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AK: Support UTF-16 string formatting

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The underlying storage used during string formatting is StringBuilder.
To support UTF-16 strings, this patch allows callers to specify a mode
during StringBuilder construction. The default mode is UTF-8, for which
StringBuilder remains unchanged.

In UTF-16 mode, we treat the StringBuilder's internal ByteBuffer as a
series of u16 code units. Appending a single character will append 2
bytes for that character (cast to a char16_t). Appending a StringView
will transcode the string to UTF-16.

Utf16String also gains the same memory optimization that we added for
String, where we hand-off the underlying buffer to Utf16String to avoid
having to re-allocate.

In the future, we may want to further optimize for ASCII strings. For
example, we could defer committing to the u16-esque storage until we
see a non-ASCII code point.
This commit is contained in:
Timothy Flynn 2025-06-17 16:08:30 -04:00 • committed by Tim Flynn
commit 2803d66d87
Notes: github-actions[bot] 2025-07-18 16:47:24 +00:00
11 changed files with 362 additions and 55 deletions
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38
AK/StringBuilder.h
View file

@ -16,6 +16,12 @@ namespace AK {
class StringBuilder {
public:
enum class Mode {
UTF8,
UTF16,
};
static constexpr auto DEFAULT_MODE = Mode::UTF8;
static constexpr size_t inline_capacity = 256;
using Buffer = Detail::ByteBuffer<inline_capacity>;
@ -24,36 +30,42 @@ public:
StringBuilder();
explicit StringBuilder(size_t initial_capacity);
explicit StringBuilder(Mode);
StringBuilder(Mode, size_t initial_capacity_in_code_units);
~StringBuilder() = default;
ErrorOr<void> try_append(StringView);
ErrorOr<void> try_append(Utf16View const&);
ErrorOr<void> try_append(Utf32View const&);
ErrorOr<void> try_append_code_point(u32);
ErrorOr<void> try_append(char);
ErrorOr<void> try_append_code_unit(char16_t);
ErrorOr<void> try_append_code_point(u32);
ErrorOr<void> try_append(char const*, size_t);
ErrorOr<void> try_append_repeated(char, size_t);
ErrorOr<void> try_append_repeated(StringView, size_t);
ErrorOr<void> try_append_escaped_for_json(StringView);
template<typename... Parameters>
ErrorOr<void> try_appendff(CheckedFormatString<Parameters...>&& fmtstr, Parameters const&... parameters)
{
VariadicFormatParams<AllowDebugOnlyFormatters::No, Parameters...> variadic_format_params { parameters... };
return vformat(*this, fmtstr.view(), variadic_format_params);
}
ErrorOr<void> try_append(char const*, size_t);
ErrorOr<void> try_append_repeated(char, size_t);
ErrorOr<void> try_append_repeated(StringView, size_t);
ErrorOr<void> try_append_escaped_for_json(StringView);
void append(StringView);
void append(Utf16View const&);
void append(Utf32View const&);
void append(char);
void append_code_unit(char16_t);
void append_code_point(u32);
void append(char const*, size_t);
void appendvf(char const*, va_list);
void append_repeated(char, size_t);
void append_repeated(StringView, size_t);
void append_as_lowercase(char);
void append_escaped_for_json(StringView);
void append_as_lowercase(char);
template<typename... Parameters>
void appendff(CheckedFormatString<Parameters...>&& fmtstr, Parameters const&... parameters)
@ -70,9 +82,13 @@ public:
[[nodiscard]] FlyString to_fly_string_without_validation() const;
ErrorOr<FlyString> to_fly_string() const;
Utf16String to_utf16_string();
Utf16String to_utf16_string_without_validation();
[[nodiscard]] ErrorOr<ByteBuffer> to_byte_buffer() const;
[[nodiscard]] StringView string_view() const;
[[nodiscard]] Utf16View utf16_string_view() const;
void clear();
[[nodiscard]] size_t length() const;
@ -98,16 +114,20 @@ public:
return {};
}
Optional<Buffer::OutlineBuffer> leak_buffer_for_string_construction(Badge<Detail::StringData>);
Optional<Buffer::OutlineBuffer> leak_buffer_for_string_construction(Badge<Detail::StringData>) { return leak_buffer_for_string_construction(); }
Optional<Buffer::OutlineBuffer> leak_buffer_for_string_construction(Badge<Detail::Utf16StringData>) { return leak_buffer_for_string_construction(); }
private:
explicit StringBuilder(Buffer);
StringBuilder(Buffer, Mode);
Optional<Buffer::OutlineBuffer> leak_buffer_for_string_construction();
ErrorOr<void> will_append(size_t);
u8* data();
u8 const* data() const;
Buffer m_buffer;
Mode m_mode { DEFAULT_MODE };
};
}