feat(es/minifier): Implement optional catch binding

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

@@ -2876,6 +2876,21 @@ impl VisitMut for Optimizer<'_> {
         n.finalizer.visit_mut_with(self);
     }
 
+    fn visit_mut_catch_clause(&mut self, n: &mut CatchClause) {
+        n.visit_mut_children_with(self);
+
+        if self.options.ecma < EsVersion::Es2019 || !self.options.unused {
+            return;
+        }
+
+        if let Some(param) = &mut n.param {
+            self.take_pat_if_unused(param, None, false);
+            if param.is_invalid() {
+                n.param = None;
+            }
+        }
+    }
+
     #[cfg_attr(feature = "debug", tracing::instrument(skip_all))]
     fn visit_mut_unary_expr(&mut self, n: &mut UnaryExpr) {
         let ctx = Ctx {

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

@@ -178,7 +178,6 @@ impl Optimizer<'_> {
                 && v.usage_count == 0
                 && !v.reassigned
                 && v.property_mutation_count == 0
-                && !v.declared_as_catch_param
             {
                 self.changed = true;
                 report_change!(

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

@@ -3,7 +3,7 @@ function f1() {
         return 1;
     } catch (ex) {
         return 2;
-    } finally {
+    } finally{
         return 3;
     }
 }

crates/swc_ecma_minifier/tests/terser/compress/drop_unused/issue_1715_1/output.js

@@ -2,9 +2,7 @@ var a = 1;
 function f() {
     try {
         x();
-    } catch (a) {
-        var a;
-    }
+    } catch (a) {}
 }
 f();
 console.log(a);

crates/swc_ecma_minifier/tests/terser/compress/drop_unused/issue_1715_4/output.js

@@ -2,8 +2,6 @@ var a = 1;
 !function() {
     try {
         x();
-    } catch (a) {
-        var a;
-    }
+    } catch (a) {}
 }();
 console.log(a);

crates/swc_ecma_minifier/tests/terser/compress/functions/issue_2604_2/output.js

@@ -1,5 +1,5 @@
 var a = "FAIL";
-(function () {
+(function() {
     try {
         throw 1;
     } catch (o) {