path: root/lib/compress.js

// 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;
    });

})();