path: root/lib/compress.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 2010 (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.

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

// The layout of the compressor follows the code generator (see
// output.js).  Basically each node will have a "squeeze" method
// that will apply all known compression rules for that node, and
// return a new node (or the original node if there was no
// compression).  We can't quite use the TreeWalker for this
// because it's too simplistic.

// The Compressor object is for storing the options and for
// maintaining various internal state that might be useful for
// squeezing nodes.

function Compressor(options, false_by_default) {
    options = defaults(options, {
        sequences     : !false_by_default,
        properties    : !false_by_default,
        dead_code     : !false_by_default,
        keep_comps    : !false_by_default,
        drop_debugger : !false_by_default,
        unsafe        : !false_by_default,

        warnings      : true
    });
    var stack = [];
    return {
        option    : function(key) { return options[key] },
        push_node : function(node) { stack.push(node) },
        pop_node  : function() { return stack.pop() },
        stack     : function() { return stack },
        parent    : function(n) {
            return stack[stack.length - 2 - (n || 0)];
        },
        warn      : function() {
            if (options.warnings)
                AST_Node.warn.apply(AST_Node, arguments);
        }
    };
};

(function(){

    AST_Node.DEFMETHOD("squeeze", function(){
        return this;
    });

    function make_node(ctor, orig, props) {
        if (!props.start) props.start = orig.start;
        if (!props.end) props.end = orig.end;
        return new ctor(props);
    };

    function SQUEEZE(nodetype, squeeze) {
        nodetype.DEFMETHOD("squeeze", function(compressor){
            compressor.push_node(this);
            var new_node = squeeze(this, compressor);
            compressor.pop_node();
            return new_node || this;
        });
    };

    function do_list(array, compressor) {
        return MAP(array, function(node){
            return node.squeeze(compressor);
        });
    };

    SQUEEZE(AST_Debugger, function(self, compressor){
        if (compressor.option("drop_debugger"))
            return new AST_EmptyStatement(self);
    });

    SQUEEZE(AST_LabeledStatement, function(self, compressor){
        self = self.clone();
        self.statement = self.statement.squeeze(compressor);
        return self.label.references.length == 0 ? self.statement : self;
    });

    SQUEEZE(AST_Statement, function(self, compressor){
        self = self.clone();
        self.body = self.body.squeeze(compressor);
        return self;
    });

    function tighten_body(statements, compressor) {
        statements = do_list(statements, compressor);
        statements = eliminate_spurious_blocks(statements);
        if (compressor.option("dead_code")) {
            statements = eliminate_dead_code(statements, compressor);
        }
        if (compressor.option("sequences")) {
            statements = sequencesize(statements);
        }
        return statements;
    };

    function eliminate_spurious_blocks(statements) {
        return statements.reduce(function(a, stat){
            if (stat.TYPE == "BlockStatement") {
                // XXX: no instanceof here because we would catch
                // AST_Lambda-s and other blocks too.  perhaps we
                // should refine the hierarchy.
                a.push.apply(a, stat.body);
            } else {
                a.push(stat);
            }
            return a;
        }, []);
    }

    function eliminate_dead_code(statements, compressor) {
        var has_quit = false;
        return statements.reduce(function(a, stat){
            if (has_quit) {
                if (stat instanceof AST_Defun) {
                    a.push(stat);
                }
                else if (compressor.option("warnings")) {
                    stat.walk(new TreeWalker(function(node){
                        if (node instanceof AST_Definitions
                            || node instanceof AST_Defun) {
                            compressor.warn("Declarations in unreachable code! [{line},{col}]", node.start);
                            if (node instanceof AST_Definitions) {
                                node = node.clone();
                                node.remove_initializers();
                                a.push(node);
                            }
                            else if (node instanceof AST_Defun) {
                                a.push(node);
                            }
                            return true;
                        }
                        if (node instanceof AST_Scope)
                            return true;
                    }))
                };
            } else {
                a.push(stat);
                if (stat instanceof AST_Jump) {
                    has_quit = true;
                }
            }
            return a;
        }, []);
    }

    function sequencesize(statements) {
        var prev = null, last = statements.length - 1;
        if (last) statements = statements.reduce(function(a, cur, i){
            if (prev instanceof AST_SimpleStatement
                && cur instanceof AST_SimpleStatement) {
                var seq = make_node(AST_Seq, prev, {
                    first: prev.body,
                    second: cur.body
                });
                prev.body = seq;
            }
            else if (i == last && cur instanceof AST_Exit
                     && cur.value && a.length == 1) {
                // it only makes sense to do this transformation
                // if the AST gets to a single statement.
                var seq = make_node(AST_Seq, prev, {
                    first: prev.body,
                    second: cur.value
                });
                cur.value = seq;
                return [ cur ];
            }
            else {
                a.push(cur);
                prev = cur;
            }
            return a;
        }, []);
        return statements;
    }

    SQUEEZE(AST_BlockStatement, function(self, compressor){
        self = self.clone();
        self.body = tighten_body(self.body, compressor);
        if (self.body.length == 1 && !self.required)
            return self.body[0];
        return self;
    });

    SQUEEZE(AST_EmptyStatement, function(self, compressor){
        return self;
    });

    SQUEEZE(AST_DWLoop, function(self, compressor){
        self = self.clone();
        self.condition = self.condition.squeeze(compressor);
        self.body = self.body.squeeze(compressor);
        return self;
    });

    SQUEEZE(AST_For, function(self, compressor){
        self = self.clone();
        if (self.init) self.init = self.init.squeeze(compressor);
        if (self.condition) self.condition = self.condition.squeeze(compressor);
        if (self.step) self.step = self.step.squeeze(compressor);
        self.body = self.body.squeeze(compressor);
        return self;
    });

    SQUEEZE(AST_ForIn, function(self, compressor){
        self = self.clone();
        self.init = self.init.squeeze(compressor);
        self.object = self.object.squeeze(compressor);
        self.body = self.body.squeeze(compressor);
        return self;
    });

    SQUEEZE(AST_With, function(self, compressor){
        self = self.clone();
        self.expression = self.expression.squeeze(compressor);
        self.body = self.body.squeeze(compressor);
    });

    SQUEEZE(AST_Exit, function(self, compressor){
        self = self.clone();
        if (self.value) self.value = self.value.squeeze(compressor);
        return self;
    });

    SQUEEZE(AST_LoopControl, function(self, compressor){
        self = self.clone();
        if (self.label) self.label = self.label.squeeze(compressor);
        return self;
    });

    SQUEEZE(AST_If, function(self, compressor){
        self = self.clone();
        self.condition = self.condition.squeeze(compressor);
        self.consequent = self.consequent.squeeze(compressor);
        if (self.alternative)
            self.alternative = self.alternative.squeeze(compressor);
        return self;
    });

    SQUEEZE(AST_Switch, function(self, compressor){
        self = self.clone();
        self.expression = self.expression.squeeze(compressor);
        self.body = self.body.squeeze(compressor);
        return self;
    });

    SQUEEZE(AST_Case, function(self, compressor){
        self = self.clone();
        self.expression = self.expression.squeeze(compressor);
        self.body = tighten_body(self.body, compressor);
        return self;
    });

    SQUEEZE(AST_Try, function(self, compressor){
        self = self.clone();
        self.btry = self.btry.squeeze(compressor);
        if (self.bcatch) self.bcatch = self.bcatch.squeeze(compressor);
        if (self.bfinally) self.bfinally = self.bfinally.squeeze(compressor);
        return self;
    });

    AST_Definitions.DEFMETHOD("remove_initializers", function(){
        this.definitions = this.definitions.map(function(def){
            var def = def.clone();
            def.value = null;
            return def;
        });
    });

    SQUEEZE(AST_Definitions, function(self, compressor){
        self = self.clone();
        self.definitions = do_list(self.definitions, compressor);
        return self;
    });

    SQUEEZE(AST_VarDef, function(self, compressor){
        self = self.clone();
        if (self.value) self.value = self.value.squeeze(compressor);
        return self;
    });

    SQUEEZE(AST_Lambda, function(self, compressor){
        self = self.clone();
        if (self.name) self.name = self.name.squeeze(compressor);
        self.argnames = do_list(self.argnames, compressor);
        self.body = self.body.squeeze(compressor);
        return self;
    });

    SQUEEZE(AST_Call, function(self, compressor){
        self = self.clone();
        self.expression = self.expression.squeeze(compressor);
        self.args = do_list(self.args, compressor);
        return self;
    });

    SQUEEZE(AST_Seq, function(self, compressor){
        self = self.clone();
        self.first = self.first.squeeze(compressor);
        self.second = self.second.squeeze(compressor);
        return self;
    });

    SQUEEZE(AST_Dot, function(self, compressor){
        self = self.clone();
        self.expression = self.expression.squeeze(compressor);
        return self;
    });

    SQUEEZE(AST_Sub, function(self, compressor){
        self = self.clone();
        self.expression = self.expression.squeeze(compressor);
        var prop = self.property = self.property.squeeze(compressor);
        if (prop instanceof AST_String && compressor.option("properties")) {
            prop = prop.getValue();
            if (is_identifier(prop)) {
                self = new AST_Dot(self);
                self.property = prop;
            }
        }
        return self;
    });

    SQUEEZE(AST_Unary, function(self, compressor){
        self = self.clone();
        self.expression = self.expression.squeeze(compressor);
        return self;
    });

    SQUEEZE(AST_Binary, function(self, compressor){
        self = self.clone();
        self.left = self.left.squeeze(compressor);
        self.right = self.right.squeeze(compressor);
        return self;
    });

    SQUEEZE(AST_Conditional, function(self, compressor){
        self = self.clone();
        self.condition = self.condition.squeeze(compressor);
        self.consequent = self.consequent.squeeze(compressor);
        self.alternative = self.alternative.squeeze(compressor);
        return self;
    });

    SQUEEZE(AST_Array, function(self, compressor){
        self = self.clone();
        self.elements = do_list(self.elements, compressor);
        return self;
    });

    SQUEEZE(AST_Object, function(self, compressor){
        self = self.clone();
        self.properties = do_list(self.properties, compressor);
        return self;
    });

    SQUEEZE(AST_ObjectProperty, function(self, compressor){
        self = self.clone();
        self.value = self.value.squeeze(compressor);
        return self;
    });

})();