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support nullish coalescing operator (#4678)

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This commit is contained in:
Alex Lam S.L
2021-02-23 21:57:11 +00:00
committed by GitHub
parent d68d155f93
commit c885660347
16 changed files with 177 additions and 36 deletions
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46
lib/compress.js
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@@ -2182,6 +2182,7 @@ merge(Compressor.prototype, {
var lazy = lazy_op[expr.operator];
if (unused
&& lazy
&& expr.operator != "??"
&& expr.right instanceof AST_Assign
&& expr.right.operator == "="
&& !(expr.right.left instanceof AST_Destructured)) {
@@ -3840,7 +3841,7 @@ merge(Compressor.prototype, {
node.DEFMETHOD("is_string", func);
});
var lazy_op = makePredicate("&& ||");
var lazy_op = makePredicate("&& || ??");
(function(def) {
function to_node(value, orig) {
@@ -4286,6 +4287,9 @@ merge(Compressor.prototype, {
switch (this.operator) {
case "&&" : result = left && right; break;
case "||" : result = left || right; break;
case "??" :
result = left == null ? right : left;
break;
case "|" : result = left | right; break;
case "&" : result = left & right; break;
case "^" : result = left ^ right; break;
@@ -7130,6 +7134,7 @@ merge(Compressor.prototype, {
node = this.clone();
node.right = right.drop_side_effect_free(compressor);
}
if (this.operator == "??") return node;
return (first_in_statement ? best_of_statement : best_of_expression)(node, make_node(AST_Binary, this, {
operator: node.operator == "&&" ? "||" : "&&",
left: node.left.negate(compressor, first_in_statement),
@@ -9159,7 +9164,7 @@ merge(Compressor.prototype, {
// (a = b, x || a = c) ---> a = x ? b : c
function to_conditional_assignment(compressor, def, value, node) {
if (!(node instanceof AST_Binary)) return;
if (!lazy_op[node.operator]) return;
if (!(node.operator == "&&" || node.operator == "||")) return;
if (!(node.right instanceof AST_Assign)) return;
if (node.right.operator != "=") return;
if (!(node.right.left instanceof AST_SymbolRef)) return;
@@ -9680,22 +9685,41 @@ merge(Compressor.prototype, {
}).optimize(compressor);
}
break;
case "??":
var nullish = true;
case "||":
var ll = fuzzy_eval(self.left);
if (!ll) {
AST_Node.warn("Condition left of || always false [{file}:{line},{col}]", self.start);
var ll = fuzzy_eval(self.left, nullish);
if (nullish ? ll == null : !ll) {
AST_Node.warn("Condition left of {operator} always {value} [{file}:{line},{col}]", {
operator: self.operator,
value: nullish ? "nulish" : "false",
file: self.start.file,
line: self.start.line,
col: self.start.col,
});
return make_sequence(self, [ self.left, self.right ]).optimize(compressor);
} else if (!(ll instanceof AST_Node)) {
AST_Node.warn("Condition left of || always true [{file}:{line},{col}]", self.start);
AST_Node.warn("Condition left of {operator} always {value} [{file}:{line},{col}]", {
operator: self.operator,
value: nullish ? "defined" : "true",
file: self.start.file,
line: self.start.line,
col: self.start.col,
});
return maintain_this_binding(compressor, parent, compressor.self(), self.left).optimize(compressor);
}
var rr = self.right.evaluate(compressor);
if (!rr) {
if (in_bool || parent.operator == "||" && parent.left === compressor.self()) {
AST_Node.warn("Dropping side-effect-free || [{file}:{line},{col}]", self.start);
AST_Node.warn("Dropping side-effect-free {operator} [{file}:{line},{col}]", {
operator: self.operator,
file: self.start.file,
line: self.start.line,
col: self.start.col,
});
return self.left.optimize(compressor);
}
} else if (!(rr instanceof AST_Node)) {
} else if (!nullish && !(rr instanceof AST_Node)) {
if (in_bool) {
AST_Node.warn("Boolean || always true [{file}:{line},{col}]", self.start);
return make_sequence(self, [
@@ -9705,7 +9729,7 @@ merge(Compressor.prototype, {
} else self.truthy = true;
}
// x && true || y ---> x ? true : y
if (self.left.operator == "&&") {
if (!nullish && self.left.operator == "&&") {
var lr = self.left.right.is_truthy() || self.left.right.evaluate(compressor, true);
if (lr && !(lr instanceof AST_Node)) return make_node(AST_Conditional, self, {
condition: self.left.left,
@@ -10047,9 +10071,9 @@ merge(Compressor.prototype, {
});
}
function fuzzy_eval(node) {
function fuzzy_eval(node, nullish) {
if (node.truthy) return true;
if (node.falsy) return false;
if (node.falsy && !nullish) return false;
if (node.is_truthy()) return true;
return node.evaluate(compressor, true);
}