enhance `pure_funcs` (#4945)

2 files changed, 87 insertions, 30 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 9a6d0191..7b8e17b8 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -136,11 +136,23 @@ function Compressor(options, false_by_default) {
         this.pure_funcs = pure_funcs;
     } else if (typeof pure_funcs == "string") {
         this.pure_funcs = function(node) {
-            return pure_funcs !== node.expression.print_to_string();
+            var expr;
+            if (node instanceof AST_Call) {
+                expr = node.expression;
+            } else if (node instanceof AST_Template) {
+                expr = node.tag;
+            }
+            return !(expr && pure_funcs === expr.print_to_string());
         };
     } else if (Array.isArray(pure_funcs)) {
         this.pure_funcs = function(node) {
-            return !member(node.expression.print_to_string(), pure_funcs);
+            var expr;
+            if (node instanceof AST_Call) {
+                expr = node.expression;
+            } else if (node instanceof AST_Template) {
+                expr = node.tag;
+            }
+            return !(expr && member(expr.print_to_string(), pure_funcs));
         };
     } else {
         this.pure_funcs = return_true;
@@ -2115,7 +2127,7 @@ merge(Compressor.prototype, {
                         def = fn.definition();
                         fn = fn.fixed_value();
                     }
-                    if (!(fn instanceof AST_Lambda)) return true;
+                    if (!(fn instanceof AST_Lambda)) return !node.is_expr_pure(compressor);
                     if (def && recursive_ref(compressor, def)) return true;
                     if (fn.collapse_scanning) return false;
                     fn.collapse_scanning = true;
@@ -2175,7 +2187,7 @@ merge(Compressor.prototype, {
                     var def = node.definition();
                     return (in_try || def.scope.resolve() !== scope) && !can_drop_symbol(node);
                 }
-                if (node instanceof AST_Template) return node.tag && !is_raw_tag(compressor, node.tag);
+                if (node instanceof AST_Template) return !node.is_expr_pure(compressor);
                 if (node instanceof AST_VarDef) {
                     if (check_destructured(node.name)) return true;
                     return (node.value || parent instanceof AST_Let) && node.name.match_symbol(function(node) {
@@ -4275,6 +4287,7 @@ merge(Compressor.prototype, {
         ],
         String: [
             "fromCharCode",
+            "raw",
         ],
     });
 
@@ -4908,6 +4921,19 @@ merge(Compressor.prototype, {
         }
         return compressor.option("annotations") && this.pure || !compressor.pure_funcs(this);
     });
+    AST_Template.DEFMETHOD("is_expr_pure", function(compressor) {
+        var tag = this.tag;
+        if (!tag) return true;
+        if (compressor.option("unsafe")) {
+            if (is_undeclared_ref(tag) && global_pure_fns[tag.name]) return true;
+            if (tag instanceof AST_Dot && is_undeclared_ref(tag.expression)) {
+                var static_fn = static_fns[tag.expression.name];
+                return static_fn && (static_fn[tag.property]
+                    || tag.expression.name == "Math" && tag.property == "random");
+            }
+        }
+        return !compressor.pure_funcs(this);
+    });
     AST_Node.DEFMETHOD("is_call_pure", return_false);
     AST_Call.DEFMETHOD("is_call_pure", function(compressor) {
         if (!compressor.option("unsafe")) return false;
@@ -5072,7 +5098,7 @@ merge(Compressor.prototype, {
             return !this.is_declared(compressor) || !can_drop_symbol(this, compressor);
         });
         def(AST_Template, function(compressor) {
-            return this.tag && !is_raw_tag(compressor, this.tag) || any(this.expressions, compressor);
+            return !this.is_expr_pure(compressor) || any(this.expressions, compressor);
         });
         def(AST_Try, function(compressor) {
             return any(this.body, compressor)
@@ -7485,27 +7511,7 @@ merge(Compressor.prototype, {
             if (!rhs) return lhs;
             return make_sequence(this, [ lhs, rhs ]);
         });
-        def(AST_Call, function(compressor, first_in_statement) {
-            var self = this;
-            if (self.is_expr_pure(compressor)) {
-                if (self.pure) AST_Node.warn("Dropping __PURE__ call [{file}:{line},{col}]", self.start);
-                var args = trim(self.args, compressor, first_in_statement, array_spread);
-                return args && make_sequence(self, args.map(convert_spread));
-            }
-            var exp = self.expression;
-            if (self.is_call_pure(compressor)) {
-                var exprs = self.args.slice();
-                exprs.unshift(exp.expression);
-                exprs = trim(exprs, compressor, first_in_statement, array_spread);
-                return exprs && make_sequence(self, exprs.map(convert_spread));
-            }
-            if (compressor.option("yields") && is_generator(exp)) {
-                var call = self.clone();
-                call.expression = make_node(AST_Function, exp, exp);
-                call.expression.body = [];
-                var opt = call.transform(compressor);
-                if (opt !== call) return opt.drop_side_effect_free(compressor, first_in_statement);
-            }
+        function drop_returns(compressor, exp) {
             var drop_body = false;
             if (compressor.option("arrows") && is_arrow(exp)) {
                 if (!exp.value) {
@@ -7539,6 +7545,31 @@ merge(Compressor.prototype, {
                         node.value = value.drop_side_effect_free(compressor);
                     }
                 });
+            }
+            return drop_body;
+        }
+        def(AST_Call, function(compressor, first_in_statement) {
+            var self = this;
+            if (self.is_expr_pure(compressor)) {
+                if (self.pure) AST_Node.warn("Dropping __PURE__ call [{file}:{line},{col}]", self.start);
+                var args = trim(self.args, compressor, first_in_statement, array_spread);
+                return args && make_sequence(self, args.map(convert_spread));
+            }
+            var exp = self.expression;
+            if (self.is_call_pure(compressor)) {
+                var exprs = self.args.slice();
+                exprs.unshift(exp.expression);
+                exprs = trim(exprs, compressor, first_in_statement, array_spread);
+                return exprs && make_sequence(self, exprs.map(convert_spread));
+            }
+            if (compressor.option("yields") && is_generator(exp)) {
+                var call = self.clone();
+                call.expression = make_node(AST_Function, exp, exp);
+                call.expression.body = [];
+                var opt = call.transform(compressor);
+                if (opt !== call) return opt.drop_side_effect_free(compressor, first_in_statement);
+            }
+            if (drop_returns(compressor, exp)) {
                 // always shallow clone to ensure stripping of negated IIFEs
                 self = self.clone();
                 self.expression = exp.clone();
@@ -7734,10 +7765,21 @@ merge(Compressor.prototype, {
             return this.is_declared(compressor) && can_drop_symbol(this, compressor) ? null : this;
         });
         def(AST_Template, function(compressor, first_in_statement) {
-            if (this.tag && !is_raw_tag(compressor, this.tag)) return this;
-            var expressions = this.expressions;
-            if (expressions.length == 0) return null;
-            return make_sequence(this, expressions).drop_side_effect_free(compressor, first_in_statement);
+            var self = this;
+            if (self.is_expr_pure(compressor)) {
+                var expressions = self.expressions;
+                if (expressions.length == 0) return null;
+                return make_sequence(self, expressions).drop_side_effect_free(compressor, first_in_statement);
+            }
+            var tag = self.tag;
+            if (drop_returns(compressor, tag)) {
+                // always shallow clone to signal internal changes
+                self = self.clone();
+                self.tag = tag.clone();
+                // avoid extraneous traversal
+                if (tag._squeezed) self.tag._squeezed = true;
+            }
+            return self;
         });
         def(AST_Unary, function(compressor, first_in_statement) {
             var exp = this.expression;
diff --git a/test/compress/templates.js b/test/compress/templates.js
index 3df3efb7..3c1661fe 100644
--- a/test/compress/templates.js
+++ b/test/compress/templates.js
@@ -315,6 +315,21 @@ unsafe_side_effects: {
     node_version: ">=4"
 }
 
+pure_funcs: {
+    options = {
+        pure_funcs: "Math.random",
+        side_effects: true,
+    }
+    input: {
+        Math.random`${console.log("PASS")}`;
+    }
+    expect: {
+        console.log("PASS");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=4"
+}
+
 issue_4604: {
     options = {
         collapse_vars: true,