Fix Bug 38926: don't merge short case labels if followed by a block

[owenpan]

Summary

https://bugs.llvm.org/show_bug.cgi?id=38926

[owenpan]

ping any review.

[owenpan]

Simplified the fix and improved the test case.

[owenpan]

This fix has become obvious, but I still prefer that it gets reviewed before I commit it.

[owenpan]

Closed by r342708.

lib/Format/UnwrappedLineFormatter.cpp

private:
 
   unsigned
   tryMergeShortCaseLabels(SmallVectorImpl<AnnotatedLine *>::const_iterator I,
                           SmallVectorImpl<AnnotatedLine *>::const_iterator E,
                           unsigned Limit) {
     if (Limit == 0 || I + 1 == E ||
         I[1]->First->isOneOf(tok::kw_case, tok::kw_default))
       return 0;
+
+    // Don't merge if a block follows the case label
+    FormatToken *Tok = I[0]->Last;
+    if (Tok->is(tok::comment))
+      Tok = Tok->getPreviousNonComment();
+    if ((Tok && Tok->is(tok::l_brace)) || I[1]->First->is(tok::l_brace))
+      return 0;
+
     unsigned NumStmts = 0;
     unsigned Length = 0;
     bool EndsWithComment = false;
     bool InPPDirective = I[0]->InPPDirective;
     const unsigned Level = I[0]->Level;
     for (; NumStmts < 3; ++NumStmts) {
       if (I + 1 + NumStmts == E)
         break;

unittests/Format/FormatTest.cpp

EXPECT_EQ("switch (n) {\n"
             "}",
             format("switch (n) {\n"
                    "default/*comments*/:\n"
                    "  return true;\n"
                    "case 0:\n"
                    "  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"
+                   "    return true;\n"
+                   "  }\n"
+                   "}",
+                   Style));
 }
 
 TEST_F(FormatTest, FormatsLabels) {
   verifyFormat("void f() {\n"
                "  some_code();\n"
                "test_label:\n"
                "  some_other_code();\n"
                "  {\n"