From 92c3fddd7ae57a69de6f4e3448ae4a06b18f2fc6 Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Mon, 12 Jul 2021 16:16:12 +0100
Subject: [PATCH] fix corner case in `unused` & `yields` (#5077)

fixes #5076
---
 lib/compress.js         | 27 +++++++++++++++++----------
 test/compress/yields.js | 29 +++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+), 10 deletions(-)

diff --git a/lib/compress.js b/lib/compress.js
index aa77ced3..f602af9c 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -7179,16 +7179,15 @@ merge(Compressor.prototype, {
                             }
                             trimmed = prop.value.transform(trimmer);
                             if (!trimmed) {
-                                if (node.rest || prop.key instanceof AST_Node) trimmed = retain_lhs(prop.value);
+                                if (node.rest || retain_key(prop)) trimmed = retain_lhs(prop.value);
                                 if (drop_keys && !(key in drop_keys)) {
                                     if (mapped) {
                                         drop_keys[key] = mapped;
                                         if (value === null) {
-                                            prop_map[key] = mapped.key instanceof AST_Node
-                                                && make_node(AST_ObjectKeyVal, mapped, {
-                                                    key: mapped.key,
-                                                    value: make_node(AST_Number, mapped, { value: 0 }),
-                                                });
+                                            prop_map[key] = retain_key(mapped) && make_node(AST_ObjectKeyVal, mapped, {
+                                                key: mapped.key,
+                                                value: make_node(AST_Number, mapped, { value: 0 }),
+                                            });
                                         }
                                     } else {
                                         drop_keys[key] = true;
@@ -7222,7 +7221,7 @@ merge(Compressor.prototype, {
                             prop.value = trimmed;
                             return prop;
                         }
-                        return prop.key instanceof AST_Node ? make_node(AST_ObjectKeyVal, prop, {
+                        return retain_key(prop) ? make_node(AST_ObjectKeyVal, prop, {
                             key: prop.key,
                             value: make_node(AST_Number, prop, { value: 0 }),
                         }) : List.skip;
@@ -7259,6 +7258,10 @@ merge(Compressor.prototype, {
                 value: value,
             };
 
+            function retain_key(prop) {
+                return prop.key instanceof AST_Node && prop.key.has_side_effects(compressor);
+            }
+
             function retain_lhs(node) {
                 if (node instanceof AST_Destructured) {
                     if (value === null) {
@@ -9604,12 +9607,16 @@ merge(Compressor.prototype, {
                             var key = prop.key;
                             var value = prop.value.transform(tt);
                             if (value) {
-                                side_effects.push(key instanceof AST_Node ? key : make_node_from_constant(key, prop));
+                                if (side_effects.length) {
+                                    if (!(key instanceof AST_Node)) key = make_node_from_constant(key, prop);
+                                    side_effects.push(key);
+                                    key = make_sequence(node, side_effects);
+                                    side_effects = [];
+                                }
                                 properties.push(make_node(AST_DestructuredKeyVal, prop, {
-                                    key: make_sequence(node, side_effects),
+                                    key: key,
                                     value: value,
                                 }));
-                                side_effects = [];
                             } else if (key instanceof AST_Node) {
                                 side_effects.push(key);
                             }
diff --git a/test/compress/yields.js b/test/compress/yields.js
index 9df533b9..37fd30e3 100644
--- a/test/compress/yields.js
+++ b/test/compress/yields.js
@@ -1246,3 +1246,32 @@ issue_5034: {
     expect_stdout: "PASS"
     node_version: ">=4"
 }
+
+issue_5076: {
+    options = {
+        evaluate: true,
+        hoist_vars: true,
+        passes: 2,
+        pure_getters: "strict",
+        side_effects: true,
+        toplevel: true,
+        unused: true,
+        yields: true,
+    }
+    input: {
+        var a;
+        console.log("PASS");
+        var b = function*({
+            p: {},
+        }) {}({
+            p: { a } = 42,
+        });
+    }
+    expect: {
+        var a;
+        console.log("PASS");
+        a = 42["a"];
+    }
+    expect_stdout: "PASS"
+    node_version: ">=6"
+}