fix corner case in collapse_vars (#3527)

fixes #3526

lib/compress.js

@@ -1228,6 +1228,7 @@ merge(Compressor.prototype, {
                     var scan_lhs = lhs && !side_effects && !is_lhs_read_only(lhs, compressor);
                     var scan_rhs = foldable(get_rhs(candidate));
                     if (!scan_lhs && !scan_rhs) continue;
+                    var modify_toplevel = false;
                     // Locate symbols which may execute code outside of scanning range
                     var lvalues = get_lvalues(candidate);
                     var lhs_local = is_lhs_local(lhs);
@@ -1580,7 +1581,16 @@ merge(Compressor.prototype, {
                 if (candidate instanceof AST_VarDef) {
                     lvalues[candidate.name.name] = lhs;
                 }
+                var scan_iife = scope instanceof AST_Toplevel;
                 var tw = new TreeWalker(function(node) {
+                    if (scan_iife && node.TYPE == "Call") {
+                        var exp = node.expression;
+                        if (exp instanceof AST_PropAccess) return;
+                        if (exp instanceof AST_Function && !exp.contains_this()) return;
+                        modify_toplevel = true;
+                        scan_iife = false;
+                        return;
+                    }
                     var value;
                     if (node instanceof AST_SymbolRef) {
                         value = node.fixed_value() || node;
@@ -1667,6 +1677,7 @@ merge(Compressor.prototype, {
                 var def = sym.definition();
                 if (def.orig.length == 1 && def.orig[0] instanceof AST_SymbolDefun) return false;
                 if (def.scope !== scope) return true;
+                if (modify_toplevel && compressor.exposed(def)) return true;
                 return !all(def.references, function(ref) {
                     return ref.scope.resolve() === scope;
                 });

test/compress/collapse_vars.js

@@ -6296,3 +6296,55 @@ issue_3520: {
     }
     expect_stdout: "2"
 }
+
+issue_3526_1: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var b = function() {
+            this.a = "FAIL";
+        }();
+        var a = "PASS";
+        var b;
+        var c = b;
+        console.log(a);
+    }
+    expect: {
+        var b = function() {
+            this.a = "FAIL";
+        }();
+        var a = "PASS";
+        var b;
+        var c = b;
+        console.log(a);
+    }
+    expect_stdout: "PASS"
+}
+
+issue_3526_2: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        function f() {
+            this.a = "FAIL";
+        }
+        var b = f();
+        var a = "PASS";
+        var b;
+        var c = b;
+        console.log(a);
+    }
+    expect: {
+        function f() {
+            this.a = "FAIL";
+        }
+        var b = f();
+        var a = "PASS";
+        var b;
+        var c = b;
+        console.log(a);
+    }
+    expect_stdout: "PASS"
+}