Index: imaps-frontend/node_modules/terser/lib/scope.js
===================================================================
--- imaps-frontend/node_modules/terser/lib/scope.js	(revision 79a03170cdde4e801d12257ee86723774970427b)
+++ imaps-frontend/node_modules/terser/lib/scope.js	(revision 79a03170cdde4e801d12257ee86723774970427b)
@@ -0,0 +1,1066 @@
+/***********************************************************************
+
+  A JavaScript tokenizer / parser / beautifier / compressor.
+  https://github.com/mishoo/UglifyJS2
+
+  -------------------------------- (C) ---------------------------------
+
+                           Author: Mihai Bazon
+                         <mihai.bazon@gmail.com>
+                       http://mihai.bazon.net/blog
+
+  Distributed under the BSD license:
+
+    Copyright 2012 (c) Mihai Bazon <mihai.bazon@gmail.com>
+
+    Redistribution and use in source and binary forms, with or without
+    modification, are permitted provided that the following conditions
+    are met:
+
+        * Redistributions of source code must retain the above
+          copyright notice, this list of conditions and the following
+          disclaimer.
+
+        * Redistributions in binary form must reproduce the above
+          copyright notice, this list of conditions and the following
+          disclaimer in the documentation and/or other materials
+          provided with the distribution.
+
+    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER “AS IS” AND ANY
+    EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+    IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+    PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE
+    LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
+    OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+    PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+    PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+    THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
+    TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
+    THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+    SUCH DAMAGE.
+
+ ***********************************************************************/
+
+"use strict";
+
+import {
+    defaults,
+    keep_name,
+    mergeSort,
+    push_uniq,
+    make_node,
+    return_false,
+    return_this,
+    return_true,
+    string_template,
+} from "./utils/index.js";
+import {
+    AST_Arrow,
+    AST_Block,
+    AST_Call,
+    AST_Class,
+    AST_Conditional,
+    AST_DefClass,
+    AST_Defun,
+    AST_Destructuring,
+    AST_Dot,
+    AST_DotHash,
+    AST_Export,
+    AST_For,
+    AST_ForIn,
+    AST_ForOf,
+    AST_Function,
+    AST_Import,
+    AST_IterationStatement,
+    AST_Label,
+    AST_LabeledStatement,
+    AST_LabelRef,
+    AST_Lambda,
+    AST_LoopControl,
+    AST_NameMapping,
+    AST_Node,
+    AST_Scope,
+    AST_Sequence,
+    AST_String,
+    AST_Sub,
+    AST_Switch,
+    AST_SwitchBranch,
+    AST_Symbol,
+    AST_SymbolBlockDeclaration,
+    AST_SymbolCatch,
+    AST_SymbolClass,
+    AST_SymbolConst,
+    AST_SymbolDefClass,
+    AST_SymbolDefun,
+    AST_SymbolExport,
+    AST_SymbolFunarg,
+    AST_SymbolImport,
+    AST_SymbolLambda,
+    AST_SymbolLet,
+    AST_SymbolMethod,
+    AST_SymbolRef,
+    AST_SymbolVar,
+    AST_Toplevel,
+    AST_VarDef,
+    AST_With,
+    TreeWalker,
+    walk,
+    walk_abort
+} from "./ast.js";
+import {
+    ALL_RESERVED_WORDS,
+    js_error,
+} from "./parse.js";
+
+const MASK_EXPORT_DONT_MANGLE = 1 << 0;
+const MASK_EXPORT_WANT_MANGLE = 1 << 1;
+
+let function_defs = null;
+let unmangleable_names = null;
+/**
+ * When defined, there is a function declaration somewhere that's inside of a block.
+ * See https://tc39.es/ecma262/multipage/additional-ecmascript-features-for-web-browsers.html#sec-block-level-function-declarations-web-legacy-compatibility-semantics
+*/
+let scopes_with_block_defuns = null;
+
+class SymbolDef {
+    constructor(scope, orig, init) {
+        this.name = orig.name;
+        this.orig = [ orig ];
+        this.init = init;
+        this.eliminated = 0;
+        this.assignments = 0;
+        this.scope = scope;
+        this.replaced = 0;
+        this.global = false;
+        this.export = 0;
+        this.mangled_name = null;
+        this.undeclared = false;
+        this.id = SymbolDef.next_id++;
+        this.chained = false;
+        this.direct_access = false;
+        this.escaped = 0;
+        this.recursive_refs = 0;
+        this.references = [];
+        this.should_replace = undefined;
+        this.single_use = false;
+        this.fixed = false;
+        Object.seal(this);
+    }
+    fixed_value() {
+        if (!this.fixed || this.fixed instanceof AST_Node) return this.fixed;
+        return this.fixed();
+    }
+    unmangleable(options) {
+        if (!options) options = {};
+
+        if (
+            function_defs &&
+            function_defs.has(this.id) &&
+            keep_name(options.keep_fnames, this.orig[0].name)
+        ) return true;
+
+        return this.global && !options.toplevel
+            || (this.export & MASK_EXPORT_DONT_MANGLE)
+            || this.undeclared
+            || !options.eval && this.scope.pinned()
+            || (this.orig[0] instanceof AST_SymbolLambda
+                  || this.orig[0] instanceof AST_SymbolDefun) && keep_name(options.keep_fnames, this.orig[0].name)
+            || this.orig[0] instanceof AST_SymbolMethod
+            || (this.orig[0] instanceof AST_SymbolClass
+                  || this.orig[0] instanceof AST_SymbolDefClass) && keep_name(options.keep_classnames, this.orig[0].name);
+    }
+    mangle(options) {
+        const cache = options.cache && options.cache.props;
+        if (this.global && cache && cache.has(this.name)) {
+            this.mangled_name = cache.get(this.name);
+        } else if (!this.mangled_name && !this.unmangleable(options)) {
+            var s = this.scope;
+            var sym = this.orig[0];
+            if (options.ie8 && sym instanceof AST_SymbolLambda)
+                s = s.parent_scope;
+            const redefinition = redefined_catch_def(this);
+            this.mangled_name = redefinition
+                ? redefinition.mangled_name || redefinition.name
+                : s.next_mangled(options, this);
+            if (this.global && cache) {
+                cache.set(this.name, this.mangled_name);
+            }
+        }
+    }
+}
+
+SymbolDef.next_id = 1;
+
+function redefined_catch_def(def) {
+    if (def.orig[0] instanceof AST_SymbolCatch
+        && def.scope.is_block_scope()
+    ) {
+        return def.scope.get_defun_scope().variables.get(def.name);
+    }
+}
+
+AST_Scope.DEFMETHOD("figure_out_scope", function(options, { parent_scope = undefined, toplevel = this } = {}) {
+    options = defaults(options, {
+        cache: null,
+        ie8: false,
+        safari10: false,
+        module: false,
+    });
+
+    if (!(toplevel instanceof AST_Toplevel)) {
+        throw new Error("Invalid toplevel scope");
+    }
+
+    // pass 1: setup scope chaining and handle definitions
+    var scope = this.parent_scope = parent_scope;
+    var labels = new Map();
+    var defun = null;
+    var in_destructuring = null;
+    var for_scopes = [];
+    var tw = new TreeWalker((node, descend) => {
+        if (node.is_block_scope()) {
+            const save_scope = scope;
+            node.block_scope = scope = new AST_Scope(node);
+            scope._block_scope = true;
+            scope.init_scope_vars(save_scope);
+            scope.uses_with = save_scope.uses_with;
+            scope.uses_eval = save_scope.uses_eval;
+
+            if (options.safari10) {
+                if (node instanceof AST_For || node instanceof AST_ForIn || node instanceof AST_ForOf) {
+                    for_scopes.push(scope);
+                }
+            }
+
+            if (node instanceof AST_Switch) {
+                // XXX: HACK! Ensure the switch expression gets the correct scope (the parent scope) and the body gets the contained scope
+                // AST_Switch has a scope within the body, but it itself "is a block scope"
+                // This means the switched expression has to belong to the outer scope
+                // while the body inside belongs to the switch itself.
+                // This is pretty nasty and warrants an AST change
+                const the_block_scope = scope;
+                scope = save_scope;
+                node.expression.walk(tw);
+                scope = the_block_scope;
+                for (let i = 0; i < node.body.length; i++) {
+                    node.body[i].walk(tw);
+                }
+            } else {
+                descend();
+            }
+            scope = save_scope;
+            return true;
+        }
+        if (node instanceof AST_Destructuring) {
+            const save_destructuring = in_destructuring;
+            in_destructuring = node;
+            descend();
+            in_destructuring = save_destructuring;
+            return true;
+        }
+        if (node instanceof AST_Scope) {
+            node.init_scope_vars(scope);
+            var save_scope = scope;
+            var save_defun = defun;
+            var save_labels = labels;
+            defun = scope = node;
+            labels = new Map();
+            descend();
+            scope = save_scope;
+            defun = save_defun;
+            labels = save_labels;
+            return true;        // don't descend again in TreeWalker
+        }
+        if (node instanceof AST_LabeledStatement) {
+            var l = node.label;
+            if (labels.has(l.name)) {
+                throw new Error(string_template("Label {name} defined twice", l));
+            }
+            labels.set(l.name, l);
+            descend();
+            labels.delete(l.name);
+            return true;        // no descend again
+        }
+        if (node instanceof AST_With) {
+            for (var s = scope; s; s = s.parent_scope)
+                s.uses_with = true;
+            return;
+        }
+        if (node instanceof AST_Symbol) {
+            node.scope = scope;
+        }
+        if (node instanceof AST_Label) {
+            node.thedef = node;
+            node.references = [];
+        }
+        if (node instanceof AST_SymbolLambda) {
+            defun.def_function(node, node.name == "arguments" ? undefined : defun);
+        } else if (node instanceof AST_SymbolDefun) {
+            // Careful here, the scope where this should be defined is
+            // the parent scope.  The reason is that we enter a new
+            // scope when we encounter the AST_Defun node (which is
+            // instanceof AST_Scope) but we get to the symbol a bit
+            // later.
+            const closest_scope = defun.parent_scope;
+
+            // In strict mode, function definitions are block-scoped
+            node.scope = tw.directives["use strict"]
+                ? closest_scope
+                : closest_scope.get_defun_scope();
+
+            mark_export(node.scope.def_function(node, defun), 1);
+        } else if (node instanceof AST_SymbolClass) {
+            mark_export(defun.def_variable(node, defun), 1);
+        } else if (node instanceof AST_SymbolImport) {
+            scope.def_variable(node);
+        } else if (node instanceof AST_SymbolDefClass) {
+            // This deals with the name of the class being available
+            // inside the class.
+            mark_export((node.scope = defun.parent_scope).def_function(node, defun), 1);
+        } else if (
+            node instanceof AST_SymbolVar
+            || node instanceof AST_SymbolLet
+            || node instanceof AST_SymbolConst
+            || node instanceof AST_SymbolCatch
+        ) {
+            var def;
+            if (node instanceof AST_SymbolBlockDeclaration) {
+                def = scope.def_variable(node, null);
+            } else {
+                def = defun.def_variable(node, node.TYPE == "SymbolVar" ? null : undefined);
+            }
+            if (!def.orig.every((sym) => {
+                if (sym === node) return true;
+                if (node instanceof AST_SymbolBlockDeclaration) {
+                    return sym instanceof AST_SymbolLambda;
+                }
+                return !(sym instanceof AST_SymbolLet || sym instanceof AST_SymbolConst);
+            })) {
+                js_error(
+                    `"${node.name}" is redeclared`,
+                    node.start.file,
+                    node.start.line,
+                    node.start.col,
+                    node.start.pos
+                );
+            }
+            if (!(node instanceof AST_SymbolFunarg)) mark_export(def, 2);
+            if (defun !== scope) {
+                node.mark_enclosed();
+                var def = scope.find_variable(node);
+                if (node.thedef !== def) {
+                    node.thedef = def;
+                    node.reference();
+                }
+            }
+        } else if (node instanceof AST_LabelRef) {
+            var sym = labels.get(node.name);
+            if (!sym) throw new Error(string_template("Undefined label {name} [{line},{col}]", {
+                name: node.name,
+                line: node.start.line,
+                col: node.start.col
+            }));
+            node.thedef = sym;
+        }
+        if (!(scope instanceof AST_Toplevel) && (node instanceof AST_Export || node instanceof AST_Import)) {
+            js_error(
+                `"${node.TYPE}" statement may only appear at the top level`,
+                node.start.file,
+                node.start.line,
+                node.start.col,
+                node.start.pos
+            );
+        }
+    });
+
+    if (options.module) {
+        tw.directives["use strict"] = true;
+    }
+
+    this.walk(tw);
+
+    function mark_export(def, level) {
+        if (in_destructuring) {
+            var i = 0;
+            do {
+                level++;
+            } while (tw.parent(i++) !== in_destructuring);
+        }
+        var node = tw.parent(level);
+        if (def.export = node instanceof AST_Export ? MASK_EXPORT_DONT_MANGLE : 0) {
+            var exported = node.exported_definition;
+            if ((exported instanceof AST_Defun || exported instanceof AST_DefClass) && node.is_default) {
+                def.export = MASK_EXPORT_WANT_MANGLE;
+            }
+        }
+    }
+
+    // pass 2: find back references and eval
+    const is_toplevel = this instanceof AST_Toplevel;
+    if (is_toplevel) {
+        this.globals = new Map();
+    }
+
+    var tw = new TreeWalker(node => {
+        if (node instanceof AST_LoopControl && node.label) {
+            node.label.thedef.references.push(node);
+            return true;
+        }
+        if (node instanceof AST_SymbolRef) {
+            var name = node.name;
+            if (name == "eval" && tw.parent() instanceof AST_Call) {
+                for (var s = node.scope; s && !s.uses_eval; s = s.parent_scope) {
+                    s.uses_eval = true;
+                }
+            }
+            var sym;
+            if (tw.parent() instanceof AST_NameMapping && tw.parent(1).module_name
+                || !(sym = node.scope.find_variable(name))) {
+
+                sym = toplevel.def_global(node);
+                if (node instanceof AST_SymbolExport) sym.export = MASK_EXPORT_DONT_MANGLE;
+            } else if (sym.scope instanceof AST_Lambda && name == "arguments") {
+                sym.scope.get_defun_scope().uses_arguments = true;
+            }
+            node.thedef = sym;
+            node.reference();
+            if (node.scope.is_block_scope()
+                && !(sym.orig[0] instanceof AST_SymbolBlockDeclaration)) {
+                node.scope = node.scope.get_defun_scope();
+            }
+            return true;
+        }
+        // ensure mangling works if catch reuses a scope variable
+        var def;
+        if (node instanceof AST_SymbolCatch && (def = redefined_catch_def(node.definition()))) {
+            var s = node.scope;
+            while (s) {
+                push_uniq(s.enclosed, def);
+                if (s === def.scope) break;
+                s = s.parent_scope;
+            }
+        }
+    });
+    this.walk(tw);
+
+    // pass 3: work around IE8 and Safari catch scope bugs
+    if (options.ie8 || options.safari10) {
+        walk(this, node => {
+            if (node instanceof AST_SymbolCatch) {
+                var name = node.name;
+                var refs = node.thedef.references;
+                var scope = node.scope.get_defun_scope();
+                var def = scope.find_variable(name)
+                    || toplevel.globals.get(name)
+                    || scope.def_variable(node);
+                refs.forEach(function(ref) {
+                    ref.thedef = def;
+                    ref.reference();
+                });
+                node.thedef = def;
+                node.reference();
+                return true;
+            }
+        });
+    }
+
+    // pass 4: add symbol definitions to loop scopes
+    // Safari/Webkit bug workaround - loop init let variable shadowing argument.
+    // https://github.com/mishoo/UglifyJS2/issues/1753
+    // https://bugs.webkit.org/show_bug.cgi?id=171041
+    if (options.safari10) {
+        for (const scope of for_scopes) {
+            scope.parent_scope.variables.forEach(function(def) {
+                push_uniq(scope.enclosed, def);
+            });
+        }
+    }
+});
+
+AST_Toplevel.DEFMETHOD("def_global", function(node) {
+    var globals = this.globals, name = node.name;
+    if (globals.has(name)) {
+        return globals.get(name);
+    } else {
+        var g = new SymbolDef(this, node);
+        g.undeclared = true;
+        g.global = true;
+        globals.set(name, g);
+        return g;
+    }
+});
+
+AST_Scope.DEFMETHOD("init_scope_vars", function(parent_scope) {
+    this.variables = new Map();         // map name to AST_SymbolVar (variables defined in this scope; includes functions)
+    this.uses_with = false;             // will be set to true if this or some nested scope uses the `with` statement
+    this.uses_eval = false;             // will be set to true if this or nested scope uses the global `eval`
+    this.parent_scope = parent_scope;   // the parent scope
+    this.enclosed = [];                 // a list of variables from this or outer scope(s) that are referenced from this or inner scopes
+    this.cname = -1;                    // the current index for mangling functions/variables
+});
+
+AST_Scope.DEFMETHOD("conflicting_def", function (name) {
+    return (
+        this.enclosed.find(def => def.name === name)
+        || this.variables.has(name)
+        || (this.parent_scope && this.parent_scope.conflicting_def(name))
+    );
+});
+
+AST_Scope.DEFMETHOD("conflicting_def_shallow", function (name) {
+    return (
+        this.enclosed.find(def => def.name === name)
+        || this.variables.has(name)
+    );
+});
+
+AST_Scope.DEFMETHOD("add_child_scope", function (scope) {
+    // `scope` is going to be moved into `this` right now.
+    // Update the required scopes' information
+
+    if (scope.parent_scope === this) return;
+
+    scope.parent_scope = this;
+
+    // Propagate to this.uses_arguments from arrow functions
+    if ((scope instanceof AST_Arrow) && (this instanceof AST_Lambda && !this.uses_arguments)) {
+        this.uses_arguments = walk(scope, node => {
+            if (
+                node instanceof AST_SymbolRef
+                && node.scope instanceof AST_Lambda
+                && node.name === "arguments"
+            ) {
+                return walk_abort;
+            }
+
+            if (node instanceof AST_Lambda && !(node instanceof AST_Arrow)) {
+                return true;
+            }
+        });
+    }
+
+    this.uses_with = this.uses_with || scope.uses_with;
+    this.uses_eval = this.uses_eval || scope.uses_eval;
+
+    const scope_ancestry = (() => {
+        const ancestry = [];
+        let cur = this;
+        do {
+            ancestry.push(cur);
+        } while ((cur = cur.parent_scope));
+        ancestry.reverse();
+        return ancestry;
+    })();
+
+    const new_scope_enclosed_set = new Set(scope.enclosed);
+    const to_enclose = [];
+    for (const scope_topdown of scope_ancestry) {
+        to_enclose.forEach(e => push_uniq(scope_topdown.enclosed, e));
+        for (const def of scope_topdown.variables.values()) {
+            if (new_scope_enclosed_set.has(def)) {
+                push_uniq(to_enclose, def);
+                push_uniq(scope_topdown.enclosed, def);
+            }
+        }
+    }
+});
+
+function find_scopes_visible_from(scopes) {
+    const found_scopes = new Set();
+
+    for (const scope of new Set(scopes)) {
+        (function bubble_up(scope) {
+            if (scope == null || found_scopes.has(scope)) return;
+
+            found_scopes.add(scope);
+
+            bubble_up(scope.parent_scope);
+        })(scope);
+    }
+
+    return [...found_scopes];
+}
+
+// Creates a symbol during compression
+AST_Scope.DEFMETHOD("create_symbol", function(SymClass, {
+    source,
+    tentative_name,
+    scope,
+    conflict_scopes = [scope],
+    init = null
+} = {}) {
+    let symbol_name;
+
+    conflict_scopes = find_scopes_visible_from(conflict_scopes);
+
+    if (tentative_name) {
+        // Implement hygiene (no new names are conflicting with existing names)
+        tentative_name =
+            symbol_name =
+            tentative_name.replace(/(?:^[^a-z_$]|[^a-z0-9_$])/ig, "_");
+
+        let i = 0;
+        while (conflict_scopes.find(s => s.conflicting_def_shallow(symbol_name))) {
+            symbol_name = tentative_name + "$" + i++;
+        }
+    }
+
+    if (!symbol_name) {
+        throw new Error("No symbol name could be generated in create_symbol()");
+    }
+
+    const symbol = make_node(SymClass, source, {
+        name: symbol_name,
+        scope
+    });
+
+    this.def_variable(symbol, init || null);
+
+    symbol.mark_enclosed();
+
+    return symbol;
+});
+
+
+AST_Node.DEFMETHOD("is_block_scope", return_false);
+AST_Class.DEFMETHOD("is_block_scope", return_false);
+AST_Lambda.DEFMETHOD("is_block_scope", return_false);
+AST_Toplevel.DEFMETHOD("is_block_scope", return_false);
+AST_SwitchBranch.DEFMETHOD("is_block_scope", return_false);
+AST_Block.DEFMETHOD("is_block_scope", return_true);
+AST_Scope.DEFMETHOD("is_block_scope", function () {
+    return this._block_scope || false;
+});
+AST_IterationStatement.DEFMETHOD("is_block_scope", return_true);
+
+AST_Lambda.DEFMETHOD("init_scope_vars", function() {
+    AST_Scope.prototype.init_scope_vars.apply(this, arguments);
+    this.uses_arguments = false;
+    this.def_variable(new AST_SymbolFunarg({
+        name: "arguments",
+        start: this.start,
+        end: this.end
+    }));
+});
+
+AST_Arrow.DEFMETHOD("init_scope_vars", function() {
+    AST_Scope.prototype.init_scope_vars.apply(this, arguments);
+    this.uses_arguments = false;
+});
+
+AST_Symbol.DEFMETHOD("mark_enclosed", function() {
+    var def = this.definition();
+    var s = this.scope;
+    while (s) {
+        push_uniq(s.enclosed, def);
+        if (s === def.scope) break;
+        s = s.parent_scope;
+    }
+});
+
+AST_Symbol.DEFMETHOD("reference", function() {
+    this.definition().references.push(this);
+    this.mark_enclosed();
+});
+
+AST_Scope.DEFMETHOD("find_variable", function(name) {
+    if (name instanceof AST_Symbol) name = name.name;
+    return this.variables.get(name)
+        || (this.parent_scope && this.parent_scope.find_variable(name));
+});
+
+AST_Scope.DEFMETHOD("def_function", function(symbol, init) {
+    var def = this.def_variable(symbol, init);
+    if (!def.init || def.init instanceof AST_Defun) def.init = init;
+    return def;
+});
+
+AST_Scope.DEFMETHOD("def_variable", function(symbol, init) {
+    var def = this.variables.get(symbol.name);
+    if (def) {
+        def.orig.push(symbol);
+        if (def.init && (def.scope !== symbol.scope || def.init instanceof AST_Function)) {
+            def.init = init;
+        }
+    } else {
+        def = new SymbolDef(this, symbol, init);
+        this.variables.set(symbol.name, def);
+        def.global = !this.parent_scope;
+    }
+    return symbol.thedef = def;
+});
+
+function next_mangled(scope, options) {
+    let defun_scope;
+    if (
+        scopes_with_block_defuns
+        && (defun_scope = scope.get_defun_scope())
+        && scopes_with_block_defuns.has(defun_scope)
+    ) {
+        scope = defun_scope;
+    }
+
+    var ext = scope.enclosed;
+    var nth_identifier = options.nth_identifier;
+    out: while (true) {
+        var m = nth_identifier.get(++scope.cname);
+        if (ALL_RESERVED_WORDS.has(m)) continue; // skip over "do"
+
+        // https://github.com/mishoo/UglifyJS2/issues/242 -- do not
+        // shadow a name reserved from mangling.
+        if (options.reserved.has(m)) continue;
+
+        // Functions with short names might collide with base54 output
+        // and therefore cause collisions when keep_fnames is true.
+        if (unmangleable_names && unmangleable_names.has(m)) continue out;
+
+        // we must ensure that the mangled name does not shadow a name
+        // from some parent scope that is referenced in this or in
+        // inner scopes.
+        for (let i = ext.length; --i >= 0;) {
+            const def = ext[i];
+            const name = def.mangled_name || (def.unmangleable(options) && def.name);
+            if (m == name) continue out;
+        }
+        return m;
+    }
+}
+
+AST_Scope.DEFMETHOD("next_mangled", function(options) {
+    return next_mangled(this, options);
+});
+
+AST_Toplevel.DEFMETHOD("next_mangled", function(options) {
+    let name;
+    const mangled_names = this.mangled_names;
+    do {
+        name = next_mangled(this, options);
+    } while (mangled_names.has(name));
+    return name;
+});
+
+AST_Function.DEFMETHOD("next_mangled", function(options, def) {
+    // #179, #326
+    // in Safari strict mode, something like (function x(x){...}) is a syntax error;
+    // a function expression's argument cannot shadow the function expression's name
+
+    var tricky_def = def.orig[0] instanceof AST_SymbolFunarg && this.name && this.name.definition();
+
+    // the function's mangled_name is null when keep_fnames is true
+    var tricky_name = tricky_def ? tricky_def.mangled_name || tricky_def.name : null;
+
+    while (true) {
+        var name = next_mangled(this, options);
+        if (!tricky_name || tricky_name != name)
+            return name;
+    }
+});
+
+AST_Symbol.DEFMETHOD("unmangleable", function(options) {
+    var def = this.definition();
+    return !def || def.unmangleable(options);
+});
+
+// labels are always mangleable
+AST_Label.DEFMETHOD("unmangleable", return_false);
+
+AST_Symbol.DEFMETHOD("unreferenced", function() {
+    return !this.definition().references.length && !this.scope.pinned();
+});
+
+AST_Symbol.DEFMETHOD("definition", function() {
+    return this.thedef;
+});
+
+AST_Symbol.DEFMETHOD("global", function() {
+    return this.thedef.global;
+});
+
+/**
+ * Format the mangler options (if any) into their appropriate types
+ */
+export function format_mangler_options(options) {
+    options = defaults(options, {
+        eval        : false,
+        nth_identifier : base54,
+        ie8         : false,
+        keep_classnames: false,
+        keep_fnames : false,
+        module      : false,
+        reserved    : [],
+        toplevel    : false,
+    });
+    if (options.module) options.toplevel = true;
+    if (!Array.isArray(options.reserved)
+        && !(options.reserved instanceof Set)
+    ) {
+        options.reserved = [];
+    }
+    options.reserved = new Set(options.reserved);
+    // Never mangle arguments
+    options.reserved.add("arguments");
+    return options;
+}
+
+AST_Toplevel.DEFMETHOD("mangle_names", function(options) {
+    options = format_mangler_options(options);
+    var nth_identifier = options.nth_identifier;
+
+    // We only need to mangle declaration nodes.  Special logic wired
+    // into the code generator will display the mangled name if it's
+    // present (and for AST_SymbolRef-s it'll use the mangled name of
+    // the AST_SymbolDeclaration that it points to).
+    var lname = -1;
+    var to_mangle = [];
+
+    if (options.keep_fnames) {
+        function_defs = new Set();
+    }
+
+    const mangled_names = this.mangled_names = new Set();
+    unmangleable_names = new Set();
+
+    if (options.cache) {
+        this.globals.forEach(collect);
+        if (options.cache.props) {
+            options.cache.props.forEach(function(mangled_name) {
+                mangled_names.add(mangled_name);
+            });
+        }
+    }
+
+    var tw = new TreeWalker(function(node, descend) {
+        if (node instanceof AST_LabeledStatement) {
+            // lname is incremented when we get to the AST_Label
+            var save_nesting = lname;
+            descend();
+            lname = save_nesting;
+            return true;        // don't descend again in TreeWalker
+        }
+        if (
+            node instanceof AST_Defun
+            && !(tw.parent() instanceof AST_Scope)
+        ) {
+            scopes_with_block_defuns = scopes_with_block_defuns || new Set();
+            scopes_with_block_defuns.add(node.parent_scope.get_defun_scope());
+        }
+        if (node instanceof AST_Scope) {
+            node.variables.forEach(collect);
+            return;
+        }
+        if (node.is_block_scope()) {
+            node.block_scope.variables.forEach(collect);
+            return;
+        }
+        if (
+            function_defs
+            && node instanceof AST_VarDef
+            && node.value instanceof AST_Lambda
+            && !node.value.name
+            && keep_name(options.keep_fnames, node.name.name)
+        ) {
+            function_defs.add(node.name.definition().id);
+            return;
+        }
+        if (node instanceof AST_Label) {
+            let name;
+            do {
+                name = nth_identifier.get(++lname);
+            } while (ALL_RESERVED_WORDS.has(name));
+            node.mangled_name = name;
+            return true;
+        }
+        if (!(options.ie8 || options.safari10) && node instanceof AST_SymbolCatch) {
+            to_mangle.push(node.definition());
+            return;
+        }
+    });
+
+    this.walk(tw);
+
+    if (options.keep_fnames || options.keep_classnames) {
+        // Collect a set of short names which are unmangleable,
+        // for use in avoiding collisions in next_mangled.
+        to_mangle.forEach(def => {
+            if (def.name.length < 6 && def.unmangleable(options)) {
+                unmangleable_names.add(def.name);
+            }
+        });
+    }
+
+    to_mangle.forEach(def => { def.mangle(options); });
+
+    function_defs = null;
+    unmangleable_names = null;
+    scopes_with_block_defuns = null;
+
+    function collect(symbol) {
+        if (symbol.export & MASK_EXPORT_DONT_MANGLE) {
+            unmangleable_names.add(symbol.name);
+        } else if (!options.reserved.has(symbol.name)) {
+            to_mangle.push(symbol);
+        }
+    }
+});
+
+AST_Toplevel.DEFMETHOD("find_colliding_names", function(options) {
+    const cache = options.cache && options.cache.props;
+    const avoid = new Set();
+    options.reserved.forEach(to_avoid);
+    this.globals.forEach(add_def);
+    this.walk(new TreeWalker(function(node) {
+        if (node instanceof AST_Scope) node.variables.forEach(add_def);
+        if (node instanceof AST_SymbolCatch) add_def(node.definition());
+    }));
+    return avoid;
+
+    function to_avoid(name) {
+        avoid.add(name);
+    }
+
+    function add_def(def) {
+        var name = def.name;
+        if (def.global && cache && cache.has(name)) name = cache.get(name);
+        else if (!def.unmangleable(options)) return;
+        to_avoid(name);
+    }
+});
+
+AST_Toplevel.DEFMETHOD("expand_names", function(options) {
+    options = format_mangler_options(options);
+    var nth_identifier = options.nth_identifier;
+    if (nth_identifier.reset && nth_identifier.sort) {
+        nth_identifier.reset();
+        nth_identifier.sort();
+    }
+    var avoid = this.find_colliding_names(options);
+    var cname = 0;
+    this.globals.forEach(rename);
+    this.walk(new TreeWalker(function(node) {
+        if (node instanceof AST_Scope) node.variables.forEach(rename);
+        if (node instanceof AST_SymbolCatch) rename(node.definition());
+    }));
+
+    function next_name() {
+        var name;
+        do {
+            name = nth_identifier.get(cname++);
+        } while (avoid.has(name) || ALL_RESERVED_WORDS.has(name));
+        return name;
+    }
+
+    function rename(def) {
+        if (def.global && options.cache) return;
+        if (def.unmangleable(options)) return;
+        if (options.reserved.has(def.name)) return;
+        const redefinition = redefined_catch_def(def);
+        const name = def.name = redefinition ? redefinition.name : next_name();
+        def.orig.forEach(function(sym) {
+            sym.name = name;
+        });
+        def.references.forEach(function(sym) {
+            sym.name = name;
+        });
+    }
+});
+
+AST_Node.DEFMETHOD("tail_node", return_this);
+AST_Sequence.DEFMETHOD("tail_node", function() {
+    return this.expressions[this.expressions.length - 1];
+});
+
+AST_Toplevel.DEFMETHOD("compute_char_frequency", function(options) {
+    options = format_mangler_options(options);
+    var nth_identifier = options.nth_identifier;
+    if (!nth_identifier.reset || !nth_identifier.consider || !nth_identifier.sort) {
+        // If the identifier mangler is invariant, skip computing character frequency.
+        return;
+    }
+    nth_identifier.reset();
+
+    try {
+        AST_Node.prototype.print = function(stream, force_parens) {
+            this._print(stream, force_parens);
+            if (this instanceof AST_Symbol && !this.unmangleable(options)) {
+                nth_identifier.consider(this.name, -1);
+            } else if (options.properties) {
+                if (this instanceof AST_DotHash) {
+                    nth_identifier.consider("#" + this.property, -1);
+                } else if (this instanceof AST_Dot) {
+                    nth_identifier.consider(this.property, -1);
+                } else if (this instanceof AST_Sub) {
+                    skip_string(this.property);
+                }
+            }
+        };
+        nth_identifier.consider(this.print_to_string(), 1);
+    } finally {
+        AST_Node.prototype.print = AST_Node.prototype._print;
+    }
+    nth_identifier.sort();
+
+    function skip_string(node) {
+        if (node instanceof AST_String) {
+            nth_identifier.consider(node.value, -1);
+        } else if (node instanceof AST_Conditional) {
+            skip_string(node.consequent);
+            skip_string(node.alternative);
+        } else if (node instanceof AST_Sequence) {
+            skip_string(node.tail_node());
+        }
+    }
+});
+
+const base54 = (() => {
+    const leading = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ$_".split("");
+    const digits = "0123456789".split("");
+    let chars;
+    let frequency;
+    function reset() {
+        frequency = new Map();
+        leading.forEach(function(ch) {
+            frequency.set(ch, 0);
+        });
+        digits.forEach(function(ch) {
+            frequency.set(ch, 0);
+        });
+    }
+    function consider(str, delta) {
+        for (var i = str.length; --i >= 0;) {
+            frequency.set(str[i], frequency.get(str[i]) + delta);
+        }
+    }
+    function compare(a, b) {
+        return frequency.get(b) - frequency.get(a);
+    }
+    function sort() {
+        chars = mergeSort(leading, compare).concat(mergeSort(digits, compare));
+    }
+    // Ensure this is in a usable initial state.
+    reset();
+    sort();
+    function base54(num) {
+        var ret = "", base = 54;
+        num++;
+        do {
+            num--;
+            ret += chars[num % base];
+            num = Math.floor(num / base);
+            base = 64;
+        } while (num > 0);
+        return ret;
+    }
+
+    return {
+        get: base54,
+        consider,
+        reset,
+        sort
+    };
+})();
+
+export {
+    base54,
+    SymbolDef,
+};
