fix corner cases in preserve_line (#3212)

lib/output.js

@@ -198,16 +198,24 @@ function OutputStream(options) {
     /* -----[ beautification/minification ]----- */
 
     var has_parens = false;
+    var line_end = 0;
+    var line_fixed = true;
     var might_need_space = false;
     var might_need_semicolon = false;
-    var might_add_newline = 0;
     var need_newline_indented = false;
     var need_space = false;
     var newline_insert = -1;
     var last = "";
     var mapping_token, mapping_name, mappings = options.source_map && [];
 
-    var do_add_mapping = mappings ? function() {
+    var adjust_mappings = mappings ? function(line, col) {
+        mappings.forEach(function(mapping) {
+            mapping.line += line;
+            mapping.col += col;
+        });
+    } : noop;
+
+    var flush_mappings = mappings ? function() {
         mappings.forEach(function(mapping) {
             try {
                 options.source_map.add(
@@ -230,31 +238,30 @@ function OutputStream(options) {
         mappings = [];
     } : noop;
 
-    var ensure_line_len = options.max_line_len ? function() {
-        if (current_col > options.max_line_len) {
-            if (might_add_newline) {
-                var left = OUTPUT.slice(0, might_add_newline);
-                var right = OUTPUT.slice(might_add_newline);
-                if (mappings) {
-                    var delta = right.length - current_col;
-                    mappings.forEach(function(mapping) {
-                        mapping.line++;
-                        mapping.col += delta;
-                    });
-                }
-                OUTPUT = left + "\n" + right;
-                current_line++;
-                current_pos++;
-                current_col = right.length;
-            }
+    function insert_newlines(count) {
+        var index = OUTPUT.lastIndexOf("\n");
+        if (line_end < index) line_end = index;
+        var left = OUTPUT.slice(0, line_end);
+        var right = OUTPUT.slice(line_end);
+        adjust_mappings(count, right.length - current_col);
+        current_line += count;
+        current_pos += count;
+        current_col = right.length;
+        OUTPUT = left;
+        while (count--) OUTPUT += "\n";
+        OUTPUT += right;
+    }
+
+    var fix_line = options.max_line_len ? function() {
+        if (line_fixed) {
             if (current_col > options.max_line_len) {
                 AST_Node.warn("Output exceeds {max_line_len} characters", options);
             }
+            return;
         }
-        if (might_add_newline) {
-            might_add_newline = 0;
-            do_add_mapping();
-        }
+        if (current_col > options.max_line_len) insert_newlines(1);
+        line_fixed = true;
+        flush_mappings();
     } : noop;
 
     var requireSemicolonChars = makePredicate("( [ + * / - , .");
@@ -286,7 +293,7 @@ function OutputStream(options) {
                     current_col++;
                     current_pos++;
                 } else {
-                    ensure_line_len();
+                    fix_line();
                     OUTPUT += "\n";
                     current_pos++;
                     current_line++;
@@ -304,18 +311,6 @@ function OutputStream(options) {
             }
         }
 
-        if (!options.beautify && options.preserve_line && stack[stack.length - 1]) {
-            var target_line = stack[stack.length - 1].start.line;
-            while (current_line < target_line) {
-                ensure_line_len();
-                OUTPUT += "\n";
-                current_pos++;
-                current_line++;
-                current_col = 0;
-                might_need_space = false;
-            }
-        }
-
         if (might_need_space) {
             if ((is_identifier_char(prev)
                     && (is_identifier_char(ch) || ch == "\\"))
@@ -337,7 +332,7 @@ function OutputStream(options) {
                 col: current_col
             });
             mapping_token = false;
-            if (!might_add_newline) do_add_mapping();
+            if (line_fixed) flush_mappings();
         }
 
         OUTPUT += str;
@@ -347,7 +342,7 @@ function OutputStream(options) {
         current_line += n;
         current_col += a[0].length;
         if (n > 0) {
-            ensure_line_len();
+            fix_line();
             current_col = a[n].length;
         }
         last = str;
@@ -374,9 +369,10 @@ function OutputStream(options) {
         return ret;
     } : function(col, cont) { return cont() };
 
-    var may_add_newline = options.max_line_len ? function() {
-        ensure_line_len();
-        might_add_newline = OUTPUT.length;
+    var may_add_newline = options.max_line_len || options.preserve_line ? function() {
+        fix_line();
+        line_end = OUTPUT.length;
+        line_fixed = false;
     } : noop;
 
     var newline = options.beautify ? function() {
@@ -455,9 +451,7 @@ function OutputStream(options) {
     } : noop;
 
     function get() {
-        if (might_add_newline) {
-            ensure_line_len();
-        }
+        if (!line_fixed) fix_line();
         return OUTPUT;
     }
 
@@ -622,7 +616,14 @@ function OutputStream(options) {
         col             : function() { return current_col },
         pos             : function() { return current_pos },
         push_node       : function(node) { stack.push(node) },
-        pop_node        : function() { return stack.pop() },
+        pop_node        : options.preserve_line ? function() {
+            var node = stack.pop();
+            if (node.start && node.start.line > current_line) {
+                insert_newlines(node.start.line - current_line);
+            }
+        } : function() {
+            stack.pop();
+        },
         parent          : function(n) {
             return stack[stack.length - 2 - (n || 0)];
         }