[clang-tidy] update FunctionSizeCheck for D56444

[aaron.ballman]

LGTM!

clang-tidy/readability/FunctionSizeCheck.cpp

void FunctionSizeCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
   Options.store(Opts, "StatementThreshold", StatementThreshold);
   Options.store(Opts, "BranchThreshold", BranchThreshold);
   Options.store(Opts, "ParameterThreshold", ParameterThreshold);
   Options.store(Opts, "NestingThreshold", NestingThreshold);
   Options.store(Opts, "VariableThreshold", VariableThreshold);
 }
 
 void FunctionSizeCheck::registerMatchers(MatchFinder *Finder) {
-  Finder->addMatcher(functionDecl(unless(isInstantiated())).bind("func"), this);
+  // Lambdas ignored - historically considered part of enclosing function.
+  // FIXME: include them instead? Top-level lambdas are currently never counted.
+  Finder->addMatcher(functionDecl(unless(isInstantiated()),
+                                  unless(cxxMethodDecl(ofClass(isLambda()))))
+                         .bind("func"),
+                     this);
 }
 
 void FunctionSizeCheck::check(const MatchFinder::MatchResult &Result) {
   const auto *Func = Result.Nodes.getNodeAs<FunctionDecl>("func");
 
   FunctionASTVisitor Visitor;
   Visitor.Info.NestingThreshold = NestingThreshold;
   Visitor.TraverseDecl(const_cast<FunctionDecl *>(Func));