fix corner case in `ie8` (#4929)

fixes #4928

3 files changed, 96 insertions, 12 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 9d83fc09..38e76620 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -6092,6 +6092,30 @@ merge(Compressor.prototype, {
         });
         tw.directives = Object.create(compressor.directives);
         self.walk(tw);
+        var drop_fn_name = compressor.option("keep_fnames") ? return_false : compressor.option("ie8") ? function(def) {
+            return !compressor.exposed(def) && def.references.length == def.replaced;
+        } : function(def) {
+            if (!(def.id in in_use_ids)) return true;
+            if (def.orig.length < 2) return false;
+            // function argument will always overshadow its name
+            if (def.orig[1] instanceof AST_SymbolFunarg) return true;
+            // retain if referenced within destructured object of argument
+            return all(def.references, function(ref) {
+                return !ref.in_arg;
+            });
+        };
+        if (compressor.option("ie8")) initializations.each(function(init, id) {
+            if (id in in_use_ids) return;
+            init.forEach(function(init) {
+                init.walk(new TreeWalker(function(node) {
+                    if (node instanceof AST_Function && node.name && !drop_fn_name(node.name.definition())) {
+                        node.walk(tw);
+                        return true;
+                    }
+                    if (node instanceof AST_Scope) return true;
+                }));
+            });
+        });
         // pass 2: for every used symbol we need to walk its
         // initialization code to figure out if it uses other
         // symbols (that may not be in_use).
@@ -6129,18 +6153,6 @@ merge(Compressor.prototype, {
                 delete assign_in_use[id];
             }
         });
-        var drop_fn_name = compressor.option("keep_fnames") ? return_false : compressor.option("ie8") ? function(def) {
-            return !compressor.exposed(def) && def.references.length == def.replaced;
-        } : function(def) {
-            if (!(def.id in in_use_ids)) return true;
-            if (def.orig.length < 2) return false;
-            // function argument will always overshadow its name
-            if (def.orig[1] instanceof AST_SymbolFunarg) return true;
-            // retain if referenced within destructured object of argument
-            return all(def.references, function(ref) {
-                return !ref.in_arg;
-            });
-        };
         // pass 3: we should drop declarations not in_use
         var trim_defns = [];
         var unused_fn_names = [];
diff --git a/test/compress/ie8.js b/test/compress/ie8.js
index 23532968..3221c92a 100644
--- a/test/compress/ie8.js
+++ b/test/compress/ie8.js
@@ -2947,3 +2947,53 @@ issue_4729: {
     }
     expect_stdout: "PASS"
 }
+
+issue_4928_1: {
+    options = {
+        ie8: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = function f() {
+            f(a);
+        };
+        console.log(typeof f);
+    }
+    expect: {
+        var a = function f() {
+            f(a);
+        };
+        console.log(typeof f);
+    }
+    expect_stdout: "undefined"
+}
+
+issue_4928_2: {
+    options = {
+        ie8: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        switch (42) {
+          case console:
+            var a = function f() {
+                f(a);
+            };
+          case 42:
+            var a = console.log("PASS");
+        }
+    }
+    expect: {
+        switch (42) {
+          case console:
+            var a = function f() {
+                f(a);
+            };
+          case 42:
+            a = console.log("PASS");
+        }
+    }
+    expect_stdout: "PASS"
+}
diff --git a/test/compress/optional-chains.js b/test/compress/optional-chains.js
index 43033c92..7f61263c 100644
--- a/test/compress/optional-chains.js
+++ b/test/compress/optional-chains.js
@@ -253,3 +253,25 @@ issue_4906: {
     expect_stdout: "PASS"
     node_version: ">=14"
 }
+
+issue_4928: {
+    options = {
+        ie8: true,
+        toplevel: true,
+        unused: true,
+    }
+    input: {
+        var a = a?.[function f() {
+            f(a);
+        }];
+        console.log(typeof f);
+    }
+    expect: {
+        var a = a?.[function f() {
+            f(a);
+        }];
+        console.log(typeof f);
+    }
+    expect_stdout: "undefined"
+    node_version: ">=14"
+}