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//===--- DesignatedInitializers.cpp - clang-tidy --------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file provides utilities for designated initializers.
///
//===----------------------------------------------------------------------===//
#include "DesignatedInitializers.h"
#include "clang/AST/DeclCXX.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/ScopeExit.h"
namespace clang::tidy::utils {
namespace {
/// Returns true if Name is reserved, like _Foo or __Vector_base.
static inline bool isReservedName(llvm::StringRef Name) {
// This doesn't catch all cases, but the most common.
return Name.size() >= 2 && Name[0] == '_' &&
(isUppercase(Name[1]) || Name[1] == '_');
}
// Helper class to iterate over the designator names of an aggregate type.
//
// For an array type, yields [0], [1], [2]...
// For aggregate classes, yields null for each base, then .field1, .field2,
// ...
class AggregateDesignatorNames {
public:
AggregateDesignatorNames(QualType T) {
if (!T.isNull()) {
T = T.getCanonicalType();
if (T->isArrayType()) {
IsArray = true;
Valid = true;
return;
}
if (const RecordDecl *RD = T->getAsRecordDecl()) {
Valid = true;
FieldsIt = RD->field_begin();
FieldsEnd = RD->field_end();
if (const auto *CRD = llvm::dyn_cast<CXXRecordDecl>(RD)) {
BasesIt = CRD->bases_begin();
BasesEnd = CRD->bases_end();
Valid = CRD->isAggregate();
}
OneField = Valid && BasesIt == BasesEnd && FieldsIt != FieldsEnd &&
std::next(FieldsIt) == FieldsEnd;
}
}
}
// Returns false if the type was not an aggregate.
operator bool() const { return Valid; }
// Advance to the next element in the aggregate.
void next() {
if (IsArray)
++Index;
else if (BasesIt != BasesEnd)
++BasesIt;
else if (FieldsIt != FieldsEnd)
++FieldsIt;
}
// Print the designator to Out.
// Returns false if we could not produce a designator for this element.
bool append(std::string &Out, bool ForSubobject) {
if (IsArray) {
Out.push_back('[');
Out.append(std::to_string(Index));
Out.push_back(']');
return true;
}
if (BasesIt != BasesEnd)
return false; // Bases can't be designated. Should we make one up?
if (FieldsIt != FieldsEnd) {
llvm::StringRef FieldName;
if (const IdentifierInfo *II = FieldsIt->getIdentifier())
FieldName = II->getName();
// For certain objects, their subobjects may be named directly.
if (ForSubobject &&
(FieldsIt->isAnonymousStructOrUnion() ||
// std::array<int,3> x = {1,2,3}. Designators not strictly valid!
(OneField && isReservedName(FieldName))))
return true;
if (!FieldName.empty() && !isReservedName(FieldName)) {
Out.push_back('.');
Out.append(FieldName.begin(), FieldName.end());
return true;
}
return false;
}
return false;
}
private:
bool Valid = false;
bool IsArray = false;
bool OneField = false; // e.g. std::array { T __elements[N]; }
unsigned Index = 0;
CXXRecordDecl::base_class_const_iterator BasesIt;
CXXRecordDecl::base_class_const_iterator BasesEnd;
RecordDecl::field_iterator FieldsIt;
RecordDecl::field_iterator FieldsEnd;
};
// Collect designator labels describing the elements of an init list.
//
// This function contributes the designators of some (sub)object, which is
// represented by the semantic InitListExpr Sem.
// This includes any nested subobjects, but *only* if they are part of the
// same original syntactic init list (due to brace elision). In other words,
// it may descend into subobjects but not written init-lists.
//
// For example: struct Outer { Inner a,b; }; struct Inner { int x, y; }
// Outer o{{1, 2}, 3};
// This function will be called with Sem = { {1, 2}, {3, ImplicitValue} }
// It should generate designators '.a:' and '.b.x:'.
// '.a:' is produced directly without recursing into the written sublist.
// (The written sublist will have a separate collectDesignators() call later).
// Recursion with Prefix='.b' and Sem = {3, ImplicitValue} produces '.b.x:'.
void collectDesignators(const InitListExpr *Sem,
llvm::DenseMap<SourceLocation, std::string> &Out,
const llvm::DenseSet<SourceLocation> &NestedBraces,
std::string &Prefix) {
if (!Sem || Sem->isTransparent())
return;
assert(Sem->isSemanticForm());
// The elements of the semantic form all correspond to direct subobjects of
// the aggregate type. `Fields` iterates over these subobject names.
AggregateDesignatorNames Fields(Sem->getType());
if (!Fields)
return;
for (const Expr *Init : Sem->inits()) {
auto Next = llvm::make_scope_exit([&, Size(Prefix.size())] {
Fields.next(); // Always advance to the next subobject name.
Prefix.resize(Size); // Erase any designator we appended.
});
// Skip for a broken initializer or if it is a "hole" in a subobject that
// was not explicitly initialized.
if (!Init || llvm::isa<ImplicitValueInitExpr>(Init))
continue;
const auto *BraceElidedSubobject = llvm::dyn_cast<InitListExpr>(Init);
if (BraceElidedSubobject &&
NestedBraces.contains(BraceElidedSubobject->getLBraceLoc()))
BraceElidedSubobject = nullptr; // there were braces!
if (!Fields.append(Prefix, BraceElidedSubobject != nullptr))
continue; // no designator available for this subobject
if (BraceElidedSubobject) {
// If the braces were elided, this aggregate subobject is initialized
// inline in the same syntactic list.
// Descend into the semantic list describing the subobject.
// (NestedBraces are still correct, they're from the same syntactic
// list).
collectDesignators(BraceElidedSubobject, Out, NestedBraces, Prefix);
continue;
}
Out.try_emplace(Init->getBeginLoc(), Prefix);
}
}
} // namespace
llvm::DenseMap<SourceLocation, std::string>
getUnwrittenDesignators(const InitListExpr *Syn) {
assert(Syn->isSyntacticForm());
// collectDesignators needs to know which InitListExprs in the semantic tree
// were actually written, but InitListExpr::isExplicit() lies.
// Instead, record where braces of sub-init-lists occur in the syntactic form.
llvm::DenseSet<SourceLocation> NestedBraces;
for (const Expr *Init : Syn->inits())
if (auto *Nested = llvm::dyn_cast<InitListExpr>(Init))
NestedBraces.insert(Nested->getLBraceLoc());
// Traverse the semantic form to find the designators.
// We use their SourceLocation to correlate with the syntactic form later.
llvm::DenseMap<SourceLocation, std::string> Designators;
std::string EmptyPrefix;
collectDesignators(Syn->isSemanticForm() ? Syn : Syn->getSemanticForm(),
Designators, NestedBraces, EmptyPrefix);
return Designators;
}
} // namespace clang::tidy::utils
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