fix comments output & improve /*@__PURE__*/

- fix whitespace around comments
- fix comment parsing around parentheses
- consider parentheses when parsing `/*@__PURE__*/`
- remove all `/*@__PURE__*/` on output

fixes #2638

lib/compress.js

@@ -2292,29 +2292,13 @@ merge(Compressor.prototype, {
         });
     });
 
-    AST_Call.DEFMETHOD("has_pure_annotation", function(compressor) {
-        if (!compressor.option("side_effects")) return false;
-        if (this.pure !== undefined) return this.pure;
-        var pure = false;
-        var comments, pure_comment;
-        if (this.start
-            && (comments = this.start.comments_before)
-            && comments.length
-            && (pure_comment = find_if(function (comment) {
-                return /[@#]__PURE__/.test(comment.value);
-            }, comments))) {
-            pure = pure_comment;
-        }
-        return this.pure = pure;
-    });
-
     var global_pure_fns = makePredicate("Boolean decodeURI decodeURIComponent Date encodeURI encodeURIComponent Error escape EvalError isFinite isNaN Number Object parseFloat parseInt RangeError ReferenceError String SyntaxError TypeError unescape URIError");
     AST_Call.DEFMETHOD("is_expr_pure", function(compressor) {
         if (compressor.option("unsafe")) {
             var expr = this.expression;
             if (is_undeclared_ref(expr) && global_pure_fns(expr.name)) return true;
         }
-        return this.has_pure_annotation(compressor) || !compressor.pure_funcs(this);
+        return this.pure || !compressor.pure_funcs(this);
     });
 
     // determine if expression has side effects
@@ -3164,7 +3148,6 @@ merge(Compressor.prototype, {
             }
             if (this.pure) {
                 compressor.warn("Dropping __PURE__ call [{file}:{line},{col}]", this.start);
-                this.pure.value = this.pure.value.replace(/[@#]__PURE__/g, ' ');
             }
             var args = trim(this.args, compressor, first_in_statement);
             return args && make_sequence(this, args);
@@ -3961,7 +3944,7 @@ merge(Compressor.prototype, {
                         && (def = exp.definition()).references.length == 1
                         && !recursive_ref(compressor, def)
                         && fn.is_constant_expression(exp.scope))
-                && !self.has_pure_annotation(compressor)
+                && !self.pure
                 && !fn.contains_this()
                 && (scope = can_flatten_args(fn))
                 && (value = flatten_body(stat))) {