fix corner case in conditionals (#5676)

Author: alexlamsl

lib/compress.js

@@ -9722,15 +9722,16 @@ Compressor.prototype.compress = function(node) {
                 if (stat.equals(alt_stat)) {
                     body_stats.splice(body_index--, 1);
                     alt_stats.splice(alt_index--, 1);
-                    stats.unshift(stat);
+                    stats.unshift(merge_expression(stat, alt_stat));
                 } else {
                     if (!(stat instanceof AST_SimpleStatement)) break;
                     if (!(alt_stat instanceof AST_SimpleStatement)) break;
-                    var expr = stat.body.tail_node();
-                    if (!expr.equals(alt_stat.body.tail_node())) break;
+                    var expr1 = stat.body.tail_node();
+                    var expr2 = alt_stat.body.tail_node();
+                    if (!expr1.equals(expr2)) break;
                     body_index = pop_expr(body_stats, stat.body, body_index);
                     alt_index = pop_expr(alt_stats, alt_stat.body, alt_index);
-                    stats.unshift(make_node(AST_SimpleStatement, expr, { body: expr }));
+                    stats.unshift(make_node(AST_SimpleStatement, expr1, { body: merge_expression(expr1, expr2) }));
                 }
             }
             if (stats.length > 0) {

test/compress/conditionals.js

@@ -278,6 +278,36 @@ merge_tail_2: {
     ]
 }
 
+merge_tail_3: {
+    options = {
+        conditionals: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        (function(a, b) {
+            if (b = a.shift())
+                console.log(b);
+            else {
+                if (b = a.shift())
+                    while (console.log("foo"));
+                console.log(b);
+            }
+        })([ false, "bar" ]);
+    }
+    expect: {
+        (function(a, b) {
+            if (!(b = a.shift()) && (b = a.shift()))
+                while (console.log("foo"));
+            console.log(b);
+        })([ false, "bar" ]);
+    }
+    expect_stdout: [
+        "foo",
+        "bar",
+    ]
+}
+
 merge_tail_sequence_1: {
     options = {
         conditionals: true,
@@ -368,6 +398,39 @@ merge_tail_sequence_2: {
     ]
 }
 
+merge_tail_sequence_3: {
+    options = {
+        conditionals: true,
+        reduce_vars: true,
+        unused: true,
+    }
+    input: {
+        (function(a, b) {
+            if (b = a.shift())
+                console.log("foo"),
+                console.log(b);
+            else {
+                if (b = a.shift())
+                    while (console.log("bar"));
+                console.log(b);
+            }
+        })([ false, "baz" ]);
+    }
+    expect: {
+        (function(a, b) {
+            if (b = a.shift())
+                console.log("foo");
+            else if (b = a.shift())
+                while (console.log("bar"));
+            console.log(b);
+        })([ false, "baz" ]);
+    }
+    expect_stdout: [
+        "bar",
+        "baz",
+    ]
+}
+
 cond_1: {
     options = {
         conditionals: true,

test/compress/spreads.js

@@ -13,12 +13,12 @@ collapse_vars_1: {
     }
     input: {
         var a;
-        [ ...a = "PASS", "PASS"].slice();
+        [ ...a = "PASS", "PASS" ].slice();
         console.log(a);
     }
     expect: {
         var a;
-        [ ...a = "PASS", "PASS"].slice();
+        [ ...a = "PASS", "PASS" ].slice();
         console.log(a);
     }
     expect_stdout: "PASS"
@@ -33,7 +33,7 @@ collapse_vars_2: {
         var a = "FAIL";
         try {
             a = "PASS";
-            [ ...42, "PASS"].slice();
+            [ ...42, "PASS" ].slice();
         } catch (e) {
             console.log(a);
         }
@@ -42,7 +42,7 @@ collapse_vars_2: {
         var a = "FAIL";
         try {
             a = "PASS";
-            [ ...42, "PASS"].slice();
+            [ ...42, "PASS" ].slice();
         } catch (e) {
             console.log(a);
         }
@@ -58,15 +58,15 @@ collapse_vars_3: {
     input: {
         var a = "FAIL";
         try {
-            [ ...(a = "PASS", 42), "PASS"].slice();
+            [ ...(a = "PASS", 42), "PASS" ].slice();
         } catch (e) {
             console.log(a);
         }
     }
     expect: {
         var a = "FAIL";
         try {
-            [ ...(a = "PASS", 42), "PASS"].slice();
+            [ ...(a = "PASS", 42), "PASS" ].slice();
         } catch (e) {
             console.log(a);
         }