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PR51018: Disallow explicit construction of StringRef from SmallString due to ambiguity in C++23

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See bug for full details, but basically there's an upcoming ambiguity in
the conversion in `StringRef(SomeSmallString)` - either the implicit
conversion operator (SmallString::operator StringRef) could be used, or
the std::string_view range-based ctor (& then `StringRef(std::string_view)`
would be used)

To address this, make such a conversion invalid up-front - most uses are
more tersely written as `SomeSmallString.str()` anyway, or more clearly
written as `StringRef x = y;` rather than `StringRef x(y);` - so if you
hit this in out-of-tree code, please update in one of those ways.
Hopefully I've fixed everything in tree prior to this patch landing.
This commit is contained in:
David Blaikie 2021-07-08 13:26:40 -07:00
parent a9632b4cd8
commit 0a392cfdcf
1 changed files with 14 additions and 3 deletions
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17
include/llvm/ADT/SmallString.h
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@ -19,10 +19,22 @@
namespace llvm {
namespace impl {
template <typename T> struct SmallStringConversionHelper1 {
operator StringRef() const { return static_cast<const T *>(this)->str(); }
};
struct SmallStringConversionHelper2 {
explicit operator StringRef() const = delete;
};
} // namespace impl
/// SmallString - A SmallString is just a SmallVector with methods and accessors
/// that make it work better as a string (e.g. operator+ etc).
template<unsigned InternalLen>
class SmallString : public SmallVector<char, InternalLen> {
template <unsigned InternalLen>
class SmallString
: public SmallVector<char, InternalLen>,
public impl::SmallStringConversionHelper1<SmallString<InternalLen>>,
public impl::SmallStringConversionHelper2 {
public:
/// Default ctor - Initialize to empty.
SmallString() = default;
@ -266,7 +278,6 @@ public:
}
/// Implicit conversion to StringRef.
operator StringRef() const { return str(); }
explicit operator std::string() const {
return std::string(this->data(), this->size());