fix multiple nested function substitutions (#2458)

fixes #2449

lib/compress.js

@@ -313,19 +313,14 @@ merge(Compressor.prototype, {
                 if (node instanceof AST_SymbolRef) {
                     var d = node.definition();
                     d.references.push(node);
+                    var value;
                     if (d.fixed === undefined || !safe_to_read(d) || d.single_use == "m") {
                         d.fixed = false;
                     } else if (d.fixed) {
-                        var value = node.fixed_value();
+                        value = node.fixed_value();
                         if (value && ref_once(d)) {
-                            if (value instanceof AST_Lambda) {
-                                d.single_use = d.scope === node.scope
-                                        && !(d.orig[0] instanceof AST_SymbolFunarg)
-                                    || value.is_constant_expression(node.scope);
-                            } else {
-                                d.single_use = d.scope === node.scope
-                                    && value.is_constant_expression();
-                            }
+                            d.single_use = value instanceof AST_Lambda
+                                || d.scope === node.scope && value.is_constant_expression();
                         } else {
                             d.single_use = false;
                         }
@@ -335,11 +330,10 @@ merge(Compressor.prototype, {
                             } else {
                                 d.fixed = false;
                             }
-                        } else {
+                        }
+                    }
                     mark_escaped(d, node, value, 0);
                 }
-                    }
-                }
                 if (node instanceof AST_SymbolCatch) {
                     node.definition().fixed = false;
                 }
@@ -385,10 +379,7 @@ merge(Compressor.prototype, {
                         d.fixed = node;
                         loop_ids[d.id] = in_loop;
                         mark(d, true);
-                        if (ref_once(d)) {
-                            d.single_use = d.scope === d.references[0].scope
-                                || node.is_constant_expression(d.references[0].scope);
-                        }
+                        d.single_use = ref_once(d);
                     }
                     var save_ids = safe_ids;
                     safe_ids = Object.create(null);
@@ -2209,7 +2200,10 @@ merge(Compressor.prototype, {
                         && !self.variables.has(def.name)) {
                         if (scope) {
                             var scope_def = scope.find_variable(node);
-                            if (def.undeclared ? !scope_def : scope_def === def) return true;
+                            if (def.undeclared ? !scope_def : scope_def === def) {
+                                result = "f";
+                                return true;
+                            }
                         }
                         result = false;
                     }
@@ -4256,11 +4250,20 @@ merge(Compressor.prototype, {
             if (fixed instanceof AST_Defun) {
                 d.fixed = fixed = make_node(AST_Function, fixed, fixed);
             }
-            if (fixed
-                && d.single_use
-                && !(fixed instanceof AST_Function
-                    && (d.escaped && d.scope !== self.scope
-                        || recursive_ref(compressor, d)))) {
+            if (d.single_use && fixed instanceof AST_Function) {
+                if (d.escaped && d.scope !== self.scope || recursive_ref(compressor, d)) {
+                    d.single_use = false;
+                } else if (d.scope !== self.scope || d.orig[0] instanceof AST_SymbolFunarg) {
+                    d.single_use = fixed.is_constant_expression(self.scope);
+                    if (d.single_use == "f") {
+                        var scope = self.scope;
+                        do {
+                            if (scope.name) scope.name.definition().single_use = false;
+                        } while (scope = scope.parent_scope);
+                    }
+                }
+            }
+            if (d.single_use && fixed) {
                 var value = fixed.optimize(compressor);
                 return value === fixed ? fixed.clone(true) : value;
             }

test/compress/collapse_vars.js

@@ -3036,6 +3036,7 @@ issue_2437: {
         conditionals: true,
         inline: true,
         join_vars: true,
+        passes: 2,
         reduce_vars: true,
         side_effects: true,
         sequences: true,

test/compress/drop-unused.js

@@ -1113,7 +1113,7 @@ issue_2105_1: {
     options = {
         collapse_vars: true,
         inline: true,
-        passes: 2,
+        passes: 3,
         reduce_vars: true,
         side_effects: true,
         unused: true,
@@ -1153,7 +1153,7 @@ issue_2105_2: {
     options = {
         collapse_vars: true,
         inline: true,
-        passes: 2,
+        passes: 3,
         properties: true,
         pure_getters: "strict",
         reduce_vars: true,

test/compress/functions.js

@@ -513,7 +513,7 @@ issue_2428: {
     options = {
         collapse_vars: true,
         inline: true,
-        passes: 2,
+        passes: 3,
         pure_getters: "strict",
         reduce_vars: true,
         side_effects: true,

test/compress/reduce_vars.js

@@ -3714,6 +3714,7 @@ recursive_inlining_2: {
 
 recursive_inlining_3: {
     options = {
+        passes: 2,
         reduce_vars: true,
         unused: true,
     }
@@ -3989,3 +3990,38 @@ issue_2450_5: {
         "true",
     ]
 }
+
+issue_2449: {
+    options = {
+        passes: 10,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = "PASS";
+        function f() {
+            return a;
+        }
+        function g() {
+            return f();
+        }
+        (function() {
+            var a = "FAIL";
+            if (a == a) console.log(g());
+        })();
+    }
+    expect: {
+        var a = "PASS";
+        function g() {
+            return function() {
+                return a;
+            }();
+        }
+        (function() {
+            var a = "FAIL";
+            if (a == a) console.log(g());
+        })();
+    }
+    expect_stdout: "PASS"
+}