`ruleStack.clone()` doesn't actually clone

[RedCMD]

The clone() function on StateStack doesn't actually clone the object, but instead just returns the original object (reference)
meaning, tokenizeLine() will still modify the ruleStack that I was given

vscode-textmate/src/main.ts

Line 262 in 09effd8

clone(): StateStack;

Problem is that the clone implementation doesn't actually do any cloning

vscode-textmate/src/grammar/grammar.ts

Lines 732 to 734 in 09effd8

	public clone(): StateStackImpl {
	return this;
	}

instead something like structuredClone() should be used or use the clone function provided in the utils.ts file

vscode-textmate/src/utils.ts

Lines 7 to 9 in 09effd8

	export function clone<T>(something: T): T {
	return doClone(something);
	}

Found this out when the _enterPos and _anchorPos kept getting modified externally

[alexdima]

This is intentional and is a technique to save memory.

The _enterPos and _anchorPos fields are used for temporary storage and they only make sense during tokenization of a line. No external user of the library should make any assumption about those two fields. Then, clone() returns this because all other fields are immutable. This is to save memory.