enhance `booleans` (#3657)

1 files changed, 36 insertions, 9 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 9c60d0ae..4252c58e 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -241,7 +241,7 @@ merge(Compressor.prototype, {
         return this.TYPE == node.TYPE && this.print_to_string() == node.print_to_string();
     });
 
-    AST_Scope.DEFMETHOD("process_expression", function(insert, compressor) {
+    AST_Scope.DEFMETHOD("process_expression", function(insert, transform) {
         var self = this;
         var tt = new TreeTransformer(function(node) {
             if (insert && node instanceof AST_SimpleStatement) {
@@ -250,13 +250,7 @@ merge(Compressor.prototype, {
                 });
             }
             if (!insert && node instanceof AST_Return) {
-                if (compressor) {
-                    var value = node.value && node.value.drop_side_effect_free(compressor, true);
-                    return value ? make_node(AST_SimpleStatement, node, {
-                        body: value
-                    }) : make_node(AST_EmptyStatement, node);
-                }
-                return make_node(AST_SimpleStatement, node, {
+                return transform ? transform(node) : make_node(AST_SimpleStatement, node, {
                     body: node.value || make_node(AST_UnaryPrefix, node, {
                         operator: "void",
                         expression: make_node(AST_Number, node, {
@@ -361,6 +355,7 @@ merge(Compressor.prototype, {
 
         function reset_def(tw, compressor, def) {
             def.assignments = 0;
+            def.bool_fn = 0;
             def.chained = false;
             def.cross_loop = false;
             def.direct_access = false;
@@ -598,6 +593,7 @@ merge(Compressor.prototype, {
             var exp = this.expression;
             if (!(exp instanceof AST_SymbolRef)) return;
             var def = exp.definition();
+            if (tw.in_boolean_context()) def.bool_fn++;
             if (!(def.fixed instanceof AST_Defun)) return;
             var defun = mark_defun(tw, def);
             if (!defun) return;
@@ -4560,7 +4556,12 @@ merge(Compressor.prototype, {
                 }
                 if (exp instanceof AST_Function && (!exp.name || !exp.name.definition().references.length)) {
                     var node = this.clone();
-                    exp.process_expression(false, compressor);
+                    exp.process_expression(false, function(node) {
+                        var value = node.value && node.value.drop_side_effect_free(compressor, true);
+                        return value ? make_node(AST_SimpleStatement, node, {
+                            body: value
+                        }) : make_node(AST_EmptyStatement, node);
+                    });
                     exp.walk(new TreeWalker(function(node) {
                         if (node instanceof AST_Return && node.value) {
                             node.value = node.value.drop_side_effect_free(compressor);
@@ -6685,6 +6686,32 @@ merge(Compressor.prototype, {
         if (compressor.option("reduce_vars") && is_lhs(compressor.self(), parent) !== compressor.self()) {
             var def = self.definition();
             var fixed = self.fixed_value();
+            if (compressor.option("booleans") && def.bool_fn === def.references.length && fixed instanceof AST_Lambda) {
+                def.bool_fn = null;
+                fixed.process_expression(false, function(node) {
+                    if (!node.value) return node;
+                    var value = node.value.is_truthy() || node.value.tail_node().evaluate(compressor);
+                    if (!value) {
+                        value = node.value.drop_side_effect_free(compressor);
+                        node.value = value ? make_sequence(node.value, [
+                            value,
+                            make_node(AST_Number, node.value, {
+                                value: 0
+                            })
+                        ]) : null;
+                    } else if (value && !(value instanceof AST_Node)) {
+                        var num = make_node(AST_Number, node.value, {
+                            value: 1
+                        });
+                        value = node.value.drop_side_effect_free(compressor);
+                        node.value = value ? make_sequence(node.value, [
+                            value,
+                            num
+                        ]) : num;
+                    }
+                    return node;
+                });
+            }
             var single_use = def.single_use && !(parent instanceof AST_Call && parent.is_expr_pure(compressor));
             if (single_use && fixed instanceof AST_Lambda) {
                 if (def.scope !== self.scope