feat(es/minifier): Drop empty static blocks (#8152)

**Related issue:**

 - Closes #8136

crates/swc/tests/tsc-references/classStaticBlock15(target=es2022).2.minified.js

@@ -4,11 +4,5 @@ class C {
     static #_1 = 1;
     static #_3 = 3;
     static #_5 = 5;
-    static{}
-    static{}
-    static{}
-    static{}
-    static{}
-    static{}
 }
 console.log(_C__1);

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

@@ -303,6 +303,28 @@ impl VisitMut for Pure<'_> {
         self.drop_arguments_of_symbol_call(e);
     }
 
+    fn visit_mut_class_member(&mut self, m: &mut ClassMember) {
+        m.visit_mut_children_with(self);
+
+        if let ClassMember::StaticBlock(sb) = m {
+            if sb.body.stmts.is_empty() {
+                *m = ClassMember::Empty(EmptyStmt { span: DUMMY_SP });
+            }
+        }
+    }
+
+    fn visit_mut_class_members(&mut self, m: &mut Vec<ClassMember>) {
+        m.visit_mut_children_with(self);
+
+        m.retain(|m| {
+            if let ClassMember::Empty(..) = m {
+                return false;
+            }
+
+            true
+        });
+    }
+
     fn visit_mut_cond_expr(&mut self, e: &mut CondExpr) {
         e.visit_mut_children_with(self);
 
@@ -560,6 +582,10 @@ impl VisitMut for Pure<'_> {
         }
     }
 
+    fn visit_mut_expr_or_spreads(&mut self, nodes: &mut Vec<ExprOrSpread>) {
+        self.visit_par(nodes);
+    }
+
     fn visit_mut_expr_stmt(&mut self, s: &mut ExprStmt) {
         s.visit_mut_children_with(self);
 
@@ -585,18 +611,6 @@ impl VisitMut for Pure<'_> {
         self.visit_par(nodes);
     }
 
-    fn visit_mut_opt_vec_expr_or_spreads(&mut self, nodes: &mut Vec<Option<ExprOrSpread>>) {
-        self.visit_par(nodes);
-    }
-
-    fn visit_mut_expr_or_spreads(&mut self, nodes: &mut Vec<ExprOrSpread>) {
-        self.visit_par(nodes);
-    }
-
-    fn visit_mut_var_declarators(&mut self, nodes: &mut Vec<VarDeclarator>) {
-        self.visit_par(nodes);
-    }
-
     fn visit_mut_fn_decl(&mut self, n: &mut FnDecl) {
         #[cfg(feature = "debug")]
         let _tracing = tracing::span!(
@@ -727,6 +741,10 @@ impl VisitMut for Pure<'_> {
         }
     }
 
+    fn visit_mut_opt_vec_expr_or_spreads(&mut self, nodes: &mut Vec<Option<ExprOrSpread>>) {
+        self.visit_par(nodes);
+    }
+
     fn visit_mut_pat_or_expr(&mut self, n: &mut PatOrExpr) {
         n.visit_mut_children_with(self);
 
@@ -1039,6 +1057,10 @@ impl VisitMut for Pure<'_> {
         }
     }
 
+    fn visit_mut_var_declarators(&mut self, nodes: &mut Vec<VarDeclarator>) {
+        self.visit_par(nodes);
+    }
+
     fn visit_mut_while_stmt(&mut self, s: &mut WhileStmt) {
         s.visit_mut_children_with(self);
 

crates/swc_ecma_minifier/tests/fixture/issues/8136/input.js

@@ -0,0 +1,4 @@
+export class Foo {
+    static { }
+    foo = 2;
+}

crates/swc_ecma_minifier/tests/fixture/issues/8136/output.js

@@ -0,0 +1,3 @@
+export class Foo {
+    foo = 2;
+}