Fix stack trace when there's no scanner in an Environment.

2 files changed, 8 insertions, 4 deletions

diff --git a/src/engine/SCons/Environment.py b/src/engine/SCons/Environment.py
index 10787a7..2f11f06 100644
--- a/src/engine/SCons/Environment.py
+++ b/src/engine/SCons/Environment.py
@@ -569,12 +569,10 @@ class Base(SubstitutionEnvironment):
         
     def get_scanner(self, skey):
         """Find the appropriate scanner given a key (usually a file suffix).
-        __cacheable__
         """
         sm = self._gsm()
-        if sm.has_key(skey):
-            return sm[skey]
-        return None
+        try: return sm[skey]
+        except (KeyError, TypeError): return None
 
     def _smd(self):
         "__reset_cache__"
diff --git a/src/engine/SCons/EnvironmentTests.py b/src/engine/SCons/EnvironmentTests.py
index bfd1262..1772407 100644
--- a/src/engine/SCons/EnvironmentTests.py
+++ b/src/engine/SCons/EnvironmentTests.py
@@ -708,6 +708,12 @@ class BaseTestCase(unittest.TestCase):
 
         suffixes = [".c", ".cc", ".cxx", ".m4", ".m5"]
 
+        env = Environment()
+        try: del env['SCANNERS']
+        except KeyError: pass
+        s = map(env.get_scanner, suffixes)
+        assert s == [None, None, None, None, None], s
+
         env = Environment(SCANNERS = [])
         s = map(env.get_scanner, suffixes)
         assert s == [None, None, None, None, None], s