Add "," as separator for pattern matching on multiple named discriminated unions fields

docs/release-notes/.FSharp.Compiler.Service/10.0.100.md

@@ -24,6 +24,7 @@
 
 ### Changed
 * Use `errorR` instead of `error` in `CheckDeclarations.fs` when possible. ([PR #18645](https://github.com/dotnet/fsharp/pull/18645))
+* Allow comma as separator for pattern matching on multiple named discriminated unions fields. ([PR #18833](https://github.com/dotnet/fsharp/pull/18833))
 
 ### Breaking Changes
 

docs/release-notes/.Language/preview.md

@@ -11,6 +11,7 @@
 * Allow `let!`, `use!`, `and!` type annotations without requiring parentheses (([PR #18508](https://github.com/dotnet/fsharp/pull/18508) and [PR #18682](https://github.com/dotnet/fsharp/pull/18682)))
 * Exception names are now validated for illegal characters using the same mechanism as types/modules/namespaces ([Issue #18763](https://github.com/dotnet/fsharp/issues/18763))
 * Support tail calls in computation expressions ([PR #18804](https://github.com/dotnet/fsharp/pull/18804))
+* Allow comma as separator for pattern matching on multiple named discriminated unions fields. ([PR #18833](https://github.com/dotnet/fsharp/pull/18833))
 
 ### Fixed
 

src/Compiler/FSComp.txt

@@ -1614,6 +1614,7 @@ featureWarningWhenMultipleRecdTypeChoice,"Raises warnings when multiple record t
 featureImprovedImpliedArgumentNames,"Improved implied argument names"
 featureStrictIndentation,"Raises errors on incorrect indentation, allows better recovery and analysis during editing"
 featureConstraintIntersectionOnFlexibleTypes,"Constraint intersection on flexible types"
+featureAllowCommaAsSeparatorForPatternMatchingOnMultipleNamedDiscriminatedUnionsFields,"Allow comma as separator for pattern matching on multiple named discriminated unions fields"
 featureChkNotTailRecursive,"Raises warnings if a member or function has the 'TailCall' attribute, but is not being used in a tail recursive way."
 featureWhileBang,"'while!' expression"
 featureExtendedFixedBindings,"extended fixed bindings for byref and GetPinnableReference"

src/Compiler/Facilities/LanguageFeatures.fs

@@ -104,6 +104,7 @@ type LanguageFeature =
     | ScopedNowarn
     | AllowTypedLetUseAndBang
     | ReturnFromFinal
+    | AllowCommaAsSeparatorForPatternMatchingOnMultipleNamedDiscriminatedUnionsFields
 
 /// LanguageVersion management
 type LanguageVersion(versionText) =
@@ -243,6 +244,7 @@ type LanguageVersion(versionText) =
 
                 // F# preview (still preview in 10.0)
                 LanguageFeature.FromEndSlicing, previewVersion // Unfinished features --- needs work
+                LanguageFeature.AllowCommaAsSeparatorForPatternMatchingOnMultipleNamedDiscriminatedUnionsFields, previewVersion
             ]
 
     static let defaultLanguageVersion = LanguageVersion("default")
@@ -412,6 +414,8 @@ type LanguageVersion(versionText) =
         | LanguageFeature.ScopedNowarn -> FSComp.SR.featureScopedNowarn ()
         | LanguageFeature.AllowTypedLetUseAndBang -> FSComp.SR.featureAllowLetOrUseBangTypeAnnotationWithoutParens ()
         | LanguageFeature.ReturnFromFinal -> FSComp.SR.featureReturnFromFinal ()
+        | LanguageFeature.AllowCommaAsSeparatorForPatternMatchingOnMultipleNamedDiscriminatedUnionsFields ->
+            FSComp.SR.featureAllowCommaAsSeparatorForPatternMatchingOnMultipleNamedDiscriminatedUnionsFields ()
 
     /// Get a version string associated with the given feature.
     static member GetFeatureVersionString feature =

src/Compiler/Facilities/LanguageFeatures.fsi

@@ -95,6 +95,7 @@ type LanguageFeature =
     | ScopedNowarn
     | AllowTypedLetUseAndBang
     | ReturnFromFinal
+    | AllowCommaAsSeparatorForPatternMatchingOnMultipleNamedDiscriminatedUnionsFields
 
 /// LanguageVersion management
 type LanguageVersion =

src/Compiler/Service/ServiceParsedInputOps.fs

@@ -1479,7 +1479,7 @@ module ParsedInput =
                         | SyntaxNode.SynExpr(SynExpr.Record(None, _, fields, _)) :: _ ->
                             let isFirstField =
                                 match field, fields with
-                                | Some contextLid, SynExprRecordField(fieldName = lid, _) :: _ -> contextLid.Range = lid.Range
+                                | Some contextLid, SynExprRecordField(fieldName = (lid, _)) :: _ -> contextLid.Range = lid.Range
                                 | _ -> false
 
                             RecordContext.New(completionPath, isFirstField)

src/Compiler/Service/SynExpr.fs

@@ -1112,7 +1112,7 @@ module SynExpr =
                     match recordFields with
                     | [] -> false
                     | SynExprRecordField(expr = Some(SynExpr.Paren(expr = Is inner)); blockSeparator = Some _) :: SynExprRecordField(
-                        fieldName = SynLongIdent(id = id :: _), _) :: _ -> problematic inner.Range id.idRange
+                        fieldName = (SynLongIdent(id = id :: _), _)) :: _ -> problematic inner.Range id.idRange
                     | _ :: recordFields -> loop recordFields
 
                 loop recordFields

src/Compiler/pars.fsy

@@ -3655,13 +3655,16 @@ conjPatternElements:
      { $3 :: $1 :: [] }
 
 namePatPairs:
-   | namePatPair opt_seps
+   | namePatPair opt_namePatSep
      { [$1] }
 
-   | namePatPair seps namePatPairs
+   | namePatPair namePatSep namePatPairs
      { $1 :: $3 }
 
-   | namePatPair seps seps namePatPairs
+   | namePatPair namePatSep UNDERSCORE
+     { [$1] }
+
+   | namePatPair namePatSep namePatSep namePatPairs
       { reportParseErrorAt (rhs parseState 3) (FSComp.SR.parsExpectingPattern ())
         ($1 :: $4) }
 
@@ -3700,6 +3703,7 @@ constrPattern:
         let m = unionRanges (rhs2 parseState 1 2) argsM
         SynPat.LongIdent(lid, None, Some $2, args, vis, m) }
 
+
   | atomicPatternLongIdent atomicPatsOrNamePatPairs %prec pat_app
       { let vis, lid = $1
         let args, argsM = $2
@@ -6987,6 +6991,20 @@ seps:
   | OBLOCKSEP SEMICOLON { Some (rhs parseState 2) }
   | SEMICOLON OBLOCKSEP { Some (rhs parseState 1) }
 
+/* Unified separator for name pattern pairs that handles both semicolon and comma */
+namePatSep:
+  | OBLOCKSEP { None }
+  | SEMICOLON { Some (rhs parseState 1) }
+  | COMMA { Some (rhs parseState 1) }
+  | OBLOCKSEP SEMICOLON { Some (rhs parseState 2) }
+  | OBLOCKSEP COMMA { Some (rhs parseState 2) }
+  | SEMICOLON OBLOCKSEP { Some (rhs parseState 1) }
+  | COMMA OBLOCKSEP { Some (rhs parseState 1) }
+
+opt_namePatSep:
+  | namePatSep { }
+  | /* EMPTY */ { }
+
 /* An 'end' that's optional only in #light, where an ODECLEND gets inserted, and explicit 'end's get converted to OEND */
 declEnd:
   | ODECLEND

tests/FSharp.Compiler.ComponentTests/Conformance/PatternMatching/NamedPatPairs/NamedPatPairs.fs

@@ -0,0 +1,32 @@
+// Copyright (c) Microsoft Corporation.  All Rights Reserved.  See License.txt in the project root for license information.
+
+namespace Conformance.PatternMatching
+
+open Xunit
+open FSharp.Test
+open FSharp.Test.Compiler
+
+module NamedPatPairs =
+    [<Theory; Directory(__SOURCE_DIRECTORY__, Includes=[|"NamedPatPairs01.fs"|])>]
+    let ``Preview: NamedPatPairs - NamedPatPairs01_fs`` compilation =
+        compilation
+        |> ignoreWarnings
+        |> withLangVersionPreview
+        |> typecheck
+        |> shouldSucceed
+
+    [<Theory; Directory(__SOURCE_DIRECTORY__, Includes=[|"NamedPatPairs01.fs"|])>]
+    let ``Version9 NamedPatPairs - NamedPatPairs01_fs`` compilation =
+        compilation
+        |> ignoreWarnings
+        |> withLangVersion90
+        |> typecheck
+        |> shouldFail
+        |> withDiagnostics [
+            (Error 3350, Line 8, Col 18, Line 8, Col 19, "Feature 'Allow comma as separator for pattern matching on multiple named discriminated unions fields' is not available in F# 9.0. Please use language version 'PREVIEW' or greater.");
+            (Error 3350, Line 9, Col 18, Line 9, Col 19, "Feature 'Allow comma as separator for pattern matching on multiple named discriminated unions fields' is not available in F# 9.0. Please use language version 'PREVIEW' or greater.");
+            (Error 3350, Line 9, Col 25, Line 9, Col 26, "Feature 'Allow comma as separator for pattern matching on multiple named discriminated unions fields' is not available in F# 9.0. Please use language version 'PREVIEW' or greater.");
+            (Error 3350, Line 19, Col 18, Line 19, Col 19, "Feature 'Allow comma as separator for pattern matching on multiple named discriminated unions fields' is not available in F# 9.0. Please use language version 'PREVIEW' or greater.");
+            (Error 3350, Line 20, Col 18, Line 20, Col 19, "Feature 'Allow comma as separator for pattern matching on multiple named discriminated unions fields' is not available in F# 9.0. Please use language version 'PREVIEW' or greater.");
+            (Error 3350, Line 21, Col 25, Line 21, Col 26, "Feature 'Allow comma as separator for pattern matching on multiple named discriminated unions fields' is not available in F# 9.0. Please use language version 'PREVIEW' or greater.")
+        ]

tests/FSharp.Compiler.ComponentTests/Conformance/PatternMatching/NamedPatPairs/NamedPatPairs01.fs

@@ -0,0 +1,21 @@
+// #Conformance #PatternMatching #NamedPatPairs 
+type MyUnion = 
+    | CaseA of a: int * b: string
+    | CaseB of x: float * y: bool * z: char
+
+let testComma value =
+    match value with
+    | CaseA(a = x, b = y) -> sprintf "CaseA: a=%d, b=%s" x y
+    | CaseB(x = p, y = q, z = r) -> sprintf "CaseB: x=%f, y=%b, z=%c" p q r
+
+let testSemicolon value =
+    match value with
+    | CaseA(a = x; b = y) -> sprintf "CaseA: a=%d, b=%s" x y
+    | CaseB(x = p; y = q; z = r) -> sprintf "CaseB: x=%f, y=%b, z=%c" p q r
+
+let testMixed value =
+    match value with
+    | CaseA(a = x; b = y) -> sprintf "CaseA: a=%d, b=%s" x y
+    | CaseB(x = p, y = q; z = r) -> sprintf "CaseB: x=%f, y=%b, z=%c" p q r
+    | CaseA(a = x, b = y) -> sprintf "CaseA: a=%d, b=%s" x y
+    | CaseB(x = p; y = q, z = r) -> sprintf "CaseB: x=%f, y=%b, z=%c" p q r