fix corner case in conditionals & if_return (#5685)

fixes #5684

Author: alexlamsl

Diff for: lib/compress.js

@@ -3529,15 +3529,15 @@ Compressor.prototype.compress = function(node) {
             var declare_only, jump, merge_jump;
             var in_iife = in_lambda && parent && parent.TYPE == "Call" && parent.expression === self;
             var chain_if_returns = in_lambda && compressor.option("conditionals") && compressor.option("sequences");
+            var drop_return_void = !(in_try && in_try.bfinally && in_async_generator(in_lambda));
             var multiple_if_returns = has_multiple_if_returns(statements);
             for (var i = statements.length; --i >= 0;) {
                 var stat = statements[i];
                 var j = next_index(i);
                 var next = statements[j];
 
                 if (in_lambda && declare_only && !next && stat instanceof AST_Return
-                    && !(self instanceof AST_SwitchBranch)
-                    && !(in_try && in_try.bfinally && in_async_generator(in_lambda))) {
+                    && drop_return_void && !(self instanceof AST_SwitchBranch)) {
                     var body = stat.value;
                     if (!body) {
                         changed = true;
@@ -3633,7 +3633,7 @@ Compressor.prototype.compress = function(node) {
                     var in_bool = stat.body.in_bool || next instanceof AST_Return && next.in_bool;
                     // if (foo()) return x; return y; ---> return foo() ? x : y;
                     if (!stat.alternative && next instanceof AST_Return
-                        && (!value == !next.value || !in_async_generator(in_lambda))) {
+                        && (drop_return_void || !value == !next.value)) {
                         changed = true;
                         stat = stat.clone();
                         stat.alternative = make_node(AST_BlockStatement, next, {
@@ -9686,7 +9686,7 @@ Compressor.prototype.compress = function(node) {
                     self.body,
                 ],
             }).optimize(compressor);
-            if (cons_value && alt_value || !in_async_generator(compressor.find_parent(AST_Scope))) {
+            if (cons_value && alt_value || !keep_return_void()) {
                 var exit = make_node(self.body.CTOR, self, {
                     value: make_node(AST_Conditional, self, {
                         condition: self.condition,
@@ -9762,6 +9762,22 @@ Compressor.prototype.compress = function(node) {
             return node instanceof AST_BlockStatement ? node.body : [ node ];
         }
 
+        function keep_return_void() {
+            var has_finally = false, level = 0, node = compressor.self();
+            do {
+                if (node instanceof AST_Catch) {
+                    if (compressor.parent(level).bfinally) has_finally = true;
+                    level++;
+                } else if (node instanceof AST_Finally) {
+                    level++;
+                } else if (node instanceof AST_Scope) {
+                    return has_finally && in_async_generator(node);
+                } else if (node instanceof AST_Try) {
+                    if (node.bfinally) has_finally = true;
+                }
+            } while (node = compressor.parent(level++));
+        }
+
         function last_index(stats) {
             for (var index = stats.length; --index >= 0;) {
                 if (!is_declaration(stats[index], true)) break;

Diff for: test/compress/yields.js

@@ -1989,3 +1989,32 @@ issue_5679_6: {
     expect_stdout: "PASS"
     node_version: ">=10"
 }
+
+issue_5684: {
+    options = {
+        conditionals: true,
+        if_return: true,
+    }
+    input: {
+        (async function*() {
+            switch (42) {
+              default:
+                if (console.log("PASS"))
+                    return;
+                return null;
+              case false:
+            }
+        })().next();
+    }
+    expect: {
+        (async function*() {
+            switch (42) {
+              default:
+                return console.log("PASS") ? void 0 : null;
+              case false:
+            }
+        })().next();
+    }
+    expect_stdout: "PASS"
+    node_version: ">=10"
+}