node_modules/terser/lib/compress/drop-side-effect-free.js

/***********************************************************************

  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
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 ***********************************************************************/

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);
});