fix corner cases with arguments (#4520)

fixes #4519

lib/scope.js

@@ -234,19 +234,24 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options) {
             if (node.label) node.label.thedef.references.push(node);
             return true;
         }
-        // ensure mangling works if `catch` reuses a scope variable
+        if (node instanceof AST_SymbolDeclaration) {
-        if (node instanceof AST_SymbolCatch) {
+            if (node instanceof AST_SymbolCatch) {
-            var def = node.definition().redefined();
+                // ensure mangling works if `catch` reuses a scope variable
-            if (def) for (var s = node.scope; s; s = s.parent_scope) {
+                var def = node.definition().redefined();
-                push_uniq(s.enclosed, def);
+                if (def) for (var s = node.scope; s; s = s.parent_scope) {
-                if (s === def.scope) break;
+                    push_uniq(s.enclosed, def);
+                    if (s === def.scope) break;
+                }
+            } else if (node instanceof AST_SymbolConst) {
+                // ensure compression works if `const` reuses a scope variable
+                var redef = node.definition().redefined();
+                if (redef) redef.const_redefs = true;
             }
-            return true;
+            if (node.name != "arguments") return true;
-        }
+            var parent = node instanceof AST_SymbolVar && tw.parent();
-        // ensure compression works if `const` reuses a scope variable
+            if (parent instanceof AST_VarDef && !parent.value) return true;
-        if (node instanceof AST_SymbolConst) {
+            var sym = node.scope.resolve().find_variable("arguments");
-            var redef = node.definition().redefined();
+            if (sym && is_arguments(sym)) sym.scope.uses_arguments = 3;
-            if (redef) redef.const_redefs = true;
             return true;
         }
         if (node instanceof AST_SymbolRef) {
@@ -295,13 +300,6 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options) {
             node.reference(options);
             return true;
         }
-        if (node instanceof AST_VarDef) {
-            if (node.value && node.name.name == "arguments") {
-                var sym = node.name.scope.resolve().find_variable("arguments");
-                if (sym && is_arguments(sym)) sym.scope.uses_arguments = 3;
-            }
-            return;
-        }
     });
     self.walk(tw);
 

test/compress/destructured.js

@@ -2189,7 +2189,7 @@ issue_4446: {
 
 issue_4456: {
     options = {
-        pure_getters: true,
+        pure_getters: "strict",
         unused: true,
     }
     input: {
@@ -2398,3 +2398,61 @@ issue_4512: {
     expect_stdout: "undefined"
     node_version: ">=6"
 }
+
+issue_4519_1: {
+    options = {
+        arguments: true,
+        keep_fargs: false,
+    }
+    input: {
+        try {
+            (function() {
+                var [ arguments ] = [];
+                arguments[0];
+            })();
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        try {
+            (function() {
+                var [ arguments ] = [];
+                arguments[0];
+            })();
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_4519_2: {
+    options = {
+        pure_getters: "strict",
+        side_effects: true,
+    }
+    input: {
+        try {
+            (function() {
+                var [ arguments ] = [];
+                arguments[0];
+            })();
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect: {
+        try {
+            (function() {
+                var [ arguments ] = [];
+                arguments[0];
+            })();
+        } catch (e) {
+            console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}