scripts/markdown-hyperlinks: prevent unwanted replacements

- don't replace @var in code spans with link to github user
- don't replace 1234567... in links with link to commit
- replace hexadecimal numbers looking like commit hashes only
  after replacing raw URIs - this together with the previous point
  prevents inadvertent replacement of long numbers in links

[skip ci]

scripts/markdown-hyperlinks.pl

@@ -17,9 +17,12 @@ my $repo = qr/ [a-zA-Z] [a-zA-Z0-9.-]* /x;
 while (<>) {
 
     # make links from @username references
-    # (except when escaped like \@foobar or `@foobar`)
-    s;(?<! \[ | \\ | \` ) \@ ($user) \b (?! \] )
-     ;[\@$1](https://github.com/$1);xg;
+    # (except when escaped like \@foobar or in code like `where !@barman! = 'Moe'`)
+    s"(?: (`++) .*? \g{-1} (*SKIP) (*FAIL) )?   # skip over code spans
+      (?<! \[ | \\ )                            # no match after [ or \
+      \@ ($user) \b
+      (?! \] )                                  # no match before ]
+     "[\@$2](https://github.com/$2)"xg;
 
     # make links from #1234 references (except when escaped like \#5)
     # we can't tell whether the number refers to an issue or a pull request,
@@ -27,11 +30,6 @@ while (<>) {
     s;(?<! \[ | \\ ) \# ([0-9]+) \b (?! \] )
      ;[\#$1](https://github.com/mapnik/mapnik/issues/$1);xg;
 
-    # make links from commit hashes
-    # (accept 7 or 9-40 hex digits, but not 8 which could be a date)
-    s;(?<! \[ | / ) \b (([0-9a-f]{7})([0-9a-f]{2,33})?) \b (?! \] )
-     ;[$2](https://github.com/mapnik/mapnik/commit/$1);xg;
-
     # make shortcut links from raw URIs (which GFM turns into proper links,
     # but doesn't contract even though it could)
     # - issues
@@ -45,5 +43,14 @@ while (<>) {
     s;(?<! \] \( ) (https://github\.com/($user/$repo)/commit/([0-9a-f]{7})[0-9a-f]{0,33}) \b
      ;[$2\@$3]($1);xg;
 
+    # make links from commit hashes
+    # (accept 7 or 9-40 hex digits, but not 8 which could be a date)
+    s"(?: (`++) .*? \g{-1} (*SKIP) (*FAIL) )?   # skip over code spans
+      (?: \[.*?\] \(.*?\)  (*SKIP) (*FAIL) )?   # skip over links
+      (?<! / )                                  # no match after /
+      \b (([0-9a-f]{7})                         # 7 digits for link text
+          ([0-9a-f]{2,33})?) \b                 # maybe 2-33 more digits
+     "[$3](https://github.com/mapnik/mapnik/commit/$2)"xg;
+
     print;
 }