clang-tools 10.0.0

UseNullptrCheck.cpp
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1 //===--- UseNullptrCheck.cpp - clang-tidy----------------------------------===//
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 #include "UseNullptrCheck.h"
10 #include "clang/AST/ASTContext.h"
11 #include "clang/AST/RecursiveASTVisitor.h"
12 #include "clang/ASTMatchers/ASTMatchFinder.h"
13 #include "clang/Lex/Lexer.h"
14
15 using namespace clang;
16 using namespace clang::ast_matchers;
17 using namespace llvm;
18
19 namespace clang {
20 namespace tidy {
21 namespace modernize {
22 namespace {
23
24 const char CastSequence[] = "sequence";
25
26 AST_MATCHER(Type, sugaredNullptrType) {
27 const Type *DesugaredType = Node.getUnqualifiedDesugaredType();
28 if (const auto *BT = dyn_cast<BuiltinType>(DesugaredType))
29 return BT->getKind() == BuiltinType::NullPtr;
30 return false;
31 }
32
33 /// Create a matcher that finds implicit casts as well as the head of a
34 /// sequence of zero or more nested explicit casts that have an implicit cast
35 /// to null within.
36 /// Finding sequences of explicit casts is necessary so that an entire sequence
37 /// can be replaced instead of just the inner-most implicit cast.
38 StatementMatcher makeCastSequenceMatcher() {
39 StatementMatcher ImplicitCastToNull = implicitCastExpr(
40 anyOf(hasCastKind(CK_NullToPointer), hasCastKind(CK_NullToMemberPointer)),
41 unless(hasImplicitDestinationType(qualType(substTemplateTypeParmType()))),
42 unless(hasSourceExpression(hasType(sugaredNullptrType()))));
43
44 return castExpr(anyOf(ImplicitCastToNull,
45 explicitCastExpr(hasDescendant(ImplicitCastToNull))),
46 unless(hasAncestor(explicitCastExpr())))
47 .bind(CastSequence);
48 }
49
50 bool isReplaceableRange(SourceLocation StartLoc, SourceLocation EndLoc,
51 const SourceManager &SM) {
52 return SM.isWrittenInSameFile(StartLoc, EndLoc);
53 }
54
55 /// Replaces the provided range with the text "nullptr", but only if
56 /// the start and end location are both in main file.
57 /// Returns true if and only if a replacement was made.
58 void replaceWithNullptr(ClangTidyCheck &Check, SourceManager &SM,
59 SourceLocation StartLoc, SourceLocation EndLoc) {
60 CharSourceRange Range(SourceRange(StartLoc, EndLoc), true);
61 // Add a space if nullptr follows an alphanumeric character. This happens
62 // whenever there is an c-style explicit cast to nullptr not surrounded by
63 // parentheses and right beside a return statement.
64 SourceLocation PreviousLocation = StartLoc.getLocWithOffset(-1);
65 bool NeedsSpace = isAlphanumeric(*SM.getCharacterData(PreviousLocation));
66 Check.diag(Range.getBegin(), "use nullptr") << FixItHint::CreateReplacement(
67 Range, NeedsSpace ? " nullptr" : "nullptr");
68 }
69
70 /// Returns the name of the outermost macro.
71 ///
72 /// Given
73 /// \code
74 /// #define MY_NULL NULL
75 /// \endcode
76 /// If \p Loc points to NULL, this function will return the name MY_NULL.
77 StringRef getOutermostMacroName(SourceLocation Loc, const SourceManager &SM,
78 const LangOptions &LO) {
79 assert(Loc.isMacroID());
80 SourceLocation OutermostMacroLoc;
81
82 while (Loc.isMacroID()) {
83 OutermostMacroLoc = Loc;
84 Loc = SM.getImmediateMacroCallerLoc(Loc);
85 }
86
87 return Lexer::getImmediateMacroName(OutermostMacroLoc, SM, LO);
88 }
89
90 /// RecursiveASTVisitor for ensuring all nodes rooted at a given AST
91 /// subtree that have file-level source locations corresponding to a macro
92 /// argument have implicit NullTo(Member)Pointer nodes as ancestors.
93 class MacroArgUsageVisitor : public RecursiveASTVisitor<MacroArgUsageVisitor> {
94 public:
95 MacroArgUsageVisitor(SourceLocation CastLoc, const SourceManager &SM)
96 : CastLoc(CastLoc), SM(SM), Visited(false), CastFound(false),
97 InvalidFound(false) {
98 assert(CastLoc.isFileID());
99 }
100
101 bool TraverseStmt(Stmt *S) {
102 bool VisitedPreviously = Visited;
103
104 if (!RecursiveASTVisitor<MacroArgUsageVisitor>::TraverseStmt(S))
105 return false;
106
107 // The point at which VisitedPreviously is false and Visited is true is the
108 // root of a subtree containing nodes whose locations match CastLoc. It's
109 // at this point we test that the Implicit NullTo(Member)Pointer cast was
110 // found or not.
111 if (!VisitedPreviously) {
112 if (Visited && !CastFound) {
113 // Found nodes with matching SourceLocations but didn't come across a
114 // cast. This is an invalid macro arg use. Can stop traversal
115 // completely now.
116 InvalidFound = true;
117 return false;
118 }
119 // Reset state as we unwind back up the tree.
120 CastFound = false;
121 Visited = false;
122 }
123 return true;
124 }
125
126 bool VisitStmt(Stmt *S) {
127 if (SM.getFileLoc(S->getBeginLoc()) != CastLoc)
128 return true;
129 Visited = true;
130
131 const ImplicitCastExpr *Cast = dyn_cast<ImplicitCastExpr>(S);
132 if (Cast && (Cast->getCastKind() == CK_NullToPointer ||
133 Cast->getCastKind() == CK_NullToMemberPointer))
134 CastFound = true;
135
136 return true;
137 }
138
139 bool TraverseInitListExpr(InitListExpr *S) {
140 // Only go through the semantic form of the InitListExpr, because
141 // ImplicitCast might not appear in the syntactic form, and this results in
142 // finding usages of the macro argument that don't have a ImplicitCast as an
143 // ancestor (thus invalidating the replacement) when they actually have.
144 return RecursiveASTVisitor<MacroArgUsageVisitor>::
145 TraverseSynOrSemInitListExpr(
146 S->isSemanticForm() ? S : S->getSemanticForm());
147 }
148
149 bool foundInvalid() const { return InvalidFound; }
150
151 private:
152 SourceLocation CastLoc;
153 const SourceManager &SM;
154
155 bool Visited;
156 bool CastFound;
157 bool InvalidFound;
158 };
159
160 /// Looks for implicit casts as well as sequences of 0 or more explicit
161 /// casts with an implicit null-to-pointer cast within.
162 ///
163 /// The matcher this visitor is used with will find a single implicit cast or a
164 /// top-most explicit cast (i.e. it has no explicit casts as an ancestor) where
165 /// an implicit cast is nested within. However, there is no guarantee that only
166 /// explicit casts exist between the found top-most explicit cast and the
167 /// possibly more than one nested implicit cast. This visitor finds all cast
168 /// sequences with an implicit cast to null within and creates a replacement
169 /// leaving the outermost explicit cast unchanged to avoid introducing
170 /// ambiguities.
171 class CastSequenceVisitor : public RecursiveASTVisitor<CastSequenceVisitor> {
172 public:
173 CastSequenceVisitor(ASTContext &Context, ArrayRef<StringRef> NullMacros,
174 ClangTidyCheck &check)
175 : SM(Context.getSourceManager()), Context(Context),
176 NullMacros(NullMacros), Check(check), FirstSubExpr(nullptr),
177 PruneSubtree(false) {}
178
179 bool TraverseStmt(Stmt *S) {
180 // Stop traversing down the tree if requested.
181 if (PruneSubtree) {
182 PruneSubtree = false;
183 return true;
184 }
185 return RecursiveASTVisitor<CastSequenceVisitor>::TraverseStmt(S);
186 }
187
188 // Only VisitStmt is overridden as we shouldn't find other base AST types
189 // within a cast expression.
190 bool VisitStmt(Stmt *S) {
191 auto *C = dyn_cast<CastExpr>(S);
192 // Catch the castExpr inside cxxDefaultArgExpr.
193 if (auto *E = dyn_cast<CXXDefaultArgExpr>(S)) {
194 C = dyn_cast<CastExpr>(E->getExpr());
195 FirstSubExpr = nullptr;
196 }
197 if (!C) {
198 FirstSubExpr = nullptr;
199 return true;
200 }
201
202 auto* CastSubExpr = C->getSubExpr()->IgnoreParens();
203 // Ignore cast expressions which cast nullptr literal.
204 if (isa<CXXNullPtrLiteralExpr>(CastSubExpr)) {
205 return true;
206 }
207
208 if (!FirstSubExpr)
209 FirstSubExpr = CastSubExpr;
210
211 if (C->getCastKind() != CK_NullToPointer &&
212 C->getCastKind() != CK_NullToMemberPointer) {
213 return true;
214 }
215
216 SourceLocation StartLoc = FirstSubExpr->getBeginLoc();
217 SourceLocation EndLoc = FirstSubExpr->getEndLoc();
218
219 // If the location comes from a macro arg expansion, *all* uses of that
220 // arg must be checked to result in NullTo(Member)Pointer casts.
221 //
222 // If the location comes from a macro body expansion, check to see if its
223 // coming from one of the allowed 'NULL' macros.
224 if (SM.isMacroArgExpansion(StartLoc) && SM.isMacroArgExpansion(EndLoc)) {
225 SourceLocation FileLocStart = SM.getFileLoc(StartLoc),
226 FileLocEnd = SM.getFileLoc(EndLoc);
227 SourceLocation ImmediateMacroArgLoc, MacroLoc;
228 // Skip NULL macros used in macro.
229 if (!getMacroAndArgLocations(StartLoc, ImmediateMacroArgLoc, MacroLoc) ||
230 ImmediateMacroArgLoc != FileLocStart)
231 return skipSubTree();
232
233 if (isReplaceableRange(FileLocStart, FileLocEnd, SM) &&
234 allArgUsesValid(C)) {
235 replaceWithNullptr(Check, SM, FileLocStart, FileLocEnd);
236 }
237 return true;
238 }
239
240 if (SM.isMacroBodyExpansion(StartLoc) && SM.isMacroBodyExpansion(EndLoc)) {
241 StringRef OutermostMacroName =
242 getOutermostMacroName(StartLoc, SM, Context.getLangOpts());
243
244 // Check to see if the user wants to replace the macro being expanded.
245 if (!llvm::is_contained(NullMacros, OutermostMacroName))
246 return skipSubTree();
247
248 StartLoc = SM.getFileLoc(StartLoc);
249 EndLoc = SM.getFileLoc(EndLoc);
250 }
251
252 if (!isReplaceableRange(StartLoc, EndLoc, SM)) {
253 return skipSubTree();
254 }
255 replaceWithNullptr(Check, SM, StartLoc, EndLoc);
256
257 return true;
258 }
259
260 private:
261 bool skipSubTree() {
262 PruneSubtree = true;
263 return true;
264 }
265
266 /// Tests that all expansions of a macro arg, one of which expands to
267 /// result in \p CE, yield NullTo(Member)Pointer casts.
268 bool allArgUsesValid(const CastExpr *CE) {
269 SourceLocation CastLoc = CE->getBeginLoc();
270
271 // Step 1: Get location of macro arg and location of the macro the arg was
272 // provided to.
273 SourceLocation ArgLoc, MacroLoc;
274 if (!getMacroAndArgLocations(CastLoc, ArgLoc, MacroLoc))
275 return false;
276
277 // Step 2: Find the first ancestor that doesn't expand from this macro.
278 ast_type_traits::DynTypedNode ContainingAncestor;
279 if (!findContainingAncestor(
280 ast_type_traits::DynTypedNode::create<Stmt>(*CE), MacroLoc,
281 ContainingAncestor))
282 return false;
283
284 // Step 3:
285 // Visit children of this containing parent looking for the least-descended
286 // nodes of the containing parent which are macro arg expansions that expand
287 // from the given arg location.
288 // Visitor needs: arg loc.
289 MacroArgUsageVisitor ArgUsageVisitor(SM.getFileLoc(CastLoc), SM);
290 if (const auto *D = ContainingAncestor.get<Decl>())
291 ArgUsageVisitor.TraverseDecl(const_cast<Decl *>(D));
292 else if (const auto *S = ContainingAncestor.get<Stmt>())
293 ArgUsageVisitor.TraverseStmt(const_cast<Stmt *>(S));
294 else
295 llvm_unreachable("Unhandled ContainingAncestor node type");
296
297 return !ArgUsageVisitor.foundInvalid();
298 }
299
300 /// Given the SourceLocation for a macro arg expansion, finds the
301 /// non-macro SourceLocation of the macro the arg was passed to and the
302 /// non-macro SourceLocation of the argument in the arg list to that macro.
303 /// These results are returned via \c MacroLoc and \c ArgLoc respectively.
304 /// These values are undefined if the return value is false.
305 ///
306 /// \returns false if one of the returned SourceLocations would be a
307 /// SourceLocation pointing within the definition of another macro.
308 bool getMacroAndArgLocations(SourceLocation Loc, SourceLocation &ArgLoc,
309 SourceLocation &MacroLoc) {
310 assert(Loc.isMacroID() && "Only reasonble to call this on macros");
311
312 ArgLoc = Loc;
313
314 // Find the location of the immediate macro expansion.
315 while (true) {
316 std::pair<FileID, unsigned> LocInfo = SM.getDecomposedLoc(ArgLoc);
317 const SrcMgr::SLocEntry *E = &SM.getSLocEntry(LocInfo.first);
318 const SrcMgr::ExpansionInfo &Expansion = E->getExpansion();
319
320 SourceLocation OldArgLoc = ArgLoc;
321 ArgLoc = Expansion.getExpansionLocStart();
322 if (!Expansion.isMacroArgExpansion()) {
323 if (!MacroLoc.isFileID())
324 return false;
325
326 StringRef Name =
327 Lexer::getImmediateMacroName(OldArgLoc, SM, Context.getLangOpts());
328 return llvm::is_contained(NullMacros, Name);
329 }
330
331 MacroLoc = SM.getExpansionRange(ArgLoc).getBegin();
332
333 ArgLoc = Expansion.getSpellingLoc().getLocWithOffset(LocInfo.second);
334 if (ArgLoc.isFileID())
335 return true;
336
337 // If spelling location resides in the same FileID as macro expansion
338 // location, it means there is no inner macro.
339 FileID MacroFID = SM.getFileID(MacroLoc);
340 if (SM.isInFileID(ArgLoc, MacroFID)) {
341 // Don't transform this case. If the characters that caused the
342 // null-conversion come from within a macro, they can't be changed.
343 return false;
344 }
345 }
346
347 llvm_unreachable("getMacroAndArgLocations");
348 }
349
350 /// Tests if TestMacroLoc is found while recursively unravelling
351 /// expansions starting at TestLoc. TestMacroLoc.isFileID() must be true.
352 /// Implementation is very similar to getMacroAndArgLocations() except in this
353 /// case, it's not assumed that TestLoc is expanded from a macro argument.
354 /// While unravelling expansions macro arguments are handled as with
355 /// getMacroAndArgLocations() but in this function macro body expansions are
356 /// also handled.
357 ///
358 /// False means either:
359 /// - TestLoc is not from a macro expansion.
360 /// - TestLoc is from a different macro expansion.
361 bool expandsFrom(SourceLocation TestLoc, SourceLocation TestMacroLoc) {
362 if (TestLoc.isFileID()) {
363 return false;
364 }
365
366 SourceLocation Loc = TestLoc, MacroLoc;
367
368 while (true) {
369 std::pair<FileID, unsigned> LocInfo = SM.getDecomposedLoc(Loc);
370 const SrcMgr::SLocEntry *E = &SM.getSLocEntry(LocInfo.first);
371 const SrcMgr::ExpansionInfo &Expansion = E->getExpansion();
372
373 Loc = Expansion.getExpansionLocStart();
374
375 if (!Expansion.isMacroArgExpansion()) {
376 if (Loc.isFileID()) {
377 return Loc == TestMacroLoc;
378 }
379 // Since Loc is still a macro ID and it's not an argument expansion, we
380 // don't need to do the work of handling an argument expansion. Simply
381 // keep recursively expanding until we hit a FileID or a macro arg
382 // expansion or a macro arg expansion.
383 continue;
384 }
385
386 MacroLoc = SM.getImmediateExpansionRange(Loc).getBegin();
387 if (MacroLoc.isFileID() && MacroLoc == TestMacroLoc) {
388 // Match made.
389 return true;
390 }
391
392 Loc = Expansion.getSpellingLoc().getLocWithOffset(LocInfo.second);
393 if (Loc.isFileID()) {
394 // If we made it this far without finding a match, there is no match to
395 // be made.
396 return false;
397 }
398 }
399
400 llvm_unreachable("expandsFrom");
401 }
402
403 /// Given a starting point \c Start in the AST, find an ancestor that
404 /// doesn't expand from the macro called at file location \c MacroLoc.
405 ///
406 /// \pre MacroLoc.isFileID()
407 /// \returns true if such an ancestor was found, false otherwise.
408 bool findContainingAncestor(ast_type_traits::DynTypedNode Start,
409 SourceLocation MacroLoc,
410 ast_type_traits::DynTypedNode &Result) {
411 // Below we're only following the first parent back up the AST. This should
412 // be fine since for the statements we care about there should only be one
413 // parent, except for the case specified below.
414
415 assert(MacroLoc.isFileID());
416
417 while (true) {
418 const auto &Parents = Context.getParents(Start);
419 if (Parents.empty())
420 return false;
421 if (Parents.size() > 1) {
422 // If there are more than one parents, don't do the replacement unless
423 // they are InitListsExpr (semantic and syntactic form). In this case we
424 // can choose any one here, and the ASTVisitor will take care of
425 // traversing the right one.
426 for (const auto &Parent : Parents) {
427 if (!Parent.get<InitListExpr>())
428 return false;
429 }
430 }
431
432 const ast_type_traits::DynTypedNode &Parent = Parents[0];
433
434 SourceLocation Loc;
435 if (const auto *D = Parent.get<Decl>())
436 Loc = D->getBeginLoc();
437 else if (const auto *S = Parent.get<Stmt>())
438 Loc = S->getBeginLoc();
439
440 // TypeLoc and NestedNameSpecifierLoc are members of the parent map. Skip
441 // them and keep going up.
442 if (Loc.isValid()) {
443 if (!expandsFrom(Loc, MacroLoc)) {
444 Result = Parent;
445 return true;
446 }
447 }
448 Start = Parent;
449 }
450
451 llvm_unreachable("findContainingAncestor");
452 }
453
454 private:
455 SourceManager &SM;
456 ASTContext &Context;
457 ArrayRef<StringRef> NullMacros;
458 ClangTidyCheck &Check;
459 Expr *FirstSubExpr;
460 bool PruneSubtree;
461 };
462
463 } // namespace
464
465 UseNullptrCheck::UseNullptrCheck(StringRef Name, ClangTidyContext *Context)
466 : ClangTidyCheck(Name, Context),
467 NullMacrosStr(Options.get("NullMacros", "")) {
468 StringRef(NullMacrosStr).split(NullMacros, ",");
469 }
470
471 void UseNullptrCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
472 Options.store(Opts, "NullMacros", NullMacrosStr);
473 }
474
475 void UseNullptrCheck::registerMatchers(MatchFinder *Finder) {
476 // Only register the matcher for C++. Because this checker is used for
477 // modernization, it is reasonable to run it on any C++ standard with the
478 // assumption the user is trying to modernize their codebase.
479 if (getLangOpts().CPlusPlus)
480 Finder->addMatcher(makeCastSequenceMatcher(), this);
481 }
482
483 void UseNullptrCheck::check(const MatchFinder::MatchResult &Result) {
484 const auto *NullCast = Result.Nodes.getNodeAs<CastExpr>(CastSequence);
485 assert(NullCast && "Bad Callback. No node provided");
486
487 // Given an implicit null-ptr cast or an explicit cast with an implicit
488 // null-to-pointer cast within use CastSequenceVisitor to identify sequences
489 // of explicit casts that can be converted into 'nullptr'.
490 CastSequenceVisitor(*Result.Context, NullMacros, *this)
491 .TraverseStmt(const_cast<CastExpr *>(NullCast));
492 }
493
494 } // namespace modernize
495 } // namespace tidy
496 } // namespace clang
Loc
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&#39;#&#39; location in the include directive
Definition: IncludeOrderCheck.cpp:37
clang::ast_matchers
Definition: AbseilMatcher.h:14
Decl
const FunctionDecl * Decl
Definition: AvoidBindCheck.cpp:93
clang::clangd::TypeHierarchyDirection::Parents
llvm
Some operations such as code completion produce a set of candidates.
Definition: YAMLGenerator.cpp:28
UseNullptrCheck.h
Parent
const Node * Parent
Definition: ExtractFunction.cpp:148
clang::ast_matchers::AST_MATCHER
AST_MATCHER(Expr, isMacroID)
Definition: PreferIsaOrDynCastInConditionalsCheck.cpp:18
clang::tidy::ClangTidyCheck
Base class for all clang-tidy checks.
Definition: ClangTidyCheck.h:47
clang::tidy::ClangTidyCheck::getLangOpts
const LangOptions & getLangOpts() const
Returns the language options from the context.
Definition: ClangTidyCheck.h:188
clang::tidy::ClangTidyCheck::Options
OptionsView Options
Definition: ClangTidyCheck.h:184
clang::tidy::modernize::UseNullptrCheck::registerMatchers
void registerMatchers(ast_matchers::MatchFinder *Finder) override
Override this to register AST matchers with Finder.
Definition: UseNullptrCheck.cpp:475
clang::tidy::ClangTidyCheck::OptionsView::store
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: ClangTidyCheck.cpp:58
Name
static constexpr llvm::StringLiteral Name
Definition: UppercaseLiteralSuffixCheck.cpp:27
clang::tidy::ClangTidyOptions::OptionMap
std::map< std::string, std::string > OptionMap
Definition: ClangTidyOptions.h:97
clang::tidy::modernize::UseNullptrCheck::storeOptions
void storeOptions(ClangTidyOptions::OptionMap &Opts) override
Should store all options supported by this check with their current values or default values for opti...
Definition: UseNullptrCheck.cpp:471
clang::tidy::modernize::UseNullptrCheck::check
void check(const ast_matchers::MatchFinder::MatchResult &Result) override
ClangTidyChecks that register ASTMatchers should do the actual work in here.
Definition: UseNullptrCheck.cpp:483
clang
===– Representation.cpp - ClangDoc Representation --------—*- C++ -*-===//
Definition: ApplyReplacements.h:27
Range
CharSourceRange Range
SourceRange for the file name.
Definition: IncludeOrderCheck.cpp:38
clang::tidy::ClangTidyContext
Every ClangTidyCheck reports errors through a DiagnosticsEngine provided by this context.
Definition: ClangTidyDiagnosticConsumer.h:77
E
const Expr * E
Definition: AvoidBindCheck.cpp:82
Type
NodeType Type
Definition: HTMLGenerator.cpp:73