1782491 - Enable "no-undef" ESLint rule for self-hosted code

Status: RESOLVED FIXED

(Core :: JavaScript Engine, task, P1)

Description

[André Bargull [:anba]]

Misspelled variable names in self-hosted code currently lead to assertion errors, but only when the relevant code is actually executed. We can improve this situation for ESLint capable editors [1] by providing an ESLint plugin which determines all self-hosted global variables.

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[1] Or when manually executing ./mach lint js/src/builtin/.

Comment 1

[André Bargull [:anba]]

Attachment: Bug 1782491 - Part 1: Add self-hosted code environment plugin. r=tcampbell!

Adds a simple ESLint plugin for custom environments.

The plugin has a single exported value named globals, which is an object with
keys for all globally available self-hosted identifiers. All self-hosted values
are read-only, so we set all properties of globals to "readonly".

BytecodeEmitter special identifiers are added to the .eslintrc.js file,
because that keeps them closer to the SpiderMonkey source tree when compared
to "tools/lint/eslint/eslint-plugin-spidermonkey-js".

Also see:

• tools/lint/eslint/eslint-plugin-mozilla/lib/environments/
• https://eslint.org/docs/latest/user-guide/configuring/language-options

Comment 2

[André Bargull [:anba]]

Attachment: Bug 1782491 - Part 2: Warn about undeclared variables in self-hosted code. r=tcampbell!

Enable the "no-undef" ESLint rule for self-hosted code.

The plugin from part 1 can't discover two special cases:

1. Dynamically generated RegExp functions.
2. The inner #define in endOfUnicodeExtensions.

Add /* global <name> */ comments to declare these names as global identifiers.

HYPHEN isn't really a global variable, part 5 will clean this up.

Depends on D153337

Comment 3

[André Bargull [:anba]]

Attachment: Bug 1782491 - Part 3: Undefine standard built-ins in self-hosted code. r=tcampbell!

Standard global identifiers aren't available in self-hosted code. Let's
undefine them, so ESLint-capable editors will warn when they're used.

It seems that names must be undeclared in ".eslintrc.js" files, because any
attempts to undeclare them in the ESLint environment plugin from part 1 didn't
work out.

The Mozilla ESLint plugin enables the "mozilla/privileged" environment by
default, see "tools/lint/eslint/eslint-plugin-mozilla/lib/configs/recommended.js".
We don't want it to be enabled for self-hosted code.

Depends on D153338

Comment 4

[André Bargull [:anba]]

Attachment: Bug 1782491 - Part 4: Enable strict-mode by default for eslint. r=tcampbell!

Self-hosted code is always strict-mode, but ESLint doesn't know about that.

Depends on D153339

Comment 5

[André Bargull [:anba]]

Attachment: Bug 1782491 - Part 5: Use simple string comparison in endOfUnicodeExtensions. r=tcampbell!

charCodeAt was faster than indexed string lookups when this function was
originally written (bug 1440315). After bug 813836 there isn't anymore any
performance difference, so we might as well use the simpler code.

Depends on D153340

Comment 6

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/24470be9cddc
Part 1: Add self-hosted code environment plugin. r=tcampbell
https://hg.mozilla.org/integration/autoland/rev/405f2f052ffb
Part 2: Warn about undeclared variables in self-hosted code. r=tcampbell
https://hg.mozilla.org/integration/autoland/rev/aec7a500c04e
Part 3: Undefine standard built-ins in self-hosted code. r=tcampbell
https://hg.mozilla.org/integration/autoland/rev/9fe496797601
Part 4: Enable strict-mode by default for eslint. r=tcampbell
https://hg.mozilla.org/integration/autoland/rev/64beab0dc780
Part 5: Use simple string comparison in endOfUnicodeExtensions. r=tcampbell

Comment 7

[Atila Butkovits]

https://hg.mozilla.org/mozilla-central/rev/24470be9cddc
https://hg.mozilla.org/mozilla-central/rev/405f2f052ffb
https://hg.mozilla.org/mozilla-central/rev/aec7a500c04e
https://hg.mozilla.org/mozilla-central/rev/9fe496797601
https://hg.mozilla.org/mozilla-central/rev/64beab0dc780