1 // Copyright 2021 The Chromium Authors 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef BASE_CONTAINERS_SPAN_RUST_H_ 6 #define BASE_CONTAINERS_SPAN_RUST_H_ 7 8 #include <stdint.h> 9 10 #include "base/containers/span.h" 11 #include "base/rust_buildflags.h" 12 #include "third_party/rust/cxx/v1/cxx.h" 13 14 #if !BUILDFLAG(BUILD_RUST_BASE_CONVERSIONS) 15 #error "span_rust.h included without BUILD_RUST_BASE_CONVERSIONS" 16 #endif 17 18 namespace base { 19 20 // Create a Rust slice from a base::span. SpanToRustSlice(span<const uint8_t> span)21inline rust::Slice<const uint8_t> SpanToRustSlice(span<const uint8_t> span) { 22 return rust::Slice<const uint8_t>(span.data(), span.size()); 23 } 24 25 // Note to future editors: if you add code to convert from a rust::Slice to 26 // a base::span, you should be aware that Rust slices (and cxx) 27 // return a fabricated non-null pointer for zero-length slices, and that 28 // this will likely need converting to NULL before constructing a span. 29 // cxx handles the conversion from NULL to an artificial pointer 30 // (specifically it uses alignof<T>) in the C++ -> Rust direction, but 31 // does nothing cunning in the other direction, presumably on the 32 // assumption that C++ won't access the data pointer if the length is 0. 33 // But we do not think (reinterpret_cast<T*>(alignof(T)), 0) can safely 34 // be stored in base::span today. The pointer arithmetic 35 // rules have special cases for NULL, but otherwise it is only defined if 36 // there is actually an object at the address, and there is no object at 37 // alignof(T). 38 // https://eel.is/c++draft/expr.add#4 39 // https://eel.is/c++draft/expr.add#5 40 41 } // namespace base 42 43 #endif // BASE_CONTAINERS_SPAN_RUST_H_ 44