fix corner case in collapse_vars (#5855)

fixes #5854

Author: alexlamsl

lib/compress.js

@@ -2722,8 +2722,10 @@ Compressor.prototype.compress = function(node) {
                 if (sym instanceof AST_PropAccess) return true;
                 if (check_destructured(sym)) return true;
                 return sym.match_symbol(function(node) {
-                    return node instanceof AST_SymbolRef
-                        && (lvalues.has(node.name) || read_toplevel && compressor.exposed(node.definition()));
+                    if (node instanceof AST_PropAccess) return true;
+                    if (node instanceof AST_SymbolRef) {
+                        return lvalues.has(node.name) || read_toplevel && compressor.exposed(node.definition());
+                    }
                 }, true);
 
                 function reject(node) {

test/compress/destructured.js

@@ -3959,3 +3959,51 @@ issue_5844: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_5854_1: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        console.log(function(a) {
+            var b = a;
+            a++;
+            [ b[0] ] = [ "foo" ];
+            return a;
+        }([]) ? "PASS" : "FAIL");
+    }
+    expect: {
+        console.log(function(a) {
+            var b = a;
+            a++;
+            [ b[0] ] = [ "foo" ];
+            return a;
+        }([]) ? "PASS" : "FAIL");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}
+
+issue_5854_2: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        console.log(function(a) {
+            var b = a;
+            a++;
+            ({ p: b[0] } = { p: "foo" });
+            return a;
+        }([]) ? "PASS" : "FAIL");
+    }
+    expect: {
+        console.log(function(a) {
+            var b = a;
+            a++;
+            ({ p: b[0] } = { p: "foo" });
+            return a;
+        }([]) ? "PASS" : "FAIL");
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}