readability-qualified-auto

Adds pointer qualifications to auto-typed variables that are deduced to pointers.

LLVM Coding Standards advises to make it obvious if a auto typed variable is a pointer. This check will transform auto to auto * when the type is deduced to be a pointer.

for (auto Data : MutatablePtrContainer) {
  change(*Data);
}
for (auto Data : ConstantPtrContainer) {
  observe(*Data);
}

Would be transformed into:

for (auto *Data : MutatablePtrContainer) {
  change(*Data);
}
for (const auto *Data : ConstantPtrContainer) {
  observe(*Data);
}

Note const volatile qualified types will retain their const and volatile qualifiers. Pointers to pointers will not be fully qualified.

const auto Foo = cast<int *>(Baz1);
const auto Bar = cast<const int *>(Baz2);
volatile auto FooBar = cast<int *>(Baz3);
auto BarFoo = cast<int **>(Baz4);

Would be transformed into:

auto *const Foo = cast<int *>(Baz1);
const auto *const Bar = cast<const int *>(Baz2);
auto *volatile FooBar = cast<int *>(Baz3);
auto *BarFoo = cast<int **>(Baz4);

Options

AddConstToQualified

When true, the check will add const qualifiers to variables defined as auto * or auto & when applicable. Default is true.

auto Foo1 = cast<const int *>(Bar1);
auto *Foo2 = cast<const int *>(Bar2);
auto &Foo3 = cast<const int &>(Bar3);

If AddConstToQualified is set to false, it will be transformed into:

const auto *Foo1 = cast<const int *>(Bar1);
auto *Foo2 = cast<const int *>(Bar2);
auto &Foo3 = cast<const int &>(Bar3);

Otherwise it will be transformed into:

const auto *Foo1 = cast<const int *>(Bar1);
const auto *Foo2 = cast<const int *>(Bar2);
const auto &Foo3 = cast<const int &>(Bar3);

For the llvm-qualified-auto alias, default is false.

AllowedTypes

A semicolon-separated list of names of types to ignore when auto is deduced to that type or a pointer to that type. Note that this distinguishes type aliases from the original type, so specifying e.g. my_int will not suppress reports about int even if it is defined as a typedef alias for int. Regular expressions are accepted, e.g. [Rr]ef(erence)?$ matches every type with suffix Ref, ref, Reference and reference. If a name in the list contains the sequence :: it is matched against the qualified type name (i.e. namespace::Type), otherwise it is matched against only the type name (i.e. Type). E.g. to suppress reports for std::array iterators use std::array<.*>::(const_)?iterator string. Default is an empty string.

IgnoreAliasing

When true, the check will use the underlying type to determine the type that auto is deduced to. When false, the check will not look beyond the first type alias. Default is true.

using IntPtr = int*;
IntPtr foo();

auto bar = foo();

If IgnoreAliasing is set to true, it will be transformed into:

auto *bar = foo();

Otherwise no changes will occur.

Limitations

When IgnoreAliasing is set to false, there are cases where Clang has not preserved the type alias and the underlying type will be used so false positives may occur.

For example:

using IntPtr = int *;

void loopPtr(const std::vector<IntPtr> &VectorIntPtr) {

  // May fail for IgnoreAliasing==false as AST does not have the 'IntPtr'
  for (auto Data : VectorIntPtr) {
  }
}