clang/lib/Analysis/FlowSensitive/HTMLLogger.cpp

   1 //===-- HTMLLogger.cpp ----------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file implements the HTML logger. Given a directory dir/, we write
  10 // dir/0.html for the first analysis, etc.
  11 // These files contain a visualization that allows inspecting the CFG and the
  12 // state of the analysis at each point.
  13 // Static assets (HTMLLogger.js, HTMLLogger.css) and SVG graphs etc are embedded
  14 // so each output file is self-contained.
  15 //
  16 // VIEWS
  17 //
  18 // The timeline and function view are always shown. These allow selecting basic
  19 // blocks, statements within them, and processing iterations (BBs are visited
  20 // multiple times when e.g. loops are involved).
  21 // These are written directly into the HTML body.
  22 //
  23 // There are also listings of particular basic blocks, and dumps of the state
  24 // at particular analysis points (i.e. BB2 iteration 3 statement 2).
  25 // These are only shown when the relevant BB/analysis point is *selected*.
  26 //
  27 // DATA AND TEMPLATES
  28 //
  29 // The HTML proper is mostly static.
  30 // The analysis data is in a JSON object HTMLLoggerData which is embedded as
  31 // a <script> in the <head>.
  32 // This gets rendered into DOM by a simple template processor which substitutes
  33 // the data into <template> tags embedded in the HTML. (see inflate() in JS).
  34 //
  35 // SELECTION
  36 //
  37 // This is the only real interactive mechanism.
  38 //
  39 // At any given time, there are several named selections, e.g.:
  40 //   bb: B2               (basic block 0 is selected)
  41 //   elt: B2.4            (statement 4 is selected)
  42 //   iter: B2:1           (iteration 1 of the basic block is selected)
  43 //   hover: B3            (hovering over basic block 3)
  44 //
  45 // The selection is updated by mouse events: hover by moving the mouse and
  46 // others by clicking. Elements that are click targets generally have attributes
  47 // (id or data-foo) that define what they should select.
  48 // See watchSelection() in JS for the exact logic.
  49 //
  50 // When the "bb" selection is set to "B2":
  51 //   - sections <section data-selection="bb"> get shown
  52 //   - templates under such sections get re-rendered
  53 //   - elements with class/id "B2" get class "bb-select"
  54 //
  55 //===----------------------------------------------------------------------===//
  56
  57 #include "clang/Analysis/FlowSensitive/ControlFlowContext.h"
  58 #include "clang/Analysis/FlowSensitive/DebugSupport.h"
  59 #include "clang/Analysis/FlowSensitive/Logger.h"
  60 #include "clang/Analysis/FlowSensitive/TypeErasedDataflowAnalysis.h"
  61 #include "clang/Analysis/FlowSensitive/Value.h"
  62 #include "clang/Basic/SourceManager.h"
  63 #include "clang/Lex/Lexer.h"
  64 #include "llvm/ADT/DenseMap.h"
  65 #include "llvm/ADT/ScopeExit.h"
  66 #include "llvm/Support/Error.h"
  67 #include "llvm/Support/FormatVariadic.h"
  68 #include "llvm/Support/JSON.h"
  69 #include "llvm/Support/Program.h"
  70 #include "llvm/Support/ScopedPrinter.h"
  71 #include "llvm/Support/raw_ostream.h"
  72 // Defines assets: HTMLLogger_{html_js,css}
  73 #include "HTMLLogger.inc"
  74
  75 namespace clang::dataflow {
  76 namespace {
  77
  78 // Render a graphviz graph specification to SVG using the `dot` tool.
  79 llvm::Expected<std::string> renderSVG(llvm::StringRef DotGraph);
  80
  81 using StreamFactory = std::function<std::unique_ptr<llvm::raw_ostream>()>;
  82
  83 // Recursively dumps Values/StorageLocations as JSON
  84 class ModelDumper {
  85 public:
  86   ModelDumper(llvm::json::OStream &JOS, const Environment &Env)
  87       : JOS(JOS), Env(Env) {}
  88
  89   void dump(Value &V) {
  90     JOS.attribute("value_id", llvm::to_string(&V));
  91     if (!Visited.insert(&V).second)
  92       return;
  93
  94     JOS.attribute("kind", debugString(V.getKind()));
  95
  96     switch (V.getKind()) {
  97     case Value::Kind::Integer:
  98     case Value::Kind::Record:
  99     case Value::Kind::TopBool:
 100     case Value::Kind::AtomicBool:
 101     case Value::Kind::FormulaBool:
 102       break;
 103     case Value::Kind::Pointer:
 104       JOS.attributeObject(
 105           "pointee", [&] { dump(cast<PointerValue>(V).getPointeeLoc()); });
 106       break;
 107     }
 108
 109     for (const auto& Prop : V.properties())
 110       JOS.attributeObject(("p:" + Prop.first()).str(),
 111                           [&] { dump(*Prop.second); });
 112
 113     // Running the SAT solver is expensive, but knowing which booleans are
 114     // guaranteed true/false here is valuable and hard to determine by hand.
 115     if (auto *B = llvm::dyn_cast<BoolValue>(&V)) {
 116       JOS.attribute("formula", llvm::to_string(B->formula()));
 117       JOS.attribute("truth", Env.proves(B->formula()) ? "true"
 118                              : Env.proves(Env.arena().makeNot(B->formula()))
 119                                  ? "false"
 120                                  : "unknown");
 121     }
 122   }
 123   void dump(const StorageLocation &L) {
 124     JOS.attribute("location", llvm::to_string(&L));
 125     if (!Visited.insert(&L).second)
 126       return;
 127
 128     JOS.attribute("type", L.getType().getAsString());
 129     if (auto *V = Env.getValue(L))
 130       dump(*V);
 131
 132     if (auto *RLoc = dyn_cast<RecordStorageLocation>(&L)) {
 133       for (const auto &Child : RLoc->children())
 134         JOS.attributeObject("f:" + Child.first->getNameAsString(), [&] {
 135           if (Child.second)
 136             if (Value *Val = Env.getValue(*Child.second))
 137               dump(*Val);
 138         });
 139
 140       for (const auto &SyntheticField : RLoc->synthetic_fields())
 141         JOS.attributeObject(("sf:" + SyntheticField.first()).str(),
 142                             [&] { dump(*SyntheticField.second); });
 143     }
 144   }
 145
 146   llvm::DenseSet<const void*> Visited;
 147   llvm::json::OStream &JOS;
 148   const Environment &Env;
 149 };
 150
 151 class HTMLLogger : public Logger {
 152   struct Iteration {
 153     const CFGBlock *Block;
 154     unsigned Iter;
 155     bool PostVisit;
 156     bool Converged;
 157   };
 158
 159   StreamFactory Streams;
 160   std::unique_ptr<llvm::raw_ostream> OS;
 161   std::optional<llvm::json::OStream> JOS;
 162
 163   const ControlFlowContext *CFG;
 164   // Timeline of iterations of CFG block visitation.
 165   std::vector<Iteration> Iters;
 166   // Indexes  in `Iters` of the iterations for each block.
 167   llvm::DenseMap<const CFGBlock *, llvm::SmallVector<size_t>> BlockIters;
 168   // The messages logged in the current context but not yet written.
 169   std::string ContextLogs;
 170   // The number of elements we have visited within the current CFG block.
 171   unsigned ElementIndex;
 172
 173 public:
 174   explicit HTMLLogger(StreamFactory Streams) : Streams(std::move(Streams)) {}
 175   void beginAnalysis(const ControlFlowContext &CFG,
 176                      TypeErasedDataflowAnalysis &A) override {
 177     OS = Streams();
 178     this->CFG = &CFG;
 179     *OS << llvm::StringRef(HTMLLogger_html).split("<?INJECT?>").first;
 180
 181     const auto &D = CFG.getDecl();
 182     const auto &SM = A.getASTContext().getSourceManager();
 183     *OS << "<title>";
 184     if (const auto *ND = dyn_cast<NamedDecl>(&D))
 185       *OS << ND->getNameAsString() << " at ";
 186     *OS << SM.getFilename(D.getLocation()) << ":"
 187         << SM.getSpellingLineNumber(D.getLocation());
 188     *OS << "</title>\n";
 189
 190     *OS << "<style>" << HTMLLogger_css << "</style>\n";
 191     *OS << "<script>" << HTMLLogger_js << "</script>\n";
 192
 193     writeCode();
 194     writeCFG();
 195
 196     *OS << "<script>var HTMLLoggerData = \n";
 197     JOS.emplace(*OS, /*Indent=*/2);
 198     JOS->objectBegin();
 199     JOS->attributeBegin("states");
 200     JOS->objectBegin();
 201   }
 202   // Between beginAnalysis() and endAnalysis() we write all the states for
 203   // particular analysis points into the `timeline` array.
 204   void endAnalysis() override {
 205     JOS->objectEnd();
 206     JOS->attributeEnd();
 207
 208     JOS->attributeArray("timeline", [&] {
 209       for (const auto &E : Iters) {
 210         JOS->object([&] {
 211           JOS->attribute("block", blockID(E.Block->getBlockID()));
 212           JOS->attribute("iter", E.Iter);
 213           JOS->attribute("post_visit", E.PostVisit);
 214           JOS->attribute("converged", E.Converged);
 215         });
 216       }
 217     });
 218     JOS->attributeObject("cfg", [&] {
 219       for (const auto &E : BlockIters)
 220         writeBlock(*E.first, E.second);
 221     });
 222
 223     JOS->objectEnd();
 224     JOS.reset();
 225     *OS << ";\n</script>\n";
 226     *OS << llvm::StringRef(HTMLLogger_html).split("<?INJECT?>").second;
 227   }
 228
 229   void enterBlock(const CFGBlock &B, bool PostVisit) override {
 230     llvm::SmallVector<size_t> &BIter = BlockIters[&B];
 231     unsigned IterNum = BIter.size() + 1;
 232     BIter.push_back(Iters.size());
 233     Iters.push_back({&B, IterNum, PostVisit, /*Converged=*/false});
 234     ElementIndex = 0;
 235   }
 236   void enterElement(const CFGElement &E) override {
 237     ++ElementIndex;
 238   }
 239
 240   static std::string blockID(unsigned Block) {
 241     return llvm::formatv("B{0}", Block);
 242   }
 243   static std::string eltID(unsigned Block, unsigned Element) {
 244     return llvm::formatv("B{0}.{1}", Block, Element);
 245   }
 246   static std::string iterID(unsigned Block, unsigned Iter) {
 247     return llvm::formatv("B{0}:{1}", Block, Iter);
 248   }
 249   static std::string elementIterID(unsigned Block, unsigned Iter,
 250                                    unsigned Element) {
 251     return llvm::formatv("B{0}:{1}_B{0}.{2}", Block, Iter, Element);
 252   }
 253
 254   // Write the analysis state associated with a particular analysis point.
 255   // FIXME: this dump is fairly opaque. We should show:
 256   //  - values associated with the current Stmt
 257   //  - values associated with its children
 258   //  - meaningful names for values
 259   //  - which boolean values are implied true/false by the flow condition
 260   void recordState(TypeErasedDataflowAnalysisState &State) override {
 261     unsigned Block = Iters.back().Block->getBlockID();
 262     unsigned Iter = Iters.back().Iter;
 263     bool PostVisit = Iters.back().PostVisit;
 264     JOS->attributeObject(elementIterID(Block, Iter, ElementIndex), [&] {
 265       JOS->attribute("block", blockID(Block));
 266       JOS->attribute("iter", Iter);
 267       JOS->attribute("post_visit", PostVisit);
 268       JOS->attribute("element", ElementIndex);
 269
 270       // If this state immediately follows an Expr, show its built-in model.
 271       if (ElementIndex > 0) {
 272         auto S =
 273             Iters.back().Block->Elements[ElementIndex - 1].getAs<CFGStmt>();
 274         if (const Expr *E = S ? llvm::dyn_cast<Expr>(S->getStmt()) : nullptr) {
 275           if (E->isPRValue()) {
 276             if (auto *V = State.Env.getValue(*E))
 277               JOS->attributeObject(
 278                   "value", [&] { ModelDumper(*JOS, State.Env).dump(*V); });
 279           } else {
 280             if (auto *Loc = State.Env.getStorageLocation(*E))
 281               JOS->attributeObject(
 282                   "value", [&] { ModelDumper(*JOS, State.Env).dump(*Loc); });
 283           }
 284         }
 285       }
 286       if (!ContextLogs.empty()) {
 287         JOS->attribute("logs", ContextLogs);
 288         ContextLogs.clear();
 289       }
 290       {
 291         std::string BuiltinLattice;
 292         llvm::raw_string_ostream BuiltinLatticeS(BuiltinLattice);
 293         State.Env.dump(BuiltinLatticeS);
 294         JOS->attribute("builtinLattice", BuiltinLattice);
 295       }
 296     });
 297   }
 298   void blockConverged() override { Iters.back().Converged = true; }
 299
 300   void logText(llvm::StringRef S) override {
 301     ContextLogs.append(S.begin(), S.end());
 302     ContextLogs.push_back('\n');
 303   }
 304
 305 private:
 306   // Write the CFG block details.
 307   // Currently this is just the list of elements in execution order.
 308   // FIXME: an AST dump would be a useful view, too.
 309   void writeBlock(const CFGBlock &B, llvm::ArrayRef<size_t> ItersForB) {
 310     JOS->attributeObject(blockID(B.getBlockID()), [&] {
 311       JOS->attributeArray("iters", [&] {
 312         for (size_t IterIdx : ItersForB) {
 313           const Iteration &Iter = Iters[IterIdx];
 314           JOS->object([&] {
 315             JOS->attribute("iter", Iter.Iter);
 316             JOS->attribute("post_visit", Iter.PostVisit);
 317             JOS->attribute("converged", Iter.Converged);
 318           });
 319         }
 320       });
 321       JOS->attributeArray("elements", [&] {
 322         for (const auto &Elt : B.Elements) {
 323           std::string Dump;
 324           llvm::raw_string_ostream DumpS(Dump);
 325           Elt.dumpToStream(DumpS);
 326           JOS->value(Dump);
 327         }
 328       });
 329     });
 330   }
 331
 332   // Write the code of function being examined.
 333   // We want to overlay the code with <span>s that mark which BB particular
 334   // tokens are associated with, and even which BB element (so that clicking
 335   // can select the right element).
 336   void writeCode() {
 337     const auto &AST = CFG->getDecl().getASTContext();
 338     bool Invalid = false;
 339
 340     // Extract the source code from the original file.
 341     // Pretty-printing from the AST would probably be nicer (no macros or
 342     // indentation to worry about), but we need the boundaries of particular
 343     // AST nodes and the printer doesn't provide this.
 344     auto Range = clang::Lexer::makeFileCharRange(
 345         CharSourceRange::getTokenRange(CFG->getDecl().getSourceRange()),
 346         AST.getSourceManager(), AST.getLangOpts());
 347     if (Range.isInvalid())
 348       return;
 349     llvm::StringRef Code = clang::Lexer::getSourceText(
 350         Range, AST.getSourceManager(), AST.getLangOpts(), &Invalid);
 351     if (Invalid)
 352       return;
 353
 354     // TokenInfo stores the BB and set of elements that a token is part of.
 355     struct TokenInfo {
 356       enum : unsigned { Missing = static_cast<unsigned>(-1) };
 357
 358       // The basic block this is part of.
 359       // This is the BB of the stmt with the smallest containing range.
 360       unsigned BB = Missing;
 361       unsigned BBPriority = 0;
 362       // The most specific stmt this is part of (smallest range).
 363       unsigned Elt = Missing;
 364       unsigned EltPriority = 0;
 365       // All stmts this is part of.
 366       SmallVector<unsigned> Elts;
 367
 368       // Mark this token as being part of BB.Elt.
 369       // RangeLen is the character length of the element's range, used to
 370       // distinguish inner vs outer statements.
 371       // For example in `a==0`, token "a" is part of the stmts "a" and "a==0".
 372       // However "a" has a smaller range, so is more specific. Clicking on the
 373       // token "a" should select the stmt "a".
 374       void assign(unsigned BB, unsigned Elt, unsigned RangeLen) {
 375         // A worse BB (larger range) => ignore.
 376         if (this->BB != Missing && BB != this->BB && BBPriority <= RangeLen)
 377           return;
 378         if (BB != this->BB) {
 379           this->BB = BB;
 380           Elts.clear();
 381           BBPriority = RangeLen;
 382         }
 383         BBPriority = std::min(BBPriority, RangeLen);
 384         Elts.push_back(Elt);
 385         if (this->Elt == Missing || EltPriority > RangeLen)
 386           this->Elt = Elt;
 387       }
 388       bool operator==(const TokenInfo &Other) const {
 389         return std::tie(BB, Elt, Elts) ==
 390                std::tie(Other.BB, Other.Elt, Other.Elts);
 391       }
 392       // Write the attributes for the <span> on this token.
 393       void write(llvm::raw_ostream &OS) const {
 394         OS << "class='c";
 395         if (BB != Missing)
 396           OS << " " << blockID(BB);
 397         for (unsigned Elt : Elts)
 398           OS << " " << eltID(BB, Elt);
 399         OS << "'";
 400
 401         if (Elt != Missing)
 402           OS << " data-elt='" << eltID(BB, Elt) << "'";
 403         if (BB != Missing)
 404           OS << " data-bb='" << blockID(BB) << "'";
 405       }
 406     };
 407
 408     // Construct one TokenInfo per character in a flat array.
 409     // This is inefficient (chars in a token all have the same info) but simple.
 410     std::vector<TokenInfo> State(Code.size());
 411     for (const auto *Block : CFG->getCFG()) {
 412       unsigned EltIndex = 0;
 413       for (const auto& Elt : *Block) {
 414         ++EltIndex;
 415         if (const auto S = Elt.getAs<CFGStmt>()) {
 416           auto EltRange = clang::Lexer::makeFileCharRange(
 417               CharSourceRange::getTokenRange(S->getStmt()->getSourceRange()),
 418               AST.getSourceManager(), AST.getLangOpts());
 419           if (EltRange.isInvalid())
 420             continue;
 421           if (EltRange.getBegin() < Range.getBegin() ||
 422               EltRange.getEnd() >= Range.getEnd() ||
 423               EltRange.getEnd() < Range.getBegin() ||
 424               EltRange.getEnd() >= Range.getEnd())
 425             continue;
 426           unsigned Off = EltRange.getBegin().getRawEncoding() -
 427                          Range.getBegin().getRawEncoding();
 428           unsigned Len = EltRange.getEnd().getRawEncoding() -
 429                          EltRange.getBegin().getRawEncoding();
 430           for (unsigned I = 0; I < Len; ++I)
 431             State[Off + I].assign(Block->getBlockID(), EltIndex, Len);
 432         }
 433       }
 434     }
 435
 436     // Finally, write the code with the correct <span>s.
 437     unsigned Line =
 438         AST.getSourceManager().getSpellingLineNumber(Range.getBegin());
 439     *OS << "<template data-copy='code'>\n";
 440     *OS << "<code class='filename'>";
 441     llvm::printHTMLEscaped(
 442         llvm::sys::path::filename(
 443             AST.getSourceManager().getFilename(Range.getBegin())),
 444         *OS);
 445     *OS << "</code>";
 446     *OS << "<code class='line' data-line='" << Line++ << "'>";
 447     for (unsigned I = 0; I < Code.size(); ++I) {
 448       // Don't actually write a <span> around each character, only break spans
 449       // when the TokenInfo changes.
 450       bool NeedOpen = I == 0 || !(State[I] == State[I-1]);
 451       bool NeedClose = I + 1 == Code.size() || !(State[I] == State[I + 1]);
 452       if (NeedOpen) {
 453         *OS << "<span ";
 454         State[I].write(*OS);
 455         *OS << ">";
 456       }
 457       if (Code[I] == '\n')
 458         *OS << "</code>\n<code class='line' data-line='" << Line++ << "'>";
 459       else
 460         llvm::printHTMLEscaped(Code.substr(I, 1), *OS);
 461       if (NeedClose) *OS << "</span>";
 462     }
 463     *OS << "</code>\n";
 464     *OS << "</template>";
 465   }
 466
 467   // Write the CFG diagram, a graph of basic blocks.
 468   // Laying out graphs is hard, so we construct a graphviz description and shell
 469   // out to `dot` to turn it into an SVG.
 470   void writeCFG() {
 471     *OS << "<template data-copy='cfg'>\n";
 472     if (auto SVG = renderSVG(buildCFGDot(CFG->getCFG())))
 473       *OS << *SVG;
 474     else
 475       *OS << "Can't draw CFG: " << toString(SVG.takeError());
 476     *OS << "</template>\n";
 477   }
 478
 479   // Produce a graphviz description of a CFG.
 480   static std::string buildCFGDot(const clang::CFG &CFG) {
 481     std::string Graph;
 482     llvm::raw_string_ostream GraphS(Graph);
 483     // Graphviz likes to add unhelpful tooltips everywhere, " " suppresses.
 484     GraphS << R"(digraph {
 485       tooltip=" "
 486       node[class=bb, shape=square, fontname="sans-serif", tooltip=" "]
 487       edge[tooltip = " "]
 488 )";
 489     for (unsigned I = 0; I < CFG.getNumBlockIDs(); ++I)
 490       GraphS << "  " << blockID(I) << " [id=" << blockID(I) << "]\n";
 491     for (const auto *Block : CFG) {
 492       for (const auto &Succ : Block->succs()) {
 493         if (Succ.getReachableBlock())
 494           GraphS << "  " << blockID(Block->getBlockID()) << " -> "
 495                  << blockID(Succ.getReachableBlock()->getBlockID()) << "\n";
 496       }
 497     }
 498     GraphS << "}\n";
 499     return Graph;
 500   }
 501 };
 502
 503 // Nothing interesting here, just subprocess/temp-file plumbing.
 504 llvm::Expected<std::string> renderSVG(llvm::StringRef DotGraph) {
 505   std::string DotPath;
 506   if (const auto *FromEnv = ::getenv("GRAPHVIZ_DOT"))
 507     DotPath = FromEnv;
 508   else {
 509     auto FromPath = llvm::sys::findProgramByName("dot");
 510     if (!FromPath)
 511       return llvm::createStringError(FromPath.getError(),
 512                                      "'dot' not found on PATH");
 513     DotPath = FromPath.get();
 514   }
 515
 516   // Create input and output files for `dot` subprocess.
 517   // (We create the output file as empty, to reserve the temp filename).
 518   llvm::SmallString<256> Input, Output;
 519   int InputFD;
 520   if (auto EC = llvm::sys::fs::createTemporaryFile("analysis", ".dot", InputFD,
 521                                                    Input))
 522     return llvm::createStringError(EC, "failed to create `dot` temp input");
 523   llvm::raw_fd_ostream(InputFD, /*shouldClose=*/true) << DotGraph;
 524   auto DeleteInput =
 525       llvm::make_scope_exit([&] { llvm::sys::fs::remove(Input); });
 526   if (auto EC = llvm::sys::fs::createTemporaryFile("analysis", ".svg", Output))
 527     return llvm::createStringError(EC, "failed to create `dot` temp output");
 528   auto DeleteOutput =
 529       llvm::make_scope_exit([&] { llvm::sys::fs::remove(Output); });
 530
 531   std::vector<std::optional<llvm::StringRef>> Redirects = {
 532       Input, Output,
 533       /*stderr=*/std::nullopt};
 534   std::string ErrMsg;
 535   int Code = llvm::sys::ExecuteAndWait(
 536       DotPath, {"dot", "-Tsvg"}, /*Env=*/std::nullopt, Redirects,
 537       /*SecondsToWait=*/0, /*MemoryLimit=*/0, &ErrMsg);
 538   if (!ErrMsg.empty())
 539     return llvm::createStringError(llvm::inconvertibleErrorCode(),
 540                                    "'dot' failed: " + ErrMsg);
 541   if (Code != 0)
 542     return llvm::createStringError(llvm::inconvertibleErrorCode(),
 543                                    "'dot' failed (" + llvm::Twine(Code) + ")");
 544
 545   auto Buf = llvm::MemoryBuffer::getFile(Output);
 546   if (!Buf)
 547     return llvm::createStringError(Buf.getError(), "Can't read `dot` output");
 548
 549   // Output has <?xml> prefix we don't want. Skip to <svg> tag.
 550   llvm::StringRef Result = Buf.get()->getBuffer();
 551   auto Pos = Result.find("<svg");
 552   if (Pos == llvm::StringRef::npos)
 553     return llvm::createStringError(llvm::inconvertibleErrorCode(),
 554                                    "Can't find <svg> tag in `dot` output");
 555   return Result.substr(Pos).str();
 556 }
 557
 558 } // namespace
 559
 560 std::unique_ptr<Logger>
 561 Logger::html(std::function<std::unique_ptr<llvm::raw_ostream>()> Streams) {
 562   return std::make_unique<HTMLLogger>(std::move(Streams));
 563 }
 564
 565 } // namespace clang::dataflow