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-rw-r--r--scons/source_list.py5
1 files changed, 4 insertions, 1 deletions
diff --git a/scons/source_list.py b/scons/source_list.py
index 1d5166ba1fe..8111f43184f 100644
--- a/scons/source_list.py
+++ b/scons/source_list.py
@@ -63,7 +63,7 @@ class SourceListParser(object):
self._error('not a variable definition')
if op_pos > 0:
- if line[op_pos - 1] in [':', '+']:
+ if line[op_pos - 1] in [':', '+', '?']:
op_pos -= 1
else:
self._error('only =, :=, and += are supported')
@@ -77,6 +77,9 @@ class SourceListParser(object):
self.symbol_table[sym] = val
elif op == '+=':
self.symbol_table[sym] += ' ' + val
+ elif op == '?=':
+ if sym not in self.symbol_table:
+ self.symbol_table[sym] = val
def _parse_line(self, line):
"""Parse a source list line."""