fix corner case in ie8 (#4232)

fixes #4231

lib/compress.js

@@ -5906,10 +5906,7 @@ merge(Compressor.prototype, {
                 this.write_only = !exp.has_side_effects(compressor);
                 return this;
             }
-            if (this.operator == "typeof" && exp instanceof AST_SymbolRef) {
+            if (this.operator == "typeof" && exp instanceof AST_SymbolRef && drop_symbol(exp)) return null;
-                if (drop_symbol(exp)) return null;
-                if (exp.is_declared(compressor)) return exp;
-            }
             var node = exp.drop_side_effect_free(compressor, first_in_statement);
             if (first_in_statement && node && is_iife_call(node)) {
                 if (node === exp && this.operator == "!") return this;

lib/scope.js

@@ -277,6 +277,9 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options) {
     function redefine(node, scope) {
         var name = node.name;
         var old_def = node.thedef;
+        if (!all(old_def.orig, function(sym) {
+            return !(sym instanceof AST_SymbolConst || sym instanceof AST_SymbolLet);
+        })) return;
         var new_def = scope.find_variable(name);
         if (new_def) {
             var redef = new_def.redefined();
@@ -294,7 +297,6 @@ AST_Toplevel.DEFMETHOD("figure_out_scope", function(options) {
             node.redef = true;
             node.thedef = new_def;
             node.reference(options);
-            if (node instanceof AST_SymbolConst || node instanceof AST_SymbolLet) new_def.orig.push(node);
         });
         if (old_def.lambda) new_def.lambda = true;
         if (new_def.undeclared) self.variables.set(name, new_def);

test/compress/const.js

@@ -438,7 +438,7 @@ catch_ie8_1: {
     }
     expect: {
         try {} catch (a) {}
-        console.log(function a() {
+        console.log(function() {
         }());
     }
     expect_stdout: "undefined"
@@ -1065,3 +1065,22 @@ issue_4229: {
     }
     expect_stdout: true
 }
+
+issue_4231: {
+    options = {
+        ie8: true,
+        side_effects: true,
+    }
+    input: {
+        typeof a == 0;
+        console.log(typeof function a() {
+            const a = 0;
+        });
+    }
+    expect: {
+        console.log(typeof function a() {
+            const a = 0;
+        });
+    }
+    expect_stdout: "function"
+}

test/compress/let.js

@@ -871,3 +871,25 @@ issue_4229: {
     expect_stdout: "PASS"
     node_version: ">=4"
 }
+
+issue_4231: {
+    options = {
+        ie8: true,
+        side_effects: true,
+    }
+    input: {
+        "use strict";
+        typeof a == 0;
+        console.log(typeof function a() {
+            let a;
+        });
+    }
+    expect: {
+        "use strict";
+        console.log(typeof function a() {
+            let a;
+        });
+    }
+    expect_stdout: "function"
+    node_version: ">=4"
+}