fix corner cases in `reduce_vars` (#5097)

fixes #5096

3 files changed, 191 insertions, 28 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 5bb378e5..e0252646 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -884,15 +884,12 @@ merge(Compressor.prototype, {
                 }
                 if (ld && right instanceof AST_LambdaExpression) {
                     walk_assign();
-                    if (ld.escaped.length) {
-                        right.walk(tw);
-                    } else {
-                        right.parent_scope.resolve().fn_defs.push(right);
-                        right.safe_ids = null;
-                        if (!node.write_only) mark_fn_def(tw, ld, right);
-                    }
+                    right.parent_scope.resolve().fn_defs.push(right);
+                    right.safe_ids = null;
+                    if (!ld.fixed || !node.write_only) mark_fn_def(tw, ld, right);
                     return true;
-                } else if (scan) {
+                }
+                if (scan) {
                     right.walk(tw);
                     walk_assign();
                     return true;
@@ -1397,31 +1394,38 @@ merge(Compressor.prototype, {
             var node = this;
             var value = node.value;
             if (value instanceof AST_LambdaExpression && node.name instanceof AST_SymbolDeclaration) {
+                walk_defn();
                 value.parent_scope.resolve().fn_defs.push(value);
                 value.safe_ids = null;
+                var ld = node.name.definition();
+                if (!ld.fixed) mark_fn_def(tw, ld, value);
             } else if (value) {
                 value.walk(tw);
-            } else if (!(tw.parent() instanceof AST_Let)) {
-                return;
+                walk_defn();
+            } else if (tw.parent() instanceof AST_Let) {
+                walk_defn();
             }
-            scan_declaration(tw, compressor, node.name, function() {
-                return node.value || make_node(AST_Undefined, node);
-            }, function(name, fixed) {
-                var d = name.definition();
-                if (fixed && safe_to_assign(tw, d, true)) {
-                    mark(tw, d);
-                    tw.loop_ids[d.id] = tw.in_loop;
-                    d.fixed = fixed;
-                    d.fixed.assigns = [ node ];
-                    if (name instanceof AST_SymbolConst && d.redefined()
-                        || !(can_drop_symbol(name) || is_safe_lexical(d))) {
-                        d.single_use = false;
-                    }
-                } else {
-                    d.fixed = false;
-                }
-            });
             return true;
+
+            function walk_defn() {
+                scan_declaration(tw, compressor, node.name, function() {
+                    return node.value || make_node(AST_Undefined, node);
+                }, function(name, fixed) {
+                    var d = name.definition();
+                    if (fixed && safe_to_assign(tw, d, true)) {
+                        mark(tw, d);
+                        tw.loop_ids[d.id] = tw.in_loop;
+                        d.fixed = fixed;
+                        d.fixed.assigns = [ node ];
+                        if (name instanceof AST_SymbolConst && d.redefined()
+                            || !(can_drop_symbol(name) || is_safe_lexical(d))) {
+                            d.single_use = false;
+                        }
+                    } else {
+                        d.fixed = false;
+                    }
+                });
+            }
         });
         def(AST_While, function(tw, descend) {
             var save_loop = tw.in_loop;
diff --git a/test/compress/arrows.js b/test/compress/arrows.js
index abbbbf90..5cbf56bc 100644
--- a/test/compress/arrows.js
+++ b/test/compress/arrows.js
@@ -556,7 +556,7 @@ reduce_iife_3: {
     node_version: ">=4"
 }
 
-reduce_lambda: {
+reduce_lambda_1: {
     options = {
         evaluate: true,
         reduce_vars: true,
@@ -588,6 +588,43 @@ reduce_lambda: {
     node_version: ">=4"
 }
 
+reduce_lambda_2: {
+    options = {
+        evaluate: true,
+        passes: 2,
+        reduce_vars: true,
+        side_effects: true,
+        unused: true,
+    }
+    input: {
+        (function(f, a, b) {
+            f = () => {
+                console.log(a, b);
+            };
+            a = "foo", b = 42;
+            f();
+            b = "bar";
+            f();
+        })();
+    }
+    expect: {
+        (function(f, a, b) {
+            f = () => {
+                console.log("foo", b);
+            };
+            b = 42;
+            f();
+            b = "bar";
+            f();
+        })();
+    }
+    expect_stdout: [
+        "foo 42",
+        "foo bar",
+    ]
+    node_version: ">=4"
+}
+
 single_use_recursive: {
     options = {
         reduce_vars: true,
diff --git a/test/compress/functions.js b/test/compress/functions.js
index 257ff7a2..ff727da4 100644
--- a/test/compress/functions.js
+++ b/test/compress/functions.js
@@ -6413,3 +6413,125 @@ issue_5067: {
     }
     expect: {}
 }
+
+issue_5096_1: {
+    options = {
+        evaluate: true,
+        passes: 2,
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+    }
+    input: {
+        var a, b = "FAIL", c = 1;
+        do {
+            a && a();
+            a = function() {
+                b = "PASS";
+            };
+        } while (c--);
+        console.log(b);
+    }
+    expect: {
+        var a, b = "FAIL", c = 1;
+        do {
+            a && a();
+            a = function() {
+                b = "PASS";
+            };
+        } while (c--);
+        console.log(b);
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5096_2: {
+    options = {
+        passes: 2,
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a, b = "FAIL", c = 1;
+        do {
+            a && a();
+            a = function() {
+                b = "PASS";
+            };
+        } while (c--);
+        console.log(b);
+    }
+    expect: {
+        var a, b = "FAIL", c = 1;
+        do {
+            a && a();
+            a = function() {
+                b = "PASS";
+            };
+        } while (c--);
+        console.log(b);
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5096_3: {
+    options = {
+        evaluate: true,
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+    }
+    input: {
+        var b = "FAIL", c = 1;
+        do {
+            a && a();
+            var a = function() {
+                b = "PASS";
+            };
+        } while (c--);
+        console.log(b);
+    }
+    expect: {
+        var b = "FAIL", c = 1;
+        do {
+            a && a();
+            var a = function() {
+                b = "PASS";
+            };
+        } while (c--);
+        console.log(b);
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5096_4: {
+    options = {
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var b = "FAIL", c = 1;
+        do {
+            a && a();
+            var a = function() {
+                b = "PASS";
+            };
+        } while (c--);
+        console.log(b);
+    }
+    expect: {
+        var b = "FAIL", c = 1;
+        do {
+            a && a();
+            var a = function() {
+                b = "PASS";
+            };
+        } while (c--);
+        console.log(b);
+    }
+    expect_stdout: "PASS"
+}