Index: lib/Format/TokenAnnotator.cpp
===================================================================
--- lib/Format/TokenAnnotator.cpp
+++ lib/Format/TokenAnnotator.cpp
@@ -432,6 +432,10 @@
       } else if (CurrentToken->is(tok::r_square) && Parent &&
                  Parent->is(TT_TemplateCloser)) {
         Left->Type = TT_ArraySubscriptLSquare;
+      } else if (Style.Language == FormatStyle::LK_TableGen) {
+        // TableGen treats '[' as array subscripts to avoid spaces, e.g.
+        // def foo : Flag<["-", "--"], "foo">;
+        Left->Type = TT_ArraySubscriptLSquare;
       } else if (Style.Language == FormatStyle::LK_Proto ||
                  Style.Language == FormatStyle::LK_TextProto) {
         // Square braces in LK_Proto can either be message field attributes:
Index: unittests/Format/FormatTestTableGen.cpp
===================================================================
--- unittests/Format/FormatTestTableGen.cpp
+++ unittests/Format/FormatTestTableGen.cpp
@@ -52,5 +52,9 @@
                "               \"very long help string\">;\n");
 }
 
+TEST_F(FormatTestTableGen, NoSpacesInSquareBracketLists) {
+  verifyFormat("def flag : Flag<[\"-\", \"--\"], \"foo\">;\n");
+}
+
 } // namespace format
 } // end namespace clang