fix(codegen): preserve quotes for cjs-module-lexer equality strings (#22551)

## Summary

- Force plain string quotes for `"default"` / `"__esModule"` operands of `==`/`===`/`!=`/`!==` during minification, so `cjs-module-lexer` can recognise the `Object.keys(mod).forEach(key => key === "default" || ...)` re-export filter emitted by Babel / TypeScript / Rollup.
- Follow-up to #22475 (which fixed `require("…")`). Same root cause: `calculate_quote_maybe_backtick`'s equal-cost tie-breaker prefers backtick, which the lexer's heuristic parser doesn't accept.
- Caught by monitor-oxc's `whitespace` runner: minifying `@babel/types/lib/index.js` previously broke `import { isIdentifier } from "@babel/types"` under `--experimental-require-module`. Raw minified size is unchanged across all `minsize` fixtures.

## Example

Input:

```js
Object.keys(mod).forEach(function (key) {
  if (key === "default" || key === "__esModule") return;
});
```

Before (broken — `cjs-module-lexer` skips the re-export):

```js
Object.keys(t).forEach(function(e){if(e===`default`||e===`__esModule`)return});
```

After:

```js
Object.keys(t).forEach(function(e){if(e==="default"||e==="__esModule")return});
```

AI disclosure: drafted with Claude Code, reviewed manually.

crates/oxc_codegen/src/binary_expr_visitor.rs

@@ -12,6 +12,52 @@ use oxc_syntax::{
 
 use crate::{Codegen, Context, Operator, r#gen::GenExpr};
 
+/// Force plain string quotes for `"default"` and `"__esModule"` when they
+/// appear as an operand of an equality comparison during minification. This
+/// keeps `cjs-module-lexer` (used by Node for CJS/ESM interop) able to
+/// recognise the re-export pattern emitted by Babel / TypeScript / Rollup:
+///
+/// ```js
+/// Object.keys(mod).forEach(function (key) {
+///   if (key === "default" || key === "__esModule") return;
+///   ...
+/// });
+/// ```
+///
+/// Without this, `print_string_literal`'s tie-breaker in
+/// `calculate_quote_maybe_backtick` prefers backtick on equal cost, and the
+/// lexer's heuristic parser does not match `key === \`default\``.
+///
+/// Companion to `try_print_require_call` and `try_print_cjs_define_property_call`
+/// in `gen.rs`, which preserve plain quotes at the other two syntactic positions
+/// `cjs-module-lexer` recognises.
+///
+/// Returns `true` if printed.
+#[inline]
+fn try_print_cjs_lexer_equality_string(
+    operator: BinaryishOperator,
+    operand: &Expression,
+    p: &mut Codegen,
+) -> bool {
+    if !p.options.minify {
+        return false;
+    }
+    let BinaryishOperator::Binary(op) = operator else {
+        return false;
+    };
+    if !op.is_equality() {
+        return false;
+    }
+    let Expression::StringLiteral(str_lit) = operand else {
+        return false;
+    };
+    if !matches!(str_lit.value.as_str(), "default" | "__esModule") {
+        return false;
+    }
+    p.print_string_literal(str_lit, false);
+    true
+}
+
 #[derive(Clone, Copy)]
 pub enum Binaryish<'a> {
     Binary(&'a BinaryExpression<'a>),
@@ -124,7 +170,9 @@ impl<'a> BinaryExpressionVisitor<'a> {
             };
 
             let Some(left_binary) = left_binary else {
-                left.gen_expr(p, v.left_precedence, v.ctx);
+                if !try_print_cjs_lexer_equality_string(v.operator, left, p) {
+                    left.gen_expr(p, v.left_precedence, v.ctx);
+                }
                 v.visit_right_and_finish(p);
                 break;
             };
@@ -223,7 +271,10 @@ impl<'a> BinaryExpressionVisitor<'a> {
         p.print_soft_space();
         self.operator.r#gen(p);
         p.print_soft_space();
-        self.e.right().gen_expr(p, self.right_precedence, self.ctx);
+        let right = self.e.right();
+        if !try_print_cjs_lexer_equality_string(self.operator, right, p) {
+            right.gen_expr(p, self.right_precedence, self.ctx);
+        }
         if self.wrap {
             p.print_ascii_byte(b')');
         }

crates/oxc_codegen/src/gen.rs

@@ -1517,6 +1517,9 @@ impl GenExpr for CallExpression<'_> {
 ///
 /// Minify-only: outside minify, `print_string_literal` already uses `self.quote` (never
 /// backtick), and this path skips the argument comments that `print_arguments` preserves.
+///
+/// Companion to `try_print_require_call` (below) and
+/// `try_print_cjs_lexer_equality_string` in `binary_expr_visitor.rs`.
 fn try_print_cjs_define_property_call(
     p: &mut Codegen<'_>,
     call: &CallExpression<'_>,
@@ -1555,6 +1558,9 @@ fn try_print_cjs_define_property_call(
 ///
 /// Minify-only: outside minify, `print_string_literal` already uses `self.quote` (never
 /// backtick), and this path skips the argument comments that `print_arguments` preserves.
+///
+/// Companion to `try_print_cjs_define_property_call` (above) and
+/// `try_print_cjs_lexer_equality_string` in `binary_expr_visitor.rs`.
 fn try_print_require_call(p: &mut Codegen<'_>, call: &CallExpression<'_>) -> bool {
     if !p.options.minify {
         return false;

crates/oxc_codegen/tests/integration/js.rs

@@ -668,6 +668,22 @@ fn string() {
     test_minify("require(foo);", "require(foo);");
     // Single-quoted require
     test_minify(r"require('./foo');", r#"require("./foo");"#);
+
+    // `cjs-module-lexer` re-export detection requires `"default"` and
+    // `"__esModule"` to stay as plain string literals in equality comparisons.
+    test_minify(
+        r#"function f(key) { if (key === "default" || key === "__esModule") return; }"#,
+        r#"function f(key){if(key==="default"||key==="__esModule")return}"#,
+    );
+    test_minify(r#"a = x !== "default""#, r#"a=x!=="default";"#);
+    test_minify(r#"a = x == "__esModule""#, r#"a=x=="__esModule";"#);
+    test_minify(r#"a = x != "default""#, r#"a=x!="default";"#);
+    // Magic string on the left side of an equality is also preserved.
+    test_minify(r#"a = "default" === x"#, r#"a="default"===x;"#);
+    // Other strings in equality comparisons are unaffected.
+    test_minify(r#"a = x === "foo""#, "a=x===`foo`;");
+    // The two magic strings are unaffected when not in equality comparisons.
+    test_minify(r#"a = "default""#, "a=`default`;");
 }
 
 #[test]

tasks/minsize/minsize.snap

@@ -21,7 +21,7 @@ Original   | minified   | minified   | gzip       | gzip       | Iterations | Fi
 
 3.20 MB    | 1.00 MB    | 1.01 MB    | 322.61 kB  | 331.56 kB  |          2 | echarts.js 
 
-6.69 MB    | 2.22 MB    | 2.31 MB    | 458.45 kB  | 488.28 kB  |          4 | antd.js    
+6.69 MB    | 2.22 MB    | 2.31 MB    | 458.46 kB  | 488.28 kB  |          4 | antd.js    
 
-10.95 MB   | 3.33 MB    | 3.49 MB    | 853.31 kB  | 915.50 kB  |          4 | typescript.js 
+10.95 MB   | 3.33 MB    | 3.49 MB    | 853.35 kB  | 915.50 kB  |          4 | typescript.js