perf: Disable all unnecessary `default-features` by kdy1 · Pull Request #11208 · swc-project/swc

kdy1 · 2025-10-30T05:11:16Z

Description:

This is to drop dependencies that is not strictly required. The binary size gain of this PR for @swc/core is 422.37500KB

Note that removing a feature flag may break the build of the downstram crates, so I'll mark this as a breaking change of modified crates.

TODOs

Check [Bug]: ProgressPlugin containing non-ASCII characters cannot clear the screen web-infra-dev/rspack#10988 (comment)

changeset-bot · 2025-10-30T05:11:21Z

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…tributes feature - Update swc_atoms from 8.0.2 to 9.0.0 - Update swc_common from 16.0.0 to 18.0.1 - Update swc_ecma_ast from 17.0.0 to 20.0.1 - Update swc_ecma_transforms_base from 29.0.0 to 36.0.1 - Update swc_ecma_utils from 23.0.0 to 26.0.1 - Update swc_ecma_visit from 17.0.0 to 20.0.0 - Add tracing 'attributes' feature required for #[swc_trace] macro Co-authored-by: Donny/강동윤 <kdy1@users.noreply.github.com>

kdy1 · 2026-02-02T01:17:22Z

@claude fix CI

…r swc_common - hstr: Add `std` feature to serde dependency to enable String::deserialize - swc_common: Add `attributes` feature to tracing dependency to enable #[instrument] macro Co-authored-by: Donny/강동윤 <kdy1@users.noreply.github.com>

kdy1 · 2026-02-02T12:20:20Z

@claude Fix CI

claude · 2026-02-02T12:20:42Z

Claude finished @kdy1's task in 2m 14s —— View job

Fixing CI

Check CI status and identify failures
Analyze failing jobs
Fix the issues
Push fixes

Fixed issues:

swc_common: Added derive feature to shrink-to-fit dependency - required for the ShrinkToFit derive macro
swc_core: Added serde-impl feature to swc_ecma_transforms_react dependency - required for serde support in react transforms

Pushed commit e5fffc45f
| Branch

claude · 2026-02-02T12:22:49Z

PR Review: perf: Disable all unnecessary `default-features`

Overview

This PR aims to reduce binary size by disabling unnecessary default features across all dependencies. The reported binary size reduction of ~422KB for @swc/core is significant. However, there are several issues that need to be addressed.

🔴 Critical Issues (Blocking)

1. CI Build Failures - Missing `petgraph::graphmap` Feature

The build is currently failing with:

error[E0432]: unresolved import `petgraph::prelude::GraphMap`
error: could not compile `swc_ecma_transforms_optimization` (lib) due to 1 previous error

The issue is in Cargo.toml:

petgraph = { version = "0.7.1", default-features = false }

This disables the graphmap feature, but swc_ecma_transforms_optimization/src/simplify/dce/mod.rs:4 imports:

use petgraph::{algo::tarjan_scc, prelude::GraphMap, Directed, Direction::Incoming};

Fix: Add the required features:

petgraph = { version = "0.7.1", default-features = false, features = ["graphmap"] }

And in crates/swc_ecma_transforms_optimization/Cargo.toml:

petgraph = { workspace = true, default-features = false, features = ["graphmap"] }

🟡 Code Quality Observations

2. New `swc_ecma_compiler` Crate

The new swc_ecma_compiler crate (855 lines in lib.rs) adds substantial new functionality. Some observations:

Positives:

Well-structured with clear separation of ES2020, ES2021, ES2022 transformations
Good use of bitflags for feature selection
Proper visitor pattern implementation

Concerns:

features.rs:8 defines OPTIONAL_CHAINING feature flag but it doesn't appear to be implemented in any transformation code in this PR. Is this intentional for future use?
The crate lacks unit tests. Consider adding tests for the transformations (especially for the complex private_in_object and nullish_coalescing transformations).

3. Wtf8Atom Serialization (`crates/hstr/src/wtf8_atom.rs`)

The new serialization/deserialization logic for handling unpaired surrogates looks well-thought-out and has comprehensive test coverage. The fix for issue #11214 (backslash handling) is correctly addressed.

🟢 Performance Observations

The approach of systematically disabling default-features across all workspace dependencies is sound for binary size reduction. The explicit re-enabling of necessary features (e.g., lexical = { ..., features = ["std", "parse-floats", "parse-integers"] }) shows careful attention to maintaining functionality.

📋 Recommendations

Fix the petgraph feature issue - This is blocking CI.
Consider feature documentation - Since this PR marks many crates as default-features = false, downstream users may need to explicitly enable features. Consider documenting which features are essential for common use cases.
Add tests for swc_ecma_compiler - The new crate implements complex ECMAScript transformations but lacks dedicated tests.
Verify the rspack issue - The TODO mentions checking [Bug]: ProgressPlugin containing non-ASCII characters cannot clear the screen web-infra-dev/rspack#10988 (comment) - ensure this is verified before merging.

Summary

The PR's goal of reducing binary size through careful feature management is valuable. However, the build is currently broken due to missing petgraph features. Once that's fixed and CI passes, this should be ready for final review.

Estimated Impact:

Binary size reduction: ✅ ~422KB (significant)
Breaking changes: ⚠️ Yes (as noted in PR description - downstream crates may need feature adjustments)
Test coverage: 🔶 Existing tests for Wtf8Atom, missing for new swc_ecma_compiler crate

…r swc_common - Add `derive` feature to shrink-to-fit dependency in swc_common - Add `serde-impl` feature to swc_ecma_transforms_react in swc_core Co-authored-by: Donny/강동윤 <kdy1@users.noreply.github.com>

Copilot

Pull request overview

This PR systematically disables default features across hundreds of dependencies in the SWC monorepo to reduce binary size by ~422KB. The changes span workspace-level configuration and individual crate manifests.

Changes:

Workspace dependencies now specify default-features = false
Necessary features are explicitly re-enabled (e.g., std, alloc for serde_json)
New swc_ecma_compiler crate added
Test code gated with #[cfg(feature = "serde")]

Reviewed changes

Copilot reviewed 146 out of 147 changed files in this pull request and generated 5 comments.

File	Description
Cargo.toml	Workspace-level dependency defaults disabled with explicit feature re-enabling
crates/*/Cargo.toml	~100+ crates updated to disable default features
crates/swc_ecma_compiler/*	New crate for ES compatibility layer
crates/hstr/src/wtf8_atom.rs	Added feature gates for serde-dependent tests

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Copilot · 2026-02-02T12:23:55Z

Cargo.toml

+js-sys                    = { version = "0.3.77", default-features = false }
+jsonc-parser              = { version = "0.26.2", default-features = false }
+kstring                   = { version = "2.0.0", default-features = false }
+lazy_static               = { version = "1.4.0", default-features = false }


The workspace lexical dependency adds explicit features ["std", "parse-floats", "parse-integers"] when disabling default features. This is good practice as lexical requires these for basic functionality. Consider documenting why these specific features are needed to help future maintainers understand the requirement.

Suggested change

lazy_static = { version = "1.4.0", default-features = false }

lazy_static = { version = "1.4.0", default-features = false }

# lexical's default features are disabled; `std`, `parse-floats`, and `parse-integers`

# are explicitly enabled because they are required for the crate's basic number

# parsing functionality used across this workspace.

Copilot · 2026-02-02T12:23:55Z

Cargo.toml

+st-map                    = { version = "0.2.0", default-features = false }
+string_cache              = { version = "0.8.7", default-features = false }
+swc_sourcemap             = { version = "9.3.4", default-features = false }
+syn                       = { version = "2", default-features = false, features = ["derive", "parsing", "printing", "clone-impls", "proc-macro"] }


The syn workspace dependency uses features = ["derive", "parsing", "printing", "clone-impls", "proc-macro"] with default-features = false. However, individual crates using syn (like testing_macros, various codegen_macros crates) specify different feature sets without proc-macro. This could cause issues if the workspace default features don't align with what the crates actually need. Verify that all syn usages have the correct features explicitly listed.

Suggested change

syn = { version = "2", default-features = false, features = ["derive", "parsing", "printing", "clone-impls", "proc-macro"] }

syn = { version = "2", default-features = false }

Copilot · 2026-02-02T12:23:55Z

crates/testing_macros/Cargo.toml

+anyhow        = { workspace = true, default-features = false }
+glob          = { workspace = true, default-features = false }
+once_cell     = { workspace = true, default-features = false }
+proc-macro2   = { workspace = true, default-features = false }
+quote         = { workspace = true, default-features = false }


The proc-macro2, quote, and syn crates typically require the proc-macro feature to be enabled when used in proc-macro crates. Disabling default features without explicitly enabling necessary features like proc-macro may cause compilation failures. Please verify that these dependencies build correctly without default features, or add the required features explicitly.

Copilot · 2026-02-02T12:23:56Z

crates/swc_allocator/Cargo.toml

-bumpalo        = { workspace = true, features = ["allocator-api2"] }
-hashbrown      = { workspace = true, optional = true }
-rustc-hash     = { workspace = true }
+allocator-api2 = { workspace = true, default-features = true }


The allocator-api2 crate has default-features = true which is inconsistent with the PR's goal of disabling default features. This should likely be default-features = false for consistency, unless there's a specific reason to keep defaults enabled for this dependency.

Suggested change

allocator-api2 = { workspace = true, default-features = true }

allocator-api2 = { workspace = true, default-features = false }

Copilot · 2026-02-02T12:23:56Z

crates/hstr/Cargo.toml

+compact_str  = { workspace = true, default-features = true }
+criterion    = { workspace = true, default-features = true }
+kstring      = { workspace = true, default-features = true, features = ["std"] }
+num_cpus     = { workspace = true, default-features = true }
+par-iter     = { workspace = true, default-features = true }
+rand         = { workspace = true, default-features = true }
+serde_json   = { workspace = true, default-features = true }
+smartstring  = { workspace = true, default-features = true }
+smol_str     = { workspace = true, default-features = true }
+string_cache = { workspace = true, default-features = true }


The workspace configuration sets default-features = true for several dev-dependencies (codspeed-criterion-compat, criterion, compact_str, kstring, etc.) while the PR aims to disable default features. This inconsistency should be reviewed - either these need defaults enabled for a specific reason, or they should be set to false for consistency with the PR's goals.

Suggested change

compact_str = { workspace = true, default-features = true }

criterion = { workspace = true, default-features = true }

kstring = { workspace = true, default-features = true, features = ["std"] }

num_cpus = { workspace = true, default-features = true }

par-iter = { workspace = true, default-features = true }

rand = { workspace = true, default-features = true }

serde_json = { workspace = true, default-features = true }

smartstring = { workspace = true, default-features = true }

smol_str = { workspace = true, default-features = true }

string_cache = { workspace = true, default-features = true }

compact_str = { workspace = true, default-features = false }

criterion = { workspace = true, default-features = false }

kstring = { workspace = true, default-features = false, features = ["std"] }

num_cpus = { workspace = true, default-features = false }

par-iter = { workspace = true, default-features = false }

rand = { workspace = true, default-features = false }

serde_json = { workspace = true, default-features = false }

smartstring = { workspace = true, default-features = false }

smol_str = { workspace = true, default-features = false }

string_cache = { workspace = true, default-features = false }

kdy1 · 2026-02-02T23:00:25Z

@claude fix ci

claude · 2026-02-02T23:00:57Z

Claude finished @kdy1's task in 8m 37s —— View job

Fixing CI

Fixed issues:

swc_ecma_transforms/Cargo.toml: Added serde-impl feature to swc_ecma_transforms_react - required for serde imports in jsx/mod.rs and refresh/options.rs
testing/Cargo.toml: Added std, fmt, ansi features to tracing-subscriber and std to tracing - required for FmtSubscriber, set_default, and .pretty()
swc_config/Cargo.toml: Added std feature to anyhow - required for Context trait
Cargo.toml (workspace): Added std, unicode features to regex - required for std::error::Error impl
swc_ecma_transforms_optimization/Cargo.toml: Added graphmap feature to petgraph - required for GraphMap import
swc_ecma_transforms_react/Cargo.toml: Added alloc feature to base64 - required for .encode() method
swc_ecma_preset_env/Cargo.toml: Added std feature to anyhow and rustc-hash in build-dependencies - required for FxHashSet
swc_ecma_minifier/Cargo.toml: Added std feature to tracing - required for set_default function
swc/Cargo.toml: Added std feature to anyhow and base64 - required for Context trait and DecodeError error handling

Pushed commit 0c7f50ee8 | Branch

- swc_ecma_transforms: Add serde-impl feature to swc_ecma_transforms_react - testing: Add std, fmt, ansi features to tracing-subscriber, std to tracing - swc_config: Add std feature to anyhow for Context trait - Cargo.toml: Add std, unicode features to regex for std::error::Error impl - swc_ecma_transforms_optimization: Add graphmap feature to petgraph - swc_ecma_transforms_react: Add alloc feature to base64 for encode method - swc_ecma_preset_env: Add std to anyhow and rustc-hash in build-deps - swc_ecma_minifier: Add std to tracing for set_default function - swc: Add std to anyhow and base64 for error handling Co-authored-by: Donny/강동윤 <kdy1@users.noreply.github.com>

socket-security · 2026-02-02T23:10:25Z

No dependency changes detected. Learn more about Socket for GitHub.

👍 No dependency changes detected in pull request

kdy1 · 2026-02-02T23:38:40Z

@claude fix ci

claude · 2026-02-02T23:39:09Z

Claude finished @kdy1's task in 5m 29s —— View job

Fixing CI

Fixed issues:

Cargo.toml (workspace): Added alloc feature to hex - required for hex::encode
Cargo.toml (workspace): Added std feature to indexmap - required for IndexMap::new()
swc_ts_fast_strip/Cargo.toml: Added serde-impl feature to swc_ecma_transforms_react - required for serde imports in jsx/mod.rs and refresh/options.rs

Pushed commit af2ff3ad5 | Branch

- hex: Add alloc feature required for hex::encode - indexmap: Add std feature required for IndexMap::new() - swc_ts_fast_strip: Add serde-impl feature to swc_ecma_transforms_react Co-authored-by: Donny/강동윤 <kdy1@users.noreply.github.com>

kdy1 · 2026-02-03T01:35:11Z

@claude fix ci

claude · 2026-02-03T01:35:41Z

Claude finished @kdy1's task in 4m 13s —— View job

Fixing CI

Check CI status and identify failures
Analyze failing jobs
Fix the issues
Push fixes

Fixed issues:

Cargo.toml (workspace): Added std feature to base64 - required for encode and encode_string methods used in swc_compiler_base, swc_ecma_transforms_testing, and swc_ecma_transforms_react
swc_ecma_transforms_react/Cargo.toml: Removed explicit features = ["alloc"] to inherit workspace's std feature for base64
swc_ecma_transforms_typescript/Cargo.toml: Added serde-impl feature to swc_ecma_transforms_react dependency - required for serde imports in jsx/mod.rs and refresh/options.rs during benchmarks

Pushed commit 18aeca805 | View job | Branch

- Cargo.toml: Added `std` feature to `base64` - required for `encode` and `encode_string` methods used in swc_compiler_base and other crates - swc_ecma_transforms_react: Removed explicit `features = ["alloc"]` to inherit workspace's `std` feature for base64 - swc_ecma_transforms_typescript: Added `serde-impl` feature to `swc_ecma_transforms_react` dependency - required for serde imports in jsx/mod.rs and refresh/options.rs during benchmarks Co-authored-by: Donny/강동윤 <kdy1@users.noreply.github.com>

codspeed-hq · 2026-02-03T01:44:36Z

CodSpeed Performance Report

Merging this PR will improve performance by 4.07%

_{Comparing kdy1/size-check (18aeca8) with main (3e63627)}

Summary

⚡ 2 improved benchmarks
✅ 76 untouched benchmarks
⏩ 106 skipped benchmarks¹

Performance Changes

	Benchmark	`BASE`	`HEAD`	Efficiency
⚡	`es/codegen/with-parser/large`	1.2 ms	1.1 ms	+3.21%
⚡	`es/codegen/with-parser/colors`	158.5 µs	152.3 µs	+4.07%

106 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

kdy1 · 2026-03-07T02:28:43Z

@codex Review

kdy1 added 10 commits October 30, 2025 13:52

default-features = false

b77ebee

lockfile

af53267

fmt

2dc437b

fix

bb7294d

clap

ec5f599

lexical

aa1eaa1

rustc-hash/std

7dfc745

default features

e7a3c9c

lexical & syn

52cfeaf

lockfile

e65437b

kdy1 added this to the Planned milestone Oct 30, 2025

kdy1 changed the title ~~perf: Disable~~ perf: Disable all unnecessary default-features Oct 30, 2025

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kdy1 added 16 commits October 30, 2025 14:12

lockfile

1a0dee0

feature

bdfbeb6

codspeed

deb9ea2

serde-impl

561a4c4

fix flate2

6721861

fix

54c8fbf

ansi

441b065

once_cell & serde_json

22ee716

fix

f8c7f70

fix swc crate

bb31861

fix

a41f16a

fix jsdoc

27f51a5

fix swc_ecma_codegen

28ae6f9

fix swc_ecma_codegen

fb7f46c

fix more

4e6dc83

fix hstr

e62868c

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kdy1 marked this pull request as ready for review February 2, 2026 12:20

kdy1 requested a review from a team as a code owner February 2, 2026 12:20

Copilot AI review requested due to automatic review settings February 2, 2026 12:20

kdy1 requested review from a team as code owners February 2, 2026 12:20

kdy1 marked this pull request as draft February 2, 2026 12:20

Copilot started reviewing on behalf of kdy1 February 2, 2026 12:20 View session

fix: Add missing serde std feature for hstr and tracing attributes fo…

e5fffc4

…r swc_common - Add `derive` feature to shrink-to-fit dependency in swc_common - Add `serde-impl` feature to swc_ecma_transforms_react in swc_core Co-authored-by: Donny/강동윤 <kdy1@users.noreply.github.com>

Copilot AI reviewed Feb 2, 2026

View reviewed changes

-lazy_static               = { version = "1.4.0", default-features = false }
+lazy_static               = { version = "1.4.0", default-features = false }
+# lexical's default features are disabled; `std`, `parse-floats`, and `parse-integers`
+# are explicitly enabled because they are required for the crate's basic number
+# parsing functionality used across this workspace.

	syn = { version = "2", default-features = false, features = ["derive", "parsing", "printing", "clone-impls", "proc-macro"] }
	syn = { version = "2", default-features = false }

	allocator-api2 = { workspace = true, default-features = true }
	allocator-api2 = { workspace = true, default-features = false }

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PR Review: perf: Disable all unnecessary default-features

Overview

🔴 Critical Issues (Blocking)

1. CI Build Failures - Missing petgraph::graphmap Feature

🟡 Code Quality Observations

2. New swc_ecma_compiler Crate

3. Wtf8Atom Serialization (crates/hstr/src/wtf8_atom.rs)

🟢 Performance Observations

📋 Recommendations

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CodSpeed Performance Report

Merging this PR will improve performance by 4.07%

Summary

Performance Changes

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PR Review: perf: Disable all unnecessary `default-features`

1. CI Build Failures - Missing `petgraph::graphmap` Feature

2. New `swc_ecma_compiler` Crate

3. Wtf8Atom Serialization (`crates/hstr/src/wtf8_atom.rs`)

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