clang-format: Prefer column layout if possible.

Add a severe penalty for not using column layout for braced lists. If
there are solutions with column layout, these are generally preferable
over bin-packed solutions.

Before:
  std::vector<MyValues> aaaaaaaaaaaaaaaaaaa{ aaaaaaa, aaaaaaaaaa, aaaaa,
                                             aaaaaaaaaaaaaaa, aaa, aaaaaaaaaa, a,
                                             aaaaaaaaaaaaaaaaaaaaa, aaaaaaaaaaaa,
                                             aaaaaaaaaaaaaaaaaaa +
                                                 aaaaaaaaaaaaaaaaaaa,
                                             aaaaaaa, a };
After:
  std::vector<MyValues> aaaaaaaaaaaaaaaaaaa{
    aaaaaaa,      aaaaaaaaaa,
    aaaaa,        aaaaaaaaaaaaaaa,
    aaa,          aaaaaaaaaa,
    a,            aaaaaaaaaaaaaaaaaaaaa,
    aaaaaaaaaaaa, aaaaaaaaaaaaaaaaaaa + aaaaaaaaaaaaaaaaaaa,
    aaaaaaa,      a
  };

llvm-svn: 195546

1 files changed, 4 insertions, 1 deletions

diff --git a/clang/lib/Format/FormatToken.cpp b/clang/lib/Format/FormatToken.cpp
index 8ac704a3bb6..bab2425205c 100644
--- a/clang/lib/Format/FormatToken.cpp
+++ b/clang/lib/Format/FormatToken.cpp
@@ -48,8 +48,11 @@ unsigned CommaSeparatedList::format(LineState &State,
 
   // Find the best ColumnFormat, i.e. the best number of columns to use.
   const ColumnFormat *Format = getColumnFormat(RemainingCodePoints);
+  // If no ColumnFormat can be used, the braced list would generally be
+  // bin-packed. Add a severe penalty to this so that column layouts are
+  // prefered if possible.
   if (!Format)
-    return 0;
+    return 10000;
 
   // Format the entire list.
   unsigned Penalty = 0;