Provide a Scanner hook to allow file scans to be avoided when it isn't necessary.

2 files changed, 33 insertions, 3 deletions

diff --git a/src/engine/SCons/Scanner/ScannerTests.py b/src/engine/SCons/Scanner/ScannerTests.py
index fce4078..2d0e47a 100644
--- a/src/engine/SCons/Scanner/ScannerTests.py
+++ b/src/engine/SCons/Scanner/ScannerTests.py
@@ -124,6 +124,21 @@ class ScannerHashTestCase(ScannerTestBase, unittest.TestCase):
         self.failUnless(hash(dict.keys()[0]) == hash(None),
                         "did not hash Scanner base class as expected")
 
+class ScannerCheckTestCase(unittest.TestCase):
+    "Test the Scanner.Base class __hash__() method"
+    def setUp(self):
+        self.checked = {}
+    def runTest(self):
+        def my_scan(filename, env, target, *args):
+            return []
+        def check(node, s=self):
+            s.checked[node] = 1
+            return 1
+        s = SCons.Scanner.Base(my_scan, "Check", scan_check = check)
+        scanned = s.scan('x', DummyEnvironment(), DummyTarget())
+        self.failUnless(self.checked['x'] == 1,
+                        "did not call check function")
+
 def suite():
     suite = unittest.TestSuite()
     suite.addTest(ScannerPositionalTestCase())
@@ -131,6 +146,7 @@ def suite():
     suite.addTest(ScannerPositionalArgumentTestCase())
     suite.addTest(ScannerKeywordArgumentTestCase())
     suite.addTest(ScannerHashTestCase())
+    suite.addTest(ScannerCheckTestCase())
     return suite
 
 if __name__ == "__main__":
diff --git a/src/engine/SCons/Scanner/__init__.py b/src/engine/SCons/Scanner/__init__.py
index 28159c9..dc10648 100644
--- a/src/engine/SCons/Scanner/__init__.py
+++ b/src/engine/SCons/Scanner/__init__.py
@@ -52,7 +52,8 @@ class Base:
                  name = "NONE",
                  argument = _null,
                  skeys = [],
-                 node_factory = SCons.Node.FS.default_fs.File):
+                 node_factory = SCons.Node.FS.default_fs.File,
+                 scan_check = None):
         """
         Construct a new scanner object given a scanner function.
 
@@ -77,7 +78,7 @@ class Base:
         Examples:
 
         s = Scanner(my_scanner_function)
-        
+
         s = Scanner(function = my_scanner_function)
 
         s = Scanner(function = my_scanner_function, argument = 'foo')
@@ -94,6 +95,7 @@ class Base:
         self.argument = argument
         self.skeys = skeys
         self.node_factory = node_factory
+        self.scan_check = scan_check
 
     def scan(self, node, env, target):
         """
@@ -102,6 +104,8 @@ class Base:
         environment that will be passed to the scanner function. A list of
         direct dependency nodes for the specified node will be returned.
         """
+        if self.scan_check and not self.scan_check(node):
+            return []
 
         if not self.argument is _null:
             list = self.function(node, env, target, self.argument)
@@ -123,7 +127,17 @@ class Base:
     def __hash__(self):
         return hash(None)
 
-class Recursive(Base):
+class RExists(Base):
+    """
+    Scan a node only if it exists (locally or in a Repository).
+    """
+    def __init__(self, *args, **kw):
+        def rexists_check(node):
+            return node.rexists()
+        kw['scan_check'] = rexists_check
+        apply(Base.__init__, (self,) + args, kw)
+
+class Recursive(RExists):
     """
     The class for recursive dependency scanning.  This will
     re-scan any new files returned by each call to the