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//===- InterpolatingCompilationDatabase.cpp ---------------------*- C++ -*-===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// InterpolatingCompilationDatabase wraps another CompilationDatabase and
// attempts to heuristically determine appropriate compile commands for files
// that are not included, such as headers or newly created files.
// Motivating cases include:
// Header files that live next to their implementation files. These typically
// share a base filename. (libclang/CXString.h, libclang/CXString.cpp).
// Some projects separate headers from includes. Filenames still typically
// match, maybe other path segments too. (include/llvm/IR/Use.h, lib/IR/
// Matches are sometimes only approximate (Sema.h, SemaDecl.cpp). This goes
// for directories too (Support/Unix/, lib/Support/Process.cpp).
// Even if we can't find a "right" compile command, even a random one from
// the project will tend to get important flags like -I and -x right.
// We "borrow" the compile command for the closest available file:
// - points are awarded if the filename matches (ignoring extension)
// - points are awarded if the directory structure matches
// - ties are broken by length of path prefix match
// The compile command is adjusted, replacing the filename and removing output
// file arguments. The -x and -std flags may be affected too.
// Source language is a tricky issue: is it OK to use a .c file's command
// for building a .cc file? What language is a .h file in?
// - We only consider compile commands for c-family languages as candidates.
// - For files whose language is implied by the filename (e.g. .m, .hpp)
// we prefer candidates from the same language.
// If we must cross languages, we drop any -x and -std flags.
// - For .h files, candidates from any c-family language are acceptable.
// We use the candidate's language, inserting e.g. -x c++-header.
// This class is only useful when wrapping databases that can enumerate all
// their compile commands. If getAllFilenames() is empty, no inference occurs.
#include "clang/Driver/Options.h"
#include "clang/Driver/Types.h"
#include "clang/Frontend/LangStandard.h"
#include "clang/Tooling/CompilationDatabase.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/ADT/StringSwitch.h"
#include "llvm/Option/ArgList.h"
#include "llvm/Option/OptTable.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/StringSaver.h"
#include "llvm/Support/raw_ostream.h"
#include <memory>
namespace clang {
namespace tooling {
namespace {
using namespace llvm;
namespace types = clang::driver::types;
namespace path = llvm::sys::path;
// The length of the prefix these two strings have in common.
size_t matchingPrefix(StringRef L, StringRef R) {
size_t Limit = std::min(L.size(), R.size());
for (size_t I = 0; I < Limit; ++I)
if (L[I] != R[I])
return I;
return Limit;
// A comparator for searching SubstringWithIndexes with std::equal_range etc.
// Optionaly prefix semantics: compares equal if the key is a prefix.
template <bool Prefix> struct Less {
bool operator()(StringRef Key, std::pair<StringRef, size_t> Value) const {
StringRef V = Prefix ? Value.first.substr(0, Key.size()) : Value.first;
return Key < V;
bool operator()(std::pair<StringRef, size_t> Value, StringRef Key) const {
StringRef V = Prefix ? Value.first.substr(0, Key.size()) : Value.first;
return V < Key;
// Infer type from filename. If we might have gotten it wrong, set *Certain.
// *.h will be inferred as a C header, but not certain.
types::ID guessType(StringRef Filename, bool *Certain = nullptr) {
// path::extension is ".cpp", lookupTypeForExtension wants "cpp".
auto Lang =
if (Certain)
*Certain = Lang != types::TY_CHeader && Lang != types::TY_INVALID;
return Lang;
// Return Lang as one of the canonical supported types.
// e.g. c-header --> c; fortran --> TY_INVALID
static types::ID foldType(types::ID Lang) {
switch (Lang) {
case types::TY_C:
case types::TY_CHeader:
return types::TY_C;
case types::TY_ObjC:
case types::TY_ObjCHeader:
return types::TY_ObjC;
case types::TY_CXX:
case types::TY_CXXHeader:
return types::TY_CXX;
case types::TY_ObjCXX:
case types::TY_ObjCXXHeader:
return types::TY_ObjCXX;
return types::TY_INVALID;
// A CompileCommand that can be applied to another file.
struct TransferableCommand {
// Flags that should not apply to all files are stripped from CommandLine.
CompileCommand Cmd;
// Language detected from -x or the filename.
types::ID Type = types::TY_INVALID;
// Standard specified by -std.
LangStandard::Kind Std = LangStandard::lang_unspecified;
TransferableCommand(CompileCommand C)
: Cmd(std::move(C)), Type(guessType(Cmd.Filename)) {
std::vector<std::string> NewArgs = {Cmd.CommandLine.front()};
// Parse the old args in order to strip out and record unwanted flags.
auto OptTable = clang::driver::createDriverOptTable();
std::vector<const char *> Argv;
for (unsigned I = 1; I < Cmd.CommandLine.size(); ++I)
unsigned MissingI, MissingC;
auto ArgList = OptTable->ParseArgs(Argv, MissingI, MissingC);
for (const auto *Arg : ArgList) {
const auto &option = Arg->getOption();
// Strip input and output files.
if (option.matches(clang::driver::options::OPT_INPUT) ||
option.matches(clang::driver::options::OPT_o)) {
// Strip -x, but record the overridden language.
if (option.matches(clang::driver::options::OPT_x)) {
for (const char *Value : Arg->getValues())
Type = types::lookupTypeForTypeSpecifier(Value);
// Strip --std, but record the value.
if (option.matches(clang::driver::options::OPT_std_EQ)) {
for (const char *Value : Arg->getValues()) {
Std = llvm::StringSwitch<LangStandard::Kind>(Value)
#define LANGSTANDARD(id, name, lang, desc, features) \
.Case(name, LangStandard::lang_##id)
#define LANGSTANDARD_ALIAS(id, alias) .Case(alias, LangStandard::lang_##id)
#include "clang/Frontend/LangStandards.def"
llvm::opt::ArgStringList ArgStrs;
Arg->render(ArgList, ArgStrs);
NewArgs.insert(NewArgs.end(), ArgStrs.begin(), ArgStrs.end());
Cmd.CommandLine = std::move(NewArgs);
if (Std != LangStandard::lang_unspecified) // -std take precedence over -x
Type = toType(LangStandard::getLangStandardForKind(Std).getLanguage());
Type = foldType(Type);
// Produce a CompileCommand for \p filename, based on this one.
CompileCommand transferTo(StringRef Filename) const {
CompileCommand Result = Cmd;
Result.Filename = Filename;
bool TypeCertain;
auto TargetType = guessType(Filename, &TypeCertain);
// If the filename doesn't determine the language (.h), transfer with -x.
if (!TypeCertain) {
TargetType = types::onlyPrecompileType(TargetType) // header?
? types::lookupHeaderTypeForSourceType(Type)
: Type;
// --std flag may only be transferred if the language is the same.
// We may consider "translating" these, e.g. c++11 -> c11.
if (Std != LangStandard::lang_unspecified && foldType(TargetType) == Type) {
"-std=" +
return Result;
// Map the language from the --std flag to that of the -x flag.
static types::ID toType(InputKind::Language Lang) {
switch (Lang) {
case InputKind::C:
return types::TY_C;
case InputKind::CXX:
return types::TY_CXX;
case InputKind::ObjC:
return types::TY_ObjC;
case InputKind::ObjCXX:
return types::TY_ObjCXX;
return types::TY_INVALID;
// CommandIndex does the real work: given a filename, it produces the best
// matching TransferableCommand by matching filenames. Basic strategy:
// - Build indexes of each of the substrings we want to look up by.
// These indexes are just sorted lists of the substrings.
// - Forward requests to the inner CDB. If it fails, we must pick a proxy.
// - Each criterion corresponds to a range lookup into the index, so we only
// need O(log N) string comparisons to determine scores.
// - We then break ties among the candidates with the highest score.
class CommandIndex {
CommandIndex(std::vector<TransferableCommand> AllCommands)
: Commands(std::move(AllCommands)), Strings(Arena) {
// Sort commands by filename for determinism (index is a tiebreaker later).
Commands.begin(), Commands.end(),
[](const TransferableCommand &Left, const TransferableCommand &Right) {
return Left.Cmd.Filename < Right.Cmd.Filename;
for (size_t I = 0; I < Commands.size(); ++I) {
StringRef Path =[I].Cmd.Filename).lower());
Paths.push_back({Path, I});
Stems.emplace_back(sys::path::stem(Path), I);
auto Dir = ++sys::path::rbegin(Path), DirEnd = sys::path::rend(Path);
for (int J = 0; J < DirectorySegmentsIndexed && Dir != DirEnd; ++J, ++Dir)
if (Dir->size() > ShortDirectorySegment) // not trivial ones
Components.emplace_back(*Dir, I);
llvm::sort(Paths.begin(), Paths.end());
llvm::sort(Stems.begin(), Stems.end());
llvm::sort(Components.begin(), Components.end());
bool empty() const { return Commands.empty(); }
// Returns the command that best fits OriginalFilename.
// Candidates with PreferLanguage will be chosen over others (unless it's
// TY_INVALID, or all candidates are bad).
const TransferableCommand &chooseProxy(StringRef OriginalFilename,
types::ID PreferLanguage) const {
assert(!empty() && "need at least one candidate!");
std::string Filename = OriginalFilename.lower();
auto Candidates = scoreCandidates(Filename);
std::pair<size_t, int> Best =
pickWinner(Candidates, Filename, PreferLanguage);
<< "interpolate: chose "
<< Commands[Best.first].Cmd.Filename << " as proxy for "
<< OriginalFilename << " preferring "
<< (PreferLanguage == types::TY_INVALID
? "none"
: types::getTypeName(PreferLanguage))
<< " score=" << Best.second << "\n");
return Commands[Best.first];
using SubstringAndIndex = std::pair<StringRef, size_t>;
// Directory matching parameters: we look at the last two segments of the
// parent directory (usually the semantically significant ones in practice).
// We search only the last four of each candidate (for efficiency).
constexpr static int DirectorySegmentsIndexed = 4;
constexpr static int DirectorySegmentsQueried = 2;
constexpr static int ShortDirectorySegment = 1; // Only look at longer names.
// Award points to candidate entries that should be considered for the file.
// Returned keys are indexes into paths, and the values are (nonzero) scores.
DenseMap<size_t, int> scoreCandidates(StringRef Filename) const {
// Decompose Filename into the parts we care about.
// /some/path/complicated/project/Interesting.h
// [-prefix--][---dir---] [-dir-] [--stem---]
StringRef Stem = sys::path::stem(Filename);
llvm::SmallVector<StringRef, DirectorySegmentsQueried> Dirs;
llvm::StringRef Prefix;
auto Dir = ++sys::path::rbegin(Filename),
DirEnd = sys::path::rend(Filename);
for (int I = 0; I < DirectorySegmentsQueried && Dir != DirEnd; ++I, ++Dir) {
if (Dir->size() > ShortDirectorySegment)
Prefix = Filename.substr(0, Dir - DirEnd);
// Now award points based on lookups into our various indexes.
DenseMap<size_t, int> Candidates; // Index -> score.
auto Award = [&](int Points, ArrayRef<SubstringAndIndex> Range) {
for (const auto &Entry : Range)
Candidates[Entry.second] += Points;
// Award one point if the file's basename is a prefix of the candidate,
// and another if it's an exact match (so exact matches get two points).
Award(1, indexLookup</*Prefix=*/true>(Stem, Stems));
Award(1, indexLookup</*Prefix=*/false>(Stem, Stems));
// For each of the last few directories in the Filename, award a point
// if it's present in the candidate.
for (StringRef Dir : Dirs)
Award(1, indexLookup</*Prefix=*/false>(Dir, Components));
// Award one more point if the whole rest of the path matches.
if (sys::path::root_directory(Prefix) != Prefix)
Award(1, indexLookup</*Prefix=*/true>(Prefix, Paths));
return Candidates;
// Pick a single winner from the set of scored candidates.
// Returns (index, score).
std::pair<size_t, int> pickWinner(const DenseMap<size_t, int> &Candidates,
StringRef Filename,
types::ID PreferredLanguage) const {
struct ScoredCandidate {
size_t Index;
bool Preferred;
int Points;
size_t PrefixLength;
// Choose the best candidate by (preferred, points, prefix length, alpha).
ScoredCandidate Best = {size_t(-1), false, 0, 0};
for (const auto &Candidate : Candidates) {
ScoredCandidate S;
S.Index = Candidate.first;
S.Preferred = PreferredLanguage == types::TY_INVALID ||
PreferredLanguage == Commands[S.Index].Type;
S.Points = Candidate.second;
if (!S.Preferred && Best.Preferred)
if (S.Preferred == Best.Preferred) {
if (S.Points < Best.Points)
if (S.Points == Best.Points) {
S.PrefixLength = matchingPrefix(Filename, Paths[S.Index].first);
if (S.PrefixLength < Best.PrefixLength)
// hidden heuristics should at least be deterministic!
if (S.PrefixLength == Best.PrefixLength)
if (S.Index > Best.Index)
// PrefixLength was only set above if actually needed for a tiebreak.
// But it definitely needs to be set to break ties in the future.
S.PrefixLength = matchingPrefix(Filename, Paths[S.Index].first);
Best = S;
// Edge case: no candidate got any points.
// We ignore PreferredLanguage at this point (not ideal).
if (Best.Index == size_t(-1))
return {longestMatch(Filename, Paths).second, 0};
return {Best.Index, Best.Points};
// Returns the range within a sorted index that compares equal to Key.
// If Prefix is true, it's instead the range starting with Key.
template <bool Prefix>
indexLookup(StringRef Key, const std::vector<SubstringAndIndex> &Idx) const {
// Use pointers as iteratiors to ease conversion of result to ArrayRef.
auto Range = std::equal_range(, + Idx.size(), Key,
return {Range.first, Range.second};
// Performs a point lookup into a nonempty index, returning a longest match.
longestMatch(StringRef Key, const std::vector<SubstringAndIndex> &Idx) const {
// Longest substring match will be adjacent to a direct lookup.
auto It =
std::lower_bound(Idx.begin(), Idx.end(), SubstringAndIndex{Key, 0});
if (It == Idx.begin())
return *It;
if (It == Idx.end())
return *--It;
// Have to choose between It and It-1
size_t Prefix = matchingPrefix(Key, It->first);
size_t PrevPrefix = matchingPrefix(Key, (It - 1)->first);
return Prefix > PrevPrefix ? *It : *--It;
std::vector<TransferableCommand> Commands; // Indexes point into this.
BumpPtrAllocator Arena;
StringSaver Strings;
// Indexes of candidates by certain substrings.
// String is lowercase and sorted, index points into OriginalPaths.
std::vector<SubstringAndIndex> Paths; // Full path.
std::vector<SubstringAndIndex> Stems; // Basename, without extension.
std::vector<SubstringAndIndex> Components; // Last path components.
// The actual CompilationDatabase wrapper delegates to its inner database.
// If no match, looks up a command in CommandIndex and transfers it to the file.
class InterpolatingCompilationDatabase : public CompilationDatabase {
InterpolatingCompilationDatabase(std::unique_ptr<CompilationDatabase> Inner)
: Inner(std::move(Inner)), Index(allCommands()) {}
getCompileCommands(StringRef Filename) const override {
auto Known = Inner->getCompileCommands(Filename);
if (Index.empty() || !Known.empty())
return Known;
bool TypeCertain;
auto Lang = guessType(Filename, &TypeCertain);
if (!TypeCertain)
Lang = types::TY_INVALID;
return {Index.chooseProxy(Filename, foldType(Lang)).transferTo(Filename)};
std::vector<std::string> getAllFiles() const override {
return Inner->getAllFiles();
std::vector<CompileCommand> getAllCompileCommands() const override {
return Inner->getAllCompileCommands();
std::vector<TransferableCommand> allCommands() {
std::vector<TransferableCommand> Result;
for (auto Command : Inner->getAllCompileCommands()) {
if (Result.back().Type == types::TY_INVALID)
return Result;
std::unique_ptr<CompilationDatabase> Inner;
CommandIndex Index;
} // namespace
inferMissingCompileCommands(std::unique_ptr<CompilationDatabase> Inner) {
return llvm::make_unique<InterpolatingCompilationDatabase>(std::move(Inner));
} // namespace tooling
} // namespace clang