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Jon Ross-Perkins
53af8f04b2
With the toolchain splitting namespaces, ostream.h's `operator<<` templates aren't reliably found with name lookup, likely due to the loss of associated namespaces (zygoloid commented on this at https://github.com/carbon-language/carbon-lang/pull/3161#discussion_r1307941999). This is especially a barrier to moving the lex files into `Carbon::Lex`; versus other parts of the toolchain, they contain more printable types which are used cross-namespace, including `Carbon::Testing`. As a consequence, I'm looking at migrating ostream.h to a more reliable approach that doesn't rely as much on everything being in the `Carbon` namespace.
86 lines
3.0 KiB
C++
86 lines
3.0 KiB
C++
// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
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// Exceptions. See /LICENSE for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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#ifndef CARBON_COMMON_OSTREAM_H_
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#define CARBON_COMMON_OSTREAM_H_
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#include <ostream>
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#include "llvm/Support/raw_os_ostream.h"
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// Libraries should include this header instead of raw_ostream.
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#include "llvm/Support/Compiler.h"
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#include "llvm/Support/raw_ostream.h" // IWYU pragma: export
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namespace Carbon {
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// CRTP base class for printable types. Children (DerivedT) must implement:
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// - auto Print(llvm::raw_ostream& out) -> void
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template <typename DerivedT>
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class Printable {
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// Provides simple printing for debuggers.
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LLVM_DUMP_METHOD void Dump() const {
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static_cast<const DerivedT*>(this)->Print(llvm::errs());
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}
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// Supports printing to llvm::raw_ostream.
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friend auto operator<<(llvm::raw_ostream& out, const DerivedT& obj)
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-> llvm::raw_ostream& {
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obj.Print(out);
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return out;
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}
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// Supports printing to std::ostream.
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friend auto operator<<(std::ostream& out, const DerivedT& obj)
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-> std::ostream& {
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llvm::raw_os_ostream raw_os(out);
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obj.Print(raw_os);
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return out;
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}
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// Allows GoogleTest and GoogleMock to print pointers by dereferencing them.
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// This is important to allow automatic printing of arguments of mocked
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// APIs.
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friend auto PrintTo(DerivedT* p, std::ostream* out) -> void {
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*out << static_cast<const void*>(p);
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// Also print the object if non-null.
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if (p) {
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*out << " pointing to " << *p;
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}
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}
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};
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} // namespace Carbon
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namespace llvm {
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// Injects an `operator<<` overload into the `llvm` namespace which detects LLVM
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// types with `raw_ostream` overloads and uses that to map to a `std::ostream`
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// overload. This allows LLVM types to be printed to `std::ostream` via their
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// `raw_ostream` operator overloads, which is needed both for logging and
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// testing.
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//
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// To make this overload be unusually low priority, it is designed to take even
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// the `std::ostream` parameter as a template, and SFINAE disable itself unless
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// that template parameter matches `std::ostream`. This ensures that an
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// *explicit* operator will be preferred when provided. Some LLVM types may have
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// this, and so we want to prioritize accordingly.
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//
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// It would be slightly cleaner for LLVM itself to provide this overload in
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// `raw_os_ostream.h` so that we wouldn't need to inject into LLVM's namespace,
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// but supporting `std::ostream` isn't a priority for LLVM so we handle it
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// locally instead.
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template <typename StreamT, typename ClassT,
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typename = std::enable_if_t<
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std::is_base_of_v<std::ostream, std::decay_t<StreamT>>>,
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typename = std::enable_if_t<
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!std::is_same_v<std::decay_t<ClassT>, raw_ostream>>>
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auto operator<<(StreamT& standard_out, const ClassT& value) -> StreamT& {
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raw_os_ostream(standard_out) << value;
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return standard_out;
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}
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} // namespace llvm
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#endif // CARBON_COMMON_OSTREAM_H_
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