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app_vue/node_modules/terser/lib/compress/drop-side-effect-free.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_Array,
+    AST_Arrow,
+    AST_Assign,
+    AST_Binary,
+    AST_Call,
+    AST_Chain,
+    AST_Class,
+    AST_ClassPrivateProperty,
+    AST_ClassProperty,
+    AST_ClassStaticBlock,
+    AST_ConciseMethod,
+    AST_Conditional,
+    AST_Constant,
+    AST_DefClass,
+    AST_Dot,
+    AST_Expansion,
+    AST_Function,
+    AST_Node,
+    AST_Number,
+    AST_Object,
+    AST_ObjectGetter,
+    AST_ObjectKeyVal,
+    AST_ObjectSetter,
+    AST_PrivateGetter,
+    AST_PrivateSetter,
+    AST_PrivateMethod,
+    AST_PropAccess,
+    AST_Scope,
+    AST_Sequence,
+    AST_SimpleStatement,
+    AST_Sub,
+    AST_SymbolRef,
+    AST_TemplateSegment,
+    AST_TemplateString,
+    AST_This,
+    AST_Unary,
+} from "../ast.js";
+import { make_node, return_null, return_this } from "../utils/index.js";
+import { first_in_statement } from "../utils/first_in_statement.js";
+
+import { pure_prop_access_globals } from "./native-objects.js";
+import { lazy_op, unary_side_effects, is_nullish_shortcircuited } from "./inference.js";
+import { WRITE_ONLY, set_flag, clear_flag } from "./compressor-flags.js";
+import { make_sequence, is_func_expr, is_iife_call } from "./common.js";
+
+// AST_Node#drop_side_effect_free() gets called when we don't care about the value,
+// only about side effects. We'll be defining this method for each node type in this module
+//
+// Examples:
+// foo++ -> foo++
+// 1 + func() -> func()
+// 10 -> (nothing)
+// knownPureFunc(foo++) -> foo++
+
+function def_drop_side_effect_free(node_or_nodes, func) {
+    for (const node of [].concat(node_or_nodes)) {
+        node.DEFMETHOD("drop_side_effect_free", func);
+    }
+}
+
+// Drop side-effect-free elements from an array of expressions.
+// Returns an array of expressions with side-effects or null
+// if all elements were dropped. Note: original array may be
+// returned if nothing changed.
+function trim(nodes, compressor, first_in_statement) {
+    var len = nodes.length;
+    if (!len)  return null;
+
+    var ret = [], changed = false;
+    for (var i = 0; i < len; i++) {
+        var node = nodes[i].drop_side_effect_free(compressor, first_in_statement);
+        changed |= node !== nodes[i];
+        if (node) {
+            ret.push(node);
+            first_in_statement = false;
+        }
+    }
+    return changed ? ret.length ? ret : null : nodes;
+}
+
+def_drop_side_effect_free(AST_Node, return_this);
+def_drop_side_effect_free(AST_Constant, return_null);
+def_drop_side_effect_free(AST_This, return_null);
+
+def_drop_side_effect_free(AST_Call, function (compressor, first_in_statement) {
+    if (is_nullish_shortcircuited(this, compressor)) {
+        return this.expression.drop_side_effect_free(compressor, first_in_statement);
+    }
+
+    if (!this.is_callee_pure(compressor)) {
+        if (this.expression.is_call_pure(compressor)) {
+            var exprs = this.args.slice();
+            exprs.unshift(this.expression.expression);
+            exprs = trim(exprs, compressor, first_in_statement);
+            return exprs && make_sequence(this, exprs);
+        }
+        if (is_func_expr(this.expression)
+            && (!this.expression.name || !this.expression.name.definition().references.length)) {
+            var node = this.clone();
+            node.expression.process_expression(false, compressor);
+            return node;
+        }
+        return this;
+    }
+
+    var args = trim(this.args, compressor, first_in_statement);
+    return args && make_sequence(this, args);
+});
+
+def_drop_side_effect_free(AST_Accessor, return_null);
+
+def_drop_side_effect_free(AST_Function, return_null);
+
+def_drop_side_effect_free(AST_Arrow, return_null);
+
+def_drop_side_effect_free(AST_Class, function (compressor) {
+    const with_effects = [];
+
+    if (this.is_self_referential() && this.has_side_effects(compressor)) {
+        return this;
+    }
+
+    const trimmed_extends = this.extends && this.extends.drop_side_effect_free(compressor);
+    if (trimmed_extends) with_effects.push(trimmed_extends);
+
+    for (const prop of this.properties) {
+        if (prop instanceof AST_ClassStaticBlock) {
+            if (prop.has_side_effects(compressor)) {
+                return this; // Be cautious about these
+            }
+        } else {
+            const trimmed_prop = prop.drop_side_effect_free(compressor);
+            if (trimmed_prop) with_effects.push(trimmed_prop);
+        }
+    }
+
+    if (!with_effects.length)
+        return null;
+
+    const exprs = make_sequence(this, with_effects);
+    if (this instanceof AST_DefClass) {
+        // We want a statement
+        return make_node(AST_SimpleStatement, this, { body: exprs });
+    } else {
+        return exprs;
+    }
+});
+
+def_drop_side_effect_free([
+    AST_ClassProperty,
+    AST_ClassPrivateProperty,
+], function (compressor) {
+    const key = this.computed_key() && this.key.drop_side_effect_free(compressor);
+
+    const value = this.static && this.value
+        && this.value.drop_side_effect_free(compressor);
+
+    if (key && value)
+        return make_sequence(this, [key, value]);
+    return key || value || null;
+});
+
+def_drop_side_effect_free(AST_Binary, function (compressor, first_in_statement) {
+    var right = this.right.drop_side_effect_free(compressor);
+    if (!right)
+        return this.left.drop_side_effect_free(compressor, first_in_statement);
+    if (lazy_op.has(this.operator)) {
+        if (right === this.right)
+            return this;
+        var node = this.clone();
+        node.right = right;
+        return node;
+    } else {
+        var left = this.left.drop_side_effect_free(compressor, first_in_statement);
+        if (!left)
+            return this.right.drop_side_effect_free(compressor, first_in_statement);
+        return make_sequence(this, [left, right]);
+    }
+});
+
+def_drop_side_effect_free(AST_Assign, function (compressor) {
+    if (this.logical)
+        return this;
+
+    var left = this.left;
+    if (left.has_side_effects(compressor)
+        || compressor.has_directive("use strict")
+        && left instanceof AST_PropAccess
+        && left.expression.is_constant()) {
+        return this;
+    }
+    set_flag(this, WRITE_ONLY);
+    while (left instanceof AST_PropAccess) {
+        left = left.expression;
+    }
+    if (left.is_constant_expression(compressor.find_parent(AST_Scope))) {
+        return this.right.drop_side_effect_free(compressor);
+    }
+    return this;
+});
+
+def_drop_side_effect_free(AST_Conditional, function (compressor) {
+    var consequent = this.consequent.drop_side_effect_free(compressor);
+    var alternative = this.alternative.drop_side_effect_free(compressor);
+    if (consequent === this.consequent && alternative === this.alternative)
+        return this;
+    if (!consequent)
+        return alternative ? make_node(AST_Binary, this, {
+            operator: "||",
+            left: this.condition,
+            right: alternative
+        }) : this.condition.drop_side_effect_free(compressor);
+    if (!alternative)
+        return make_node(AST_Binary, this, {
+            operator: "&&",
+            left: this.condition,
+            right: consequent
+        });
+    var node = this.clone();
+    node.consequent = consequent;
+    node.alternative = alternative;
+    return node;
+});
+
+def_drop_side_effect_free(AST_Unary, function (compressor, first_in_statement) {
+    if (unary_side_effects.has(this.operator)) {
+        if (!this.expression.has_side_effects(compressor)) {
+            set_flag(this, WRITE_ONLY);
+        } else {
+            clear_flag(this, WRITE_ONLY);
+        }
+        return this;
+    }
+    if (this.operator == "typeof" && this.expression instanceof AST_SymbolRef)
+        return null;
+    var expression = this.expression.drop_side_effect_free(compressor, first_in_statement);
+    if (first_in_statement && expression && is_iife_call(expression)) {
+        if (expression === this.expression && this.operator == "!")
+            return this;
+        return expression.negate(compressor, first_in_statement);
+    }
+    return expression;
+});
+
+def_drop_side_effect_free(AST_SymbolRef, function (compressor) {
+    const safe_access = this.is_declared(compressor)
+        || pure_prop_access_globals.has(this.name);
+    return safe_access ? null : this;
+});
+
+def_drop_side_effect_free(AST_Object, function (compressor, first_in_statement) {
+    var values = trim(this.properties, compressor, first_in_statement);
+    return values && make_sequence(this, values);
+});
+
+def_drop_side_effect_free(AST_ObjectKeyVal, function (compressor, first_in_statement) {
+    const computed_key = this.key instanceof AST_Node;
+    const key = computed_key && this.key.drop_side_effect_free(compressor, first_in_statement);
+    const value = this.value.drop_side_effect_free(compressor, first_in_statement);
+    if (key && value) {
+        return make_sequence(this, [key, value]);
+    }
+    return key || value;
+});
+
+def_drop_side_effect_free([
+    AST_ConciseMethod,
+    AST_ObjectGetter,
+    AST_ObjectSetter,
+], function () {
+    return this.computed_key() ? this.key : null;
+});
+
+def_drop_side_effect_free([
+    AST_PrivateMethod,
+    AST_PrivateGetter,
+    AST_PrivateSetter,
+], function () {
+    return null;
+});
+
+def_drop_side_effect_free(AST_Array, function (compressor, first_in_statement) {
+    var values = trim(this.elements, compressor, first_in_statement);
+    return values && make_sequence(this, values);
+});
+
+def_drop_side_effect_free(AST_Dot, function (compressor, first_in_statement) {
+    if (is_nullish_shortcircuited(this, compressor)) {
+        return this.expression.drop_side_effect_free(compressor, first_in_statement);
+    }
+    if (!this.optional && this.expression.may_throw_on_access(compressor)) {
+        return this;
+    }
+
+    return this.expression.drop_side_effect_free(compressor, first_in_statement);
+});
+
+def_drop_side_effect_free(AST_Sub, function (compressor, first_in_statement) {
+    if (is_nullish_shortcircuited(this, compressor)) {
+        return this.expression.drop_side_effect_free(compressor, first_in_statement);
+    }
+    if (!this.optional && this.expression.may_throw_on_access(compressor)) {
+        return this;
+    }
+
+    var property = this.property.drop_side_effect_free(compressor);
+    if (property && this.optional) return this;
+
+    var expression = this.expression.drop_side_effect_free(compressor, first_in_statement);
+
+    if (expression && property) return make_sequence(this, [expression, property]);
+    return expression || property;
+});
+
+def_drop_side_effect_free(AST_Chain, function (compressor, first_in_statement) {
+    return this.expression.drop_side_effect_free(compressor, first_in_statement);
+});
+
+def_drop_side_effect_free(AST_Sequence, function (compressor) {
+    var last = this.tail_node();
+    var expr = last.drop_side_effect_free(compressor);
+    if (expr === last)
+        return this;
+    var expressions = this.expressions.slice(0, -1);
+    if (expr)
+        expressions.push(expr);
+    if (!expressions.length) {
+        return make_node(AST_Number, this, { value: 0 });
+    }
+    return make_sequence(this, expressions);
+});
+
+def_drop_side_effect_free(AST_Expansion, function (compressor, first_in_statement) {
+    return this.expression.drop_side_effect_free(compressor, first_in_statement);
+});
+
+def_drop_side_effect_free(AST_TemplateSegment, return_null);
+
+def_drop_side_effect_free(AST_TemplateString, function (compressor) {
+    var values = trim(this.segments, compressor, first_in_statement);
+    return values && make_sequence(this, values);
+});