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

[via cfe-commits]

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

>From fe22ab60bdf87e46f504e850d9b5417983c571b0 Mon Sep 17 00:00:00 2001
From: Gautam Neelakantan Sankar <gautam.neelakantan.sankar at gmail.com>
Date: Mon, 29 Jun 2026 15:08:44 +0900
Subject: [PATCH] [clang-format] Respect definition separators when
 MaxEmptyLinesToKeep: 0

---
 clang/lib/Format/UnwrappedLineFormatter.cpp   | 12 +++++--
 .../Format/DefinitionBlockSeparatorTest.cpp   | 31 +++++++++++++++++++
 2 files changed, 41 insertions(+), 2 deletions(-)

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..960ed5be335f9 100644
--- a/clang/unittests/Format/DefinitionBlockSeparatorTest.cpp
+++ b/clang/unittests/Format/DefinitionBlockSeparatorTest.cpp
@@ -391,6 +391,37 @@ 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;
+  Style.AllowShortFunctionsOnASingleLine = FormatStyle::ShortFunctionStyle();
+
+  constexpr StringRef Input = "int my_function(int a)\n"
+                              "\n"
+                              "{\n"
+                              "  return a;\n"
+                              "}\n"
+                              "int other_function(int a)\n"
+                              "\n"
+                              "{\n"
+                              "  return a;\n"
+                              "}\n";
+
+  constexpr StringRef Expected = "int my_function(int a)\n"
+                                 "{\n"
+                                 "  return a;\n"
+                                 "}\n"
+                                 "\n"
+                                 "int other_function(int a)\n"
+                                 "{\n"
+                                 "  return a;\n"
+                                 "}\n";
+
+  verifyFormat(Input, Style, Expected);
+}
+
 TEST_F(DefinitionBlockSeparatorTest, Never) {
   FormatStyle Style = getLLVMStyle();
   Style.SeparateDefinitionBlocks = FormatStyle::SDS_Never;