From d0e3f6955d956a4977d701e9027eb54d15b6f77c Mon Sep 17 00:00:00 2001
From: "Alex Lam S.L" <alexlamsl@gmail.com>
Date: Mon, 5 Jul 2021 19:43:09 +0100
Subject: [PATCH] enhance `functions` (#5052)

---
 lib/compress.js            | 45 ++++++++++++++++++++------------------
 test/compress/functions.js | 30 +++++++++++++++++++++++++
 2 files changed, 54 insertions(+), 21 deletions(-)

diff --git a/lib/compress.js b/lib/compress.js
index e0b7597b..714d3cd7 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -519,6 +519,13 @@ merge(Compressor.prototype, {
             });
         }
 
+        function walk_fn_def(tw, fn) {
+            var was_scanning = tw.fn_scanning;
+            tw.fn_scanning = fn;
+            fn.walk(tw);
+            tw.fn_scanning = was_scanning;
+        }
+
         function mark_fn_def(tw, def, fn) {
             if (!HOP(fn, "safe_ids")) return;
             var marker = fn.safe_ids;
@@ -526,29 +533,25 @@ merge(Compressor.prototype, {
             if (fn.parent_scope.resolve().may_call_this === return_true) return;
             if (marker) {
                 var visited = member(fn, tw.fn_visited);
-                if (marker === tw.safe_ids) return !visited && walk_fn_def(tw, fn);
-                if (visited) {
-                    fn.enclosed.forEach(function(d) {
-                        if (fn.variables.get(d.name) === d) return;
-                        if (safe_to_read(tw, d)) return;
-                        d.single_use = false;
-                        if (d.fixed instanceof AST_LambdaDefinition) return;
-                        d.fixed = false;
-                    });
-                    return;
-                }
-            } else if (!tw.in_loop && !(tw.fn_scanning && tw.fn_scanning !== def.scope.resolve())) {
+                if (marker === tw.safe_ids) {
+                    if (!visited) walk_fn_def(tw, fn);
+                } else if (!visited) {
+                    fn.safe_ids = false;
+                } else fn.enclosed.forEach(function(d) {
+                    if (fn.variables.get(d.name) === d) return;
+                    if (safe_to_read(tw, d)) return;
+                    d.single_use = false;
+                    var fixed = d.fixed;
+                    if (typeof fixed == "function") fixed = fixed();
+                    if (fixed instanceof AST_Lambda && HOP(fixed, "safe_ids")) return;
+                    d.fixed = false;
+                });
+            } else if (tw.fn_scanning && tw.fn_scanning !== def.scope.resolve()) {
+                fn.safe_ids = false;
+            } else {
                 fn.safe_ids = tw.safe_ids;
-                return walk_fn_def(tw, fn);
+                walk_fn_def(tw, fn);
             }
-            fn.safe_ids = false;
-        }
-
-        function walk_fn_def(tw, fn) {
-            var was_scanning = tw.fn_scanning;
-            tw.fn_scanning = fn;
-            fn.walk(tw);
-            tw.fn_scanning = was_scanning;
         }
 
         function pop_scope(tw, scope) {
diff --git a/test/compress/functions.js b/test/compress/functions.js
index 6e75e8fb..6d41a265 100644
--- a/test/compress/functions.js
+++ b/test/compress/functions.js
@@ -2826,6 +2826,36 @@ functions_use_strict: {
     expect_stdout: "a true 42 function function function"
 }
 
+functions_cross_scope_reference: {
+    options = {
+        functions: true,
+        reduce_vars: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        log = function(fn) {
+            console.log(typeof fn());
+        };
+        var a = function() {};
+        function f() {
+            return a;
+        }
+        while (log(f));
+    }
+    expect: {
+        log = function(fn) {
+            console.log(typeof fn());
+        };
+        function a() {}
+        function f() {
+            return a;
+        }
+        while (log(f));
+    }
+    expect_stdout: "function"
+}
+
 functions_inner_var: {
     options = {
         functions: true,