Ensure that scripts without the notion of upper/lower case can create du identifiers (#9199)

* Ensure that scripts without the notion of upper/lower case can create du identifiers

* Feedback and improvements

* feedback

* correct comment

src/absil/illib.fs

@@ -503,9 +503,20 @@ module String =
     let uppercase (s: string) =
         s.ToUpperInvariant()
 
-    let isUpper (s: string) = 
-        s.Length >= 1 && Char.IsUpper s.[0] && not (Char.IsLower s.[0])
-        
+    // Scripts that distinguish between upper and lower case (bicameral) DU Discriminators and Active Pattern identifiers are required to start with an upper case character.
+    // For valid identifiers where the case of the identifier can not be determined because there is no upper and lower case we will allow DU Discriminators and upper case characters 
+    // to be used.  This means that developers using unicameral scripts such as hindi, are not required to prefix these identifiers with an Upper case latin character. 
+    //
+    let isLeadingIdentifierCharacterUpperCase (s:string) =
+        let isUpperCaseCharacter c =
+            // if IsUpper and IsLower return the same value, then we can't tell if it's upper or lower case, so ensure it is a letter
+            // otherwise it is bicameral, so must be upper case
+            let isUpper = Char.IsUpper c
+            if isUpper = Char.IsLower c then Char.IsLetter c
+            else isUpper
+
+        s.Length >= 1 && isUpperCaseCharacter s.[0]
+
     let capitalize (s: string) =
         if s.Length = 0 then s 
         else uppercase s.[0..0] + s.[ 1.. s.Length - 1 ]

src/fsharp/TypeChecker.fs

@@ -5233,7 +5233,7 @@ and TcPatBindingName cenv env id ty isMemberThis vis1 topValData (inlineFlag, de
             let name = id.idText
             match values.TryGetValue name with
             | true, value ->
-                if not (String.IsNullOrEmpty name) && Char.IsLower(name.[0]) then
+                if not (String.IsNullOrEmpty name) && not (String.isLeadingIdentifierCharacterUpperCase name) then
                     match env.eNameResEnv.ePatItems.TryGetValue name with
                     | true, Item.Value vref when vref.LiteralValue.IsSome ->
                         warning(Error(FSComp.SR.checkLowercaseLiteralBindingInPattern name, id.idRange))
@@ -12775,7 +12775,7 @@ module TcRecdUnionAndEnumDeclarations = begin
             errorR(Error(FSComp.SR.tcUnionCaseNameConflictsWithGeneratedType(name, "Tags"), id.idRange))
 
         CheckNamespaceModuleOrTypeName cenv.g id
-        if not (String.isUpper name) && name <> opNameCons && name <> opNameNil then
+        if not (String.isLeadingIdentifierCharacterUpperCase name) && name <> opNameCons && name <> opNameNil then
             errorR(NotUpperCaseConstructor(id.idRange))
 
     let ValidateFieldNames (synFields: SynField list, tastFields: RecdField list) = 
@@ -15174,7 +15174,7 @@ module TcExceptionDeclarations =
 
     let TcExnDefnCore_Phase1A cenv env parent (SynExceptionDefnRepr(Attributes synAttrs, UnionCase(_, id, _, _, _, _), _, doc, vis, m)) =
         let attrs = TcAttributes cenv env AttributeTargets.ExnDecl synAttrs
-        if not (String.isUpper id.idText) then errorR(NotUpperCaseConstructor m)
+        if not (String.isLeadingIdentifierCharacterUpperCase id.idText) then errorR(NotUpperCaseConstructor m)
         let vis, cpath = ComputeAccessAndCompPath env None m vis None parent
         let vis = TcRecdUnionAndEnumDeclarations.CombineReprAccess parent vis
         CheckForDuplicateConcreteType env (id.idText + "Exception") id.idRange

src/fsharp/pars.fsy

@@ -3050,7 +3050,7 @@ atomicPattern:
 
   | atomicPatternLongIdent %prec prec_atompat_pathop 
       { let vis, lidwd = $1 
-        if not (isNilOrSingleton lidwd.Lid) || (let c = (List.head lidwd.Lid).idText.[0] in Char.IsUpper(c) && not (Char.IsLower c)) 
+        if not (isNilOrSingleton lidwd.Lid) || String.isLeadingIdentifierCharacterUpperCase (List.head lidwd.Lid).idText
         then mkSynPatMaybeVar lidwd vis (lhs parseState)
         else mkSynPatVar vis (List.head lidwd.Lid) }
 
@@ -5293,8 +5293,8 @@ operatorName:
 
 /* One part of an active pattern name */
 activePatternCaseName: 
-  | IDENT 
-     { if not (String.isUpper $1) then reportParseErrorAt (rhs parseState 1) (FSComp.SR.parsActivePatternCaseMustBeginWithUpperCase());  
+  | IDENT
+     { if not (String.isLeadingIdentifierCharacterUpperCase _1) then reportParseErrorAt (rhs parseState 1) (FSComp.SR.parsActivePatternCaseMustBeginWithUpperCase());  
        if ($1.IndexOf('|') <> -1) then reportParseErrorAt (rhs parseState 1) (FSComp.SR.parsActivePatternCaseContainsPipe());  
        $1 }
 

tests/fsharpqa/Source/Conformance/PatternMatching/Named/E_ActivePatterns01.fs

 // #Regression #Conformance #PatternMatching #ActivePatterns 
 // Verify error if Active Patterns do not start with an upper case letter
-//<Expects id="FS0623" status="error" span="(11,7)">Active pattern case identifiers must begin with an uppercase letter</Expects>
-//<Expects id="FS0623" status="error" span="(11,16)">Active pattern case identifiers must begin with an uppercase letter</Expects>
 //<Expects id="FS0623" status="error" span="(12,7)">Active pattern case identifiers must begin with an uppercase letter</Expects>
-//<Expects id="FS0623" status="error" span="(13,10)">Active pattern case identifiers must begin with an uppercase letter</Expects>
-//<Expects id="FS0623" status="error" span="(14,7)">Active pattern case identifiers must begin with an uppercase letter</Expects>
-//<Expects id="FS0624" status="error" span="(15,7)">The '\|' character is not permitted in active pattern case identifiers</Expects>
-//<Expects id="FS0624" status="error" span="(16,9)">The '\|' character is not permitted in active pattern case identifiers</Expects>
+//<Expects id="FS0623" status="error" span="(12,16)">Active pattern case identifiers must begin with an uppercase letter</Expects>
+//<Expects id="FS0623" status="error" span="(13,7)">Active pattern case identifiers must begin with an uppercase letter</Expects>
+//<Expects id="FS0623" status="error" span="(14,10)">Active pattern case identifiers must begin with an uppercase letter</Expects>
+//<Expects id="FS0623" status="error" span="(15,7)">Active pattern case identifiers must begin with an uppercase letter</Expects>
+//<Expects id="FS0624" status="error" span="(16,7)">The '\|' character is not permitted in active pattern case identifiers</Expects>
+//<Expects id="FS0624" status="error" span="(17,9)">The '\|' character is not permitted in active pattern case identifiers</Expects>
+//<Expects id="FS0623" status="error" span="(18,7)">Active pattern case identifiers must begin with an uppercase letter</Expects>
 
 let (|positive|negative|) n = if n < 0 then positive else negative
 let (|`` A``|) (x:int) = x
@@ -14,5 +15,6 @@ let (|B1|``+B2``|) (x:int) = if x = 0 then OneA else ``+B2``
 let (|`` C``|_|) (x:int) = if x = 0 then Some(x) else None
 let (|``D|E``|F|) (x:int) = if x = 0 then D elif x = 1 then E else F
 let (|G|``H||I``|) (x:int) = if x = 0 then G elif x = 1 then H else ``|I``
+let (|_J|) (x:int) = _J
 
 exit 1

tests/fsharpqa/Source/Conformance/PatternMatching/Named/discUnion01.fs

@@ -6,17 +6,17 @@
 type Foo =
     | A of int
     | B of string * int
-    
+
 let test x =
     match x with
     | A(1) | B(_,1) -> 1
     | A(2) | B(_,2) -> 2
     | B(_, _) -> -1
     | A(_)    -> -2
-    
+
 if test (A(1))    <> 1 then exit 1
 if test (B("",1)) <> 1 then exit 1
-    
+
 if test (A(2))    <> 2 then exit 1
 if test (B("",2)) <> 2 then exit 1
 

tests/fsharpqa/Source/Globalization/Hindi.fs

@@ -14,8 +14,8 @@ module पिछले =
   
   // DU
   type ख़तरxनाक = 
-               | Uअलगाववादी     // There's no uppercase/lowercase in Hindi, so I'm adding a latin char
-               | Aमिलती of ख़तरनाक
+               | अलगाववादी     // There's no uppercase/lowercase in Hindi, ensure that a Hindi character will suffice to start the DU case name
+               | मिलती of ख़तरनाक
                | X
   
   // Record