[clang-format] Do not merge short case labels if followed by a block.

Do not allow short case labels on a single line if the label is followed by a
left brace.

Fixes PR38926.

llvm-svn: 342708
diff --git a/clang/unittests/Format/FormatTest.cpp b/clang/unittests/Format/FormatTest.cpp
index db2e226..dac8497 100644
--- a/clang/unittests/Format/FormatTest.cpp
+++ b/clang/unittests/Format/FormatTest.cpp
@@ -1241,6 +1241,30 @@
                    "  return false;\n"
                    "}",
                    Style));
+  Style.AllowShortCaseLabelsOnASingleLine = true;
+  Style.BreakBeforeBraces = FormatStyle::BS_Custom;
+  Style.BraceWrapping.AfterControlStatement = true;
+  EXPECT_EQ("switch (n)\n"
+            "{\n"
+            "  case 0:\n"
+            "  {\n"
+            "    return false;\n"
+            "  }\n"
+            "  default:\n"
+            "  {\n"
+            "    return true;\n"
+            "  }\n"
+            "}",
+            format("switch (n) {\n"
+                   "  case 0: {\n"
+                   "    return false;\n"
+                   "  }\n"
+                   "  default:\n"
+                   "  {\n"
+                   "    return true;\n"
+                   "  }\n"
+                   "}",
+                   Style));
 }
 
 TEST_F(FormatTest, FormatsLabels) {