handle AST_Super in collapse_vars & side_effects

lib/compress.js

@@ -579,6 +579,7 @@ merge(Compressor.prototype, {
     }
 
     function is_lhs_read_only(lhs) {
+        if (lhs instanceof AST_Super) return true;
         if (lhs instanceof AST_This) return true;
         if (lhs instanceof AST_SymbolRef) return lhs.definition().orig[0] instanceof AST_SymbolLambda;
         if (lhs instanceof AST_PropAccess) {
@@ -2109,6 +2110,7 @@ merge(Compressor.prototype, {
 
         def(AST_EmptyStatement, return_false);
         def(AST_Constant, return_false);
+        def(AST_Super, return_false);
         def(AST_This, return_false);
 
         def(AST_Call, function(compressor){
@@ -2787,6 +2789,7 @@ merge(Compressor.prototype, {
 
         def(AST_Node, return_this);
         def(AST_Constant, return_null);
+        def(AST_Super, return_null);
         def(AST_This, return_null);
         def(AST_Call, function(compressor, first_in_statement){
             if (!this.is_expr_pure(compressor)) {

test/compress/pure_getters.js

@@ -672,3 +672,51 @@ issue_2313_6: {
         x();
     }
 }
+
+issue_2313_7: {
+    options = {
+        collapse_vars: true,
+        conditionals: true,
+        pure_getters: true,
+    }
+    input: {
+        var a = 0, b = 0;
+        class foo {
+            get c() {
+                a++;
+                return 42;
+            }
+            set c(c) {
+                b++;
+            }
+        }
+        class bar extends foo {
+            d() {
+                super.c++;
+                if (super.c) console.log(a, b);
+            }
+        }
+        new bar().d();
+    }
+    expect: {
+        var a = 0, b = 0;
+        class foo {
+            get c() {
+                a++;
+                return 42;
+            }
+            set c(c) {
+                b++;
+            }
+        }
+        class bar extends foo {
+            d() {
+                super.c++;
+                super.c && console.log(a, b);
+            }
+        }
+        new bar().d();
+    }
+    expect_stdout: "2 1"
+    node_version: ">=6"
+}