clang-tools  3.8.0
UseNullptrCheck.cpp
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1 //===--- UseNullptrCheck.cpp - clang-tidy----------------------------------===//
2 //
3 // The LLVM Compiler Infrastructure
4 //
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
7 //
8 //===----------------------------------------------------------------------===//
9 
10 #include "UseNullptrCheck.h"
11 #include "clang/AST/ASTContext.h"
12 #include "clang/AST/RecursiveASTVisitor.h"
13 #include "clang/ASTMatchers/ASTMatchFinder.h"
14 #include "clang/Lex/Lexer.h"
15 
16 using namespace clang;
17 using namespace clang::ast_matchers;
18 using namespace llvm;
19 
20 namespace clang {
21 namespace tidy {
22 namespace modernize {
23 namespace {
24 
25 const char CastSequence[] = "sequence";
26 
27 /// \brief Matches cast expressions that have a cast kind of CK_NullToPointer
28 /// or CK_NullToMemberPointer.
29 ///
30 /// Given
31 /// \code
32 /// int *p = 0;
33 /// \endcode
34 /// implicitCastExpr(isNullToPointer()) matches the implicit cast clang adds
35 /// around \c 0.
36 AST_MATCHER(CastExpr, isNullToPointer) {
37  return Node.getCastKind() == CK_NullToPointer ||
38  Node.getCastKind() == CK_NullToMemberPointer;
39 }
40 
41 AST_MATCHER(Type, sugaredNullptrType) {
42  const Type *DesugaredType = Node.getUnqualifiedDesugaredType();
43  if (const BuiltinType *BT = dyn_cast<BuiltinType>(DesugaredType))
44  return BT->getKind() == BuiltinType::NullPtr;
45  return false;
46 }
47 
48 /// \brief Create a matcher that finds implicit casts as well as the head of a
49 /// sequence of zero or more nested explicit casts that have an implicit cast
50 /// to null within.
51 /// Finding sequences of explict casts is necessary so that an entire sequence
52 /// can be replaced instead of just the inner-most implicit cast.
53 StatementMatcher makeCastSequenceMatcher() {
54  StatementMatcher ImplicitCastToNull = implicitCastExpr(
55  isNullToPointer(),
56  unless(hasSourceExpression(hasType(sugaredNullptrType()))));
57 
58  return castExpr(anyOf(ImplicitCastToNull,
59  explicitCastExpr(hasDescendant(ImplicitCastToNull))),
60  unless(hasAncestor(explicitCastExpr())))
61  .bind(CastSequence);
62 }
63 
64 bool isReplaceableRange(SourceLocation StartLoc, SourceLocation EndLoc,
65  const SourceManager &SM) {
66  return SM.isWrittenInSameFile(StartLoc, EndLoc);
67 }
68 
69 /// \brief Replaces the provided range with the text "nullptr", but only if
70 /// the start and end location are both in main file.
71 /// Returns true if and only if a replacement was made.
72 void replaceWithNullptr(ClangTidyCheck &Check, SourceManager &SM,
73  SourceLocation StartLoc, SourceLocation EndLoc) {
74  CharSourceRange Range(SourceRange(StartLoc, EndLoc), true);
75  // Add a space if nullptr follows an alphanumeric character. This happens
76  // whenever there is an c-style explicit cast to nullptr not surrounded by
77  // parentheses and right beside a return statement.
78  SourceLocation PreviousLocation = StartLoc.getLocWithOffset(-1);
79  bool NeedsSpace = isAlphanumeric(*SM.getCharacterData(PreviousLocation));
80  Check.diag(Range.getBegin(), "use nullptr") << FixItHint::CreateReplacement(
81  Range, NeedsSpace ? " nullptr" : "nullptr");
82 }
83 
84 /// \brief Returns the name of the outermost macro.
85 ///
86 /// Given
87 /// \code
88 /// #define MY_NULL NULL
89 /// \endcode
90 /// If \p Loc points to NULL, this function will return the name MY_NULL.
91 StringRef getOutermostMacroName(SourceLocation Loc, const SourceManager &SM,
92  const LangOptions &LO) {
93  assert(Loc.isMacroID());
94  SourceLocation OutermostMacroLoc;
95 
96  while (Loc.isMacroID()) {
97  OutermostMacroLoc = Loc;
98  Loc = SM.getImmediateMacroCallerLoc(Loc);
99  }
100 
101  return Lexer::getImmediateMacroName(OutermostMacroLoc, SM, LO);
102 }
103 
104 /// \brief RecursiveASTVisitor for ensuring all nodes rooted at a given AST
105 /// subtree that have file-level source locations corresponding to a macro
106 /// argument have implicit NullTo(Member)Pointer nodes as ancestors.
107 class MacroArgUsageVisitor : public RecursiveASTVisitor<MacroArgUsageVisitor> {
108 public:
109  MacroArgUsageVisitor(SourceLocation CastLoc, const SourceManager &SM)
110  : CastLoc(CastLoc), SM(SM), Visited(false), CastFound(false),
111  InvalidFound(false) {
112  assert(CastLoc.isFileID());
113  }
114 
115  bool TraverseStmt(Stmt *S) {
116  bool VisitedPreviously = Visited;
117 
118  if (!RecursiveASTVisitor<MacroArgUsageVisitor>::TraverseStmt(S))
119  return false;
120 
121  // The point at which VisitedPreviously is false and Visited is true is the
122  // root of a subtree containing nodes whose locations match CastLoc. It's
123  // at this point we test that the Implicit NullTo(Member)Pointer cast was
124  // found or not.
125  if (!VisitedPreviously) {
126  if (Visited && !CastFound) {
127  // Found nodes with matching SourceLocations but didn't come across a
128  // cast. This is an invalid macro arg use. Can stop traversal
129  // completely now.
130  InvalidFound = true;
131  return false;
132  }
133  // Reset state as we unwind back up the tree.
134  CastFound = false;
135  Visited = false;
136  }
137  return true;
138  }
139 
140  bool VisitStmt(Stmt *S) {
141  if (SM.getFileLoc(S->getLocStart()) != CastLoc)
142  return true;
143  Visited = true;
144 
145  const ImplicitCastExpr *Cast = dyn_cast<ImplicitCastExpr>(S);
146  if (Cast && (Cast->getCastKind() == CK_NullToPointer ||
147  Cast->getCastKind() == CK_NullToMemberPointer))
148  CastFound = true;
149 
150  return true;
151  }
152 
153  bool TraverseInitListExpr(InitListExpr *S) {
154  // Only go through the semantic form of the InitListExpr, because
155  // ImplicitCast might not appear in the syntactic form, and this results in
156  // finding usages of the macro argument that don't have a ImplicitCast as an
157  // ancestor (thus invalidating the replacement) when they actually have.
158  return RecursiveASTVisitor<MacroArgUsageVisitor>::
159  TraverseSynOrSemInitListExpr(
160  S->isSemanticForm() ? S : S->getSemanticForm());
161  }
162 
163  bool foundInvalid() const { return InvalidFound; }
164 
165 private:
166  SourceLocation CastLoc;
167  const SourceManager &SM;
168 
169  bool Visited;
170  bool CastFound;
172 };
173 
174 /// \brief Looks for implicit casts as well as sequences of 0 or more explicit
175 /// casts with an implicit null-to-pointer cast within.
176 ///
177 /// The matcher this visitor is used with will find a single implicit cast or a
178 /// top-most explicit cast (i.e. it has no explicit casts as an ancestor) where
179 /// an implicit cast is nested within. However, there is no guarantee that only
180 /// explicit casts exist between the found top-most explicit cast and the
181 /// possibly more than one nested implicit cast. This visitor finds all cast
182 /// sequences with an implicit cast to null within and creates a replacement
183 /// leaving the outermost explicit cast unchanged to avoid introducing
184 /// ambiguities.
185 class CastSequenceVisitor : public RecursiveASTVisitor<CastSequenceVisitor> {
186 public:
187  CastSequenceVisitor(ASTContext &Context, ArrayRef<StringRef> NullMacros,
188  ClangTidyCheck &check)
189  : SM(Context.getSourceManager()), Context(Context),
190  NullMacros(NullMacros), Check(check), FirstSubExpr(nullptr),
191  PruneSubtree(false) {}
192 
193  bool TraverseStmt(Stmt *S) {
194  // Stop traversing down the tree if requested.
195  if (PruneSubtree) {
196  PruneSubtree = false;
197  return true;
198  }
199  return RecursiveASTVisitor<CastSequenceVisitor>::TraverseStmt(S);
200  }
201 
202  // Only VisitStmt is overridden as we shouldn't find other base AST types
203  // within a cast expression.
204  bool VisitStmt(Stmt *S) {
205  CastExpr *C = dyn_cast<CastExpr>(S);
206  if (!C) {
207  FirstSubExpr = nullptr;
208  return true;
209  }
210  if (!FirstSubExpr)
211  FirstSubExpr = C->getSubExpr()->IgnoreParens();
212 
213  if (C->getCastKind() != CK_NullToPointer &&
214  C->getCastKind() != CK_NullToMemberPointer) {
215  return true;
216  }
217 
218  SourceLocation StartLoc = FirstSubExpr->getLocStart();
219  SourceLocation EndLoc = FirstSubExpr->getLocEnd();
220 
221  // If the location comes from a macro arg expansion, *all* uses of that
222  // arg must be checked to result in NullTo(Member)Pointer casts.
223  //
224  // If the location comes from a macro body expansion, check to see if its
225  // coming from one of the allowed 'NULL' macros.
226  if (SM.isMacroArgExpansion(StartLoc) && SM.isMacroArgExpansion(EndLoc)) {
227  SourceLocation FileLocStart = SM.getFileLoc(StartLoc),
228  FileLocEnd = SM.getFileLoc(EndLoc);
229  if (isReplaceableRange(FileLocStart, FileLocEnd, SM) &&
230  allArgUsesValid(C)) {
231  replaceWithNullptr(Check, SM, FileLocStart, FileLocEnd);
232  }
233  return skipSubTree();
234  }
235 
236  if (SM.isMacroBodyExpansion(StartLoc) && SM.isMacroBodyExpansion(EndLoc)) {
237  StringRef OutermostMacroName =
238  getOutermostMacroName(StartLoc, SM, Context.getLangOpts());
239 
240  // Check to see if the user wants to replace the macro being expanded.
241  if (std::find(NullMacros.begin(), NullMacros.end(), OutermostMacroName) ==
242  NullMacros.end()) {
243  return skipSubTree();
244  }
245 
246  StartLoc = SM.getFileLoc(StartLoc);
247  EndLoc = SM.getFileLoc(EndLoc);
248  }
249 
250  if (!isReplaceableRange(StartLoc, EndLoc, SM)) {
251  return skipSubTree();
252  }
253  replaceWithNullptr(Check, SM, StartLoc, EndLoc);
254 
255  return skipSubTree();
256  }
257 
258 private:
259  bool skipSubTree() {
260  PruneSubtree = true;
261  return true;
262  }
263 
264  /// \brief Tests that all expansions of a macro arg, one of which expands to
265  /// result in \p CE, yield NullTo(Member)Pointer casts.
266  bool allArgUsesValid(const CastExpr *CE) {
267  SourceLocation CastLoc = CE->getLocStart();
268 
269  // Step 1: Get location of macro arg and location of the macro the arg was
270  // provided to.
271  SourceLocation ArgLoc, MacroLoc;
272  if (!getMacroAndArgLocations(CastLoc, ArgLoc, MacroLoc))
273  return false;
274 
275  // Step 2: Find the first ancestor that doesn't expand from this macro.
276  ast_type_traits::DynTypedNode ContainingAncestor;
277  if (!findContainingAncestor(
278  ast_type_traits::DynTypedNode::create<Stmt>(*CE), MacroLoc,
279  ContainingAncestor))
280  return false;
281 
282  // Step 3:
283  // Visit children of this containing parent looking for the least-descended
284  // nodes of the containing parent which are macro arg expansions that expand
285  // from the given arg location.
286  // Visitor needs: arg loc.
287  MacroArgUsageVisitor ArgUsageVisitor(SM.getFileLoc(CastLoc), SM);
288  if (const auto *D = ContainingAncestor.get<Decl>())
289  ArgUsageVisitor.TraverseDecl(const_cast<Decl *>(D));
290  else if (const auto *S = ContainingAncestor.get<Stmt>())
291  ArgUsageVisitor.TraverseStmt(const_cast<Stmt *>(S));
292  else
293  llvm_unreachable("Unhandled ContainingAncestor node type");
294 
295  return !ArgUsageVisitor.foundInvalid();
296  }
297 
298  /// \brief Given the SourceLocation for a macro arg expansion, finds the
299  /// non-macro SourceLocation of the macro the arg was passed to and the
300  /// non-macro SourceLocation of the argument in the arg list to that macro.
301  /// These results are returned via \c MacroLoc and \c ArgLoc respectively.
302  /// These values are undefined if the return value is false.
303  ///
304  /// \returns false if one of the returned SourceLocations would be a
305  /// SourceLocation pointing within the definition of another macro.
306  bool getMacroAndArgLocations(SourceLocation Loc, SourceLocation &ArgLoc,
307  SourceLocation &MacroLoc) {
308  assert(Loc.isMacroID() && "Only reasonble to call this on macros");
309 
310  ArgLoc = Loc;
311 
312  // Find the location of the immediate macro expansion.
313  while (true) {
314  std::pair<FileID, unsigned> LocInfo = SM.getDecomposedLoc(ArgLoc);
315  const SrcMgr::SLocEntry *E = &SM.getSLocEntry(LocInfo.first);
316  const SrcMgr::ExpansionInfo &Expansion = E->getExpansion();
317 
318  SourceLocation OldArgLoc = ArgLoc;
319  ArgLoc = Expansion.getExpansionLocStart();
320  if (!Expansion.isMacroArgExpansion()) {
321  if (!MacroLoc.isFileID())
322  return false;
323 
324  StringRef Name =
325  Lexer::getImmediateMacroName(OldArgLoc, SM, Context.getLangOpts());
326  return std::find(NullMacros.begin(), NullMacros.end(), Name) !=
327  NullMacros.end();
328  }
329 
330  MacroLoc = SM.getImmediateExpansionRange(ArgLoc).first;
331 
332  ArgLoc = Expansion.getSpellingLoc().getLocWithOffset(LocInfo.second);
333  if (ArgLoc.isFileID())
334  return true;
335 
336  // If spelling location resides in the same FileID as macro expansion
337  // location, it means there is no inner macro.
338  FileID MacroFID = SM.getFileID(MacroLoc);
339  if (SM.isInFileID(ArgLoc, MacroFID)) {
340  // Don't transform this case. If the characters that caused the
341  // null-conversion come from within a macro, they can't be changed.
342  return false;
343  }
344  }
345 
346  llvm_unreachable("getMacroAndArgLocations");
347  }
348 
349  /// \brief Tests if TestMacroLoc is found while recursively unravelling
350  /// expansions starting at TestLoc. TestMacroLoc.isFileID() must be true.
351  /// Implementation is very similar to getMacroAndArgLocations() except in this
352  /// case, it's not assumed that TestLoc is expanded from a macro argument.
353  /// While unravelling expansions macro arguments are handled as with
354  /// getMacroAndArgLocations() but in this function macro body expansions are
355  /// also handled.
356  ///
357  /// False means either:
358  /// - TestLoc is not from a macro expansion.
359  /// - TestLoc is from a different macro expansion.
360  bool expandsFrom(SourceLocation TestLoc, SourceLocation TestMacroLoc) {
361  if (TestLoc.isFileID()) {
362  return false;
363  }
364 
365  SourceLocation Loc = TestLoc, MacroLoc;
366 
367  while (true) {
368  std::pair<FileID, unsigned> LocInfo = SM.getDecomposedLoc(Loc);
369  const SrcMgr::SLocEntry *E = &SM.getSLocEntry(LocInfo.first);
370  const SrcMgr::ExpansionInfo &Expansion = E->getExpansion();
371 
372  Loc = Expansion.getExpansionLocStart();
373 
374  if (!Expansion.isMacroArgExpansion()) {
375  if (Loc.isFileID()) {
376  return Loc == TestMacroLoc;
377  }
378  // Since Loc is still a macro ID and it's not an argument expansion, we
379  // don't need to do the work of handling an argument expansion. Simply
380  // keep recursively expanding until we hit a FileID or a macro arg
381  // expansion or a macro arg expansion.
382  continue;
383  }
384 
385  MacroLoc = SM.getImmediateExpansionRange(Loc).first;
386  if (MacroLoc.isFileID() && MacroLoc == TestMacroLoc) {
387  // Match made.
388  return true;
389  }
390 
391  Loc = Expansion.getSpellingLoc().getLocWithOffset(LocInfo.second);
392  if (Loc.isFileID()) {
393  // If we made it this far without finding a match, there is no match to
394  // be made.
395  return false;
396  }
397  }
398 
399  llvm_unreachable("expandsFrom");
400  }
401 
402  /// \brief Given a starting point \c Start in the AST, find an ancestor that
403  /// doesn't expand from the macro called at file location \c MacroLoc.
404  ///
405  /// \pre MacroLoc.isFileID()
406  /// \returns true if such an ancestor was found, false otherwise.
407  bool findContainingAncestor(ast_type_traits::DynTypedNode Start,
408  SourceLocation MacroLoc,
409  ast_type_traits::DynTypedNode &Result) {
410  // Below we're only following the first parent back up the AST. This should
411  // be fine since for the statements we care about there should only be one
412  // parent, except for the case specified below.
413 
414  assert(MacroLoc.isFileID());
415 
416  while (true) {
417  const auto &Parents = Context.getParents(Start);
418  if (Parents.empty())
419  return false;
420  if (Parents.size() > 1) {
421  // If there are more than one parents, don't do the replacement unless
422  // they are InitListsExpr (semantic and syntactic form). In this case we
423  // can choose any one here, and the ASTVisitor will take care of
424  // traversing the right one.
425  for (const auto &Parent : Parents) {
426  if (!Parent.get<InitListExpr>())
427  return false;
428  }
429  }
430 
431  const ast_type_traits::DynTypedNode &Parent = Parents[0];
432 
433  SourceLocation Loc;
434  if (const auto *D = Parent.get<Decl>())
435  Loc = D->getLocStart();
436  else if (const auto *S = Parent.get<Stmt>())
437  Loc = S->getLocStart();
438 
439  // TypeLoc and NestedNameSpecifierLoc are members of the parent map. Skip
440  // them and keep going up.
441  if (Loc.isValid()) {
442  if (!expandsFrom(Loc, MacroLoc)) {
443  Result = Parent;
444  return true;
445  }
446  }
447  Start = Parent;
448  }
449 
450  llvm_unreachable("findContainingAncestor");
451  }
452 
453 private:
454  SourceManager &SM;
455  ASTContext &Context;
456  ArrayRef<StringRef> NullMacros;
457  ClangTidyCheck &Check;
460 };
461 
462 } // namespace
463 
464 UseNullptrCheck::UseNullptrCheck(StringRef Name, ClangTidyContext *Context)
465  : ClangTidyCheck(Name, Context),
466  NullMacrosStr(Options.get("NullMacros", "")) {
467  StringRef(NullMacrosStr).split(NullMacros, ",");
468 }
469 
471  Options.store(Opts, "NullMacros", NullMacrosStr);
472 }
473 
475  // Only register the matcher for C++. Because this checker is used for
476  // modernization, it is reasonable to run it on any C++ standard with the
477  // assumption the user is trying to modernize their codebase.
478  if (getLangOpts().CPlusPlus)
479  Finder->addMatcher(makeCastSequenceMatcher(), this);
480 }
481 
482 void UseNullptrCheck::check(const MatchFinder::MatchResult &Result) {
483  const auto *NullCast = Result.Nodes.getNodeAs<CastExpr>(CastSequence);
484  assert(NullCast && "Bad Callback. No node provided");
485 
486  // Given an implicit null-ptr cast or an explicit cast with an implicit
487  // null-to-pointer cast within use CastSequenceVisitor to identify sequences
488  // of explicit casts that can be converted into 'nullptr'.
489  CastSequenceVisitor(*Result.Context, NullMacros, *this)
490  .TraverseStmt(const_cast<CastExpr *>(NullCast));
491 }
492 
493 } // namespace modernize
494 } // namespace tidy
495 } // namespace clang
SourceLocation Loc
'#' location in the include directive
LangOptions getLangOpts() const
Returns the language options from the context.
Definition: ClangTidy.h:162
ASTContext & Context
StringHandle Name
std::unique_ptr< ast_matchers::MatchFinder > Finder
Definition: ClangTidy.cpp:188
Base class for all clang-tidy checks.
Definition: ClangTidy.h:102
bool CastFound
AST_MATCHER(Stmt, isInsideOfRangeBeginEndStmt)
void registerMatchers(ast_matchers::MatchFinder *Finder) override
Override this to register ASTMatchers with Finder.
const SourceManager & SM
bool Visited
bool InvalidFound
bool PruneSubtree
void store(ClangTidyOptions::OptionMap &Options, StringRef LocalName, StringRef Value) const
Stores an option with the check-local name LocalName with string value Value to Options.
Definition: ClangTidy.cpp:344
std::map< std::string, std::string > OptionMap
Expr * FirstSubExpr
void storeOptions(ClangTidyOptions::OptionMap &Opts) override
Should store all options supported by this check with their current values or default values for opti...
void check(const ast_matchers::MatchFinder::MatchResult &Result) override
ClangTidyChecks that register ASTMatchers should do the actual work in here.
CharSourceRange Range
SourceRange for the file name.
Every ClangTidyCheck reports errors through a DiagnosticsEngine provided by this context.
ClangTidyCheck & Check
const NamedDecl * Result
Definition: USRFinder.cpp:121
ArrayRef< StringRef > NullMacros
SourceLocation CastLoc