@ -29,6 +29,7 @@
 * Allow object expression without overrides. ([Language suggestion #632](https://github.com/fsharp/fslang-suggestions/issues/632), [PR #17387](https://github.com/dotnet/fsharp/pull/17387))
 * Enable FSharp 9.0 Language Version ([Issue #17497](https://github.com/dotnet/fsharp/issues/17438)), [PR](https://github.com/dotnet/fsharp/pull/17500)))
 * Enable LanguageFeature.EnforceAttributeTargets in F# 9.0. ([Issue #17514](https://github.com/dotnet/fsharp/issues/17558), [PR #17516](https://github.com/dotnet/fsharp/pull/17558))
+* Parser: better recovery for unfinished patterns ([PR #17231](https://github.com/dotnet/fsharp/pull/17231), [PR #17232](https://github.com/dotnet/fsharp/pull/17232)))
 * Enable consuming generic arguments defined as `allows ref struct` in C# ([Issue #17597](https://github.com/dotnet/fsharp/issues/17597)
 
 ### Changed

src/Compiler/pars.fsy

@@ -172,6 +172,7 @@ let parse_error_rich = Some(fun (ctxt: ParseErrorContext<_>) ->
 %type <SynPat> headBindingPattern
 %type <SynType> appTypeNullableInParens
 %type <SynType> atomTypeNonAtomicDeprecated
+%type <SynType> atomTypeOrAnonRecdType
 %type <SynExpr> atomicExprAfterType
 %type <SynExpr> typedSequentialExprBlock
 %type <SynExpr * bool> atomicExpr
@@ -3550,7 +3551,7 @@ headBindingPattern:
       { let mColonColon = rhs parseState 2
         SynPat.ListCons($1, $3, rhs2 parseState 1 3, { ColonColonRange = mColonColon }) }
 
-  | headBindingPattern COLON_COLON recover
+  | headBindingPattern COLON_COLON ends_coming_soon_or_recover 
       { let mColonColon = rhs parseState 2
         let pat2 = SynPat.Wild(mColonColon.EndRange)
         SynPat.ListCons($1, pat2, rhs2 parseState 1 2, { ColonColonRange = mColonColon }) }
@@ -3679,7 +3680,21 @@ constrPattern:
         SynPat.LongIdent(lid, None, None, args, vis, m) }
 
   | COLON_QMARK atomTypeOrAnonRecdType %prec pat_isinst
-      { SynPat.IsInst($2, lhs parseState) }
+      { let m = unionRanges (rhs parseState 1) $2.Range
+        SynPat.IsInst($2, m) }
+
+  | COLON_QMARK recover %prec pat_isinst
+      { let mColon = rhs parseState 1
+        if not $2 then
+            reportParseErrorAt mColon (FSComp.SR.parsExpectingPattern ())
+        let ty = SynType.FromParseError(mColon.EndRange)
+        SynPat.IsInst(ty, mColon) }
+
+  | COLON_QMARK %prec pat_isinst
+      { let mColon = rhs parseState 1
+        let ty = SynType.FromParseError(mColon.EndRange)
+        reportParseErrorAt mColon (FSComp.SR.parsExpectingType ())
+        SynPat.IsInst(ty, mColon) }
 
   | atomicPattern
       { $1 }
@@ -3856,6 +3871,8 @@ parenPattern:
 
   | parenPattern COLON recover
       { let mColon = rhs parseState 2
+        if not $3 then
+            reportParseErrorAt mColon (FSComp.SR.parsExpectingPattern ())
         let ty = SynType.FromParseError(mColon.EndRange)
         SynPat.Typed($1, ty, unionRanges $1.Range mColon) }
 
@@ -3869,6 +3886,8 @@ parenPattern:
 
   | parenPattern COLON_COLON recover
       { let mColonColon = rhs parseState 2
+        if not $3 then
+            reportParseErrorAt mColonColon (FSComp.SR.parsExpectingPattern ())
         let pat2 = SynPat.Wild(mColonColon.EndRange)
         SynPat.ListCons($1, pat2, rhs2 parseState 1 2, { ColonColonRange = mColonColon }) }
 

tests/service/data/SyntaxTree/MatchClause/Missing pat 05.fs

@@ -0,0 +1,6 @@
+module Module
+
+match () with
+|
+
+()

tests/service/data/SyntaxTree/MatchClause/Missing pat 05.fs.bsl

@@ -0,0 +1,18 @@
+ImplFile
+  (ParsedImplFileInput
+     ("/root/MatchClause/Missing pat 05.fs", false, QualifiedNameOfFile Module,
+      [], [],
+      [SynModuleOrNamespace
+         ([Module], false, NamedModule,
+          [Expr
+             (Match
+                (Yes (3,0--3,13), Const (Unit, (3,6--3,8)), [], (3,0--4,1),
+                 { MatchKeyword = (3,0--3,5)
+                   WithKeyword = (3,9--3,13) }), (3,0--4,1));
+           Expr (Const (Unit, (6,0--6,2)), (6,0--6,2))],
+          PreXmlDoc ((1,0), FSharp.Compiler.Xml.XmlDocCollector), [], None,
+          (1,0--6,2), { LeadingKeyword = Module (1,0--1,6) })], (true, true),
+      { ConditionalDirectives = []
+        CodeComments = [] }, set []))
+
+(6,0)-(6,1) parse error Incomplete structured construct at or before this point in expression

tests/service/data/SyntaxTree/Pattern/IsInst 01.fs

@@ -0,0 +1,6 @@
+module Module
+
+match () with
+| :? T -> ()
+
+()

tests/service/data/SyntaxTree/Pattern/IsInst 01.fs.bsl

@@ -0,0 +1,21 @@
+ImplFile
+  (ParsedImplFileInput
+     ("/root/Pattern/IsInst 01.fs", false, QualifiedNameOfFile Module, [], [],
+      [SynModuleOrNamespace
+         ([Module], false, NamedModule,
+          [Expr
+             (Match
+                (Yes (3,0--3,13), Const (Unit, (3,6--3,8)),
+                 [SynMatchClause
+                    (IsInst
+                       (LongIdent (SynLongIdent ([T], [], [None])), (4,2--4,6)),
+                     None, Const (Unit, (4,10--4,12)), (4,2--4,12), Yes,
+                     { ArrowRange = Some (4,7--4,9)
+                       BarRange = Some (4,0--4,1) })], (3,0--4,12),
+                 { MatchKeyword = (3,0--3,5)
+                   WithKeyword = (3,9--3,13) }), (3,0--4,12));
+           Expr (Const (Unit, (6,0--6,2)), (6,0--6,2))],
+          PreXmlDoc ((1,0), FSharp.Compiler.Xml.XmlDocCollector), [], None,
+          (1,0--6,2), { LeadingKeyword = Module (1,0--1,6) })], (true, true),
+      { ConditionalDirectives = []
+        CodeComments = [] }, set []))

tests/service/data/SyntaxTree/Pattern/IsInst 02.fs

@@ -0,0 +1,6 @@
+module Module
+
+match () with
+| :? T
+
+()

tests/service/data/SyntaxTree/Pattern/IsInst 02.fs.bsl

@@ -0,0 +1,23 @@
+ImplFile
+  (ParsedImplFileInput
+     ("/root/Pattern/IsInst 02.fs", false, QualifiedNameOfFile Module, [], [],
+      [SynModuleOrNamespace
+         ([Module], false, NamedModule,
+          [Expr
+             (Match
+                (Yes (3,0--3,13), Const (Unit, (3,6--3,8)),
+                 [SynMatchClause
+                    (IsInst
+                       (LongIdent (SynLongIdent ([T], [], [None])), (4,2--4,6)),
+                     None, ArbitraryAfterError ("patternClauses2", (4,6--4,6)),
+                     (4,2--4,6), Yes, { ArrowRange = None
+                                        BarRange = Some (4,0--4,1) })],
+                 (3,0--4,6), { MatchKeyword = (3,0--3,5)
+                               WithKeyword = (3,9--3,13) }), (3,0--4,6));
+           Expr (Const (Unit, (6,0--6,2)), (6,0--6,2))],
+          PreXmlDoc ((1,0), FSharp.Compiler.Xml.XmlDocCollector), [], None,
+          (1,0--6,2), { LeadingKeyword = Module (1,0--1,6) })], (true, true),
+      { ConditionalDirectives = []
+        CodeComments = [] }, set []))
+
+(6,0)-(6,1) parse error Incomplete structured construct at or before this point in pattern matching. Expected '->' or other token.

tests/service/data/SyntaxTree/Pattern/IsInst 03.fs

@@ -0,0 +1,6 @@
+module Module
+
+match () with
+| :? -> ()
+
+()

tests/service/data/SyntaxTree/Pattern/IsInst 03.fs.bsl

@@ -0,0 +1,22 @@
+ImplFile
+  (ParsedImplFileInput
+     ("/root/Pattern/IsInst 03.fs", false, QualifiedNameOfFile Module, [], [],
+      [SynModuleOrNamespace
+         ([Module], false, NamedModule,
+          [Expr
+             (Match
+                (Yes (3,0--3,13), Const (Unit, (3,6--3,8)),
+                 [SynMatchClause
+                    (IsInst (FromParseError (4,4--4,4), (4,2--4,4)), None,
+                     Const (Unit, (4,8--4,10)), (4,2--4,10), Yes,
+                     { ArrowRange = Some (4,5--4,7)
+                       BarRange = Some (4,0--4,1) })], (3,0--4,10),
+                 { MatchKeyword = (3,0--3,5)
+                   WithKeyword = (3,9--3,13) }), (3,0--4,10));
+           Expr (Const (Unit, (6,0--6,2)), (6,0--6,2))],
+          PreXmlDoc ((1,0), FSharp.Compiler.Xml.XmlDocCollector), [], None,
+          (1,0--6,2), { LeadingKeyword = Module (1,0--1,6) })], (true, true),
+      { ConditionalDirectives = []
+        CodeComments = [] }, set []))
+
+(4,2)-(4,4) parse error Expecting type

tests/service/data/SyntaxTree/Pattern/IsInst 04.fs

@@ -0,0 +1,6 @@
+module Module
+
+match () with
+| :?
+
+()

tests/service/data/SyntaxTree/Pattern/IsInst 04.fs.bsl

@@ -0,0 +1,23 @@
+ImplFile
+  (ParsedImplFileInput
+     ("/root/Pattern/IsInst 04.fs", false, QualifiedNameOfFile Module, [], [],
+      [SynModuleOrNamespace
+         ([Module], false, NamedModule,
+          [Expr
+             (Match
+                (Yes (3,0--3,13), Const (Unit, (3,6--3,8)),
+                 [SynMatchClause
+                    (IsInst (FromParseError (4,4--4,4), (4,2--4,4)), None,
+                     ArbitraryAfterError ("patternClauses2", (4,4--4,4)),
+                     (4,2--4,4), Yes, { ArrowRange = None
+                                        BarRange = Some (4,0--4,1) })],
+                 (3,0--4,4), { MatchKeyword = (3,0--3,5)
+                               WithKeyword = (3,9--3,13) }), (3,0--4,4));
+           Expr (Const (Unit, (6,0--6,2)), (6,0--6,2))],
+          PreXmlDoc ((1,0), FSharp.Compiler.Xml.XmlDocCollector), [], None,
+          (1,0--6,2), { LeadingKeyword = Module (1,0--1,6) })], (true, true),
+      { ConditionalDirectives = []
+        CodeComments = [] }, set []))
+
+(4,2)-(4,4) parse error Expecting type
+(6,0)-(6,1) parse error Incomplete structured construct at or before this point in pattern matching. Expected '->' or other token.

tests/service/data/SyntaxTree/Pattern/IsInst 05.fs

@@ -0,0 +1,7 @@
+module Module
+
+match () with
+| :?
+| _ -> ()
+
+()

tests/service/data/SyntaxTree/Pattern/IsInst 05.fs.bsl

@@ -0,0 +1,24 @@
+ImplFile
+  (ParsedImplFileInput
+     ("/root/Pattern/IsInst 05.fs", false, QualifiedNameOfFile Module, [], [],
+      [SynModuleOrNamespace
+         ([Module], false, NamedModule,
+          [Expr
+             (Match
+                (Yes (3,0--3,13), Const (Unit, (3,6--3,8)),
+                 [SynMatchClause
+                    (Or
+                       (IsInst (FromParseError (4,4--4,4), (4,2--4,4)),
+                        Wild (5,2--5,3), (4,2--5,3), { BarRange = (5,0--5,1) }),
+                     None, Const (Unit, (5,7--5,9)), (4,2--5,9), Yes,
+                     { ArrowRange = Some (5,4--5,6)
+                       BarRange = Some (4,0--4,1) })], (3,0--5,9),
+                 { MatchKeyword = (3,0--3,5)
+                   WithKeyword = (3,9--3,13) }), (3,0--5,9));
+           Expr (Const (Unit, (7,0--7,2)), (7,0--7,2))],
+          PreXmlDoc ((1,0), FSharp.Compiler.Xml.XmlDocCollector), [], None,
+          (1,0--7,2), { LeadingKeyword = Module (1,0--1,6) })], (true, true),
+      { ConditionalDirectives = []
+        CodeComments = [] }, set []))
+
+(4,2)-(4,4) parse error Expecting type