As of Firefox 155, we intend to enable the WebAssembly compact import
section encoding by default on all platforms. This is a binary-only
change to reduce module sizes with no impact to WebAssembly semantics.
*Summary:*
The import section
<https://webassembly.github.io/spec/core/binary/modules.html#binary-importsec>
of a WebAssembly binary currently is a simple list of (module name, item
name, type) tuples. In practice, the module names are highly redundant
(usually all "env" or similar), and for modules with many imports, this
can be surprisingly wasteful.
The impact is particularly large for users of imported JS string
constants
<https://developer.mozilla.org/en-US/docs/WebAssembly/Guides/Imported_string_constants>.
In this case, the expected overhead is so high that MDN recommends using
an empty string as the module name to minimize binary size, which is
absurd and points to the need for a less wasteful encoding.
The Compact Import Section proposal, which we champion, addresses this
problem by providing two new binary encoding options that deduplicate
module names, and optionally the import types as well. This is an
encoding-only change with no impact to the behavior or semantics of
WebAssembly.
*Bugs:*
Tracker: https://bugzilla.mozilla.org/show_bug.cgi?id=wasm-compact-imports
Enable by default: https://bugzilla.mozilla.org/show_bug.cgi?id=2062344
*Specification:*
https://github.com/WebAssembly/compact-import-section
*Standards Body:*
W3C (WebAssembly CG & WG)
*Platform Coverage:*
All platforms
*Preference:*
javascript.options.wasm_compact_imports
*DevTools Bug:*
N/A
*Extensions Bug:*
N/A
*Use Counter:*
N/A
*Standards-Position Discussion:*
None, covered by our blanket policy for Wasm proposals.
*Other Browsers:*
- Blink: Implemented, not yet shipped
(https://chromium-review.googlesource.com/c/v8/v8/+/7573949)
- WebKit: No public signals
*web-platform-tests:*
None yet, but we run the official spec tests that will eventually be
upstreamed into WPT.
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