[clang-format] Ensure we can correctly parse lambda in the template argument list

[MyDeveloperDay]

Summary

https://github.com/llvm/llvm-project/issues/46505

The presence of a lambda in an argument template list ignored the [] as a lambda at all, this caused the contents of the <> to be incorrectly analyzed.

struct Y : X < [] {
  return 0;
} > {};

Fixes: #46505

[curdeius]

LGTM.

clang/unittests/Format/FormatTest.cpp

23171

Is this line necessary? It doesn't seem to test anything new, no?

[HazardyKnusperkeks]

clang/lib/Format/UnwrappedLineParser.cpp

2872–2874

Fewer ifs and lines.

clang/lib/Format/UnwrappedLineParser.cpp

void UnwrappedLineParser::parseRecord(bool ParseAsExpr) {
   // and class declarations).
   if (FormatTok->isOneOf(tok::colon, tok::less)) {
     while (!eof()) {
       if (FormatTok->is(tok::l_brace)) {
         calculateBraceTypes(/*ExpectClassBody=*/true);
         if (!tryToParseBracedList())
           break;
       }
+      if (FormatTok->is(tok::l_square))
+        if (!tryToParseLambda())
+          break;
       if (FormatTok->Tok.is(tok::semi))
         return;
       if (Style.isCSharp() && FormatTok->is(Keywords.kw_where)) {
         addUnwrappedLine();
         nextToken();
         parseCSharpGenericTypeConstraint();
         break;
       }

clang/unittests/Format/FormatTest.cpp

verifyFormat("try {\n"
                Style);
 
   verifyFormat("try {\n"
                "  doA();\n"
                "} catch (Exception &e) {}\n",
                Style);
 }
 
+TEST_F(FormatTest, ShortTemplatedArgumentLists) {
+  auto Style = getLLVMStyle();
+
+  verifyFormat("struct Y : X<[] { return 0; }> {};", Style);
+  verifyFormat("struct Y<[] { return 0; }> {};", Style);
+
+  verifyFormat("struct Z : X<decltype([] { return 0; }){}> {};", Style);
+  verifyFormat("template <auto> struct X {};", Style);
+}
+
 } // namespace
 } // namespace format
 } // namespace clang