fix corner case in collapse_vars (#5901)

fixes #5899

Author: alexlamsl

lib/compress.js

@@ -3285,14 +3285,24 @@ Compressor.prototype.compress = function(node) {
                 if (expr instanceof AST_Assign && expr.right.single_use) return;
                 var lhs_ids = Object.create(null);
                 var marker = new TreeWalker(function(node) {
-                    if (node instanceof AST_SymbolRef) lhs_ids[node.definition().id] = true;
+                    if (!(node instanceof AST_SymbolRef)) return;
+                    for (var level = 0, parent, child = node; parent = marker.parent(level++); child = parent) {
+                        if (is_direct_assignment(child, parent)) {
+                            if (parent instanceof AST_DestructuredKeyVal) parent = marker.parent(level++);
+                            continue;
+                        }
+                        lhs_ids[node.definition().id] = true;
+                        return;
+                    }
+                    lhs_ids[node.definition().id] = "a";
                 });
                 while (expr instanceof AST_Assign && expr.operator == "=") {
                     expr.left.walk(marker);
                     expr = expr.right;
                 }
                 if (expr instanceof AST_ObjectIdentity) return rhs_exact_match;
                 if (expr instanceof AST_SymbolRef) {
+                    if (lhs_ids[expr.definition().id] === "a") return;
                     var value = expr.evaluate(compressor);
                     if (value === expr) return rhs_exact_match;
                     return rhs_fuzzy_match(value, rhs_exact_match);

test/compress/destructured.js

@@ -4241,3 +4241,51 @@ issue_5866_12: {
     expect_stdout: "PASS"
     node_version: ">=6"
 }
+
+issue_5899_1: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var log = console.log, a, b;
+        a = "foo";
+        log(a && a);
+        b = { p: a } = a;
+        log(a);
+    }
+    expect: {
+        var log = console.log, a, b;
+        log((a = "foo") && a);
+        b = { p: a } = a;
+        log(a);
+    }
+    expect_stdout: [
+        "foo",
+        "undefined",
+    ]
+    node_version: ">=6"
+}
+
+issue_5899_2: {
+    options = {
+        collapse_vars: true,
+    }
+    input: {
+        var log = console.log, a, b;
+        a = "foo";
+        log(a && a);
+        b = [ a ] = a;
+        log(a);
+    }
+    expect: {
+        var log = console.log, a, b;
+        log((a = "foo") && a);
+        b = [ a ] = a;
+        log(a);
+    }
+    expect_stdout: [
+        "foo",
+        "f",
+    ]
+    node_version: ">=6"
+}