[codex] Return hosted string accessors as string_view

README.md

@@ -448,11 +448,13 @@ Hosted users who want standard-library interoperability can opt in:
 target_compile_definitions(my_target PRIVATE PROTOCYTE_ENABLE_STD_STRING_VIEW=1)
 ```
 
-When `PROTOCYTE_ENABLE_STD_STRING_VIEW` is defined, the runtime includes
-`<string_view>` and both `::protocyte::Span<char>` / `Span<const char>` and
-`::protocyte::String` are implicitly convertible to `std::string_view`. The
-default accessor return type remains `Span<const char>`, so code that does not
-enable the option keeps the smaller no-exception surface.
+When `PROTOCYTE_ENABLE_STD_STRING_VIEW` is set to a nonzero value, the runtime
+includes `<string_view>` and both `::protocyte::Span<char>` / `Span<const char>`
+and `::protocyte::String` are implicitly convertible to `std::string_view`.
+Generated immutable `string` field accessors also return `std::string_view` under
+this opt-in, so hosted code can pass string fields directly to
+standard-library APIs such as `std::format`. Code that does not enable the
+option keeps the smaller no-exception `Span<const char>` accessor surface.
 
 In a Windows kernel driver, one technically possible MSVC/STL-specific escape
 hatch is to provide the STL's internal out-of-range throw helper yourself so

smoke/generated/compat.protocyte.hpp

@@ -65,7 +65,7 @@ namespace protocyte_smoke::test::compat {
         }
         constexpr void clear_value() noexcept { value_ = {}; }
 
-        ::protocyte::Span<const char> label() const noexcept { return label_.view(); }
+        ::protocyte::StringView label() const noexcept { return label_.view(); }
         typename Config::String &mutable_label() noexcept { return label_; }
         template<class Value>::protocyte::Status set_label(const Value &value) noexcept
             requires(::protocyte::ByteSpanSource<Value> && !::protocyte::TextSource<Value>)
@@ -652,7 +652,7 @@ namespace protocyte_smoke::test::compat {
         }
         constexpr void clear_f_double() noexcept { f_double_ = {}; }
 
-        ::protocyte::Span<const char> f_string() const noexcept { return f_string_.view(); }
+        ::protocyte::StringView f_string() const noexcept { return f_string_.view(); }
         typename Config::String &mutable_f_string() noexcept { return f_string_; }
         template<class Value>::protocyte::Status set_f_string(const Value &value) noexcept
             requires(::protocyte::ByteSpanSource<Value> && !::protocyte::TextSource<Value>)
@@ -741,8 +741,8 @@ namespace protocyte_smoke::test::compat {
         constexpr bool has_oneof_string() const noexcept {
             return special_oneof_case_ == Special_oneofCase::oneof_string;
         }
-        ::protocyte::Span<const char> oneof_string() const noexcept {
-            return has_oneof_string() ? special_oneof.oneof_string.view() : ::protocyte::Span<const char> {};
+        ::protocyte::StringView oneof_string() const noexcept {
+            return has_oneof_string() ? special_oneof.oneof_string.view() : ::protocyte::StringView {};
         }
         template<class Value>::protocyte::Status set_oneof_string(const Value &value) noexcept
             requires(::protocyte::ByteSpanSource<Value> && !::protocyte::TextSource<Value>)
@@ -852,7 +852,7 @@ namespace protocyte_smoke::test::compat {
             has_opt_int32_ = false;
         }
 
-        ::protocyte::Span<const char> opt_string() const noexcept { return opt_string_.view(); }
+        ::protocyte::StringView opt_string() const noexcept { return opt_string_.view(); }
         bool has_opt_string() const noexcept { return has_opt_string_; }
         typename Config::String &mutable_opt_string() noexcept {
             has_opt_string_ = true;

smoke/generated/cross_package.protocyte.hpp

@@ -5,7 +5,9 @@
 
 #include <protocyte/runtime/runtime.hpp>
 
+#if !PROTOCYTE_ENABLE_STD_STRING_VIEW
 #include <string_view>
+#endif
 
 namespace test::crosspkg {
 

smoke/generated/example.protocyte.hpp

@@ -5,7 +5,9 @@
 
 #include <protocyte/runtime/runtime.hpp>
 
+#if !PROTOCYTE_ENABLE_STD_STRING_VIEW
 #include <string_view>
+#endif
 
 namespace test::ultimate {
 
@@ -96,7 +98,7 @@ namespace test::ultimate {
             return out;
         }
 
-        ::protocyte::Span<const char> description() const noexcept { return description_.view(); }
+        ::protocyte::StringView description() const noexcept { return description_.view(); }
         typename Config::String &mutable_description() noexcept { return description_; }
         template<class Value>::protocyte::Status set_description(const Value &value) noexcept
             requires(::protocyte::ByteSpanSource<Value> && !::protocyte::TextSource<Value>)
@@ -394,7 +396,7 @@ namespace test::ultimate {
             return out;
         }
 
-        ::protocyte::Span<const char> name() const noexcept { return name_.view(); }
+        ::protocyte::StringView name() const noexcept { return name_.view(); }
         typename Config::String &mutable_name() noexcept { return name_; }
         template<class Value>::protocyte::Status set_name(const Value &value) noexcept
             requires(::protocyte::ByteSpanSource<Value> && !::protocyte::TextSource<Value>)
@@ -1118,7 +1120,7 @@ namespace test::ultimate {
             deep_oneof_case_ = Deep_oneofCase::none;
         }
 
-        ::protocyte::Span<const char> extreme() const noexcept { return extreme_.view(); }
+        ::protocyte::StringView extreme() const noexcept { return extreme_.view(); }
         typename Config::String &mutable_extreme() noexcept { return extreme_; }
         template<class Value>::protocyte::Status set_extreme(const Value &value) noexcept
             requires(::protocyte::ByteSpanSource<Value> && !::protocyte::TextSource<Value>)
@@ -1168,8 +1170,8 @@ namespace test::ultimate {
         }
 
         constexpr bool has_text() const noexcept { return deep_oneof_case_ == Deep_oneofCase::text; }
-        ::protocyte::Span<const char> text() const noexcept {
-            return has_text() ? deep_oneof.text.view() : ::protocyte::Span<const char> {};
+        ::protocyte::StringView text() const noexcept {
+            return has_text() ? deep_oneof.text.view() : ::protocyte::StringView {};
         }
         template<class Value>::protocyte::Status set_text(const Value &value) noexcept
             requires(::protocyte::ByteSpanSource<Value> && !::protocyte::TextSource<Value>)
@@ -2297,7 +2299,7 @@ namespace test::ultimate {
         }
         constexpr void clear_f_bool() noexcept { f_bool_ = {}; }
 
-        ::protocyte::Span<const char> f_string() const noexcept { return f_string_.view(); }
+        ::protocyte::StringView f_string() const noexcept { return f_string_.view(); }
         typename Config::String &mutable_f_string() noexcept { return f_string_; }
         template<class Value>::protocyte::Status set_f_string(const Value &value) noexcept
             requires(::protocyte::ByteSpanSource<Value> && !::protocyte::TextSource<Value>)
@@ -2399,8 +2401,8 @@ namespace test::ultimate {
         constexpr bool has_oneof_string() const noexcept {
             return special_oneof_case_ == Special_oneofCase::oneof_string;
         }
-        ::protocyte::Span<const char> oneof_string() const noexcept {
-            return has_oneof_string() ? special_oneof.oneof_string.view() : ::protocyte::Span<const char> {};
+        ::protocyte::StringView oneof_string() const noexcept {
+            return has_oneof_string() ? special_oneof.oneof_string.view() : ::protocyte::StringView {};
         }
         template<class Value>::protocyte::Status set_oneof_string(const Value &value) noexcept
             requires(::protocyte::ByteSpanSource<Value> && !::protocyte::TextSource<Value>)
@@ -2749,7 +2751,7 @@ namespace test::ultimate {
             has_opt_int32_ = false;
         }
 
-        ::protocyte::Span<const char> opt_string() const noexcept { return opt_string_.view(); }
+        ::protocyte::StringView opt_string() const noexcept { return opt_string_.view(); }
         bool has_opt_string() const noexcept { return has_opt_string_; }
         typename Config::String &mutable_opt_string() noexcept {
             has_opt_string_ = true;
@@ -6063,7 +6065,7 @@ namespace test::ultimate {
             return out;
         }
 
-        ::protocyte::Span<const char> tag() const noexcept { return tag_.view(); }
+        ::protocyte::StringView tag() const noexcept { return tag_.view(); }
         typename Config::String &mutable_tag() noexcept { return tag_; }
         template<class Value>::protocyte::Status set_tag(const Value &value) noexcept
             requires(::protocyte::ByteSpanSource<Value> && !::protocyte::TextSource<Value>)

smoke/generated/protocyte/runtime/runtime.hpp

@@ -11,7 +11,7 @@
 #include <new>
 #include <type_traits>
 
-#ifdef PROTOCYTE_ENABLE_STD_STRING_VIEW
+#if PROTOCYTE_ENABLE_STD_STRING_VIEW
 #include <string_view>
 #endif
 
@@ -1269,11 +1269,11 @@ namespace protocyte {
         constexpr usize size() const noexcept { return size_; }
         constexpr usize size_bytes() const noexcept { return size_ * sizeof(T); }
         constexpr bool empty() const noexcept { return size_ == 0u; }
-#ifdef PROTOCYTE_ENABLE_STD_STRING_VIEW
+#if PROTOCYTE_ENABLE_STD_STRING_VIEW
         constexpr operator ::std::string_view() const noexcept
             requires(::std::same_as<::std::remove_cv_t<T>, char>)
         {
-            return data_ == nullptr ? ::std::string_view {} : ::std::string_view {data_, size_};
+            return ::std::string_view {data_, size_};
         }
 #endif
         template<usize Count> constexpr Span<T, Count> first() const noexcept
@@ -1316,6 +1316,12 @@ namespace protocyte {
         requires(!DataSizeSpanSource<Range &> && PointerSpanSource<Range &>)
     Span(Range &) -> Span<::std::remove_pointer_t<SpanBeginPointer<Range &>>>;
 
+#if PROTOCYTE_ENABLE_STD_STRING_VIEW
+    using StringView = ::std::string_view;
+#else
+    using StringView = Span<const char>;
+#endif
+
     template<class T>
     concept SpanSource = requires(T &value) { Span {value}; } || requires(const T &value) { Span {value}; };
 
@@ -2869,7 +2875,7 @@ namespace protocyte {
         usize size() const noexcept { return bytes_.size(); }
         usize length() const noexcept { return size(); }
         bool empty() const noexcept { return bytes_.empty(); }
-#ifdef PROTOCYTE_ENABLE_STD_STRING_VIEW
+#if PROTOCYTE_ENABLE_STD_STRING_VIEW
         operator ::std::string_view() const noexcept { return view(); }
 #endif
         void clear() noexcept { bytes_.clear(); }

smoke/src/host_smoke.cpp

@@ -2,6 +2,9 @@
 #include <cstddef>
 #include <cstdint>
 #include <cstdlib>
+#if __has_include(<format>)
+#include <format>
+#endif
 #include <limits>
 #include <string>
 #include <string_view>
@@ -214,6 +217,16 @@ namespace {
         return protocyte::bytes_equal(lhs, rhs);
     }
 
+    template<class R, protocyte::usize RExtent>
+    bool view_equal(std::string_view lhs, protocyte::Span<R, RExtent> rhs) noexcept {
+        return view_equal(protocyte::Span<const char> {lhs.data(), lhs.size()}, rhs);
+    }
+
+    template<class L, protocyte::usize LExtent>
+    bool view_equal(protocyte::Span<L, LExtent> lhs, std::string_view rhs) noexcept {
+        return view_equal(lhs, protocyte::Span<const char> {rhs.data(), rhs.size()});
+    }
+
     template<size_t N> protocyte::Span<const protocyte::u8> view_of(const uint8_t (&data)[N]) noexcept {
         return protocyte::Span<const protocyte::u8> {data, N};
     }
@@ -2603,8 +2616,12 @@ TEST_CASE("byte setters accept contiguous byte containers", "[smoke][runtime][by
     const auto string_view = protocyte::byte_span_of(string_payload);
     REQUIRE(string_view);
     CHECK(view_equal(message.f_string(), *string_view));
+    static_assert(std::is_same_v<decltype(message.f_string()), std::string_view>);
     const std::string_view converted_span = message.f_string();
     CHECK(converted_span == std::string_view {"hello"});
+#if defined(__cpp_lib_format)
+    CHECK(std::format("{}", message.f_string()) == "hello");
+#endif
     const std::string_view converted_string = message.mutable_f_string();
     CHECK(converted_string == converted_span);
 

smoke/src/kernel_driver_smoke.cpp

@@ -24,6 +24,34 @@ void __cdecl operator delete[](void *ptr) noexcept { ::operator delete(ptr); }
 void __cdecl operator delete[](void *ptr, size_t) noexcept { ::operator delete(ptr); }
 #endif
 
+#if PROTOCYTE_ENABLE_STD_STRING_VIEW && defined(_DEBUG)
+// MSVC's debug STL imports these CRT assertion hooks through __imp_* data symbols.
+__declspec(noreturn) void protocyte_debug_crt_shim_bugcheck(const char *symbol_name) {
+    DbgPrintEx(DPFLTR_IHVDRIVER_ID, DPFLTR_ERROR_LEVEL,
+               "Protocyte kernel smoke: MSVC STL debug CRT fallback called for %s.\n", symbol_name);
+    KeBugCheckEx(MANUALLY_INITIATED_CRASH, 0x50535643u, 0u, 0u, 0u);
+    for (;;) {}
+}
+
+extern "C" __declspec(noreturn) void __cdecl protocyte_invoke_watson_shim(const wchar_t *, const wchar_t *,
+                                                                          const wchar_t *, unsigned int, uintptr_t) {
+    protocyte_debug_crt_shim_bugcheck("_invoke_watson");
+}
+
+extern "C" int __cdecl protocyte_crt_dbg_report_shim(int, const char *, int, const char *, const char *, ...) {
+    protocyte_debug_crt_shim_bugcheck("_CrtDbgReport");
+}
+
+using protocyte_invoke_watson_fn = void(__cdecl *)(const wchar_t *, const wchar_t *, const wchar_t *, unsigned int,
+                                                   uintptr_t);
+using protocyte_crt_dbg_report_fn = int(__cdecl *)(int, const char *, int, const char *, const char *, ...);
+
+extern "C" {
+    protocyte_invoke_watson_fn __imp__invoke_watson = &protocyte_invoke_watson_shim;
+    protocyte_crt_dbg_report_fn __imp__CrtDbgReport = &protocyte_crt_dbg_report_shim;
+}
+#endif
+
 namespace {
 
     constexpr ULONG protocyte_pool_tag = 'TyCP';

src/protocyte/cpp.py

@@ -210,7 +210,7 @@ def generate_header(file_model: FileModel, options: GeneratorOptions) -> str:
     w.line(f"#include <{options.runtime_prefix}/runtime.hpp>")
     extra_includes: list[str] = []
     if _file_uses_string_view(file_model):
-        extra_includes.append("#include <string_view>")
+        extra_includes.extend(["#if !PROTOCYTE_ENABLE_STD_STRING_VIEW", "#include <string_view>", "#endif"])
     for dependency in sorted(file_model.dependencies):
         extra_includes.append(f'#include "{_include_path(dependency, options)}"')
     if extra_includes:
@@ -813,11 +813,13 @@ def emit_setter_body() -> None:
         return
     if item.kind in {"string", "bytes"}:
         typ = _field_type(item, options)
-        view_type = "::protocyte::Span<const char>" if item.kind == "string" else "::protocyte::Span<const ::protocyte::u8>"
-        w.line(f"{view_type} {item.cpp_name}() const noexcept {{ return {_member(item)}.view(); }}")
-        if item.proto3_optional:
-            w.line(f"bool has_{item.cpp_name}() const noexcept {{ return has_{item.cpp_name}_; }}")
-        w.line(f"{typ}& mutable_{item.cpp_name}() noexcept {{")
+        if item.kind == "string":
+            _emit_string_view_accessor(w, item.cpp_name, f"{_member(item)}.view()")
+        else:
+            w.line(f"::protocyte::Span<const ::protocyte::u8> {item.cpp_name}() const noexcept {{ return {_member(item)}.view(); }}")
+        if item.proto3_optional:
+            w.line(f"bool has_{item.cpp_name}() const noexcept {{ return has_{item.cpp_name}_; }}")
+        w.line(f"{typ}& mutable_{item.cpp_name}() noexcept {{")
         w.push()
         if item.proto3_optional:
             w.line(f"has_{item.cpp_name}_ = true;")
@@ -879,10 +881,17 @@ def _emit_oneof_accessors(w: CppWriter, item: FieldModel, options: GeneratorOpti
         f"constexpr bool has_{item.cpp_name}() const noexcept {{ return {case_member} == {case_type}::{item.cpp_name}; }}"
     )
     if item.kind in {"string", "bytes"}:
-        view_type = "::protocyte::Span<const char>" if item.kind == "string" else "::protocyte::Span<const ::protocyte::u8>"
-        w.line(
-            f"{view_type} {item.cpp_name}() const noexcept {{ return has_{item.cpp_name}() ? {_member(item)}.view() : {view_type}{{}}; }}"
-        )
+        if item.kind == "string":
+            _emit_string_view_accessor(
+                w,
+                item.cpp_name,
+                f"has_{item.cpp_name}() ? {_member(item)}.view() : ::protocyte::StringView{{}}",
+            )
+        else:
+            view_type = "::protocyte::Span<const ::protocyte::u8>"
+            w.line(
+                f"{view_type} {item.cpp_name}() const noexcept {{ return has_{item.cpp_name}() ? {_member(item)}.view() : {view_type}{{}}; }}"
+            )
         def emit_setter_body() -> None:
             if item.kind == "bytes" and item.array_enabled:
                 w.line(
@@ -1961,6 +1970,14 @@ def _runtime_scalar_type(cpp_type: str) -> str:
     return _RUNTIME_SCALAR_TYPES.get(cpp_type, cpp_type)
 
 
+def _emit_string_view_accessor(
+    w: CppWriter,
+    name: str,
+    expr: str,
+) -> None:
+    w.line(f"::protocyte::StringView {name}() const noexcept {{ return {expr}; }}")
+
+
 def _file_uses_string_view(file_model: FileModel) -> bool:
     if any(constant.kind == CONSTANT_KIND_STRING for constant in file_model.constants):
         return True

src/protocyte/runtime/runtime.hpp

@@ -11,7 +11,7 @@
 #include <new>
 #include <type_traits>
 
-#ifdef PROTOCYTE_ENABLE_STD_STRING_VIEW
+#if PROTOCYTE_ENABLE_STD_STRING_VIEW
 #include <string_view>
 #endif
 
@@ -1269,11 +1269,11 @@ namespace protocyte {
         constexpr usize size() const noexcept { return size_; }
         constexpr usize size_bytes() const noexcept { return size_ * sizeof(T); }
         constexpr bool empty() const noexcept { return size_ == 0u; }
-#ifdef PROTOCYTE_ENABLE_STD_STRING_VIEW
+#if PROTOCYTE_ENABLE_STD_STRING_VIEW
         constexpr operator ::std::string_view() const noexcept
             requires(::std::same_as<::std::remove_cv_t<T>, char>)
         {
-            return data_ == nullptr ? ::std::string_view {} : ::std::string_view {data_, size_};
+            return ::std::string_view {data_, size_};
         }
 #endif
         template<usize Count> constexpr Span<T, Count> first() const noexcept
@@ -1316,6 +1316,12 @@ namespace protocyte {
         requires(!DataSizeSpanSource<Range &> && PointerSpanSource<Range &>)
     Span(Range &) -> Span<::std::remove_pointer_t<SpanBeginPointer<Range &>>>;
 
+#if PROTOCYTE_ENABLE_STD_STRING_VIEW
+    using StringView = ::std::string_view;
+#else
+    using StringView = Span<const char>;
+#endif
+
     template<class T>
     concept SpanSource = requires(T &value) { Span {value}; } || requires(const T &value) { Span {value}; };
 
@@ -2869,7 +2875,7 @@ namespace protocyte {
         usize size() const noexcept { return bytes_.size(); }
         usize length() const noexcept { return size(); }
         bool empty() const noexcept { return bytes_.empty(); }
-#ifdef PROTOCYTE_ENABLE_STD_STRING_VIEW
+#if PROTOCYTE_ENABLE_STD_STRING_VIEW
         operator ::std::string_view() const noexcept { return view(); }
 #endif
         void clear() noexcept { bytes_.clear(); }