# HG changeset patch
# User Matt Mackall <mpm@selenic.com>
# Date 2012-04-17 16:11:59
# Node ID 154219f3a6a40b9596e4f3e36d5f1a89180559f2
# Parent  92c7e917b647768b23ba6554af44ed0e74b28925

opener: introduce tryread helper

This makes it easier to follow the common pattern "read a file or give
an empty string if it's missing".

diff --git a/mercurial/scmutil.py b/mercurial/scmutil.py
--- a/mercurial/scmutil.py
+++ b/mercurial/scmutil.py
@@ -159,6 +159,15 @@ class abstractopener(object):
         '''Prevent instantiation; don't call this from subclasses.'''
         raise NotImplementedError('attempted instantiating ' + str(type(self)))
 
+    def tryread(self, path):
+        'gracefully return an empty string for missing files'
+        try:
+            return self.read(path)
+        except IOError, inst:
+            if inst.errno != errno.ENOENT:
+                raise
+        return ""
+
     def read(self, path):
         fp = self(path, 'rb')
         try: