CST: Add initial support for types (#231)

This PR adds initial support for serializing types as part of the CST.
This includes serializing type references, singleton strings and
booleans, types wrapped in parentheses (type group) and typeof. We also
serialize type alias statements (for now, excluding generics. We will
introduce generic declarations in a follow up commit)

Author: JohnnyMorganz

batteries/syntax/ast_types.luau

@@ -281,6 +281,15 @@ export type AstStatLocalFunction = {
 	body: AstFunctionBody,
 }
 
+export type AstStatTypeAlias = {
+	tag: "typealias",
+	["export"]: Token<"export">?,
+	typeToken: Token<"type">,
+	name: Token,
+	equals: Token<"=">,
+	type: AstType,
+}
+
 export type AstStat =
 	| AstStatBlock
 	| AstStatIf
@@ -297,5 +306,43 @@ export type AstStat =
 	| AstStatCompoundAssign
 	| AstStatFunction
 	| AstStatLocalFunction
+	| AstStatTypeAlias
+
+export type AstTypeReference = {
+	tag: "reference",
+	prefix: Token<string>?,
+	prefixPoint: Token<".">?,
+	name: Token<string>,
+	openParameters: Token<"<">?,
+	parameters: Punctuated<AstType>?,
+	closeParameters: Token<">">?,
+}
+
+export type AstTypeSingletonBool = Token<"true" | "false"> & {
+	tag: "boolean",
+	value: boolean,
+}
+
+export type AstTypeSingletonString = Token<string> & {
+	tag: "string",
+	quoteStyle: "single" | "double",
+}
+
+export type AstTypeTypeof = {
+	tag: "typeof",
+	typeof: Token<"typeof">,
+	openParens: Token<"(">,
+	expr: AstExpr,
+	closeParens: Token<")">,
+}
+
+export type AstTypeGroup = {
+	tag: "group",
+	openParens: Token<"(">,
+	type: AstType,
+	closeParens: Token<">">,
+}
+
+export type AstType = | AstTypeReference | AstTypeSingletonBool | AstTypeSingletonString | AstTypeTypeof | AstTypeGroup
 
 return {}

batteries/syntax/printer.luau

@@ -61,6 +61,11 @@ local function printBlock(block: T.AstStatBlock): string
 		return false
 	end
 
+	printer.visitTypeString = function(node: T.AstTypeSingletonString)
+		result ..= printString(node)
+		return false
+	end
+
 	visitor.visitBlock(block, printer)
 
 	return result

batteries/syntax/visitor.luau

@@ -15,6 +15,7 @@ type Visitor = {
 	visitCompoundAssign: (T.AstStatCompoundAssign) -> boolean,
 	visitFunction: (T.AstStatFunction) -> boolean,
 	visitLocalFunction: (T.AstStatLocalFunction) -> boolean,
+	visitTypeAlias: (T.AstStatTypeAlias) -> boolean,
 
 	visitLocalReference: (T.AstExprLocal) -> boolean,
 	visitGlobal: (T.AstExprGlobal) -> boolean,
@@ -28,6 +29,12 @@ type Visitor = {
 	visitIndexExpr: (T.AstExprIndexExpr) -> boolean,
 	visitGroup: (T.AstExprGroup) -> boolean,
 
+	visitTypeReference: (T.AstTypeReference) -> boolean,
+	visitTypeBoolean: (T.AstTypeSingletonBool) -> boolean,
+	visitTypeString: (T.AstTypeSingletonString) -> boolean,
+	visitTypeTypeof: (T.AstTypeTypeof) -> boolean,
+	visitTypeGroup: (T.AstTypeGroup) -> boolean,
+
 	visitToken: (T.Token) -> boolean,
 	visitNil: (T.AstExprConstantNil) -> boolean,
 	visitString: (T.AstExprConstantString) -> boolean,
@@ -54,6 +61,7 @@ local defaultVisitor: Visitor = {
 	visitCompoundAssign = alwaysVisit :: any,
 	visitFunction = alwaysVisit :: any,
 	visitLocalFunction = alwaysVisit :: any,
+	visitTypeAlias = alwaysVisit :: any,
 
 	visitLocalReference = alwaysVisit :: any,
 	visitGlobal = alwaysVisit :: any,
@@ -67,6 +75,12 @@ local defaultVisitor: Visitor = {
 	visitIndexExpr = alwaysVisit :: any,
 	visitGroup = alwaysVisit :: any,
 
+	visitTypeReference = alwaysVisit :: any,
+	visitTypeBoolean = alwaysVisit :: any,
+	visitTypeString = alwaysVisit :: any,
+	visitTypeTypeof = alwaysVisit :: any,
+	visitTypeGroup = alwaysVisit :: any,
+
 	visitToken = alwaysVisit :: any,
 	visitNil = alwaysVisit :: any,
 	visitString = alwaysVisit :: any,
@@ -209,6 +223,18 @@ local function visitCompoundAssign(node: T.AstStatCompoundAssign, visitor: Visit
 	end
 end
 
+local function visitTypeAlias(node: T.AstStatTypeAlias, visitor: Visitor)
+	if visitor.visitTypeAlias(node) then
+		if node.export then
+			visitToken(node.export, visitor)
+		end
+		visitToken(node.typeToken, visitor)
+		visitToken(node.name, visitor)
+		visitToken(node.equals, visitor)
+		visitType(node.type, visitor)
+	end
+end
+
 local function visitString(node: T.AstExprConstantString, visitor: Visitor)
 	if visitor.visitString(node) then
 		visitor.visitToken(node)
@@ -370,6 +396,56 @@ local function visitGroup(node: T.AstExprGroup, visitor: Visitor)
 	end
 end
 
+local function visitTypeReference(node: T.AstTypeReference, visitor: Visitor)
+	if visitor.visitTypeReference(node) then
+		if node.prefix then
+			visitToken(node.prefix, visitor)
+		end
+		if node.prefixPoint then
+			visitToken(node.prefixPoint, visitor)
+		end
+		visitToken(node.name, visitor)
+		if node.openParameters then
+			visitToken(node.openParameters, visitor)
+		end
+		if node.parameters then
+			visitPunctuated(node.parameters, visitor, visitType)
+		end
+		if node.closeParameters then
+			visitToken(node.closeParameters, visitor)
+		end
+	end
+end
+
+local function visitTypeBoolean(node: T.AstTypeSingletonBool, visitor: Visitor)
+	if visitor.visitTypeBoolean(node) then
+		visitToken(node, visitor)
+	end
+end
+
+local function visitTypeString(node: T.AstTypeSingletonString, visitor: Visitor)
+	if visitor.visitTypeString(node) then
+		visitToken(node, visitor)
+	end
+end
+
+local function visitTypeTypeof(node: T.AstTypeTypeof, visitor: Visitor)
+	if visitor.visitTypeTypeof(node) then
+		visitToken(node.typeof, visitor)
+		visitToken(node.openParens, visitor)
+		visitExpression(node.expr, visitor)
+		visitToken(node.closeParens, visitor)
+	end
+end
+
+local function visitTypeGroup(node: T.AstTypeGroup, visitor: Visitor)
+	if visitor.visitTypeGroup(node) then
+		visitToken(node.openParens, visitor)
+		visitType(node.type, visitor)
+		visitToken(node.closeParens, visitor)
+	end
+end
+
 function visitExpression(expression: T.AstExpr, visitor: Visitor)
 	if expression.tag == "nil" then
 		visitNil(expression, visitor)
@@ -437,11 +513,29 @@ function visitStatement(statement: T.AstStat, visitor: Visitor)
 		visitFunction(statement, visitor)
 	elseif statement.tag == "localfunction" then
 		visitLocalFunction(statement, visitor)
+	elseif statement.tag == "typealias" then
+		visitTypeAlias(statement, visitor)
 	else
 		exhaustiveMatch(statement.tag)
 	end
 end
 
+function visitType(type: T.AstType, visitor: Visitor)
+	if type.tag == "reference" then
+		visitTypeReference(type, visitor)
+	elseif type.tag == "boolean" then
+		visitTypeBoolean(type, visitor)
+	elseif type.tag == "string" then
+		visitTypeString(type, visitor)
+	elseif type.tag == "typeof" then
+		visitTypeTypeof(type, visitor)
+	elseif type.tag == "group" then
+		visitTypeGroup(type, visitor)
+	else
+		exhaustiveMatch(type.tag)
+	end
+end
+
 local function createVisitor()
 	return table.clone(defaultVisitor)
 end