[CONSOLIDATED,PULL,03/12] oe.types: give the regex type more sane semantics

Submitted by Saul Wold on May 17, 2012, 4:51 p.m. | Patch ID: 27899


Message ID dc7e4a79d9a1884b4c5705ef3173613958204b50.1337273095.git.sgw@linux.intel.com
State New
Headers show

Commit Message

Saul Wold May 17, 2012, 4:51 p.m.
From: Christopher Larson <chris_larson@mentor.com>

Currently, if a variable is unset or has an empty value, the regex type
will return a match object which always matches. Not all variable types
will necessarily have the same behavior for handling defaults. I believe
that returning a match object which matches nothing when a variable is
unset is superior to returning one which matches anything, and the user
can always explicitly request anything via '.*', if that's what they

This constructs a null pattern object which will never match, and uses
it when encountering an unset or empty variable (currently, these two
things are one and the same, as maketype is handling the default. we may
well want to shift that logic into the individual types, giving them
more control over default behavior, but currently the behavior is at
least relatively consistent -- no difference between unset and empty

Signed-off-by: Christopher Larson <chris_larson@mentor.com>
 meta/lib/oe/types.py |   31 +++++++++++++++++++++++++++++++
 1 files changed, 31 insertions(+), 0 deletions(-)

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diff --git a/meta/lib/oe/types.py b/meta/lib/oe/types.py
index ea31cf4..ea53df9 100644
--- a/meta/lib/oe/types.py
+++ b/meta/lib/oe/types.py
@@ -40,6 +40,31 @@  def choice(value, choices):
                          (value, choices))
     return value
+class NoMatch(object):
+    """Stub python regex pattern object which never matches anything"""
+    def findall(self, string, flags=0):
+        return None
+    def finditer(self, string, flags=0):
+        return None
+    def match(self, flags=0):
+        return None
+    def search(self, string, flags=0):
+        return None
+    def split(self, string, maxsplit=0):
+        return None
+    def sub(pattern, repl, string, count=0):
+        return None
+    def subn(pattern, repl, string, count=0):
+        return None
+NoMatch = NoMatch()
 def regex(value, regexflags=None):
     """OpenEmbedded 'regex' type
@@ -59,6 +84,12 @@  def regex(value, regexflags=None):
             except AttributeError:
                 raise ValueError("Invalid regex flag '%s'" % flag)
+    if not value:
+        # Let's ensure that the default behavior for an undefined or empty
+        # variable is to match nothing. If the user explicitly wants to match
+        # anything, they can match '.*' instead.
+        return NoMatch
         return re.compile(value, flagval)
     except re.error, exc: