[clang] [clang-format] Respect definition separators when MaxEmptyLinesToKeep: 0 (PR #206406)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-format

Author: gautamnsankar

<details>
<summary>Changes</summary>

Fixes #<!-- -->206340.

The formatter should remove empty lines before Allman opening braces, but should preserve the required empty line between function definitions.

I have added a test case "AlwaysMaxEmptyLinesZeroAllman", and have ensured other test cases run fine along with this one.

---
Full diff: https://github.com/llvm/llvm-project/pull/206406.diff


2 Files Affected:

- (modified) clang/lib/Format/UnwrappedLineFormatter.cpp (+10-2) 
- (modified) clang/unittests/Format/DefinitionBlockSeparatorTest.cpp (+34) 


``````````diff
diff --git a/clang/lib/Format/UnwrappedLineFormatter.cpp b/clang/lib/Format/UnwrappedLineFormatter.cpp
index 7ea424349d923..e7ce95b1d5628 100644
--- a/clang/lib/Format/UnwrappedLineFormatter.cpp
+++ b/clang/lib/Format/UnwrappedLineFormatter.cpp
@@ -1633,8 +1633,16 @@ static auto computeNewlines(const AnnotatedLine &Line,
                             const SmallVectorImpl<AnnotatedLine *> &Lines,
                             const FormatStyle &Style) {
   const auto &RootToken = *Line.First;
-  auto Newlines =
-      std::min(RootToken.NewlinesBefore, Style.MaxEmptyLinesToKeep + 1);
+
+  unsigned MaxNewlines = Style.MaxEmptyLinesToKeep + 1;
+  if (Style.SeparateDefinitionBlocks == FormatStyle::SDS_Always &&
+      RootToken.NewlinesBefore > 1 && PreviousLine &&
+      !RootToken.is(tok::l_brace) && Line.MightBeFunctionDecl &&
+      Line.mightBeFunctionDefinition()) {
+    MaxNewlines = std::max(MaxNewlines, 2u);
+  }
+
+  auto Newlines = std::min(RootToken.NewlinesBefore, MaxNewlines);
   // Remove empty lines before "}" where applicable.
   if (RootToken.is(tok::r_brace) &&
       (!RootToken.Next ||
diff --git a/clang/unittests/Format/DefinitionBlockSeparatorTest.cpp b/clang/unittests/Format/DefinitionBlockSeparatorTest.cpp
index 5e4c574d68dbb..0bdfc433ceee9 100644
--- a/clang/unittests/Format/DefinitionBlockSeparatorTest.cpp
+++ b/clang/unittests/Format/DefinitionBlockSeparatorTest.cpp
@@ -391,6 +391,40 @@ TEST_F(DefinitionBlockSeparatorTest, Always) {
                Style, Prefix + Infix + Postfix);
 }
 
+TEST_F(DefinitionBlockSeparatorTest, AlwaysMaxEmptyLinesZeroAllman) {
+  FormatStyle Style = getLLVMStyle();
+  Style.BreakBeforeBraces = FormatStyle::BS_Allman;
+  Style.MaxEmptyLinesToKeep = 0;
+  Style.SeparateDefinitionBlocks = FormatStyle::SDS_Always;
+
+  constexpr StringRef Expected = "uint32_t my_function(uint32_t a1)\n"
+                                 "{\n"
+                                 "  uint32_t b = a1 + 1;\n"
+                                 "  return a1;\n"
+                                 "}\n"
+                                 "\n"
+                                 "uint32_t other_function(uint32_t a1)\n"
+                                 "{\n"
+                                 "  uint32_t b = a1 + 1;\n"
+                                 "  return a1;\n"
+                                 "}\n";
+
+  constexpr StringRef Input = "uint32_t my_function(uint32_t a1)\n"
+                              "\n"
+                              "{\n"
+                              "  uint32_t b = a1 + 1;\n"
+                              "  return a1;\n"
+                              "}\n"
+                              "uint32_t other_function(uint32_t a1)\n"
+                              "\n"
+                              "{\n"
+                              "  uint32_t b = a1 + 1;\n"
+                              "  return a1;\n"
+                              "}\n";
+
+  verifyFormat(Input, Style, Expected);
+}
+
 TEST_F(DefinitionBlockSeparatorTest, Never) {
   FormatStyle Style = getLLVMStyle();
   Style.SeparateDefinitionBlocks = FormatStyle::SDS_Never;

``````````

</details>


https://github.com/llvm/llvm-project/pull/206406