[clang-format] Don't insert braces for loops with a null statement

[owenpan]

Summary

This is a workaround for https://github.com/llvm/llvm-project/issues/57539.

Fixes https://github.com/llvm/llvm-project/issues/57509.

[MyDeveloperDay]

Can't tell you how much I love this InsertBraces feature @owenpan, I work for a team (with a large code base) that uses them all the time, and we are catching missing braces in decade-old code! Thank you

[owenpan]

In D133635#3782222, @MyDeveloperDay wrote:

Can't tell you how much I love this InsertBraces feature @owenpan, I work for a team (with a large code base) that uses them all the time, and we are catching missing braces in decade-old code! Thank you

Glad to hear that InsertBraces is useful in the real world!

[sstwcw]

clang/unittests/Format/FormatTest.cpp

25370

Can you confirm that there is supposed to be only one space here while there are two in the next test? messUp turns two spaces into one space. The formatter doesn't change things inside the #if 0 block, both before and after D133647.

[owenpan]

clang/unittests/Format/FormatTest.cpp

25370

Good catch. Can you delete this line and line 25383 below when rebasing and updating D133647?

25383

Delete this line when landing D133647.

clang/lib/Format/UnwrappedLineParser.cpp

static FormatToken *getLastNonComment(const UnwrappedLine &Line) {
 
   return nullptr;
 }
 
 void UnwrappedLineParser::parseUnbracedBody(bool CheckEOF) {
   FormatToken *Tok = nullptr;
 
   if (Style.InsertBraces && !Line->InPPDirective && !Line->Tokens.empty() &&
-      PreprocessorDirectives.empty()) {
-    assert(!Line->Tokens.empty());
+      PreprocessorDirectives.empty() && FormatTok->isNot(tok::semi)) {
     Tok = Style.BraceWrapping.AfterControlStatement == FormatStyle::BWACS_Never
               ? getLastNonComment(*Line)
               : Line->Tokens.back().Tok;
     assert(Tok);
     if (Tok->BraceCount < 0) {
       assert(Tok->BraceCount == -1);
       Tok = nullptr;
     } else {

clang/unittests/Format/FormatTest.cpp

verifyFormat("#if 0\n"
                "#if 0\n"
                "#elif 1\n"
                "#endif\n"
                "void f() {\n"
                "  if (a) g();\n"
                "}",
                Style);
 
+  verifyFormat("do {\n"
+               "#if 0\n"
+               " if (a) {\n"
+               "#else\n"
+               "  if (b) {\n"
+               "#endif\n"
+               "}\n"
+               "}\n"
+               "while (0)\n"
+               "  ;",
+               Style);
+  // TODO: Replace the test above with the one below after #57539 is fixed.
+#if 0
+  verifyFormat("do {\n"
+               "#if 0\n"
+               "  if (a) {\n"
+               "#else\n"
+               "  if (b) {\n"
+               "#endif\n"
+               "  }\n"
+               "} while (0);",
+               Style);
+#endif
+
   Style.ColumnLimit = 15;
 
   verifyFormat("#define A     \\\n"
                "  if (a)      \\\n"
                "    f();",
                Style);
 
   verifyFormat("if (a + b >\n"