releasenotes: display release notes when no filename is specified

If the filename is not specified while using --rev, the notes for the specified
revs will just be displayed on screen.

Differential Revision: https://phab.mercurial-scm.org/D877

hgext/releasenotes.py

@@ -576,6 +576,9 b' def releasenotes(ui, repo, file_=None, *'
 
     incoming = parsenotesfromrevisions(repo, sections.names(), revs)
 
+    if file_ is None:
+        return ui.write(serializenotes(sections, incoming))
+
     try:
         with open(file_, 'rb') as fh:
             notes = parsereleasenotesfile(sections, fh.read())

tests/test-releasenotes-formatting.t

@@ -434,3 +434,26 b' Raise error on simultaneous usage of fla'
   $ hg releasenotes -l -c
   abort: cannot use both '--list' and '--check'
   [255]
+
+Display release notes for specified revs if no file is mentioned
+
+  $ hg init relnotes-nofile
+  $ cd relnotes-nofile
+
+  $ touch fix1
+  $ hg -q commit -A -l - << EOF
+  > commit 1
+  > 
+  > .. fix:: Title of First Fix
+  > 
+  >    First paragraph of fix 1.
+  > EOF
+
+  $ hg releasenote -r .
+  Bug Fixes
+  =========
+  
+  Title of First Fix
+  ------------------
+  
+  First paragraph of fix 1.