From b54f298ce9a722bb419ecdad56aed45d5f5ad4c4 Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L." <alexlamsl@gmail.com>
Date: Thu, 5 Sep 2024 15:33:38 +0300
Subject: [PATCH] fix corner case in `merge_vars` (#5931)

fixes #5930
---
 lib/compress.js        | 20 +++++++-------
 test/compress/const.js | 63 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 73 insertions(+), 10 deletions(-)

diff --git a/lib/compress.js b/lib/compress.js
index f0d470fa706..831050c9ef2 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -6791,7 +6791,7 @@ Compressor.prototype.compress = function(node) {
                         var id = node.definition().id;
                         var refs = references[id];
                         if (refs) {
-                            refs.push(node);
+                            push_ref(refs, node);
                         } else if (!(id in references)) {
                             declarations.add(id, node);
                         }
@@ -6936,6 +6936,13 @@ Compressor.prototype.compress = function(node) {
             segment = Object.getPrototypeOf(segment);
         }
 
+        function push_ref(refs, sym) {
+            refs.push(sym);
+            push_uniq(refs.scopes, sym.scope);
+            var scope = find_scope(tw);
+            if (scope !== sym.scope) push_uniq(refs.scopes, scope);
+        }
+
         function walk_destructured(symbol_type, mark, lhs) {
             var marker = new TreeWalker(function(node) {
                 if (node instanceof AST_Destructured) return;
@@ -6987,7 +6994,7 @@ Compressor.prototype.compress = function(node) {
                 var refs = references[def.id];
                 if (!refs) return;
                 if (refs.start.block !== seg.block) return references[def.id] = false;
-                push_ref(sym);
+                push_ref(refs, sym);
                 refs.end = seg;
                 if (def.id in prev) {
                     last[prev[def.id]] = null;
@@ -7002,7 +7009,7 @@ Compressor.prototype.compress = function(node) {
             } else {
                 var refs = declarations.get(def.id) || [];
                 refs.scopes = [];
-                push_ref(sym);
+                push_ref(refs, sym);
                 references[def.id] = refs;
                 if (!read) {
                     refs.start = seg;
@@ -7019,13 +7026,6 @@ Compressor.prototype.compress = function(node) {
                 index: index++,
                 definition: def,
             });
-
-            function push_ref(sym) {
-                refs.push(sym);
-                push_uniq(refs.scopes, sym.scope);
-                var scope = find_scope(tw);
-                if (scope !== sym.scope) push_uniq(refs.scopes, scope);
-            }
         }
 
         function insert(target) {
diff --git a/test/compress/const.js b/test/compress/const.js
index df948ac4d9e..d991f1b4a81 100644
--- a/test/compress/const.js
+++ b/test/compress/const.js
@@ -2231,3 +2231,66 @@ issue_5787: {
     }
     expect_stdout: true
 }
+
+issue_5930_1: {
+    options = {
+        merge_vars: true,
+    }
+    input: {
+        console.log(function() {
+            var a;
+            (f = a) && f();
+            {
+                const a = 42;
+                var f;
+            }
+        }());
+    }
+    expect: {
+        console.log(function() {
+            var a;
+            (f = a) && f();
+            {
+                const a = 42;
+                var f;
+            }
+        }());
+    }
+    expect_stdout: true
+}
+
+issue_5930_2: {
+    options = {
+        collapse_vars: true,
+        inline: true,
+        merge_vars: true,
+        unused: true,
+    }
+    input: {
+        "use strict";
+        (function() {
+            f = function g(a) {
+                a.p;
+            }();
+            f && f();
+            {
+                const a = 42;
+                var b = false;
+                var f;
+            }
+        })();
+    }
+    expect: {
+        "use strict";
+        (function() {
+            var a;
+            (f = void a.p) && f();
+            {
+                const a = 42;
+                var f;
+            }
+        })();
+    }
+    expect_stdout: TypeError("Cannot read properties of undefined")
+    node_version: ">=4"
+}