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added some comments about the rules governing parens
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@mishoo
mishoo committed Aug 17, 2012
1 parent 4fb6021 commit 07cbc8d
Showing 1 changed file with 37 additions and 22 deletions.
59 changes: 37 additions & 22 deletions lib/output.js
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Original file line number Diff line number Diff line change
Expand Up @@ -228,6 +228,7 @@ function OutputStream(options) {
nodetype.DEFMETHOD("print", function(stream){
var self = this;
stream.push_node(self);
//stream.print("«" + self.TYPE + ":" + self.start.line + ":" + self.start.col + "»");
if (self.needs_parens(stream)) {
stream.with_parens(function(){
generator(self, stream);
Expand Down Expand Up @@ -268,23 +269,29 @@ function OutputStream(options) {

PARENS(AST_Seq, function(output){
var p = output.parent();
return p instanceof AST_Call
|| p instanceof AST_Binary
|| p instanceof AST_VarDef
|| p instanceof AST_Dot
|| p instanceof AST_Array
|| p instanceof AST_ObjectProperty
|| p instanceof AST_Conditional;
return p instanceof AST_Call // (foo, bar)() —or— foo(1, (2, 3), 4)
|| p instanceof AST_Binary // 1 + (2, 3) + 4 → 7
|| p instanceof AST_VarDef // var a = (1, 2), b = a + a; → b = 4
|| p instanceof AST_Dot // (1, {foo:2}).foo → 2
|| p instanceof AST_Array // [ 1, (2, 3), 4 ] → [ 1, 3, 4 ]
|| p instanceof AST_ObjectProperty // { foo: (1, 2) }.foo → 2
|| p instanceof AST_Conditional /* (false, true) ? (a = 10, b = 20) : (c = 30)
* → 20 (side effect, set a = 10 and b = 20) */
;
});

PARENS(AST_Binary, function(output){
var p = output.parent();
// (foo && bar)()
if (p instanceof AST_Call && p.expression === this)
return true;
// typeof (foo && bar)
if (p instanceof AST_Unary)
return true;
// (foo && bar)["prop"], (foo && bar).prop
if (p instanceof AST_PropAccess && p.expression === this)
return true;
// this deals with precedence: 3 * (2 + 1)
if (p instanceof AST_Binary) {
var po = p.operator, pp = PRECEDENCE[po];
var so = this.operator, sp = PRECEDENCE[so];
Expand All @@ -298,6 +305,7 @@ function OutputStream(options) {
return true;
}
}
// for (var i = (foo in bar);;); ← perhaps useless, but valid syntax
if (this.operator == "in") {
// the “NoIn” stuff :-\
// UglifyJS 1.3.3 misses this one.
Expand All @@ -313,26 +321,32 @@ function OutputStream(options) {

PARENS(AST_New, function(output){
var p = output.parent();
// (new Date).getTime();
if (p instanceof AST_Dot && no_constructor_parens(this, output))
return true;
});

function assign_and_conditional_paren_rules(output) {
var p = output.parent();
// !(a = false) → true
if (p instanceof AST_Unary)
return true;
// 1 + (a = 2) + 3 → 3, side effect setting a = 2
if (p instanceof AST_Binary && !(p instanceof AST_Assign))
return true;
// (a = func)() —or— new (a = Object)()
if (p instanceof AST_Call && p.expression === this)
return true;
// (a = foo) ? bar : baz
if (p instanceof AST_Conditional && p.condition === this)
return true;
// (a = foo)["prop"] —or— (a = foo).prop
if (p instanceof AST_PropAccess && p.expression === this)
return true;
};

PARENS(AST_Conditional, assign_and_conditional_paren_rules);
PARENS(AST_Assign, assign_and_conditional_paren_rules);
PARENS(AST_Conditional, assign_and_conditional_paren_rules);

/* -----[ PRINTERS ]----- */

Expand Down Expand Up @@ -639,11 +653,6 @@ function OutputStream(options) {
});
});
});
function no_constructor_parens(self, output) {
return (self.args.length == 0
// && !output.options("beautify")
);
};
DEFPRINT(AST_New, function(self, output){
output.print("new");
output.space();
Expand Down Expand Up @@ -779,15 +788,16 @@ function OutputStream(options) {
function first_in_statement(output) {
var a = output.stack(), i = a.length, node = a[--i], p = a[--i];
while (i > 0) {
if (p instanceof AST_Statement) return true;
if ((p instanceof AST_Seq && p.first === node) ||
(p instanceof AST_Call && p.expression === node) ||
(p instanceof AST_Dot && p.expression === node) ||
(p instanceof AST_Sub && p.expression === node) ||
(p instanceof AST_Conditional && p.condition === node) ||
(p instanceof AST_Binary && p.first === node) ||
(p instanceof AST_Assign && p.first === node) ||
(p instanceof AST_UnaryPostfix && p.expression === node))
if (p instanceof AST_Statement)
return true;
if ((p instanceof AST_Seq && p.first === node ) ||
(p instanceof AST_Call && p.expression === node ) ||
(p instanceof AST_Dot && p.expression === node ) ||
(p instanceof AST_Sub && p.expression === node ) ||
(p instanceof AST_Conditional && p.condition === node ) ||
(p instanceof AST_Binary && p.first === node ) ||
(p instanceof AST_Assign && p.first === node ) ||
(p instanceof AST_UnaryPostfix && p.expression === node ))
{
node = p;
p = a[--i];
Expand All @@ -797,6 +807,11 @@ function OutputStream(options) {
}
};

// self should be AST_New. decide if we want to show parens or not.
function no_constructor_parens(self, output) {
return self.args.length == 0 && !output.options("beautify");
};

function best_of(a) {
var best = a[0], len = best.length;
for (var i = 1; i < a.length; ++i) {
Expand Down

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