1 files changed, 32 insertions, 5 deletions
diff --git a/SCons/Scanner/C.py b/SCons/Scanner/C.py
index 418454ff6..31ab7e62e 100644
--- a/SCons/Scanner/C.py
+++ b/SCons/Scanner/C.py
@@ -21,7 +21,12 @@
 # OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
 # WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 
-"""Dependency scanner for C/C++ code."""
+"""Dependency scanner for C/C++ code.
+
+Two scanners are defined here: the default CScanner, and the optional
+CConditionalScanner, which must be explicitly selected by calling
+add_scanner() for each affected suffix.
+"""
 
 import SCons.Node.FS
 import SCons.cpp
@@ -62,11 +67,30 @@ class SConsCPPScanner(SCons.cpp.PreProcessor):
             return ''
 
 def dictify_CPPDEFINES(env) -> dict:
-    """Returns CPPDEFINES converted to a dict."""
+    """Returns CPPDEFINES converted to a dict.
+
+    This should be similar to :func:`~SCons.Defaults.processDefines`.
+    Unfortunately, we can't do the simple thing of calling that routine and
+    passing the result to the dict() constructor, because it turns the defines
+    into a list of "name=value" pairs, which the dict constructor won't
+    consume correctly.  Also cannot just call dict on CPPDEFINES itself - it's
+    fine if it's stored in the converted form (currently deque of tuples), but
+    CPPDEFINES could be in other formats too.
+
+    So we have to do all the work here - keep concepts in sync with
+    ``processDefines``.
+    """
     cppdefines = env.get('CPPDEFINES', {})
     result = {}
     if cppdefines is None:
         return result
+
+    if SCons.Util.is_Tuple(cppdefines):
+        try:
+            return {cppdefines[0]: cppdefines[1]}
+        except IndexError:
+            return {cppdefines[0]: None}
+
     if SCons.Util.is_Sequence(cppdefines):
         for c in cppdefines:
             if SCons.Util.is_Sequence(c):
@@ -85,15 +109,18 @@ def dictify_CPPDEFINES(env) -> dict:
                 # don't really know what to do here
                 result[c] = None
         return result
+
     if SCons.Util.is_String(cppdefines):
         try:
             name, value = cppdefines.split('=')
             return {name: value}
         except ValueError:
             return {cppdefines: None}
-    if not SCons.Util.is_Dict(cppdefines):
-        return {cppdefines: None}
-    return cppdefines
+
+    if SCons.Util.is_Dict(cppdefines):
+        return cppdefines
+
+    return {cppdefines: None}
 
 class SConsCPPScannerWrapper:
     """The SCons wrapper around a cpp.py scanner.