clang-format: Improve <<-formatting.

This fixes a regression caused by r186115.

Before:
  Diag(aaaaaaaaaaaaaaaaaaaaaaaaaaaaa,
       bbbbbbbbb) << aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
                  << aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa;

After:
  Diag(aaaaaaaaaaaaaaaaaaaaaaaaaaaaa, bbbbbbbbb)
      << aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
      << aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa;

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186164 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Format/Format.cpp

@@ -1174,6 +1174,11 @@ private:
         State.Stack.back().BreakBeforeParameter)
       return true;
 
+    // Same as above, but for the first "<<" operator.
+    if (Current.is(tok::lessless) && State.Stack.back().BreakBeforeParameter &&
+        State.Stack.back().FirstLessLess == 0)
+      return true;
+
     // FIXME: Comparing LongestObjCSelectorName to 0 is a hacky way of finding
     // out whether it is the first parameter. Clean this up.
     if (Current.Type == TT_ObjCSelectorName &&

unittests/Format/FormatTest.cpp

@@ -3026,6 +3026,11 @@ TEST_F(FormatTest, AlignsPipes) {
                "             << aaaaaaaaaaaaaaaaaaaaaaaaaaaa;",
                getLLVMStyleWithColumns(70));
 
+  // But sometimes, breaking before the first "<<" is necessary.
+  verifyFormat("Diag(aaaaaaaaaaaaaaaaaaaaaaaaaaaaa, bbbbbbbbb)\n"
+               "    << aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\n"
+               "    << aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa;");
+
   verifyFormat(
       "llvm::errs() << aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa\n"
       "                    .aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa();");