Added using for switch statements

Author: BrettRToomey

Sources/Core/Ast.swift

@@ -1071,6 +1071,7 @@ init(keyword: Pos, match: [Expr], colon: Pos, block: Block, label: Entity!) {
 class Switch: Node, Stmt {
     var keyword: Pos
     var match: Expr?
+    var usingMatch: Bool
     var cases: [CaseClause]
     var rbrace: Pos
 
@@ -1080,9 +1081,10 @@ class Switch: Node, Stmt {
     var end: Pos { return rbrace }
 
 // sourcery:inline:auto:Switch.Init
-init(keyword: Pos, match: Expr?, cases: [CaseClause], rbrace: Pos, label: Entity!) {
+init(keyword: Pos, match: Expr?, usingMatch: Bool, cases: [CaseClause], rbrace: Pos, label: Entity!) {
     self.keyword = keyword
     self.match = match
+    self.usingMatch = usingMatch
     self.cases = cases
     self.rbrace = rbrace
     self.label = label

Sources/Core/Checker.swift

@@ -930,6 +930,21 @@ extension Checker {
                 reportError("Can only switch on integer and enum types", at: match.start)
                 return dependencies
             }
+
+            if sw.usingMatch {
+                guard let type = baseType(match.type) as? ty.Enum else {
+                    reportError("using is invalid on \(operand)", at: match.start)
+                    return dependencies
+                }
+
+                for c in type.cases.orderedValues {
+                    let entity = newEntity(ident: c.ident, type: type, flags: [.field, .constant], owningScope: context.scope)
+                    entity.constant = c.constant ?? UInt64(c.number)
+                    declare(entity)
+                }
+            }
+        } else if sw.usingMatch {
+            reportError("Using expects an entity", at: sw.start)
         }
 
         var seenDefault = false

Sources/Core/Parser.swift

@@ -938,6 +938,13 @@ extension Parser {
     mutating func parseSwitchStmt() -> Switch {
         let keyword = eatToken()
         var match: Expr?
+
+        var usingMatch = false
+        if tok == .using {
+            next()
+            usingMatch = true
+        }
+
         if tok != .lbrace && tok != .semicolon {
             match = parseExpr()
         }
@@ -952,7 +959,7 @@ extension Parser {
         }
         let rbrace = expect(.rbrace)
         expectTerm()
-        return Switch(keyword: keyword, match: match, cases: cases, rbrace: rbrace, label: nil)
+        return Switch(keyword: keyword, match: match, usingMatch: usingMatch, cases: cases, rbrace: rbrace, label: nil)
     }
 
     mutating func parseCaseClause() -> CaseClause {

Sources/Core/generated/Copy.generated.swift

@@ -685,6 +685,7 @@ func copy(_ node: Switch) -> Switch {
     return Switch(
         keyword: node.keyword,
         match: node.match.map(copy),
+        usingMatch: node.usingMatch,
         cases: copy(node.cases),
         rbrace: node.rbrace,
         label: node.label