[clang-format] Merge inline short functions for BS_Whitesmiths (llvm#134473)

Fix llvm#126747

Author: owenca

clang/lib/Format/UnwrappedLineFormatter.cpp

@@ -316,8 +316,13 @@ class LineJoiner {
           const AnnotatedLine *Line = nullptr;
           for (auto J = I - 1; J >= AnnotatedLines.begin(); --J) {
             assert(*J);
-            if (!(*J)->InPPDirective && !(*J)->isComment() &&
-                (*J)->Level < TheLine->Level) {
+            if ((*J)->InPPDirective || (*J)->isComment() ||
+                (*J)->Level > TheLine->Level) {
+              continue;
+            }
+            if ((*J)->Level < TheLine->Level ||
+                (Style.BreakBeforeBraces == FormatStyle::BS_Whitesmiths &&
+                 (*J)->First->is(tok::l_brace))) {
               Line = *J;
               break;
             }

clang/unittests/Format/FormatTest.cpp

@@ -15142,6 +15142,13 @@ TEST_F(FormatTest, PullInlineOnlyFunctionDefinitionsIntoSingleLine) {
                "}",
                MergeInlineOnly);
 
+  MergeInlineOnly.BreakBeforeBraces = FormatStyle::BS_Whitesmiths;
+  verifyFormat("class Foo\n"
+               "  {\n"
+               "  void f() { foo(); }\n"
+               "  };",
+               MergeInlineOnly);
+
   // Also verify behavior when BraceWrapping.AfterFunction = true
   MergeInlineOnly.BreakBeforeBraces = FormatStyle::BS_Custom;
   MergeInlineOnly.BraceWrapping.AfterFunction = true;