From 21bd4c4a9dfd230ebbf37d646a59e1ee826ddd96 Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Wed, 6 Apr 2022 21:12:03 +0100
Subject: [PATCH] fix corner cases in `collapse_vars` & `hoist_vars` (#5412)

fixes #5411
---
 lib/compress.js             | 37 ++++++++++++-----
 test/compress/hoist_vars.js | 83 ++++++++++++++++++++++++++++++++++---
 2 files changed, 105 insertions(+), 15 deletions(-)

diff --git a/lib/compress.js b/lib/compress.js
index 88231a47..a345f100 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -2059,13 +2059,17 @@ Compressor.prototype.compress = function(node) {
                     if (is_lhs(node, parent)) {
                         if (value_def && !hit_rhs) assign_used = true;
                         return node;
-                    } else if (value_def) {
+                    }
+                    if (!hit_rhs && verify_ref && node.fixed !== lhs.fixed) {
+                        abort = true;
+                        return node;
+                    }
+                    if (value_def) {
                         if (stop_if_hit && assign_pos == 0) assign_pos = remaining - replaced;
                         if (!hit_rhs) replaced++;
                         return node;
-                    } else {
-                        replaced++;
                     }
+                    replaced++;
                     changed = abort = true;
                     AST_Node.info("Collapsing {node} [{file}:{line},{col}]", {
                         node: node,
@@ -2240,6 +2244,7 @@ Compressor.prototype.compress = function(node) {
                     var candidate = hit_stack[hit_stack.length - 1];
                     var assign_pos = -1;
                     var assign_used = false;
+                    var verify_ref = false;
                     var remaining;
                     var value_def = null;
                     var stop_after = null;
@@ -2958,6 +2963,7 @@ Compressor.prototype.compress = function(node) {
                         if (matches < remaining) {
                             remaining = matches;
                             assign_pos = 0;
+                            verify_ref = true;
                         }
                     }
                     if (expr.operator == "=") mangleable_var(expr.right);
@@ -3266,9 +3272,13 @@ Compressor.prototype.compress = function(node) {
                 }
                 var def = lhs.definition();
                 if (def.references.length - def.replaced == referenced) return true;
-                return def.fixed && lhs.fixed && def.references.filter(function(ref) {
+                if (!def.fixed) return false;
+                if (!lhs.fixed) return false;
+                if (def.references.filter(function(ref) {
                     return ref.fixed === lhs.fixed;
-                }).length == referenced;
+                }).length != referenced) return false;
+                verify_ref = true;
+                return true;
             }
 
             function symbol_in_lvalues(sym, parent) {
@@ -7843,7 +7853,7 @@ Compressor.prototype.compress = function(node) {
         var consts = new Dictionary();
         var dirs = [];
         var hoisted = [];
-        var vars = new Dictionary(), vars_found = 0;
+        var vars = new Dictionary();
         var tt = new TreeTransformer(function(node, descend, in_list) {
             if (node === self) return;
             if (node instanceof AST_Directive) {
@@ -7871,7 +7881,6 @@ Compressor.prototype.compress = function(node) {
                 })) return node;
                 node.definitions.forEach(function(defn) {
                     vars.set(defn.name.name, defn);
-                    ++vars_found;
                 });
                 var seq = node.to_assignments();
                 if (p instanceof AST_ForEnumeration && p.init === node) {
@@ -7890,7 +7899,7 @@ Compressor.prototype.compress = function(node) {
             }
         });
         self.transform(tt);
-        if (vars_found > 0) {
+        if (vars.size() > 0) {
             // collect only vars which don't show up in self's arguments list
             var defns = [];
             if (self instanceof AST_Lambda) self.each_argname(function(argname) {
@@ -9658,8 +9667,16 @@ Compressor.prototype.compress = function(node) {
                 fixed.escaped = def.escaped;
                 name.fixed = fixed;
                 def.references.forEach(function(ref) {
-                    var assigns = ref.fixed && ref.fixed.assigns;
-                    if (assigns && assigns[0] === defn) assigns[0] = assign;
+                    if (!ref.fixed) return;
+                    var assigns = ref.fixed.assigns;
+                    if (!assigns) return;
+                    if (assigns[0] !== defn) return;
+                    if (assigns.length > 1 || ref.fixed.to_binary || ref.fixed.to_prefix) {
+                        assigns[0] = assign;
+                    } else {
+                        ref.fixed = fixed;
+                        if (def.fixed === ref.fixed) def.fixed = fixed;
+                    }
                 });
                 def.references.push(name);
             }
diff --git a/test/compress/hoist_vars.js b/test/compress/hoist_vars.js
index 30fb4837..99a13fe6 100644
--- a/test/compress/hoist_vars.js
+++ b/test/compress/hoist_vars.js
@@ -224,8 +224,7 @@ issue_4489: {
         console.log(k);
     }
     expect: {
-        !(A = 0);
-        for (var k in true);
+        for (var k in !(A = 0));
         console.log(k);
     }
     expect_stdout: "undefined"
@@ -407,9 +406,9 @@ issue_4893_2: {
     expect: {
         try{
             (function() {
-                var b;
-                b = null;
-                b.p += 42;
+                var a;
+                a = null;
+                a.p += 42;
             })();
         } catch (e) {
             console.log("PASS");
@@ -530,3 +529,77 @@ issue_5378: {
         "undefined",
     ]
 }
+
+issue_5411_1: {
+    options = {
+        collapse_vars: true,
+        dead_code: true,
+        hoist_vars: true,
+        reduce_vars: true,
+        side_effects: true,
+        toplevel: true,
+    }
+    input: {
+        var a = "PASS";
+        b++;
+        b = a;
+        var b = b, c = c && c[b];
+        console.log(b);
+    }
+    expect: {
+        var b, c, a = "PASS";
+        b++;
+        b = a;
+        c = c && c[b];
+        console.log(b);
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5411_2: {
+    options = {
+        collapse_vars: true,
+        dead_code: true,
+        evaluate: true,
+        hoist_vars: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = "PASS";
+        b++;
+        b = a;
+        var b = b, c = c && c[b];
+        console.log(b);
+    }
+    expect: {
+        var b, c;
+        b++;
+        b = "PASS",
+        c = c && c[b];
+        console.log(b);
+    }
+    expect_stdout: "PASS"
+}
+
+issue_5411_3: {
+    options = {
+        collapse_vars: true,
+        hoist_vars: true,
+        reduce_vars: true,
+        toplevel: true,
+    }
+    input: {
+        var a = console;
+        a++;
+        var a = A = a;
+        console.log(A);
+    }
+    expect: {
+        var a = console;
+        a = A = ++a;
+        console.log(A);
+    }
+    expect_stdout: "NaN"
+}