fix corner case in `collapse_vars` (#4896)

fixes #4895

2 files changed, 33 insertions, 6 deletions

diff --git a/lib/compress.js b/lib/compress.js
index b02a1163..73c9d653 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1886,8 +1886,7 @@ merge(Compressor.prototype, {
                     if (is_lhs(node, multi_replacer.parent())) return node;
                     var ref = rvalue.clone();
                     value_def.references.push(ref);
-                    if (abort && candidate instanceof AST_Assign
-                        && def.references.length - def.replaced - (assignments[def.name] || 0) > 1) {
+                    if (abort && candidate instanceof AST_Assign && remaining_refs(def) > 1) {
                         return make_node(AST_Assign, candidate, {
                             operator: "=",
                             left: node,
@@ -2281,7 +2280,9 @@ merge(Compressor.prototype, {
                     if (!(lhs instanceof AST_Destructured)) candidates.push(hit_stack.slice());
                     extract_candidates(lhs);
                     extract_candidates(expr.right);
-                    if (lhs instanceof AST_SymbolRef) assignments[lhs.name] = (assignments[lhs.name] || 0) + 1;
+                    if (lhs instanceof AST_SymbolRef && expr.operator == "=") {
+                        assignments[lhs.name] = (assignments[lhs.name] || 0) + 1;
+                    }
                 } else if (expr instanceof AST_Await) {
                     extract_candidates(expr.expression, unused);
                 } else if (expr instanceof AST_Binary) {
@@ -2584,6 +2585,10 @@ merge(Compressor.prototype, {
                 return value_def = def;
             }
 
+            function remaining_refs(def) {
+                return def.references.length - def.replaced - (assignments[def.name] || 0);
+            }
+
             function get_lhs(expr) {
                 if (expr instanceof AST_Assign) {
                     var lhs = expr.left;
@@ -2592,7 +2597,7 @@ merge(Compressor.prototype, {
                     var def = lhs.definition();
                     if (scope.uses_arguments && is_funarg(def)) return lhs;
                     if (compressor.exposed(def)) return lhs;
-                    remaining = def.references.length - def.replaced - (assignments[def.name] || 0);
+                    remaining = remaining_refs(def);
                     if (def.fixed && lhs.fixed) remaining = Math.min(remaining, def.references.filter(function(ref) {
                         return ref.fixed === lhs.fixed;
                     }).length - 1);
@@ -2608,7 +2613,7 @@ merge(Compressor.prototype, {
                     if (!member(lhs, def.orig)) return;
                     if (scope.uses_arguments && is_funarg(def)) return;
                     var declared = def.orig.length - def.eliminated - (declare_only[def.name] || 0);
-                    remaining = def.references.length - def.replaced - (assignments[def.name] || 0);
+                    remaining = remaining_refs(def);
                     if (def.fixed) remaining = Math.min(remaining, def.references.filter(function(ref) {
                         if (!ref.fixed) return true;
                         if (!ref.fixed.assigns) return true;
diff --git a/test/compress/collapse_vars.js b/test/compress/collapse_vars.js
index 3ac8894a..f8a8a31a 100644
--- a/test/compress/collapse_vars.js
+++ b/test/compress/collapse_vars.js
@@ -8560,7 +8560,7 @@ issue_4047_1: {
     expect: {
         var b = 1;
         var a;
-        console.log((a = --b + ((a = 0) !== typeof A), +void ((a >>= 0) && console.log("PASS"))));
+        console.log((a = --b + (0 !== typeof A), +void ((a >>= 0) && console.log("PASS"))));
     }
     expect_stdout: [
         "PASS",
@@ -9085,3 +9085,25 @@ issue_4891: {
         "0",
     ]
 }
+
+issue_4895: {
+    options = {
+        collapse_vars: true,
+        toplevel: true,
+    }
+    input: {
+        var a, b;
+        (function f() {
+            a = 42;
+        })();
+        console.log((b = a) || b, b += 0);
+    }
+    expect: {
+        var a, b;
+        (function f() {
+            a = 42;
+        })();
+        console.log((b = a) || b, b += 0);
+    }
+    expect_stdout: "42 42"
+}