fix(es/minifier): More strict check if cannot add ident when invoking IIFE #11399

Austaras · 2025-12-28T12:12:58Z

… IIFE

Description:

BREAKING CHANGE:

Related issue (if exists):
Closes #11368

changeset-bot · 2025-12-28T12:13:03Z

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Latest commit: a99de98

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crates/swc_ecma_minifier/src/compress/optimize/iife.rs

Copilot

Pull request overview

This PR fixes a bug in the ECMAScript minifier where IIFE (Immediately Invoked Function Expression) inlining was incorrectly applied in contexts where new identifiers cannot be added, particularly in class field initializers. The fix addresses issue #10931.

Key Changes:

Refactored IIFE inlining to use ExactSizeIterator instead of passing parameter length separately
Added stricter checks in can_extract_param to verify that arguments are simple literals when identifiers cannot be added
Removed the DontInvokeIife flag mechanism in favor of the more comprehensive may_add_ident() check

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
`crates/swc_ecma_minifier/src/compress/optimize/iife.rs`	Refactored IIFE inlining functions to accept `ExactSizeIterator` parameters and added new validation logic to check argument types when identifiers cannot be added
`crates/swc_ecma_minifier/src/compress/optimize/mod.rs`	Commented out the unused `DontInvokeIife` flag and its usage in class visitor
`crates/swc_ecma_minifier/tests/fixture/issues/11368/input.js`	Added test case demonstrating the bug with class field initialization
`crates/swc_ecma_minifier/tests/fixture/issues/11368/output.js`	Expected output showing the fix prevents incorrect inlining
Multiple test output files	Updated expected outputs to reflect the fix preventing over-aggressive IIFE inlining

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Copilot · 2025-12-28T12:16:37Z

crates/swc_ecma_minifier/src/compress/optimize/iife.rs

+                        || !matches!(
+                            &*arg.expr,
+                            Expr::Lit(
+                                Lit::Num(..) | Lit::Str(..) | Lit::Bool(..) | Lit::BigInt(..)


The literal type check should include Lit::Null(..) to be consistent with other parts of the codebase. In other optimization functions like inline.rs and sequences.rs, null literals are treated as safe, side-effect-free values that can be inlined without creating variables. Omitting null from this check may unnecessarily prevent valid IIFE inlining optimizations when null is passed as an argument.

Suggested change

Lit::Num(..) | Lit::Str(..) | Lit::Bool(..) | Lit::BigInt(..)

Lit::Num(..)

| Lit::Str(..)

| Lit::Bool(..)

| Lit::BigInt(..)

| Lit::Null(..)

crates/swc_ecma_minifier/src/compress/optimize/mod.rs

Copilot · 2025-12-28T12:16:38Z

crates/swc_ecma_minifier/src/compress/optimize/mod.rs

                .ctx
                .clone()
-                .with(BitCtx::DontInvokeIife, true)
+                // .with(BitCtx::DontInvokeIife, true)


The commented-out code should be removed rather than left in place. This code is no longer needed after the refactoring, as evidenced by the removal of the DontInvokeIife flag usage throughout the codebase. Leaving commented code reduces readability and can cause confusion for future maintainers.

Suggested change

// .with(BitCtx::DontInvokeIife, true)

Copilot · 2025-12-28T12:16:38Z

crates/swc_ecma_minifier/src/compress/optimize/iife.rs

+        // if self.ctx.bit_ctx.contains(BitCtx::DontInvokeIife) {
+        //     log_abort!("iife: Inline is prevented");
+        //     return false;
+        // }



The commented-out code should be removed rather than left in place. This check is no longer needed after the refactoring, which now relies on the more comprehensive may_add_ident() check. Leaving commented code reduces readability and can cause confusion for future maintainers.

Suggested change

// if self.ctx.bit_ctx.contains(BitCtx::DontInvokeIife) {

// log_abort!("iife: Inline is prevented");

// return false;

// }

github-actions · 2025-12-28T12:22:44Z

Binary Sizes

File	Size
`swc.linux-x64-gnu.node`	28M (28527432 bytes)

Commit: c85e8ad

codspeed-hq · 2025-12-28T12:25:14Z

CodSpeed Performance Report

Merging #11399 will not alter performance

_{Comparing Austaras:main (a99de98) with main (55a5083)}

Summary

✅ 138 untouched

crates/swc_ecma_minifier/tests/terser/compress/collapse_vars/issue_2187_3/output.js

kdy1

Thank you!

crates/swc_ecma_minifier/src/compress/optimize/mod.rs

Copilot

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

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Copilot · 2025-12-29T06:53:01Z

crates/swc_ecma_minifier/src/compress/optimize/iife.rs

+    fn can_inline_fn_arg(usage: &VarUsageInfo, arg: &Expr) -> bool {
+        if usage.ref_count > 1
+            || usage.assign_count > 0
+            || usage.flags.contains(VarUsageInfoFlags::REASSIGNED)
+            || usage.flags.contains(VarUsageInfoFlags::INLINE_PREVENTED)
+        {
+            return false;
+        }
+
+        match arg {
+            Expr::Lit(Lit::Num(..) | Lit::Str(..) | Lit::Bool(..) | Lit::BigInt(..)) => true,
+            Expr::Fn(..) if usage.can_inline_fn_once() => true,
+            _ => false,
+        }
+    }


The condition usage.property_mutation_count == 0 check was removed from the inlining logic in inline_fn_param_stmt. Previously, the code checked this condition before inlining, but now can_inline_fn_arg doesn't verify property mutations. This could potentially lead to incorrect inlining when the parameter has property mutations. Consider adding this check to the can_inline_fn_arg function to maintain the same safety guarantees.

crates/swc_ecma_minifier/src/compress/optimize/iife.rs

… IIFE

kdy1 · 2025-12-29T07:57:36Z

Thanks!

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kdy1 changed the title ~~fix(es/minifier): More strict check if cannot add ident when invoking…~~ fix(es/minifier): More strict check if cannot add ident when invoking IIFE Dec 29, 2025

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fix(es/minifier): More strict check if cannot add ident when invoking…

affd2c6

… IIFE

Austaras force-pushed the main branch from 0a0d6d3 to affd2c6 Compare December 29, 2025 07:37

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fix(es/minifier): More strict check if cannot add ident when invoking IIFE #11399

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