drop unused extends properly (#5461)

lib/compress.js

@@ -6788,7 +6788,6 @@ Compressor.prototype.compress = function(node) {
             }
         });
         // pass 3: we should drop declarations not in_use
-        var unused_fn_names = [];
         var calls_to_drop_args = [];
         var fns_with_marked_args = [];
         var trimmer = new TreeTransformer(function(node) {
@@ -6909,7 +6908,7 @@ Compressor.prototype.compress = function(node) {
                 }
             }
             if (node instanceof AST_ClassExpression && node.name && drop_fn_name(node.name.definition())) {
-                unused_fn_names.push(node);
+                node.name = null;
             }
             if (node instanceof AST_Lambda) {
                 if (drop_funcs && node !== self && node instanceof AST_LambdaDefinition) {
@@ -6925,7 +6924,7 @@ Compressor.prototype.compress = function(node) {
                     }
                 }
                 if (node instanceof AST_LambdaExpression && node.name && drop_fn_name(node.name.definition())) {
-                    unused_fn_names.push(node);
+                    node.name = null;
                 }
                 if (!(node instanceof AST_Accessor)) {
                     var args, spread, trim = compressor.drop_fargs(node, parent);
@@ -6966,6 +6965,7 @@ Compressor.prototype.compress = function(node) {
                         }
                     }
                     var default_length = trim ? -1 : node.length();
+                    var trim_value = args && !node.uses_arguments && parent !== compressor.parent();
                     for (var i = argnames.length; --i >= 0;) {
                         var sym = argnames[i];
                         if (sym instanceof AST_SymbolFunarg) {
@@ -6987,7 +6987,7 @@ Compressor.prototype.compress = function(node) {
                             } else {
                                 var trimmed = trim_destructured(sym, args[i], function(node) {
                                     return node.definition().id in in_use_ids ? node : null;
-                                }, !node.uses_arguments, sym);
+                                }, trim_value, sym);
                                 funarg = trimmed.name;
                                 if (trimmed.value) args[i] = trimmed.value;
                             }
@@ -7363,9 +7363,6 @@ Compressor.prototype.compress = function(node) {
             && self.body[0].value == "use strict") {
             self.body.length = 0;
         }
-        unused_fn_names.forEach(function(fn) {
-            fn.name = null;
-        });
         calls_to_drop_args.forEach(function(call) {
             drop_unused_call_args(call, compressor, fns_with_marked_args);
         });

test/compress/classes.js

@@ -341,7 +341,7 @@ drop_extends: {
     node_version: ">=4"
 }
 
-keep_extends: {
+keep_extends_1: {
     options = {
         toplevel: true,
         unused: true,
@@ -366,6 +366,43 @@ keep_extends: {
     node_version: ">=4"
 }
 
+keep_extends_2: {
+    options = {
+        side_effects: true,
+    }
+    input: {
+        "use strict";
+        (class extends Function {});
+        console.log("PASS");
+    }
+    expect: {
+        "use strict";
+        (class extends Function {});
+        console.log("PASS");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=4"
+}
+
+keep_extends_3: {
+    options = {
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        "use strict";
+        class A extends Function {}
+        console.log("PASS");
+    }
+    expect: {
+        "use strict";
+        (class extends Function {});
+        console.log("PASS");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=4"
+}
+
 drop_name: {
     options = {
         unused: true,
@@ -670,6 +707,58 @@ single_use_7: {
     node_version: ">=4"
 }
 
+single_use_extends: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        "use strict";
+        class A extends class B {
+            f() {
+                return "PASS";
+            }
+        } {}
+        console.log(new A().f());
+    }
+    expect: {
+        "use strict";
+        console.log(new class extends class {
+            f() {
+                return "PASS";
+            }
+        } {}().f());
+    }
+    expect_stdout: "PASS"
+    node_version: ">=4"
+}
+
+single_use_extends_non_strict: {
+    options = {
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        class A extends class B {
+            f() {
+                return "PASS";
+            }
+        } {}
+        console.log(new A().f());
+    }
+    expect: {
+        console.log(new class extends class {
+            f() {
+                return "PASS";
+            }
+        } {}().f());
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
 collapse_non_strict: {
     options = {
         collapse_vars: true,

test/compress/destructured.js

@@ -3401,7 +3401,7 @@ issue_5222: {
     node_version: ">=6"
 }
 
-issue_5288: {
+issue_5288_1: {
     options = {
         conditionals: true,
         inline: true,
@@ -3421,7 +3421,37 @@ issue_5288: {
         }() ]));
     }
     expect: {
-        while (console ? console.log("PASS") : 0, void 0);
+        while (function() {
+            if (console)
+                console.log("PASS");
+        }(), void 0);
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_5288_2: {
+    options = {
+        conditionals: true,
+        inline: true,
+        keep_fargs: false,
+        passes: 2,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+        varify: true,
+    }
+    input: {
+        while (function([]) {}([ function f() {
+            if (console)
+                return console.log("PASS");
+            else {
+                let a = 0;
+            }
+        }() ]));
+    }
+    expect: {
+        while (console && console.log("PASS"), void 0);
     }
     expect_stdout: "PASS"
     node_version: ">=6"