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app_vue/node_modules/terser/lib/compress/drop-unused.js

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+/***********************************************************************
+
+  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.
+
+ ***********************************************************************/
+
+import {
+    AST_Accessor,
+    AST_Assign,
+    AST_BlockStatement,
+    AST_Call,
+    AST_Class,
+    AST_ClassExpression,
+    AST_ClassStaticBlock,
+    AST_DefaultAssign,
+    AST_DefClass,
+    AST_Definitions,
+    AST_Defun,
+    AST_Destructuring,
+    AST_EmptyStatement,
+    AST_Expansion,
+    AST_Export,
+    AST_For,
+    AST_ForIn,
+    AST_Function,
+    AST_LabeledStatement,
+    AST_Lambda,
+    AST_Number,
+    AST_Scope,
+    AST_Sequence,
+    AST_SimpleStatement,
+    AST_SymbolBlockDeclaration,
+    AST_SymbolCatch,
+    AST_SymbolDeclaration,
+    AST_SymbolFunarg,
+    AST_SymbolRef,
+    AST_SymbolVar,
+    AST_Toplevel,
+    AST_Unary,
+    AST_Var,
+
+    TreeTransformer,
+    TreeWalker,
+    walk,
+} from "../ast.js";
+import {
+    keep_name,
+    make_node,
+    map_add,
+    MAP,
+    remove,
+    return_false,
+} from "../utils/index.js";
+import { SymbolDef } from "../scope.js";
+
+import {
+    WRITE_ONLY,
+    UNUSED,
+
+    has_flag,
+    set_flag,
+} from "./compressor-flags.js";
+import {
+    make_sequence,
+    maintain_this_binding,
+    is_empty,
+    is_ref_of,
+    can_be_evicted_from_block,
+} from "./common.js";
+import { is_used_in_expression } from "./inference.js";
+
+const r_keep_assign = /keep_assign/;
+
+/** Drop unused variables from this scope */
+AST_Scope.DEFMETHOD("drop_unused", function(compressor) {
+    if (!compressor.option("unused")) return;
+    if (compressor.has_directive("use asm")) return;
+    if (!this.variables) return; // not really a scope (eg: AST_Class)
+
+    var self = this;
+    if (self.pinned()) return;
+    var drop_funcs = !(self instanceof AST_Toplevel) || compressor.toplevel.funcs;
+    var drop_vars = !(self instanceof AST_Toplevel) || compressor.toplevel.vars;
+    const assign_as_unused = r_keep_assign.test(compressor.option("unused")) ? return_false : function(node) {
+        if (node instanceof AST_Assign
+            && !node.logical
+            && (has_flag(node, WRITE_ONLY) || node.operator == "=")
+        ) {
+            return node.left;
+        }
+        if (node instanceof AST_Unary && has_flag(node, WRITE_ONLY)) {
+            return node.expression;
+        }
+    };
+    var in_use_ids = new Map();
+    var fixed_ids = new Map();
+    if (self instanceof AST_Toplevel && compressor.top_retain) {
+        self.variables.forEach(function(def) {
+            if (compressor.top_retain(def)) {
+                in_use_ids.set(def.id, def);
+            }
+        });
+    }
+    var var_defs_by_id = new Map();
+    var initializations = new Map();
+
+    // pass 1: find out which symbols are directly used in
+    // this scope (not in nested scopes).
+    var scope = this;
+    var tw = new TreeWalker(function(node, descend) {
+        if (node instanceof AST_Lambda && node.uses_arguments && !tw.has_directive("use strict")) {
+            node.argnames.forEach(function(argname) {
+                if (!(argname instanceof AST_SymbolDeclaration)) return;
+                var def = argname.definition();
+                in_use_ids.set(def.id, def);
+            });
+        }
+        if (node === self) return;
+        if (node instanceof AST_Class && node.has_side_effects(compressor)) {
+            if (node.is_self_referential()) {
+                descend();
+            } else {
+                node.visit_nondeferred_class_parts(tw);
+            }
+        }
+        if (node instanceof AST_Defun || node instanceof AST_DefClass) {
+            var node_def = node.name.definition();
+            const in_export = tw.parent() instanceof AST_Export;
+            if (in_export || !drop_funcs && scope === self) {
+                if (node_def.global) {
+                    in_use_ids.set(node_def.id, node_def);
+                }
+            }
+
+            map_add(initializations, node_def.id, node);
+            return true; // don't go in nested scopes
+        }
+        // In the root scope, we drop things. In inner scopes, we just check for uses.
+        const in_root_scope = scope === self;
+        if (node instanceof AST_SymbolFunarg && in_root_scope) {
+            map_add(var_defs_by_id, node.definition().id, node);
+        }
+        if (node instanceof AST_Definitions && in_root_scope) {
+            const in_export = tw.parent() instanceof AST_Export;
+            node.definitions.forEach(function(def) {
+                if (def.name instanceof AST_SymbolVar) {
+                    map_add(var_defs_by_id, def.name.definition().id, def);
+                }
+                if (in_export || !drop_vars) {
+                    walk(def.name, node => {
+                        if (node instanceof AST_SymbolDeclaration) {
+                            const def = node.definition();
+                            if (def.global) {
+                                in_use_ids.set(def.id, def);
+                            }
+                        }
+                    });
+                }
+                if (def.name instanceof AST_Destructuring) {
+                    def.walk(tw);
+                }
+                if (def.name instanceof AST_SymbolDeclaration && def.value) {
+                    var node_def = def.name.definition();
+                    map_add(initializations, node_def.id, def.value);
+                    if (!node_def.chained && def.name.fixed_value() === def.value) {
+                        fixed_ids.set(node_def.id, def);
+                    }
+                    if (def.value.has_side_effects(compressor)) {
+                        def.value.walk(tw);
+                    }
+                }
+            });
+            return true;
+        }
+        return scan_ref_scoped(node, descend);
+    });
+    self.walk(tw);
+    // pass 2: for every used symbol we need to walk its
+    // initialization code to figure out if it uses other
+    // symbols (that may not be in_use).
+    tw = new TreeWalker(scan_ref_scoped);
+    in_use_ids.forEach(function (def) {
+        var init = initializations.get(def.id);
+        if (init) init.forEach(function(init) {
+            init.walk(tw);
+        });
+    });
+    // pass 3: we should drop declarations not in_use
+    var tt = new TreeTransformer(
+        function before(node, descend, in_list) {
+            var parent = tt.parent();
+            if (drop_vars) {
+                const sym = assign_as_unused(node);
+                if (sym instanceof AST_SymbolRef) {
+                    var def = sym.definition();
+                    var in_use = in_use_ids.has(def.id);
+                    if (node instanceof AST_Assign) {
+                        if (!in_use || fixed_ids.has(def.id) && fixed_ids.get(def.id) !== node) {
+                            const assignee = node.right.transform(tt);
+                            if (!in_use && !assignee.has_side_effects(compressor) && !is_used_in_expression(tt)) {
+                                return in_list ? MAP.skip : make_node(AST_Number, node, { value: 0 });
+                            }
+                            return maintain_this_binding(parent, node, assignee);
+                        }
+                    } else if (!in_use) {
+                        return in_list ? MAP.skip : make_node(AST_Number, node, { value: 0 });
+                    }
+                }
+            }
+            if (scope !== self) return;
+            var def;
+            if (node.name
+                && (node instanceof AST_ClassExpression
+                    && !keep_name(compressor.option("keep_classnames"), (def = node.name.definition()).name)
+                || node instanceof AST_Function
+                    && !keep_name(compressor.option("keep_fnames"), (def = node.name.definition()).name))) {
+                // any declarations with same name will overshadow
+                // name of this anonymous function and can therefore
+                // never be used anywhere
+                if (!in_use_ids.has(def.id) || def.orig.length > 1) node.name = null;
+            }
+            if (node instanceof AST_Lambda && !(node instanceof AST_Accessor)) {
+                var trim =
+                    !compressor.option("keep_fargs")
+                    // Is this an IIFE that won't refer to its name?
+                    || parent instanceof AST_Call
+                        && parent.expression === node
+                        && !node.pinned()
+                        && (!node.name || node.name.unreferenced());
+                for (var a = node.argnames, i = a.length; --i >= 0;) {
+                    var sym = a[i];
+                    if (sym instanceof AST_Expansion) {
+                        sym = sym.expression;
+                    }
+                    if (sym instanceof AST_DefaultAssign) {
+                        sym = sym.left;
+                    }
+                    // Do not drop destructuring arguments.
+                    // They constitute a type assertion of sorts
+                    if (
+                        !(sym instanceof AST_Destructuring)
+                        && !in_use_ids.has(sym.definition().id)
+                    ) {
+                        set_flag(sym, UNUSED);
+                        if (trim) {
+                            a.pop();
+                        }
+                    } else {
+                        trim = false;
+                    }
+                }
+            }
+            if (node instanceof AST_DefClass && node !== self) {
+                const def = node.name.definition();
+                descend(node, this);
+                const keep_class = def.global && !drop_funcs || in_use_ids.has(def.id);
+                if (!keep_class) {
+                    const kept = node.drop_side_effect_free(compressor);
+                    if (kept == null) {
+                        def.eliminated++;
+                        return in_list ? MAP.skip : make_node(AST_EmptyStatement, node);
+                    }
+                    return kept;
+                }
+                return node;
+            }
+            if (node instanceof AST_Defun && node !== self) {
+                const def = node.name.definition();
+                const keep = def.global && !drop_funcs || in_use_ids.has(def.id);
+                if (!keep) {
+                    def.eliminated++;
+                    return in_list ? MAP.skip : make_node(AST_EmptyStatement, node);
+                }
+            }
+            if (node instanceof AST_Definitions && !(parent instanceof AST_ForIn && parent.init === node)) {
+                var drop_block = !(parent instanceof AST_Toplevel) && !(node instanceof AST_Var);
+                // place uninitialized names at the start
+                var body = [], head = [], tail = [];
+                // for unused names whose initialization has
+                // side effects, we can cascade the init. code
+                // into the next one, or next statement.
+                var side_effects = [];
+                node.definitions.forEach(function(def) {
+                    if (def.value) def.value = def.value.transform(tt);
+                    var is_destructure = def.name instanceof AST_Destructuring;
+                    var sym = is_destructure
+                        ? new SymbolDef(null, { name: "<destructure>" }) /* fake SymbolDef */
+                        : def.name.definition();
+                    if (drop_block && sym.global) return tail.push(def);
+                    if (!(drop_vars || drop_block)
+                        || is_destructure
+                            && (def.name.names.length
+                                || def.name.is_array
+                                || compressor.option("pure_getters") != true)
+                        || in_use_ids.has(sym.id)
+                    ) {
+                        if (def.value && fixed_ids.has(sym.id) && fixed_ids.get(sym.id) !== def) {
+                            def.value = def.value.drop_side_effect_free(compressor);
+                        }
+                        if (def.name instanceof AST_SymbolVar) {
+                            var var_defs = var_defs_by_id.get(sym.id);
+                            if (var_defs.length > 1 && (!def.value || sym.orig.indexOf(def.name) > sym.eliminated)) {
+                                if (def.value) {
+                                    var ref = make_node(AST_SymbolRef, def.name, def.name);
+                                    sym.references.push(ref);
+                                    var assign = make_node(AST_Assign, def, {
+                                        operator: "=",
+                                        logical: false,
+                                        left: ref,
+                                        right: def.value
+                                    });
+                                    if (fixed_ids.get(sym.id) === def) {
+                                        fixed_ids.set(sym.id, assign);
+                                    }
+                                    side_effects.push(assign.transform(tt));
+                                }
+                                remove(var_defs, def);
+                                sym.eliminated++;
+                                return;
+                            }
+                        }
+                        if (def.value) {
+                            if (side_effects.length > 0) {
+                                if (tail.length > 0) {
+                                    side_effects.push(def.value);
+                                    def.value = make_sequence(def.value, side_effects);
+                                } else {
+                                    body.push(make_node(AST_SimpleStatement, node, {
+                                        body: make_sequence(node, side_effects)
+                                    }));
+                                }
+                                side_effects = [];
+                            }
+                            tail.push(def);
+                        } else {
+                            head.push(def);
+                        }
+                    } else if (sym.orig[0] instanceof AST_SymbolCatch) {
+                        var value = def.value && def.value.drop_side_effect_free(compressor);
+                        if (value) side_effects.push(value);
+                        def.value = null;
+                        head.push(def);
+                    } else {
+                        var value = def.value && def.value.drop_side_effect_free(compressor);
+                        if (value) {
+                            side_effects.push(value);
+                        }
+                        sym.eliminated++;
+                    }
+                });
+                if (head.length > 0 || tail.length > 0) {
+                    node.definitions = head.concat(tail);
+                    body.push(node);
+                }
+                if (side_effects.length > 0) {
+                    body.push(make_node(AST_SimpleStatement, node, {
+                        body: make_sequence(node, side_effects)
+                    }));
+                }
+                switch (body.length) {
+                  case 0:
+                    return in_list ? MAP.skip : make_node(AST_EmptyStatement, node);
+                  case 1:
+                    return body[0];
+                  default:
+                    return in_list ? MAP.splice(body) : make_node(AST_BlockStatement, node, { body });
+                }
+            }
+            // certain combination of unused name + side effect leads to:
+            //    https://github.com/mishoo/UglifyJS2/issues/44
+            //    https://github.com/mishoo/UglifyJS2/issues/1830
+            //    https://github.com/mishoo/UglifyJS2/issues/1838
+            // that's an invalid AST.
+            // We fix it at this stage by moving the `var` outside the `for`.
+            if (node instanceof AST_For) {
+                descend(node, this);
+                var block;
+                if (node.init instanceof AST_BlockStatement) {
+                    block = node.init;
+                    node.init = block.body.pop();
+                    block.body.push(node);
+                }
+                if (node.init instanceof AST_SimpleStatement) {
+                    node.init = node.init.body;
+                } else if (is_empty(node.init)) {
+                    node.init = null;
+                }
+                return !block ? node : in_list ? MAP.splice(block.body) : block;
+            }
+            if (node instanceof AST_LabeledStatement
+                && node.body instanceof AST_For
+            ) {
+                descend(node, this);
+                if (node.body instanceof AST_BlockStatement) {
+                    var block = node.body;
+                    node.body = block.body.pop();
+                    block.body.push(node);
+                    return in_list ? MAP.splice(block.body) : block;
+                }
+                return node;
+            }
+            if (node instanceof AST_BlockStatement) {
+                descend(node, this);
+                if (in_list && node.body.every(can_be_evicted_from_block)) {
+                    return MAP.splice(node.body);
+                }
+                return node;
+            }
+            if (node instanceof AST_Scope && !(node instanceof AST_ClassStaticBlock)) {
+                const save_scope = scope;
+                scope = node;
+                descend(node, this);
+                scope = save_scope;
+                return node;
+            }
+        },
+        function after(node, in_list) {
+            if (node instanceof AST_Sequence) {
+                switch (node.expressions.length) {
+                    case 0: return in_list ? MAP.skip : make_node(AST_Number, node, { value: 0 });
+                    case 1: return node.expressions[0];
+                }
+            }
+        }
+    );
+
+    self.transform(tt);
+
+    function scan_ref_scoped(node, descend) {
+        var node_def;
+        const sym = assign_as_unused(node);
+        if (sym instanceof AST_SymbolRef
+            && !is_ref_of(node.left, AST_SymbolBlockDeclaration)
+            && self.variables.get(sym.name) === (node_def = sym.definition())
+        ) {
+            if (node instanceof AST_Assign) {
+                node.right.walk(tw);
+                if (!node_def.chained && node.left.fixed_value() === node.right) {
+                    fixed_ids.set(node_def.id, node);
+                }
+            }
+            return true;
+        }
+        if (node instanceof AST_SymbolRef) {
+            node_def = node.definition();
+            if (!in_use_ids.has(node_def.id)) {
+                in_use_ids.set(node_def.id, node_def);
+                if (node_def.orig[0] instanceof AST_SymbolCatch) {
+                    const redef = node_def.scope.is_block_scope()
+                        && node_def.scope.get_defun_scope().variables.get(node_def.name);
+                    if (redef) in_use_ids.set(redef.id, redef);
+                }
+            }
+            return true;
+        }
+        if (node instanceof AST_Class) {
+            descend();
+            return true;
+        }
+        if (node instanceof AST_Scope && !(node instanceof AST_ClassStaticBlock)) {
+            var save_scope = scope;
+            scope = node;
+            descend();
+            scope = save_scope;
+            return true;
+        }
+    }
+});