linkchecker: add a reminder on broken links to add new/renamed pages to SUMMARY.md for mdBooks

Author: jieyouxu

src/tools/linkchecker/main.rs

@@ -100,6 +100,7 @@ fn main() {
 links_ignored_external:0,
 links_ignored_exception:0,
 intra_doc_exceptions:0,
+has_broken_urls:false,
 };
  checker.walk(&docs,&mut report);
  report.report();
@@ -116,6 +117,8 @@ struct Checker {
 
 structReport{
 errors:u32,
+// Used to provide help message to remind the user to register a page in `SUMMARY.md`.
+has_broken_urls:bool,
 start:Instant,
 html_files:u32,
 html_redirects:u32,
@@ -274,6 +277,7 @@ impl Checker {
  report.links_ignored_exception += 1;
 }else{
  report.errors += 1;
+ report.has_broken_urls = true;
 println!("{}:{}: broken link - `{}`", pretty_path, i, target_pretty_path);
 }
 return;
@@ -438,6 +442,13 @@ impl Report {
 println!("number of links ignored due to exceptions: {}",self.links_ignored_exception);
 println!("number of intra doc links ignored: {}",self.intra_doc_exceptions);
 println!("errors found: {}",self.errors);
+
+ifself.has_broken_urls{
+eprintln!(
+"NOTE: if you are adding or renaming a markdown file in a mdBook, don't forget to \
+ register the page in SUMMARY.md"
+);
+}
 }
 }