Bug 774032 part 1 - Avoid Preprocessor.py replacing undefined variables with the attemptSubstitution filter. r=ted

config/Preprocessor.py

@@ -392,7 +392,7 @@ class Preprocessor:
         return str(self.context[varname])
       if fatal:
         raise Preprocessor.Error(self, 'UNDEFINED_VAR', varname)
-      return ''
+      return matchobj.group(0)
     return self.varsubst.sub(repl, aLine)
   def filter_attemptSubstitution(self, aLine):
     return self.filter_substitution(aLine, fatal=False)

config/tests/unit-Preprocessor.py

@@ -172,11 +172,11 @@ BAR
   
   def test_filter_attemptSubstitution(self):
     f = NamedIO('filter_attemptSubstitution.in', '''#filter attemptSubstitution
-P@VAR@ASS
+@PASS@
 #unfilter attemptSubstitution
 ''')
     self.pp.do_include(f)
-    self.assertEqual(self.pp.out.getvalue(), "PASS\n")
+    self.assertEqual(self.pp.out.getvalue(), "@PASS@\n")
   
   def test_filter_emptyLines(self):
     f = NamedIO('filter_emptyLines.in', '''lines with a

js/src/config/Preprocessor.py

@@ -392,7 +392,7 @@ class Preprocessor:
         return str(self.context[varname])
       if fatal:
         raise Preprocessor.Error(self, 'UNDEFINED_VAR', varname)
-      return ''
+      return matchobj.group(0)
     return self.varsubst.sub(repl, aLine)
   def filter_attemptSubstitution(self, aLine):
     return self.filter_substitution(aLine, fatal=False)