fix(parser): apply no-side-effects annotations after export (#27504)

`export /*@__NO_SIDE_EFFECTS__*/ function f() {}` left the function’s `pure` flag unset because statement parsing only captured annotations before `export`. Capture annotations immediately after `export` and apply the existing function purity handling.

crates/oxc_minifier/tests/peephole/remove_unused_expression.rs

@@ -626,6 +626,10 @@ fn no_side_effects() {
     }
     check("/* @__NO_SIDE_EFFECTS__ */ function f() {}");
     check("/* @__NO_SIDE_EFFECTS__ */ export function f() {}");
+    check("export /*@__NO_SIDE_EFFECTS__*/ function f() { sideEffect() }");
+    check("export /* @__NO_SIDE_EFFECTS__ */ async function f() { sideEffect() }");
+    check("export /* @__NO_SIDE_EFFECTS__ */ function* f() { sideEffect() }");
+    check("export /* @__NO_SIDE_EFFECTS__ */ async function* f() { sideEffect() }");
     check("/* @__NO_SIDE_EFFECTS__ */ export default function f() {}");
     check("export default /* @__NO_SIDE_EFFECTS__ */ function f() {}");
     check("const f = /* @__NO_SIDE_EFFECTS__ */ function() {}");

crates/oxc_parser/src/js/module.rs

@@ -477,6 +477,9 @@ impl<'a, C: Config> ParserImpl<'a, C> {
     ) -> Statement<'a> {
         self.check_module_declaration(stmt_ctx);
         self.bump_any(); // bump `export`
+        // export /* @__NO_SIDE_EFFECTS__ */ ...
+        let no_side_effects_comments =
+            self.lexer.trivia_builder.previous_token_no_side_effects_comments();
         // `export` is unambiguously module syntax (ECMA-262 §16.2.3): commit to the
         // Module goal so the declaration parses under `Await` on the first pass and
         // isn't reparsed. e.g. `@foo export default class C { x = await + 1 }`
@@ -567,7 +570,13 @@ impl<'a, C: Config> ParserImpl<'a, C> {
                 )
             }
         };
-        Statement::from(decl)
+        let mut stmt = Statement::from(decl);
+        if let Some(comments) = no_side_effects_comments
+            && Self::set_pure_on_function_stmt(&mut stmt)
+        {
+            self.lexer.trivia_builder.mark_no_side_effects_comments_applied(comments);
+        }
+        stmt
     }
 
     // export NamedExports ;

crates/oxc_parser/src/js/statement.rs

@@ -207,7 +207,7 @@ impl<'a, C: Config> ParserImpl<'a, C> {
         stmt
     }
 
-    fn set_pure_on_function_stmt(stmt: &mut Statement<'a>) -> bool {
+    pub(super) fn set_pure_on_function_stmt(stmt: &mut Statement<'a>) -> bool {
         match stmt {
             Statement::FunctionDeclaration(func) => {
                 func.pure = true;

crates/oxc_parser/src/lexer/trivia_builder.rs

@@ -1100,6 +1100,10 @@ function bar() {}";
             "/* #__NO_SIDE_EFFECTS__ */ let foo = () => {};",
             "/* #__NO_SIDE_EFFECTS__ */ var foo = function() {};",
             "const foo /* #__NO_SIDE_EFFECTS__ */ = () => {};",
+            "export /* #__NO_SIDE_EFFECTS__ */ class Foo {}",
+            "export /* #__NO_SIDE_EFFECTS__ */ let foo = () => {};",
+            "export /* #__NO_SIDE_EFFECTS__ */ var foo = function() {};",
+            "export /* #__NO_SIDE_EFFECTS__ */ const foo = 1, bar = () => {};",
         ];
         for source_text in cases {
             let comments = get_comments(source_text);
@@ -1117,11 +1121,18 @@ function bar() {}";
             "/* #__NO_SIDE_EFFECTS__ */ function foo() {}",
             "/* #__NO_SIDE_EFFECTS__ */ async function foo() {}",
             "/* #__NO_SIDE_EFFECTS__ */ export function foo() {}",
+            "export /*@__NO_SIDE_EFFECTS__*/ function foo() {}",
+            "export /* #__NO_SIDE_EFFECTS__ */ async function foo() {}",
+            "export /* #__NO_SIDE_EFFECTS__ */ function* foo() {}",
+            "export /* #__NO_SIDE_EFFECTS__ */ async function* foo() {}",
+            "export /* #__NO_SIDE_EFFECTS__ */ default function foo() {}",
             "export default /* #__NO_SIDE_EFFECTS__ */ function foo() {}",
             "const foo = /* #__NO_SIDE_EFFECTS__ */ function() {};",
             "const foo = /* #__NO_SIDE_EFFECTS__ */ () => {};",
             "/* #__NO_SIDE_EFFECTS__ */ const foo = () => {};",
             "/* #__NO_SIDE_EFFECTS__ */ export const foo = () => {};",
+            "export /* #__NO_SIDE_EFFECTS__ */ const foo = () => {};",
+            "export /* #__NO_SIDE_EFFECTS__ */ const foo = function() {};",
             "[/* #__NO_SIDE_EFFECTS__ */ function() {}];",
         ];
         for source_text in cases {