perf: avoid cloning in parser advanceBy

packages/compiler-core/src/parse.ts

@@ -1,4 +1,5 @@
 import { ErrorCodes, CompilerError, createCompilerError } from './errors'
+import { assert, advancePositionWithMutation } from './utils'
 import {
   Namespace,
   Namespaces,
@@ -15,7 +16,6 @@ import {
   TextNode,
   ChildNode
 } from './ast'
-import { assert, advancePositionBy } from './utils'
 
 export interface ParserOptions {
   isVoidTag?: (tag: string) => boolean // e.g. img, br, hr
@@ -794,15 +794,9 @@ function startsWith(source: string, searchString: string): boolean {
 }
 
 function advanceBy(context: ParserContext, numberOfCharacters: number): void {
-  __DEV__ && assert(numberOfCharacters <= context.source.length)
-
   const { source } = context
-  const pos = advancePositionBy(context, source, numberOfCharacters)
-
+  advancePositionWithMutation(context, source, numberOfCharacters)
   context.source = source.slice(numberOfCharacters)
-  context.offset = pos.offset
-  context.line = pos.line
-  context.column = pos.column
 }
 
 function advanceSpaces(context: ParserContext): void {

packages/compiler-core/src/utils.ts

@@ -24,23 +24,29 @@ export function advancePositionBy(
   source: string,
   numberOfCharacters: number
 ): Position {
-  __DEV__ && assert(numberOfCharacters <= source.length)
+  return advancePositionWithMutation({ ...pos }, source, numberOfCharacters)
+}
 
-  const newPosition = {
-    ...pos
-  }
+// advance by mutation without cloning (for performance reasons), since this
+// gets called a lot in the parser
+export function advancePositionWithMutation(
+  pos: Position,
+  source: string,
+  numberOfCharacters: number
+): Position {
+  __DEV__ && assert(numberOfCharacters <= source.length)
 
   const str = source.slice(0, numberOfCharacters)
   const lines = str.split(/\r?\n/)
 
-  newPosition.offset += numberOfCharacters
-  newPosition.line += lines.length - 1
-  newPosition.column =
+  pos.offset += numberOfCharacters
+  pos.line += lines.length - 1
+  pos.column =
     lines.length === 1
       ? pos.column + numberOfCharacters
       : Math.max(1, lines.pop()!.length)
 
-  return newPosition
+  return pos
 }
 
 export function assert(condition: boolean, msg?: string) {