Fix dictify_CPPDEFINES exeception

In converting CPPDEFINES to a dict, if an element is a single-item
sequence c, it would take an IndexError trying to access c[1]. This
could happen if AppendUnique has been called as it converts to tuples.

Fixes #4108

Signed-off-by: Mats Wichmann <mats@linux.com>

2 files changed, 19 insertions, 2 deletions

diff --git a/SCons/Scanner/C.py b/SCons/Scanner/C.py
index 8506fe6..a066104 100644
--- a/SCons/Scanner/C.py
+++ b/SCons/Scanner/C.py
@@ -61,7 +61,8 @@ class SConsCPPScanner(SCons.cpp.PreProcessor):
             self.missing.append((file, self.current_file))
             return ''
 
-def dictify_CPPDEFINES(env):
+def dictify_CPPDEFINES(env) -> dict:
+    """Returns CPPDEFINES converted to a dict."""
     cppdefines = env.get('CPPDEFINES', {})
     if cppdefines is None:
         return {}
@@ -69,7 +70,11 @@ def dictify_CPPDEFINES(env):
         result = {}
         for c in cppdefines:
             if SCons.Util.is_Sequence(c):
-                result[c[0]] = c[1]
+                try:
+                    result[c[0]] = c[1]
+                except IndexError:
+                    # it could be a one-item sequence
+                    result[c[0]] = None
             else:
                 result[c] = None
         return result
diff --git a/SCons/Scanner/CTests.py b/SCons/Scanner/CTests.py
index 67ff312..14e156e 100644
--- a/SCons/Scanner/CTests.py
+++ b/SCons/Scanner/CTests.py
@@ -490,6 +490,17 @@ class CConditionalScannerTestCase3(unittest.TestCase):
         headers = ['d1/f1.h']
         deps_match(self, deps, headers)
 
+class dictify_CPPDEFINESTestCase(unittest.TestCase):
+    def runTest(self):
+        """Make sure single-item tuples convert correctly.
+
+        This is a regression test: AppendUnique turns sequences into
+        lists of tuples, and dictify could gack on these.
+        """
+        env = DummyEnvironment(CPPDEFINES=(("VALUED_DEFINE", 1), ("UNVALUED_DEFINE", )))
+        d = SCons.Scanner.C.dictify_CPPDEFINES(env)
+        expect = {'VALUED_DEFINE': 1, 'UNVALUED_DEFINE': None}
+        assert d == expect
 
 def suite():
     suite = unittest.TestSuite()
@@ -510,6 +521,7 @@ def suite():
     suite.addTest(CConditionalScannerTestCase1())
     suite.addTest(CConditionalScannerTestCase2())
     suite.addTest(CConditionalScannerTestCase3())
+    suite.addTest(dictify_CPPDEFINESTestCase())
     return suite
 
 if __name__ == "__main__":