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add new arrows compress option (#2154)

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Convert ES5 style anonymous function expressions
to arrow functions if permissible by language semantics.

Note: `arrows` requires that the `ecma` compress option
is set to `6` or greater.

fixes #2150
This commit is contained in:
Alex Lam S.L
2017-06-24 14:45:24 +08:00
committed by GitHub
parent 7b95b63ca1
commit d1f085bce7
7 changed files with 140 additions and 10 deletions
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32
lib/compress.js
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@@ -48,6 +48,7 @@ function Compressor(options, false_by_default) {
return new Compressor(options, false_by_default);
TreeTransformer.call(this, this.before, this.after);
this.options = defaults(options, {
arrows : !false_by_default,
booleans : !false_by_default,
cascade : !false_by_default,
collapse_vars : !false_by_default,
@@ -2047,7 +2048,7 @@ merge(Compressor.prototype, {
});
OPT(AST_Block, function(self, compressor){
if (!(self.body instanceof AST_Node)) tighten_body(self.body, compressor);
tighten_body(self.body, compressor);
return self;
});
@@ -3273,11 +3274,12 @@ merge(Compressor.prototype, {
var fun;
ast.walk(new TreeWalker(function(node) {
if (fun) return true;
if (node instanceof AST_Lambda) {
if (node instanceof AST_Function) {
fun = node;
return true;
}
}));
if (!fun) return self;
var args = fun.argnames.map(function(arg, i) {
return make_node(AST_String, self.args[i], {
value: arg.print_to_string()
@@ -4499,13 +4501,37 @@ merge(Compressor.prototype, {
});
OPT(AST_Arrow, function(self, compressor){
if (self.body.length === 1 && self.body[0] instanceof AST_Return) {
if (!(self.body instanceof AST_Node)) tighten_body(self.body, compressor);
if (compressor.option("arrows")
&& self.body.length == 1
&& self.body[0] instanceof AST_Return) {
var value = self.body[0].value;
self.body = value ? value : [];
}
return self;
});
OPT(AST_Function, function(self, compressor){
tighten_body(self.body, compressor);
if (compressor.option("arrows")
&& compressor.option("ecma") >= 6
&& !self.name
&& !self.is_generator
&& !self.uses_arguments
&& !self.uses_eval) {
var has_special_symbol = false;
self.walk(new TreeWalker(function(node) {
if (has_special_symbol) return true;
if (node instanceof AST_Symbol && !node.definition()) {
has_special_symbol = true;
return true;
}
}));
if (!has_special_symbol) return make_node(AST_Arrow, self, self).optimize(compressor);
}
return self;
});
OPT(AST_Class, function(self, compressor){
// HACK to avoid compress failure.
// AST_Class is not really an AST_Scope/AST_Block as it lacks a body.