enhance `if_return` (#2703)

2 files changed, 86 insertions, 14 deletions

diff --git a/lib/compress.js b/lib/compress.js
index 203c1443..5da07f71 100644
--- a/lib/compress.js
+++ b/lib/compress.js
@@ -1343,12 +1343,13 @@ merge(Compressor.prototype, {
             var in_lambda = self instanceof AST_Lambda;
             for (var i = statements.length; --i >= 0;) {
                 var stat = statements[i];
-                var next = statements[i + 1];
+                var j = next_index(i);
+                var next = statements[j];
 
                 if (in_lambda && !next && stat instanceof AST_Return) {
                     if (!stat.value) {
                         CHANGED = true;
-                        statements.length--;
+                        statements.splice(i, 1);
                         continue;
                     }
                     if (stat.value instanceof AST_UnaryPrefix && stat.value.operator == "void") {
@@ -1418,7 +1419,8 @@ merge(Compressor.prototype, {
                         CHANGED = true;
                         stat = stat.clone();
                         stat.alternative = next;
-                        statements.splice(i, 2, stat.transform(compressor));
+                        statements.splice(i, 1, stat.transform(compressor));
+                        statements.splice(j, 1);
                         continue;
                     }
                     //---
@@ -1430,7 +1432,8 @@ merge(Compressor.prototype, {
                         stat.alternative = next || make_node(AST_Return, stat, {
                             value: null
                         });
-                        statements.splice(i, next ? 2 : 1, stat.transform(compressor));
+                        statements.splice(i, 1, stat.transform(compressor));
+                        if (next) statements.splice(j, 1);
                         continue;
                     }
                     //---
@@ -1439,10 +1442,10 @@ merge(Compressor.prototype, {
                     // if sequences is not enabled, this can lead to an endless loop (issue #866).
                     // however, with sequences on this helps producing slightly better output for
                     // the example code.
-                    var prev = statements[i - 1];
+                    var prev = statements[prev_index(i)];
                     if (compressor.option("sequences") && in_lambda && !stat.alternative
                         && prev instanceof AST_If && prev.body instanceof AST_Return
-                        && i + 2 == statements.length && next instanceof AST_SimpleStatement) {
+                        && next_index(j) == statements.length && next instanceof AST_SimpleStatement) {
                         CHANGED = true;
                         stat = stat.clone();
                         stat.alternative = make_node(AST_BlockStatement, next, {
@@ -1453,7 +1456,8 @@ merge(Compressor.prototype, {
                                 })
                             ]
                         });
-                        statements.splice(i, 2, stat.transform(compressor));
+                        statements.splice(i, 1, stat.transform(compressor));
+                        statements.splice(j, 1);
                         continue;
                     }
                 }
@@ -1503,6 +1507,26 @@ merge(Compressor.prototype, {
                 }
                 return body;
             }
+
+            function next_index(i) {
+                for (var j = i + 1, len = statements.length; j < len; j++) {
+                    var stat = statements[j];
+                    if (!(stat instanceof AST_Definitions && declarations_only(stat))) {
+                        break;
+                    }
+                }
+                return j;
+            }
+
+            function prev_index(i) {
+                for (var j = i; --j >= 0;) {
+                    var stat = statements[j];
+                    if (!(stat instanceof AST_Definitions && declarations_only(stat))) {
+                        break;
+                    }
+                }
+                return j;
+            }
         }
 
         function eliminate_dead_code(statements, compressor) {
@@ -1575,19 +1599,17 @@ merge(Compressor.prototype, {
 
         function to_simple_statement(block, decls) {
             if (!(block instanceof AST_BlockStatement)) return block;
-            var defs = [];
             var stat = null;
             for (var i = 0, len = block.body.length; i < len; i++) {
                 var line = block.body[i];
                 if (line instanceof AST_Definitions && declarations_only(line)) {
-                    defs.push(line);
+                    decls.push(line);
                 } else if (stat) {
                     return false;
                 } else {
                     stat = line;
                 }
             }
-            [].push.apply(decls, defs);
             return stat;
         }
 
@@ -1599,7 +1621,7 @@ merge(Compressor.prototype, {
                 return make_sequence(left, [ left, right ]).transform(compressor);
             };
             var n = 0, prev;
-            for (var i = 0, len = statements.length; i < len; i++) {
+            for (var i = 0; i < statements.length; i++) {
                 var stat = statements[i];
                 if (prev) {
                     if (stat instanceof AST_For && !(stat.init instanceof AST_Definitions)) {
@@ -1641,15 +1663,19 @@ merge(Compressor.prototype, {
                     var body = to_simple_statement(stat.body, decls);
                     var alt = to_simple_statement(stat.alternative, decls);
                     if (body !== false && alt !== false && decls.length > 0) {
+                        var len = decls.length;
                         decls.push(make_node(AST_If, stat, {
                             condition: stat.condition,
                             body: body || make_node(AST_EmptyStatement, stat.body),
                             alternative: alt
                         }));
-                        stat = make_node(AST_BlockStatement, stat, {
-                            body: decls
-                        });
+                        decls.unshift(n, 1);
+                        [].splice.apply(statements, decls);
+                        i += len;
+                        n += len + 1;
+                        prev = null;
                         CHANGED = true;
+                        continue;
                     }
                 }
                 statements[n++] = stat;
diff --git a/test/compress/if_return.js b/test/compress/if_return.js
index 72b69e70..a0dfdc9a 100644
--- a/test/compress/if_return.js
+++ b/test/compress/if_return.js
@@ -326,3 +326,49 @@ issue_512: {
         }
     }
 }
+
+if_var_return: {
+    options = {
+        conditionals: true,
+        if_return: true,
+        join_vars: true,
+        sequences: true,
+    }
+    input: {
+        function f() {
+            var a;
+            return;
+            var b;
+        }
+        function g() {
+            var a;
+            if (u()) {
+                var b;
+                return v();
+                var c;
+            }
+            var d;
+            if (w()) {
+                var e;
+                return x();
+                var f;
+            } else {
+                var g;
+                y();
+                var h;
+            }
+            var i;
+            z();
+            var j;
+        }
+    }
+    expect: {
+        function f() {
+            var a, b;
+        }
+        function g() {
+            var a, b, c, d, e, f, g, h, i, j;
+            return u() ? v() : w() ? x() : (y(), z(), void 0);
+        }
+    }
+}