clang-format: Keep empty lines and format 1-line nested blocks.

Let clang-format consistently keep up to one empty line (configured via
FormatStyle::MaxEmptyLinesToKeep) in nested blocks, e.g. lambdas. Also,
actually format single statements in nested blocks.

Before:
  DEBUG({ int     i; });
  DEBUG({
    int i;
    // an empty line here would just be removed.
    int j;
  });

After:
  DEBUG({ int i; });
  DEBUG({
    int i;

    int j;
  });

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190278 91177308-0d34-0410-b5e6-96231b3b80d8

Author: djasper-gh

lib/Format/Format.cpp

@@ -530,10 +530,14 @@ class UnwrappedLineFormatter {
            I != E; ++I) {
         unsigned Indent =
             ParentIndent + ((*I)->Level - Line.Level) * Style.IndentWidth;
-        if (!DryRun)
+        if (!DryRun) {
+          unsigned Newlines = std::min((*I)->First->NewlinesBefore,
+                                       Style.MaxEmptyLinesToKeep + 1);
+          Newlines = std::max(1u, Newlines);
           Whitespaces->replaceWhitespace(
-              *(*I)->First, /*Newlines=*/1, /*Spaces=*/Indent,
+              *(*I)->First, Newlines, /*Spaces=*/Indent,
               /*StartOfTokenColumn=*/Indent, Line.InPPDirective);
+        }
         UnwrappedLineFormatter Formatter(Indenter, Whitespaces, Style, **I);
         Penalty += Formatter.format(Indent, DryRun);
       }
@@ -552,6 +556,9 @@ class UnwrappedLineFormatter {
                                      /*Newlines=*/0, /*Spaces=*/1,
                                      /*StartOfTokenColumn=*/State.Column,
                                      State.Line->InPPDirective);
+      UnwrappedLineFormatter Formatter(Indenter, Whitespaces, Style,
+                                       *LBrace.Children[0]);
+      Penalty += Formatter.format(State.Column + 1, DryRun);
     }
 
     State.Column += 1 + LBrace.Children[0]->Last->TotalLength;

unittests/Format/FormatTest.cpp

@@ -2276,6 +2276,19 @@ TEST_F(FormatTest, LayoutNestedBlocks) {
                    "  somethingElse();\n"
                    "});",
                    getLLVMStyleWithColumns(29)));
+  EXPECT_EQ("DEBUG({ int i; });", format("DEBUG({ int   i; });"));
+  EXPECT_EQ("DEBUG({\n"
+            "  int i;\n"
+            "\n"
+            "  // comment\n"
+            "  int j;\n"
+            "});",
+            format("DEBUG({\n"
+                   "  int  i;\n"
+                   "\n"
+                   "  // comment\n"
+                   "  int  j;\n"
+                   "});"));
 }
 
 TEST_F(FormatTest, PutEmptyBlocksIntoOneLine) {
@@ -6395,7 +6408,7 @@ TEST_F(FormatTest, FormatsLambdas) {
   verifyFormat("auto c = { [&a, &a, a] {\n"
                "  [=, a, b, &c] { return b++; }();\n"
                "} }\n");
-  verifyFormat("auto c = { [&a, &a, a] { [=, a, b, &c] { }(); } }\n");
+  verifyFormat("auto c = { [&a, &a, a] { [=, a, b, &c] {}(); } }\n");
   verifyFormat("void f() {\n"
                "  other(x.begin(), x.end(), [&](int, int) { return 1; });\n"
                "}\n");