[clang-format] Improve UnwrappedLineParser::mightFitOnOneLine()

Account for an r_brace that precedes an "else if" statement when
calculating whether the line might fit on one line if the r_brace
is removed.

Fixes #59778.

Differential Revision: https://reviews.llvm.org/D140835

Author: owenca

Diff for: clang/lib/Format/UnwrappedLineParser.cpp

@@ -836,6 +836,11 @@ bool UnwrappedLineParser::mightFitOnOneLine(
     Length -= OpeningBrace->TokenText.size() + 1;
   }
 
+  if (const auto *FirstToken = Line.First; FirstToken->is(tok::r_brace)) {
+    assert(!OpeningBrace || OpeningBrace->is(TT_ControlStatementLBrace));
+    Length -= FirstToken->TokenText.size() + 1;
+  }
+
   Index = 0;
   for (auto &Token : Tokens) {
     const auto &SavedToken = SavedTokens[Index++];

Diff for: clang/unittests/Format/BracesRemoverTest.cpp

@@ -828,6 +828,17 @@ TEST_F(BracesRemoverTest, RemoveBraces) {
                "}",
                Style);
 
+  verifyFormat("if (foo)\n"
+               "  f();\n"
+               "else if (bar || baz)\n"
+               "  g();",
+               "if (foo) {\n"
+               "  f();\n"
+               "} else if (bar || baz) {\n"
+               "  g();\n"
+               "}",
+               Style);
+
   Style.ColumnLimit = 0;
   verifyFormat("if (a)\n"
                "  b234567890223456789032345678904234567890 = "