GN: Trim newlines in markdown help blocks

tools/gn/standard_out.cc

 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "tools/gn/standard_out.h"
 
 #include <stddef.h>
 
 #include <vector>
 
@@ skipping 233 matching lines @@
   }
 
   OutputString(line.substr(first_normal) + "\n");
 }
 
 void PrintLongHelp(const std::string& text, const std::string& tag) {
   EnsureInitialized();
 
   bool first_header = true;
   bool in_body = false;
+  std::size_t empty_lines = 0;
   for (const std::string& line : base::SplitString(
            text, "\n", base::KEEP_WHITESPACE, base::SPLIT_WANT_ALL)) {
     // Check for a heading line.
     if (!line.empty() && line[0] != ' ') {
+      // New paragraph, just skip any trailing empty lines.
+      empty_lines = 0;
+
       if (is_markdown) {
         // GN's block-level formatting is converted to markdown as follows:
         // * The first heading is treated as an H3.
         // * Subsequent heading are treated as H4s.
         // * Any other text is wrapped in a code block and displayed as-is.
         //
         // Span-level formatting (the decorations) is converted inside
         // OutputString().
         if (in_body) {
           OutputString("```\n\n", DECORATION_NONE);
@@ skipping 23 matching lines @@
 
       OutputString(line.substr(0, chars_to_highlight), DECORATION_YELLOW);
       OutputString(line.substr(chars_to_highlight));
       OutputString("\n");
       continue;
     } else if (is_markdown && !line.empty() && !in_body) {
       OutputString("```\n", DECORATION_NONE);
       in_body = true;
     }
 
+    // We buffer empty lines, so we can skip them if needed
+    // (i.e. new paragraph body, end of final paragraph body).
+    if (in_body && is_markdown) {
+      if (!line.empty() && empty_lines != 0) {
+        OutputString(std::string(empty_lines, '\n'));
+        empty_lines = 0;
+      } else if (line.empty()) {
+        ++empty_lines;
+        continue;
+      }
+    }
+
     // Check for a comment.
     TextDecoration dec = DECORATION_NONE;
     for (const auto& elem : line) {
       if (elem == '#' && !is_markdown) {
         // Got a comment, draw dimmed.
         dec = DECORATION_DIM;
         break;
       } else if (elem != ' ') {
         break;
       }
     }
 
     OutputString(line + "\n", dec);
   }
 
   if (is_markdown && in_body)
-    OutputString("\n```\n");
+    OutputString("```\n");
 }