Comment Diagnosis.h and add missing headers

clang/include/clang/Analysis/FlowSensitive/Diagnosis.h

 
 #ifndef LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_DIAGNOSIS_H
 #define LLVM_CLANG_ANALYSIS_FLOWSENSITIVE_DIAGNOSIS_H
 
 #include "clang/Analysis/FlowSensitive/ControlFlowContext.h"
 #include "clang/Analysis/FlowSensitive/DataflowEnvironment.h"
 #include "clang/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.h"
 #include "llvm/ADT/DenseSet.h"
+#include "llvm/ADT/Optional.h"
+#include <functional>
+#include <utility>
+#include <vector>
 
 namespace clang {
 namespace dataflow {
 
+/// Looks at a single statement using the `Lattice` and `Environment` at that
+/// program point from running a dataflow analysis, and returns any diagnostics.
 template <typename Lattice, typename Diags>
 using Diagnosis =
     std::function<Diags(const Stmt *, const Lattice &, const Environment &)>;
 
+/// Collects diagnostics from all blocks in a CFG, given some dataflow analysis
+/// results and a `Diagnose` function which can be run on individual statements.
 template <typename Lattice, typename Diag>
 llvm::DenseSet<Diag> diagnoseCFG(
     const ControlFlowContext &CFCtx,
     std::vector<llvm::Optional<TypeErasedDataflowAnalysisState>> &BlockStates,
     const Environment &Env, TypeErasedDataflowAnalysis &Analysis,
     Diagnosis<Lattice, llvm::DenseSet<Diag>> Diagnose) {
   llvm::DenseSet<Diag> Diags;
   for (const CFGBlock *Block : CFCtx.getCFG()) {