workaround quirks on latter specs (#4172)

closes #4171

lib/compress.js

@@ -4851,8 +4851,8 @@ merge(Compressor.prototype, {
                                 && (old_def.name == def.name.name || all(old_def.references, function(ref) {
                                     return ref.scope.find_variable(def.name) === def.name.definition();
                                 })))
-                            && can_rename(def.value, def.name.name)
+                            && can_declare_defun()
-                            && (!compressor.has_directive("use strict") || parent instanceof AST_Scope)) {
+                            && can_rename(def.value, def.name.name)) {
                             AST_Node.warn("Declaring {name} as function [{file}:{line},{col}]", template(def.name));
                             var defun = make_node(AST_Defun, def, def.value);
                             defun.name = make_node(AST_SymbolDefun, def.name, def.name);
@@ -4908,6 +4908,13 @@ merge(Compressor.prototype, {
                         var def = fn.variables.get(name);
                         return !def || fn.name && def === fn.name.definition();
                     }
+
+                    function can_declare_defun() {
+                        if (compressor.has_directive("use strict")) return parent instanceof AST_Scope;
+                        return parent instanceof AST_Block
+                            || parent instanceof AST_For && parent.init === node
+                            || parent instanceof AST_If;
+                    }
                 });
                 switch (head.length) {
                   case 0:

test/compress/functions.js

@@ -4892,3 +4892,71 @@ direct_inline_catch_redefined: {
     }
     expect_stdout: true
 }
+
+issue_4171_1: {
+    options = {
+        functions: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        console.log(function(a) {
+            try {
+                while (a)
+                    var e = function() {};
+            } catch (e) {
+                return function() {
+                    return e;
+                };
+            }
+        }(!console));
+    }
+    expect: {
+        console.log(function(a) {
+            try {
+                while (a)
+                    var e = function() {};
+            } catch (e) {
+                return function() {
+                    return e;
+                };
+            }
+        }(!console));
+    }
+    expect_stdout: "undefined"
+}
+
+issue_4171_2: {
+    options = {
+        functions: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        console.log(function(a) {
+            try {
+                while (a);
+            } catch (e) {
+                return function() {
+                    return e;
+                };
+            } finally {
+                var e = function() {};
+            }
+        }(!console));
+    }
+    expect: {
+        console.log(function(a) {
+            try {
+                while (a);
+            } catch (e) {
+                return function() {
+                    return e;
+                };
+            } finally {
+                function e() {}
+            }
+        }(!console));
+    }
+    expect_stdout: "undefined"
+}