Allow semicolon between type match cases

Fixes #13331

Author: odersky

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -2604,7 +2604,7 @@ object Parsers {
       })
     }
 
-    /** TypeCaseClause     ::= ‘case’ InfixType ‘=>’ Type [nl]
+    /** TypeCaseClause     ::= ‘case’ InfixType ‘=>’ Type [semi]
      */
     def typeCaseClause(): CaseDef = atSpan(in.offset) {
       val pat = inSepRegion(InCase) {
@@ -2613,6 +2613,7 @@ object Parsers {
       }
       CaseDef(pat, EmptyTree, atSpan(accept(ARROW)) {
         val t = typ()
+        if in.token == SEMI then in.nextToken()
         newLinesOptWhenFollowedBy(CASE)
         t
       })

docs/docs/internals/syntax.md

@@ -287,7 +287,7 @@ CaseClauses       ::=  CaseClause { CaseClause }
 CaseClause        ::=  ‘case’ Pattern [Guard] ‘=>’ Block                        CaseDef(pat, guard?, block)   // block starts at =>
 ExprCaseClause    ::=  ‘case’ Pattern [Guard] ‘=>’ Expr
 TypeCaseClauses   ::=  TypeCaseClause { TypeCaseClause }
-TypeCaseClause    ::=  ‘case’ InfixType ‘=>’ Type [nl]
+TypeCaseClause    ::=  ‘case’ InfixType ‘=>’ Type [semi]
 
 Pattern           ::=  Pattern1 { ‘|’ Pattern1 }                                Alternative(pats)
 Pattern1          ::=  Pattern2 [‘:’ RefinedType]                               Bind(name, Typed(Ident(wildcard), tpe))

docs/docs/reference/syntax.md

@@ -279,7 +279,7 @@ CaseClauses       ::=  CaseClause { CaseClause }
 CaseClause        ::=  ‘case’ Pattern [Guard] ‘=>’ Block
 ExprCaseClause    ::=  ‘case’ Pattern [Guard] ‘=>’ Expr
 TypeCaseClauses   ::=  TypeCaseClause { TypeCaseClause }
-TypeCaseClause    ::=  ‘case’ InfixType ‘=>’ Type [nl]
+TypeCaseClause    ::=  ‘case’ InfixType ‘=>’ Type [semi]
 
 Pattern           ::=  Pattern1 { ‘|’ Pattern1 }
 Pattern1          ::=  Pattern2 [‘:’ RefinedType]

tests/pos/i13331.scala

@@ -0,0 +1,3 @@
+def Choice = (_: Any) match { case Int => Long; case Long => Int } // ok
+
+type Choice[A] = A match { case Int => Long ; case Long => Int } // error