[clang-format] Allow short function body on a single line (#151428)

Fix #145161

Author: brandb97

clang/lib/Format/UnwrappedLineFormatter.cpp

@@ -251,10 +251,13 @@ class LineJoiner {
                 : Limit - TheLine->Last->TotalLength;
 
     if (TheLine->Last->is(TT_FunctionLBrace) &&
-        TheLine->First == TheLine->Last &&
-        !Style.BraceWrapping.SplitEmptyFunction &&
-        NextLine.First->is(tok::r_brace)) {
-      return tryMergeSimpleBlock(I, E, Limit);
+        TheLine->First == TheLine->Last) {
+      const bool EmptyFunctionBody = NextLine.First->is(tok::r_brace);
+      if ((EmptyFunctionBody && !Style.BraceWrapping.SplitEmptyFunction) ||
+          (!EmptyFunctionBody &&
+           Style.AllowShortBlocksOnASingleLine == FormatStyle::SBS_Always)) {
+        return tryMergeSimpleBlock(I, E, Limit);
+      }
     }
 
     const auto *PreviousLine = I != AnnotatedLines.begin() ? I[-1] : nullptr;

clang/unittests/Format/FormatTest.cpp

@@ -14996,6 +14996,18 @@ TEST_F(FormatTest, SplitEmptyFunctionButNotRecord) {
                Style);
 }
 
+TEST_F(FormatTest, MergeShortFunctionBody) {
+  auto Style = getLLVMStyle();
+  Style.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_None;
+  Style.AllowShortBlocksOnASingleLine = FormatStyle::SBS_Always;
+  Style.BreakBeforeBraces = FormatStyle::BS_Custom;
+  Style.BraceWrapping.AfterFunction = true;
+
+  verifyFormat("int foo()\n"
+               "{ return 1; }",
+               Style);
+}
+
 TEST_F(FormatTest, KeepShortFunctionAfterPPElse) {
   FormatStyle Style = getLLVMStyle();
   Style.AllowShortFunctionsOnASingleLine = FormatStyle::SFS_All;