1//===- InterpolatingCompilationDatabase.cpp ---------------------*- C++ -*-===//
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// InterpolatingCompilationDatabase wraps another CompilationDatabase and
10// attempts to heuristically determine appropriate compile commands for files
11// that are not included, such as headers or newly created files.
12//
13// Motivating cases include:
14//   Header files that live next to their implementation files. These typically
15// share a base filename. (libclang/CXString.h, libclang/CXString.cpp).
16//   Some projects separate headers from includes. Filenames still typically
17// match, maybe other path segments too. (include/llvm/IR/Use.h, lib/IR/Use.cc).
18//   Matches are sometimes only approximate (Sema.h, SemaDecl.cpp). This goes
19// for directories too (Support/Unix/Process.inc, lib/Support/Process.cpp).
20//   Even if we can't find a "right" compile command, even a random one from
21// the project will tend to get important flags like -I and -x right.
22//
23// We "borrow" the compile command for the closest available file:
24//   - points are awarded if the filename matches (ignoring extension)
25//   - points are awarded if the directory structure matches
26//   - ties are broken by length of path prefix match
27//
28// The compile command is adjusted, replacing the filename and removing output
29// file arguments. The -x and -std flags may be affected too.
30//
31// Source language is a tricky issue: is it OK to use a .c file's command
32// for building a .cc file? What language is a .h file in?
33//   - We only consider compile commands for c-family languages as candidates.
34//   - For files whose language is implied by the filename (e.g. .m, .hpp)
35//     we prefer candidates from the same language.
36//     If we must cross languages, we drop any -x and -std flags.
37//   - For .h files, candidates from any c-family language are acceptable.
38//     We use the candidate's language, inserting  e.g. -x c++-header.
39//
40// This class is only useful when wrapping databases that can enumerate all
41// their compile commands. If getAllFilenames() is empty, no inference occurs.
42//
43//===----------------------------------------------------------------------===//
44
45#include "clang/Basic/LangStandard.h"
46#include "clang/Driver/Driver.h"
47#include "clang/Driver/Options.h"
48#include "clang/Driver/Types.h"
49#include "clang/Tooling/CompilationDatabase.h"
50#include "llvm/ADT/ArrayRef.h"
51#include "llvm/ADT/DenseMap.h"
52#include "llvm/ADT/StringExtras.h"
53#include "llvm/Option/ArgList.h"
54#include "llvm/Option/OptTable.h"
55#include "llvm/Support/Debug.h"
56#include "llvm/Support/Path.h"
57#include "llvm/Support/StringSaver.h"
58#include "llvm/Support/raw_ostream.h"
59#include <memory>
60#include <optional>
61
62namespace clang {
63namespace tooling {
64namespace {
65using namespace llvm;
66namespace types = clang::driver::types;
67namespace path = llvm::sys::path;
68
69// The length of the prefix these two strings have in common.
70size_t matchingPrefix(StringRef L, StringRef R) {
71  size_t Limit = std::min(L.size(), R.size());
72  for (size_t I = 0; I < Limit; ++I)
73    if (L[I] != R[I])
74      return I;
75  return Limit;
76}
77
78// A comparator for searching SubstringWithIndexes with std::equal_range etc.
79// Optionaly prefix semantics: compares equal if the key is a prefix.
80template <bool Prefix> struct Less {
81  bool operator()(StringRef Key, std::pair<StringRef, size_t> Value) const {
82    StringRef V = Prefix ? Value.first.substr(0, Key.size()) : Value.first;
83    return Key < V;
84  }
85  bool operator()(std::pair<StringRef, size_t> Value, StringRef Key) const {
86    StringRef V = Prefix ? Value.first.substr(0, Key.size()) : Value.first;
87    return V < Key;
88  }
89};
90
91// Infer type from filename. If we might have gotten it wrong, set *Certain.
92// *.h will be inferred as a C header, but not certain.
93types::ID guessType(StringRef Filename, bool *Certain = nullptr) {
94  // path::extension is ".cpp", lookupTypeForExtension wants "cpp".
95  auto Lang =
96      types::lookupTypeForExtension(path::extension(Filename).substr(1));
97  if (Certain)
98    *Certain = Lang != types::TY_CHeader && Lang != types::TY_INVALID;
99  return Lang;
100}
101
102// Return Lang as one of the canonical supported types.
103// e.g. c-header --> c; fortran --> TY_INVALID
104static types::ID foldType(types::ID Lang) {
105  switch (Lang) {
106  case types::TY_C:
107  case types::TY_CHeader:
108    return types::TY_C;
109  case types::TY_ObjC:
110  case types::TY_ObjCHeader:
111    return types::TY_ObjC;
112  case types::TY_CXX:
113  case types::TY_CXXHeader:
114    return types::TY_CXX;
115  case types::TY_ObjCXX:
116  case types::TY_ObjCXXHeader:
117    return types::TY_ObjCXX;
118  case types::TY_CUDA:
119  case types::TY_CUDA_DEVICE:
120    return types::TY_CUDA;
121  default:
122    return types::TY_INVALID;
123  }
124}
125
126// A CompileCommand that can be applied to another file.
127struct TransferableCommand {
128  // Flags that should not apply to all files are stripped from CommandLine.
129  CompileCommand Cmd;
130  // Language detected from -x or the filename. Never TY_INVALID.
131  std::optional<types::ID> Type;
132  // Standard specified by -std.
133  LangStandard::Kind Std = LangStandard::lang_unspecified;
134  // Whether the command line is for the cl-compatible driver.
135  bool ClangCLMode;
136
137  TransferableCommand(CompileCommand C)
138      : Cmd(std::move(C)), Type(guessType(Cmd.Filename)) {
139    std::vector<std::string> OldArgs = std::move(Cmd.CommandLine);
140    Cmd.CommandLine.clear();
141
142    // Wrap the old arguments in an InputArgList.
143    llvm::opt::InputArgList ArgList;
144    {
145      SmallVector<const char *, 16> TmpArgv;
146      for (const std::string &S : OldArgs)
147        TmpArgv.push_back(S.c_str());
148      ClangCLMode = !TmpArgv.empty() &&
149                    driver::IsClangCL(driver::getDriverMode(
150                        TmpArgv.front(), llvm::ArrayRef(TmpArgv).slice(1)));
151      ArgList = {TmpArgv.begin(), TmpArgv.end()};
152    }
153
154    // Parse the old args in order to strip out and record unwanted flags.
155    // We parse each argument individually so that we can retain the exact
156    // spelling of each argument; re-rendering is lossy for aliased flags.
157    // E.g. in CL mode, /W4 maps to -Wall.
158    auto &OptTable = clang::driver::getDriverOptTable();
159    if (!OldArgs.empty())
160      Cmd.CommandLine.emplace_back(OldArgs.front());
161    for (unsigned Pos = 1; Pos < OldArgs.size();) {
162      using namespace driver::options;
163
164      const unsigned OldPos = Pos;
165      std::unique_ptr<llvm::opt::Arg> Arg(OptTable.ParseOneArg(
166          ArgList, Pos,
167          llvm::opt::Visibility(ClangCLMode ? CLOption : ClangOption)));
168
169      if (!Arg)
170        continue;
171
172      const llvm::opt::Option &Opt = Arg->getOption();
173
174      // Strip input and output files.
175      if (Opt.matches(OPT_INPUT) || Opt.matches(OPT_o) ||
176          (ClangCLMode && (Opt.matches(OPT__SLASH_Fa) ||
177                           Opt.matches(OPT__SLASH_Fe) ||
178                           Opt.matches(OPT__SLASH_Fi) ||
179                           Opt.matches(OPT__SLASH_Fo))))
180        continue;
181
182      // ...including when the inputs are passed after --.
183      if (Opt.matches(OPT__DASH_DASH))
184        break;
185
186      // Strip -x, but record the overridden language.
187      if (const auto GivenType = tryParseTypeArg(*Arg)) {
188        Type = *GivenType;
189        continue;
190      }
191
192      // Strip -std, but record the value.
193      if (const auto GivenStd = tryParseStdArg(*Arg)) {
194        if (*GivenStd != LangStandard::lang_unspecified)
195          Std = *GivenStd;
196        continue;
197      }
198
199      Cmd.CommandLine.insert(Cmd.CommandLine.end(),
200                             OldArgs.data() + OldPos, OldArgs.data() + Pos);
201    }
202
203    // Make use of -std iff -x was missing.
204    if (Type == types::TY_INVALID && Std != LangStandard::lang_unspecified)
205      Type = toType(LangStandard::getLangStandardForKind(Std).getLanguage());
206    Type = foldType(*Type);
207    // The contract is to store None instead of TY_INVALID.
208    if (Type == types::TY_INVALID)
209      Type = std::nullopt;
210  }
211
212  // Produce a CompileCommand for \p filename, based on this one.
213  // (This consumes the TransferableCommand just to avoid copying Cmd).
214  CompileCommand transferTo(StringRef Filename) && {
215    CompileCommand Result = std::move(Cmd);
216    Result.Heuristic = "inferred from " + Result.Filename;
217    Result.Filename = std::string(Filename);
218    bool TypeCertain;
219    auto TargetType = guessType(Filename, &TypeCertain);
220    // If the filename doesn't determine the language (.h), transfer with -x.
221    if ((!TargetType || !TypeCertain) && Type) {
222      // Use *Type, or its header variant if the file is a header.
223      // Treat no/invalid extension as header (e.g. C++ standard library).
224      TargetType =
225          (!TargetType || types::onlyPrecompileType(TargetType)) // header?
226              ? types::lookupHeaderTypeForSourceType(*Type)
227              : *Type;
228      if (ClangCLMode) {
229        const StringRef Flag = toCLFlag(TargetType);
230        if (!Flag.empty())
231          Result.CommandLine.push_back(std::string(Flag));
232      } else {
233        Result.CommandLine.push_back("-x");
234        Result.CommandLine.push_back(types::getTypeName(TargetType));
235      }
236    }
237    // --std flag may only be transferred if the language is the same.
238    // We may consider "translating" these, e.g. c++11 -> c11.
239    if (Std != LangStandard::lang_unspecified && foldType(TargetType) == Type) {
240      Result.CommandLine.emplace_back((
241          llvm::Twine(ClangCLMode ? "/std:" : "-std=") +
242          LangStandard::getLangStandardForKind(Std).getName()).str());
243    }
244    Result.CommandLine.push_back("--");
245    Result.CommandLine.push_back(std::string(Filename));
246    return Result;
247  }
248
249private:
250  // Map the language from the --std flag to that of the -x flag.
251  static types::ID toType(Language Lang) {
252    switch (Lang) {
253    case Language::C:
254      return types::TY_C;
255    case Language::CXX:
256      return types::TY_CXX;
257    case Language::ObjC:
258      return types::TY_ObjC;
259    case Language::ObjCXX:
260      return types::TY_ObjCXX;
261    default:
262      return types::TY_INVALID;
263    }
264  }
265
266  // Convert a file type to the matching CL-style type flag.
267  static StringRef toCLFlag(types::ID Type) {
268    switch (Type) {
269    case types::TY_C:
270    case types::TY_CHeader:
271      return "/TC";
272    case types::TY_CXX:
273    case types::TY_CXXHeader:
274      return "/TP";
275    default:
276      return StringRef();
277    }
278  }
279
280  // Try to interpret the argument as a type specifier, e.g. '-x'.
281  std::optional<types::ID> tryParseTypeArg(const llvm::opt::Arg &Arg) {
282    const llvm::opt::Option &Opt = Arg.getOption();
283    using namespace driver::options;
284    if (ClangCLMode) {
285      if (Opt.matches(OPT__SLASH_TC) || Opt.matches(OPT__SLASH_Tc))
286        return types::TY_C;
287      if (Opt.matches(OPT__SLASH_TP) || Opt.matches(OPT__SLASH_Tp))
288        return types::TY_CXX;
289    } else {
290      if (Opt.matches(driver::options::OPT_x))
291        return types::lookupTypeForTypeSpecifier(Arg.getValue());
292    }
293    return std::nullopt;
294  }
295
296  // Try to interpret the argument as '-std='.
297  std::optional<LangStandard::Kind> tryParseStdArg(const llvm::opt::Arg &Arg) {
298    using namespace driver::options;
299    if (Arg.getOption().matches(ClangCLMode ? OPT__SLASH_std : OPT_std_EQ))
300      return LangStandard::getLangKind(Arg.getValue());
301    return std::nullopt;
302  }
303};
304
305// Given a filename, FileIndex picks the best matching file from the underlying
306// DB. This is the proxy file whose CompileCommand will be reused. The
307// heuristics incorporate file name, extension, and directory structure.
308// Strategy:
309// - Build indexes of each of the substrings we want to look up by.
310//   These indexes are just sorted lists of the substrings.
311// - Each criterion corresponds to a range lookup into the index, so we only
312//   need O(log N) string comparisons to determine scores.
313//
314// Apart from path proximity signals, also takes file extensions into account
315// when scoring the candidates.
316class FileIndex {
317public:
318  FileIndex(std::vector<std::string> Files)
319      : OriginalPaths(std::move(Files)), Strings(Arena) {
320    // Sort commands by filename for determinism (index is a tiebreaker later).
321    llvm::sort(OriginalPaths);
322    Paths.reserve(OriginalPaths.size());
323    Types.reserve(OriginalPaths.size());
324    Stems.reserve(OriginalPaths.size());
325    for (size_t I = 0; I < OriginalPaths.size(); ++I) {
326      StringRef Path = Strings.save(StringRef(OriginalPaths[I]).lower());
327
328      Paths.emplace_back(Path, I);
329      Types.push_back(foldType(guessType(OriginalPaths[I])));
330      Stems.emplace_back(sys::path::stem(Path), I);
331      auto Dir = ++sys::path::rbegin(Path), DirEnd = sys::path::rend(Path);
332      for (int J = 0; J < DirectorySegmentsIndexed && Dir != DirEnd; ++J, ++Dir)
333        if (Dir->size() > ShortDirectorySegment) // not trivial ones
334          Components.emplace_back(*Dir, I);
335    }
336    llvm::sort(Paths);
337    llvm::sort(Stems);
338    llvm::sort(Components);
339  }
340
341  bool empty() const { return Paths.empty(); }
342
343  // Returns the path for the file that best fits OriginalFilename.
344  // Candidates with extensions matching PreferLanguage will be chosen over
345  // others (unless it's TY_INVALID, or all candidates are bad).
346  StringRef chooseProxy(StringRef OriginalFilename,
347                        types::ID PreferLanguage) const {
348    assert(!empty() && "need at least one candidate!");
349    std::string Filename = OriginalFilename.lower();
350    auto Candidates = scoreCandidates(Filename);
351    std::pair<size_t, int> Best =
352        pickWinner(Candidates, Filename, PreferLanguage);
353
354    DEBUG_WITH_TYPE(
355        "interpolate",
356        llvm::dbgs() << "interpolate: chose " << OriginalPaths[Best.first]
357                     << " as proxy for " << OriginalFilename << " preferring "
358                     << (PreferLanguage == types::TY_INVALID
359                             ? "none"
360                             : types::getTypeName(PreferLanguage))
361                     << " score=" << Best.second << "\n");
362    return OriginalPaths[Best.first];
363  }
364
365private:
366  using SubstringAndIndex = std::pair<StringRef, size_t>;
367  // Directory matching parameters: we look at the last two segments of the
368  // parent directory (usually the semantically significant ones in practice).
369  // We search only the last four of each candidate (for efficiency).
370  constexpr static int DirectorySegmentsIndexed = 4;
371  constexpr static int DirectorySegmentsQueried = 2;
372  constexpr static int ShortDirectorySegment = 1; // Only look at longer names.
373
374  // Award points to candidate entries that should be considered for the file.
375  // Returned keys are indexes into paths, and the values are (nonzero) scores.
376  DenseMap<size_t, int> scoreCandidates(StringRef Filename) const {
377    // Decompose Filename into the parts we care about.
378    // /some/path/complicated/project/Interesting.h
379    // [-prefix--][---dir---] [-dir-] [--stem---]
380    StringRef Stem = sys::path::stem(Filename);
381    llvm::SmallVector<StringRef, DirectorySegmentsQueried> Dirs;
382    llvm::StringRef Prefix;
383    auto Dir = ++sys::path::rbegin(Filename),
384         DirEnd = sys::path::rend(Filename);
385    for (int I = 0; I < DirectorySegmentsQueried && Dir != DirEnd; ++I, ++Dir) {
386      if (Dir->size() > ShortDirectorySegment)
387        Dirs.push_back(*Dir);
388      Prefix = Filename.substr(0, Dir - DirEnd);
389    }
390
391    // Now award points based on lookups into our various indexes.
392    DenseMap<size_t, int> Candidates; // Index -> score.
393    auto Award = [&](int Points, ArrayRef<SubstringAndIndex> Range) {
394      for (const auto &Entry : Range)
395        Candidates[Entry.second] += Points;
396    };
397    // Award one point if the file's basename is a prefix of the candidate,
398    // and another if it's an exact match (so exact matches get two points).
399    Award(1, indexLookup</*Prefix=*/true>(Stem, Stems));
400    Award(1, indexLookup</*Prefix=*/false>(Stem, Stems));
401    // For each of the last few directories in the Filename, award a point
402    // if it's present in the candidate.
403    for (StringRef Dir : Dirs)
404      Award(1, indexLookup</*Prefix=*/false>(Dir, Components));
405    // Award one more point if the whole rest of the path matches.
406    if (sys::path::root_directory(Prefix) != Prefix)
407      Award(1, indexLookup</*Prefix=*/true>(Prefix, Paths));
408    return Candidates;
409  }
410
411  // Pick a single winner from the set of scored candidates.
412  // Returns (index, score).
413  std::pair<size_t, int> pickWinner(const DenseMap<size_t, int> &Candidates,
414                                    StringRef Filename,
415                                    types::ID PreferredLanguage) const {
416    struct ScoredCandidate {
417      size_t Index;
418      bool Preferred;
419      int Points;
420      size_t PrefixLength;
421    };
422    // Choose the best candidate by (preferred, points, prefix length, alpha).
423    ScoredCandidate Best = {size_t(-1), false, 0, 0};
424    for (const auto &Candidate : Candidates) {
425      ScoredCandidate S;
426      S.Index = Candidate.first;
427      S.Preferred = PreferredLanguage == types::TY_INVALID ||
428                    PreferredLanguage == Types[S.Index];
429      S.Points = Candidate.second;
430      if (!S.Preferred && Best.Preferred)
431        continue;
432      if (S.Preferred == Best.Preferred) {
433        if (S.Points < Best.Points)
434          continue;
435        if (S.Points == Best.Points) {
436          S.PrefixLength = matchingPrefix(Filename, Paths[S.Index].first);
437          if (S.PrefixLength < Best.PrefixLength)
438            continue;
439          // hidden heuristics should at least be deterministic!
440          if (S.PrefixLength == Best.PrefixLength)
441            if (S.Index > Best.Index)
442              continue;
443        }
444      }
445      // PrefixLength was only set above if actually needed for a tiebreak.
446      // But it definitely needs to be set to break ties in the future.
447      S.PrefixLength = matchingPrefix(Filename, Paths[S.Index].first);
448      Best = S;
449    }
450    // Edge case: no candidate got any points.
451    // We ignore PreferredLanguage at this point (not ideal).
452    if (Best.Index == size_t(-1))
453      return {longestMatch(Filename, Paths).second, 0};
454    return {Best.Index, Best.Points};
455  }
456
457  // Returns the range within a sorted index that compares equal to Key.
458  // If Prefix is true, it's instead the range starting with Key.
459  template <bool Prefix>
460  ArrayRef<SubstringAndIndex>
461  indexLookup(StringRef Key, ArrayRef<SubstringAndIndex> Idx) const {
462    // Use pointers as iteratiors to ease conversion of result to ArrayRef.
463    auto Range = std::equal_range(Idx.data(), Idx.data() + Idx.size(), Key,
464                                  Less<Prefix>());
465    return {Range.first, Range.second};
466  }
467
468  // Performs a point lookup into a nonempty index, returning a longest match.
469  SubstringAndIndex longestMatch(StringRef Key,
470                                 ArrayRef<SubstringAndIndex> Idx) const {
471    assert(!Idx.empty());
472    // Longest substring match will be adjacent to a direct lookup.
473    auto It = llvm::lower_bound(Idx, SubstringAndIndex{Key, 0});
474    if (It == Idx.begin())
475      return *It;
476    if (It == Idx.end())
477      return *--It;
478    // Have to choose between It and It-1
479    size_t Prefix = matchingPrefix(Key, It->first);
480    size_t PrevPrefix = matchingPrefix(Key, (It - 1)->first);
481    return Prefix > PrevPrefix ? *It : *--It;
482  }
483
484  // Original paths, everything else is in lowercase.
485  std::vector<std::string> OriginalPaths;
486  BumpPtrAllocator Arena;
487  StringSaver Strings;
488  // Indexes of candidates by certain substrings.
489  // String is lowercase and sorted, index points into OriginalPaths.
490  std::vector<SubstringAndIndex> Paths;      // Full path.
491  // Lang types obtained by guessing on the corresponding path. I-th element is
492  // a type for the I-th path.
493  std::vector<types::ID> Types;
494  std::vector<SubstringAndIndex> Stems;      // Basename, without extension.
495  std::vector<SubstringAndIndex> Components; // Last path components.
496};
497
498// The actual CompilationDatabase wrapper delegates to its inner database.
499// If no match, looks up a proxy file in FileIndex and transfers its
500// command to the requested file.
501class InterpolatingCompilationDatabase : public CompilationDatabase {
502public:
503  InterpolatingCompilationDatabase(std::unique_ptr<CompilationDatabase> Inner)
504      : Inner(std::move(Inner)), Index(this->Inner->getAllFiles()) {}
505
506  std::vector<CompileCommand>
507  getCompileCommands(StringRef Filename) const override {
508    auto Known = Inner->getCompileCommands(Filename);
509    if (Index.empty() || !Known.empty())
510      return Known;
511    bool TypeCertain;
512    auto Lang = guessType(Filename, &TypeCertain);
513    if (!TypeCertain)
514      Lang = types::TY_INVALID;
515    auto ProxyCommands =
516        Inner->getCompileCommands(Index.chooseProxy(Filename, foldType(Lang)));
517    if (ProxyCommands.empty())
518      return {};
519    return {transferCompileCommand(std::move(ProxyCommands.front()), Filename)};
520  }
521
522  std::vector<std::string> getAllFiles() const override {
523    return Inner->getAllFiles();
524  }
525
526  std::vector<CompileCommand> getAllCompileCommands() const override {
527    return Inner->getAllCompileCommands();
528  }
529
530private:
531  std::unique_ptr<CompilationDatabase> Inner;
532  FileIndex Index;
533};
534
535} // namespace
536
537std::unique_ptr<CompilationDatabase>
538inferMissingCompileCommands(std::unique_ptr<CompilationDatabase> Inner) {
539  return std::make_unique<InterpolatingCompilationDatabase>(std::move(Inner));
540}
541
542tooling::CompileCommand transferCompileCommand(CompileCommand Cmd,
543                                               StringRef Filename) {
544  return TransferableCommand(std::move(Cmd)).transferTo(Filename);
545}
546
547} // namespace tooling
548} // namespace clang
549