fix corner case in dead_code (#5507)

fixes #5506

Author: alexlamsl

lib/compress.js

@@ -12329,7 +12329,7 @@ Compressor.prototype.compress = function(node) {
                     parent = compressor.parent(level++);
                     if (parent instanceof AST_Assign) {
                         if (parent.left instanceof AST_SymbolRef && parent.left.definition() === def) {
-                            if (in_try(level, parent)) break;
+                            if (in_try(level, parent, !local)) break;
                             return strip_assignment(def);
                         }
                         if (parent.left.match_symbol(function(node) {
@@ -12441,14 +12441,16 @@ Compressor.prototype.compress = function(node) {
             if (parent instanceof AST_Try) return parent.bfinally ? parent.bfinally === stat : parent.bcatch === stat;
         }
 
-        function in_try(level, node) {
+        function in_try(level, node, sync) {
             var right = self.right;
             self.right = make_node(AST_Null, right);
             var may_throw = node.may_throw(compressor);
             self.right = right;
             for (var parent; parent = compressor.parent(level++); node = parent) {
                 if (parent === scope) return false;
-                if (parent instanceof AST_Try) {
+                if (sync && parent instanceof AST_Lambda) {
+                    if (parent.name || is_async(parent) || is_generator(parent)) return true;
+                } else if (parent instanceof AST_Try) {
                     if (parent.bfinally && parent.bfinally !== node) return true;
                     if (may_throw && parent.bcatch && parent.bcatch !== node) return true;
                 }

test/compress/awaits.js

@@ -2982,3 +2982,27 @@ issue_5493: {
     expect_stdout: "undefined"
     node_version: ">=8"
 }
+
+issue_5506: {
+    options = {
+        dead_code: true,
+    }
+    input: {
+        console.log(function(a) {
+            (async function() {
+                a = null in (a = "PASS");
+            })();
+            return a;
+        }("FAIL"));
+    }
+    expect: {
+        console.log(function(a) {
+            (async function() {
+                a = null in (a = "PASS");
+            })();
+            return a;
+        }("FAIL"));
+    }
+    expect_stdout: "PASS"
+    node_version: ">=8"
+}

test/compress/dead-code.js

@@ -1669,3 +1669,41 @@ issue_5106_2: {
     }
     expect_stdout: "PASS"
 }
+
+issue_5506: {
+    options = {
+        dead_code: true,
+    }
+    input: {
+        try {
+            (function(a) {
+                var b = 1;
+                (function f() {
+                    try {
+                        b-- && f();
+                    } catch (c) {}
+                    console.log(a);
+                    a = 42 in (a = "bar");
+                })();
+            })("foo");
+        } catch (e) {}
+    }
+    expect: {
+        try {
+            (function(a) {
+                var b = 1;
+                (function f() {
+                    try {
+                        b-- && f();
+                    } catch (c) {}
+                    console.log(a);
+                    a = 42 in (a = "bar");
+                })();
+            })("foo");
+        } catch (e) {}
+    }
+    expect_stdout: [
+        "foo",
+        "bar",
+    ]
+}

test/compress/yields.js

@@ -1515,3 +1515,35 @@ issue_5456: {
     expect_stdout: "foo"
     node_version: ">=4"
 }
+
+issue_5506: {
+    options = {
+        dead_code: true,
+    }
+    input: {
+        console.log(function(a) {
+            var b = function*() {
+                a = null in (a = "PASS");
+            }();
+            try {
+                b.next();
+            } catch (e) {
+                return a;
+            }
+        }("FAIL"));
+    }
+    expect: {
+        console.log(function(a) {
+            var b = function*() {
+                a = null in (a = "PASS");
+            }();
+            try {
+                b.next();
+            } catch (e) {
+                return a;
+            }
+        }("FAIL"));
+    }
+    expect_stdout: "PASS"
+    node_version: ">=4"
+}