Add plugin for import.meta proposal #544

jkrems · 2017-05-27T17:51:37Z

Fixes #539

Q	A
Bug fix?	no
Breaking change?	no
New feature?	yes
Deprecations?	no
Spec compliancy?	yes
Tests added/pass?	yes
Fixed tickets	#539
License	MIT

Relatively straight-forward: Parses import.meta as a new MetaProperty. The expression is valid in modules but not in scripts. It can be enabled even when dynamicImport isn't enabled.

Fixes babel#539

codecov · 2017-05-27T17:56:15Z

Codecov Report

Merging #544 into master will decrease coverage by 1.32%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #544      +/-   ##
==========================================
- Coverage   98.14%   96.82%   -1.33%     
==========================================
  Files          22       22              
  Lines        3607     3617      +10     
  Branches     1007     1010       +3     
==========================================
- Hits         3540     3502      -38     
- Misses         24       58      +34     
- Partials       43       57      +14

Flag	Coverage Δ
#babel	`?`
#babylon	`96.82% <100%> (ø)`	⬆️

Impacted Files	Coverage Δ
src/parser/expression.js	`93.48% <100%> (-3.37%)`	⬇️
src/parser/statement.js	`98.23% <100%> (-0.89%)`	⬇️
src/parser/comments.js	`87.87% <0%> (-6.07%)`	⬇️
src/tokenizer/state.js	`97.14% <0%> (-2.86%)`	⬇️
src/plugins/flow.js	`97.35% <0%> (-1.04%)`	⬇️
src/tokenizer/index.js	`97.41% <0%> (-1%)`	⬇️

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jkrems · 2017-05-27T18:04:59Z

The CI failure seems to be unrelated to this change..?

bakkot · 2017-05-27T18:25:49Z

Should make sure to disallow import.meta = val. I don't think it's specced yet, but it will be.

jkrems · 2017-05-27T18:49:47Z

Added tests to verify that:

import.meta is not a valid assignment target
import.meta.prop is a valid assignment target

hzoo · 2017-05-28T03:41:23Z

test/fixtures/experimental/import-meta/without-dynamic-import/actual.js

+const x = import.meta;
+const url = import.meta.url;
+import.meta;
+import.meta.url;


Was there a reason this test didn't also have import.meta.couldBeMutable = true;? But the other did?

No deeper reason than "order of copy&paste". ^^ Copied the actual.js/expected.json over again to keep them in sync.

hzoo

Nice work! really fast 😄

cc @domenic

Jessidhia

Looks good to me (but I'm not familiar with the parser at all).

AST format is:

MetaProperty {
  meta: Identifier { name: 'import' }
  property: Identifier { name: 'meta' }
}

Just need to do something about the error message when parsing, say, import.notMeta.

Jessidhia · 2017-05-29T01:41:15Z

src/parser/expression.js

+    if (this.options.sourceType !== "module") {
+      this.raise(id.start, "import.meta can only be used in modules");
+    }
+    return this.parseMetaProperty(node, id, "meta");


The error message if the meta property isn't .meta is confusing (it's hardcoded to mention new)

Oops, good point. Added a test that checks for that & made it use the correct name.

existentialism

Nice work!

existentialism · 2017-05-29T02:17:21Z

src/parser/expression.js

+    const node = this.startNode();
+    const id = this.parseIdentifier(true);
+    this.expect(tt.dot);
+    if (this.options.sourceType !== "module") {


Can also do if (!this.inModule) here

Weird, I thought I tried that first but .inModule was only true top-level. Must have missed something. You're right, definitely works fine.

existentialism · 2017-05-29T02:18:12Z

src/parser/expression.js

+    const id = this.parseIdentifier(true);
+    this.expect(tt.dot);
+    if (this.options.sourceType !== "module") {
+      this.raise(id.start, "import.meta can only be used in modules");


May want to make this consistent with other sourceType errors?

'import.meta' can only be used with 'sourceType: module'

Heh, good point. Copied the wording from "can only be used in functions". Should've taken the wording from import/export statements. Fixed.

rwaldron · 2017-05-30T18:09:22Z

This might be irrelevant, or possibly a subject to have in a new issue, but I'm curious about the drops in coverage? For example, it says above that six files were impacted, but four of them aren't changed at all:

src/parser/comments.js 87.87% <0%> (-6.07%) ⬇️
src/tokenizer/state.js 97.14% <0%> (-2.86%) ⬇️
src/plugins/flow.js 97.35% <0%> (-1.04%) ⬇️
src/tokenizer/index.js 97.41% <0%> (-1%) ⬇️

jkrems · 2017-05-30T18:12:27Z

@rwaldron Yeah, I was wondering about the same thing. I tried rebasing on master in case it was using some weird merge head but afaict that wasn't it.

Add plugin for import.meta proposal

826ced9

Fixes babel#539

hzoo reviewed May 28, 2017

View reviewed changes

hzoo added spec-new Tag: New Feature Spec: import.meta labels May 28, 2017

hzoo assigned Jessidhia and bakkot and unassigned Jessidhia May 28, 2017

hzoo approved these changes May 28, 2017

View reviewed changes

Tests for assignment/mutation of import.meta

60ac623

jkrems force-pushed the jk-import-meta branch from dfd1074 to 60ac623 Compare May 28, 2017 16:15

Jessidhia suggested changes May 29, 2017

View reviewed changes

Use correct identifier in failure message

937f3ba

Jessidhia approved these changes May 29, 2017

View reviewed changes

existentialism approved these changes May 29, 2017

View reviewed changes

Simpler & more consistent script errors for import.meta

aa7baab

hzoo merged commit d4e842d into babel:master May 30, 2017

jkrems deleted the jk-import-meta branch May 30, 2017 23:30

hzoo mentioned this pull request Jun 7, 2017

import.meta: Stage 2 babel/babel#5832

Closed

babel-bot mentioned this pull request Jul 10, 2017

import.meta: (Stage 3) babel/proposals#10

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Add plugin for import.meta proposal #544

Add plugin for import.meta proposal #544

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Add plugin for import.meta proposal #544

Add plugin for import.meta proposal #544

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