"use strict"/etc directives should be labeled as such

[josephfrazier]

What version of TypeScript are you using?

2.3.2

What version of typescript-eslint-parser are you using?

a294afa

What code were you trying to parse?

"use strict";
"other directive";

What did you expect to happen?

I expected an AST indicating that these literals are part of a Directive Prologue.

What happened?

The AST doesn't differentiate between directive literals and non-directive literals. For example:

typescript-eslint-parser/tests/fixtures/ast/Tolerant-parse.json

Lines 4104 to 4167 in f5fcc87

	"function hello() { \"octal directive\\1\"; \"use strict\"; }": {
	"type": "Program",
	"body": [
	{
	"type": "FunctionDeclaration",
	"id": {
	"type": "Identifier",
	"name": "hello",
	"range": [
	9,
	14
	],
	"loc": {
	"start": {
	"line": 1,
	"column": 9
	},
	"end": {
	"line": 1,
	"column": 14
	}
	}
	},
	"params": [],
	"body": {
	"type": "BlockStatement",
	"body": [
	{
	"type": "ExpressionStatement",
	"expression": {
	"type": "Literal",
	"value": "octal directive\u0001",
	"raw": "\"octal directive\\1\"",
	"range": [
	19,
	38
	],
	"loc": {
	"start": {
	"line": 1,
	"column": 19
	},
	"end": {
	"line": 1,
	"column": 38
	}
	}
	},
	"range": [
	19,
	39
	],
	"loc": {
	"start": {
	"line": 1,
	"column": 19
	},
	"end": {
	"line": 1,
	"column": 39
	}
	}
	},

For comparison, here are some other ASTs for "octal directive", both of which indicate that the literal is a directive:

• Babylon: http://astexplorer.net/#/gist/29393e8fc8313aa11944f9146ceca787/0c135e856c8212bfe68702ae122261ecd4d08330
• Flow: http://astexplorer.net/#/gist/29393e8fc8313aa11944f9146ceca787/a59985860d2ee2faef66046f1d22180364a2e53b

---

Discovered in prettier/prettier#1560 (comment)

[soda0289]

This is not yet part of the ESTree spec. There has been a lot of discussion about it here:
estree/estree#6
and a PR:
estree/estree#152

We could implement the proposal and change it if its modified. But it might be better to wait for it to become official.

[josephfrazier]

Thanks for the quick response and references! That makes sense, why it's not implemented yet. Cheers!

[JamesHenry]

We will implement this if it gets accepted into ESTree

[azz]

Good news! estree/estree#152