fix(es/minifier): Preserve exports in DCE (#5973)

crates/swc_ecma_minifier/tests/fixture/issues/5955/input.js

@@ -0,0 +1,16 @@
+export var foo;
+export function init() {
+    function bar() {
+        foo = bar;
+        console.log(111);
+    }
+    return bar;
+}
+
+function bar() {
+    foo = bar;
+    console.log(111);
+}
+export function init1() {
+    return bar;
+}

crates/swc_ecma_minifier/tests/fixture/issues/5955/output.js

@@ -0,0 +1,13 @@
+export var foo;
+export function init() {
+    function bar() {
+        foo = bar, console.log(111);
+    }
+    return bar;
+}
+function bar() {
+    foo = bar, console.log(111);
+}
+export function init1() {
+    return bar;
+}

crates/swc_ecma_minifier/tests/fixture/issues/5955/output.mangleOnly.js

@@ -0,0 +1,15 @@
+export var foo;
+export function init() {
+    function o() {
+        foo = o;
+        console.log(111);
+    }
+    return o;
+}
+function o() {
+    foo = o;
+    console.log(111);
+}
+export function init1() {
+    return o;
+}

crates/swc_ecma_transforms_optimization/src/simplify/dce/mod.rs

@@ -402,6 +402,24 @@ impl Visit for Analyzer<'_> {
         }
     }
 
+    fn visit_export_decl(&mut self, n: &ExportDecl) {
+        let name = match &n.decl {
+            Decl::Class(c) => vec![c.ident.to_id()],
+            Decl::Fn(f) => vec![f.ident.to_id()],
+            Decl::Var(v) => v
+                .decls
+                .iter()
+                .flat_map(|d| find_pat_ids(d).into_iter())
+                .collect(),
+            _ => Vec::new(),
+        };
+        for ident in name {
+            self.add(ident, false);
+        }
+
+        n.visit_children_with(self)
+    }
+
     fn visit_expr(&mut self, e: &Expr) {
         let old_in_var_decl = self.in_var_decl;
 

crates/swc_ecma_utils/src/lib.rs

@@ -2136,26 +2136,22 @@ impl IdentExt for Ident {
 }
 
 /// Finds all **binding** idents of variables.
-pub struct DestructuringFinder<'a, I: IdentLike> {
-    pub found: &'a mut Vec<I>,
+pub struct DestructuringFinder<I: IdentLike> {
+    pub found: Vec<I>,
 }
 
 /// Finds all **binding** idents of `node`.
 pub fn find_pat_ids<T, I: IdentLike>(node: &T) -> Vec<I>
 where
-    T: for<'any> VisitWith<DestructuringFinder<'any, I>>,
+    T: VisitWith<DestructuringFinder<I>>,
 {
-    let mut found = vec![];
-
-    {
-        let mut v = DestructuringFinder { found: &mut found };
-        node.visit_with(&mut v);
-    }
+    let mut v = DestructuringFinder { found: Vec::new() };
+    node.visit_with(&mut v);
 
-    found
+    v.found
 }
 
-impl<'a, I: IdentLike> Visit for DestructuringFinder<'a, I> {
+impl<I: IdentLike> Visit for DestructuringFinder<I> {
     noop_visit_type!();
 
     /// No-op (we don't care about expressions)