AK+Everywhere: Remove the null state of DeprecatedString

This commit removes DeprecatedString's "null" state, and replaces all
its users with one of the following:
- A normal, empty DeprecatedString
- Optional<DeprecatedString>

Note that null states of DeprecatedFlyString/StringView/etc are *not*
affected by this commit. However, DeprecatedString::empty() is now
considered equal to a null StringView.

AK/DeprecatedFlyString.cpp

@@ -38,8 +38,6 @@ void DeprecatedFlyString::did_destroy_impl(Badge<StringImpl>, StringImpl& impl)
 
 DeprecatedFlyString::DeprecatedFlyString(DeprecatedString const& string)
 {
-    if (string.is_null())
-        return;
     if (string.impl()->is_fly()) {
         m_impl = string.impl();
         return;
@@ -60,7 +58,7 @@ DeprecatedFlyString::DeprecatedFlyString(StringView string)
     if (string.is_null())
         return;
     auto it = fly_impls().find(string.hash(), [&](auto& candidate) {
-        return string == candidate;
+        return string == *candidate;
     });
     if (it == fly_impls().end()) {
         auto new_string = string.to_deprecated_string();

AK/DeprecatedString.cpp

@@ -28,6 +28,9 @@ bool DeprecatedString::operator==(DeprecatedString const& other) const
 
 bool DeprecatedString::operator==(StringView other) const
 {
+    if (other.is_null())
+        return is_empty();
+
     return view() == other;
 }
 
@@ -55,9 +58,7 @@ bool DeprecatedString::copy_characters_to_buffer(char* buffer, size_t buffer_siz
 
 DeprecatedString DeprecatedString::isolated_copy() const
 {
-    if (!m_impl)
-        return {};
-    if (!m_impl->length())
+    if (m_impl->length() == 0)
         return empty();
     char* buffer;
     auto impl = StringImpl::create_uninitialized(length(), buffer);
@@ -69,7 +70,6 @@ DeprecatedString DeprecatedString::substring(size_t start, size_t length) const
 {
     if (!length)
         return DeprecatedString::empty();
-    VERIFY(m_impl);
     VERIFY(!Checked<size_t>::addition_would_overflow(start, length));
     VERIFY(start + length <= m_impl->length());
     return { characters() + start, length };
@@ -77,14 +77,12 @@ DeprecatedString DeprecatedString::substring(size_t start, size_t length) const
 
 DeprecatedString DeprecatedString::substring(size_t start) const
 {
-    VERIFY(m_impl);
     VERIFY(start <= length());
     return { characters() + start, length() - start };
 }
 
 StringView DeprecatedString::substring_view(size_t start, size_t length) const
 {
-    VERIFY(m_impl);
     VERIFY(!Checked<size_t>::addition_would_overflow(start, length));
     VERIFY(start + length <= m_impl->length());
     return { characters() + start, length };
@@ -92,7 +90,6 @@ StringView DeprecatedString::substring_view(size_t start, size_t length) const
 
 StringView DeprecatedString::substring_view(size_t start) const
 {
-    VERIFY(m_impl);
     VERIFY(start <= length());
     return { characters() + start, length() - start };
 }
@@ -157,8 +154,6 @@ Vector<StringView> DeprecatedString::split_view(char const separator, SplitBehav
 
 ByteBuffer DeprecatedString::to_byte_buffer() const
 {
-    if (!m_impl)
-        return {};
     // FIXME: Handle OOM failure.
     return ByteBuffer::copy(bytes()).release_value_but_fixme_should_propagate_errors();
 }
@@ -379,21 +374,17 @@ DeprecatedString escape_html_entities(StringView html)
 }
 
 DeprecatedString::DeprecatedString(DeprecatedFlyString const& string)
-    : m_impl(string.impl())
+    : m_impl(*string.impl())
 {
 }
 
 DeprecatedString DeprecatedString::to_lowercase() const
 {
-    if (!m_impl)
-        return {};
     return m_impl->to_lowercase();
 }
 
 DeprecatedString DeprecatedString::to_uppercase() const
 {
-    if (!m_impl)
-        return {};
     return m_impl->to_uppercase();
 }
 
@@ -414,6 +405,9 @@ DeprecatedString DeprecatedString::invert_case() const
 
 bool DeprecatedString::operator==(char const* cstring) const
 {
+    if (!cstring)
+        return is_empty();
+
     return view() == cstring;
 }
 
@@ -438,7 +432,7 @@ ErrorOr<DeprecatedString> DeprecatedString::from_utf8(ReadonlyBytes bytes)
 {
     if (!Utf8View(bytes).validate())
         return Error::from_string_literal("DeprecatedString::from_utf8: Input was not valid UTF-8");
-    return DeprecatedString { StringImpl::create(bytes) };
+    return DeprecatedString { *StringImpl::create(bytes) };
 }
 
 }

AK/DeprecatedString.h

@@ -40,10 +40,13 @@ class DeprecatedString {
 public:
     ~DeprecatedString() = default;
 
-    DeprecatedString() = default;
+    DeprecatedString()
+        : m_impl(StringImpl::the_empty_stringimpl())
+    {
+    }
 
     DeprecatedString(StringView view)
-        : m_impl(StringImpl::create(view.characters_without_null_termination(), view.length()))
+        : m_impl(*StringImpl::create(view.characters_without_null_termination(), view.length()))
     {
     }
 
@@ -55,20 +58,21 @@ public:
     DeprecatedString(DeprecatedString&& other)
         : m_impl(move(other.m_impl))
     {
+        other.m_impl = StringImpl::the_empty_stringimpl();
     }
 
     DeprecatedString(char const* cstring, ShouldChomp shouldChomp = NoChomp)
-        : m_impl(StringImpl::create(cstring, shouldChomp))
+        : m_impl(*StringImpl::create(cstring, shouldChomp))
     {
     }
 
     DeprecatedString(char const* cstring, size_t length, ShouldChomp shouldChomp = NoChomp)
-        : m_impl(StringImpl::create(cstring, length, shouldChomp))
+        : m_impl(*StringImpl::create(cstring, length, shouldChomp))
     {
     }
 
     explicit DeprecatedString(ReadonlyBytes bytes, ShouldChomp shouldChomp = NoChomp)
-        : m_impl(StringImpl::create(bytes, shouldChomp))
+        : m_impl(*StringImpl::create(bytes, shouldChomp))
     {
     }
 
@@ -77,18 +81,8 @@ public:
     {
     }
 
-    DeprecatedString(StringImpl const* impl)
-        : m_impl(impl)
-    {
-    }
-
-    DeprecatedString(RefPtr<StringImpl const>&& impl)
-        : m_impl(move(impl))
-    {
-    }
-
     DeprecatedString(NonnullRefPtr<StringImpl const>&& impl)
-        : m_impl(move(impl))
+        : m_impl(*move(impl))
     {
     }
 
@@ -174,31 +168,25 @@ public:
     [[nodiscard]] StringView substring_view(size_t start, size_t length) const;
     [[nodiscard]] StringView substring_view(size_t start) const;
 
-    [[nodiscard]] bool is_null() const { return !m_impl; }
     [[nodiscard]] ALWAYS_INLINE bool is_empty() const { return length() == 0; }
-    [[nodiscard]] ALWAYS_INLINE size_t length() const { return m_impl ? m_impl->length() : 0; }
-    // Includes NUL-terminator, if non-nullptr.
-    [[nodiscard]] ALWAYS_INLINE char const* characters() const { return m_impl ? m_impl->characters() : nullptr; }
+    [[nodiscard]] ALWAYS_INLINE size_t length() const { return m_impl->length(); }
+    // Includes NUL-terminator.
+    [[nodiscard]] ALWAYS_INLINE char const* characters() const { return m_impl->characters(); }
 
     [[nodiscard]] bool copy_characters_to_buffer(char* buffer, size_t buffer_size) const;
 
     [[nodiscard]] ALWAYS_INLINE ReadonlyBytes bytes() const
     {
-        if (m_impl) {
-            return m_impl->bytes();
-        }
-        return {};
+        return m_impl->bytes();
     }
 
     [[nodiscard]] ALWAYS_INLINE char const& operator[](size_t i) const
     {
-        VERIFY(!is_null());
         return (*m_impl)[i];
     }
 
     [[nodiscard]] ALWAYS_INLINE u8 byte_at(size_t i) const
     {
-        VERIFY(!is_null());
         return bit_cast<u8>((*m_impl)[i]);
     }
 
@@ -251,22 +239,15 @@ public:
         return *this;
     }
 
-    DeprecatedString& operator=(nullptr_t)
+    template<OneOf<ReadonlyBytes, Bytes> T>
+    DeprecatedString& operator=(T bytes)
     {
-        m_impl = nullptr;
-        return *this;
-    }
-
-    DeprecatedString& operator=(ReadonlyBytes bytes)
-    {
-        m_impl = StringImpl::create(bytes);
+        m_impl = *StringImpl::create(bytes);
         return *this;
     }
 
     [[nodiscard]] u32 hash() const
     {
-        if (!m_impl)
-            return 0;
         return m_impl->hash();
     }
 
@@ -323,7 +304,7 @@ public:
     }
 
 private:
-    RefPtr<StringImpl const> m_impl;
+    NonnullRefPtr<StringImpl const> m_impl;
 };
 
 template<>

AK/GenericLexer.cpp

@@ -129,7 +129,7 @@ StringView GenericLexer::consume_quoted_string(char escape_char)
 }
 
 #ifndef KERNEL
-DeprecatedString GenericLexer::consume_and_unescape_string(char escape_char)
+Optional<DeprecatedString> GenericLexer::consume_and_unescape_string(char escape_char)
 {
     auto view = consume_quoted_string(escape_char);
     if (view.is_null())

AK/GenericLexer.h

@@ -119,7 +119,7 @@ public:
     StringView consume_until(StringView);
     StringView consume_quoted_string(char escape_char = 0);
 #ifndef KERNEL
-    DeprecatedString consume_and_unescape_string(char escape_char = '\\');
+    Optional<DeprecatedString> consume_and_unescape_string(char escape_char = '\\');
 #endif
 
     enum class UnicodeEscapeError {

AK/JsonParser.cpp

@@ -132,8 +132,6 @@ ErrorOr<JsonValue> JsonParser::parse_object()
             break;
         ignore_while(is_space);
         auto name = TRY(consume_and_unescape_string());
-        if (name.is_null())
-            return Error::from_string_literal("JsonParser: Expected object property name");
         ignore_while(is_space);
         if (!consume_specific(':'))
             return Error::from_string_literal("JsonParser: Expected ':'");

AK/JsonValue.cpp

@@ -174,13 +174,9 @@ JsonValue::JsonValue(double value)
 
 JsonValue::JsonValue(DeprecatedString const& value)
 {
-    if (value.is_null()) {
-        m_type = Type::Null;
-    } else {
-        m_type = Type::String;
-        m_value.as_string = const_cast<StringImpl*>(value.impl());
-        m_value.as_string->ref();
-    }
+    m_type = Type::String;
+    m_value.as_string = const_cast<StringImpl*>(value.impl());
+    m_value.as_string->ref();
 }
 
 JsonValue::JsonValue(StringView value)

AK/LexicalPath.cpp

@@ -90,9 +90,6 @@ bool LexicalPath::is_child_of(LexicalPath const& possible_parent) const
 
 DeprecatedString LexicalPath::canonicalized_path(DeprecatedString path)
 {
-    if (path.is_null())
-        return {};
-
     // NOTE: We never allow an empty m_string, if it's empty, we just set it to '.'.
     if (path.is_empty())
         return ".";

AK/StringImpl.cpp

@@ -47,9 +47,6 @@ NonnullRefPtr<StringImpl const> StringImpl::create_uninitialized(size_t length,
 
 RefPtr<StringImpl const> StringImpl::create(char const* cstring, size_t length, ShouldChomp should_chomp)
 {
-    if (!cstring)
-        return nullptr;
-
     if (should_chomp) {
         while (length) {
             char last_ch = cstring[length - 1];
@@ -72,10 +69,7 @@ RefPtr<StringImpl const> StringImpl::create(char const* cstring, size_t length,
 
 RefPtr<StringImpl const> StringImpl::create(char const* cstring, ShouldChomp shouldChomp)
 {
-    if (!cstring)
-        return nullptr;
-
-    if (!*cstring)
+    if (!cstring || !*cstring)
         return the_empty_stringimpl();
 
     return create(cstring, strlen(cstring), shouldChomp);
@@ -88,8 +82,6 @@ RefPtr<StringImpl const> StringImpl::create(ReadonlyBytes bytes, ShouldChomp sho
 
 RefPtr<StringImpl const> StringImpl::create_lowercased(char const* cstring, size_t length)
 {
-    if (!cstring)
-        return nullptr;
     if (!length)
         return the_empty_stringimpl();
     char* buffer;
@@ -101,8 +93,6 @@ RefPtr<StringImpl const> StringImpl::create_lowercased(char const* cstring, size
 
 RefPtr<StringImpl const> StringImpl::create_uppercased(char const* cstring, size_t length)
 {
-    if (!cstring)
-        return nullptr;
     if (!length)
         return the_empty_stringimpl();
     char* buffer;

AK/StringView.cpp

@@ -178,12 +178,12 @@ bool StringView::equals_ignoring_ascii_case(StringView other) const
 #ifndef KERNEL
 DeprecatedString StringView::to_lowercase_string() const
 {
-    return StringImpl::create_lowercased(characters_without_null_termination(), length());
+    return StringImpl::create_lowercased(characters_without_null_termination(), length()).release_nonnull();
 }
 
 DeprecatedString StringView::to_uppercase_string() const
 {
-    return StringImpl::create_uppercased(characters_without_null_termination(), length());
+    return StringImpl::create_uppercased(characters_without_null_termination(), length()).release_nonnull();
 }
 
 DeprecatedString StringView::to_titlecase_string() const

AK/URL.cpp

@@ -191,13 +191,11 @@ URL URL::create_with_file_scheme(DeprecatedString const& path, DeprecatedString
 
     URL url;
     url.set_scheme("file"_string);
-    // NOTE: If the hostname is localhost (or null, which implies localhost), it should be set to the empty string.
-    //       This is because a file URL always needs a non-null hostname.
-    url.set_host(hostname.is_null() || hostname == "localhost" ? String {} : String::from_deprecated_string(hostname).release_value_but_fixme_should_propagate_errors());
+    url.set_host(hostname == "localhost" ? String {} : String::from_deprecated_string(hostname).release_value_but_fixme_should_propagate_errors());
     url.set_paths(lexical_path.parts());
     if (path.ends_with('/'))
         url.append_slash();
-    if (!fragment.is_null())
+    if (!fragment.is_empty())
         url.set_fragment(String::from_deprecated_string(fragment).release_value_but_fixme_should_propagate_errors());
     return url;
 }
@@ -208,14 +206,12 @@ URL URL::create_with_help_scheme(DeprecatedString const& path, DeprecatedString
 
     URL url;
     url.set_scheme("help"_string);
-    // NOTE: If the hostname is localhost (or null, which implies localhost), it should be set to the empty string.
-    //       This is because a file URL always needs a non-null hostname.
-    url.set_host(hostname.is_null() || hostname == "localhost" ? String {} : String::from_deprecated_string(hostname).release_value_but_fixme_should_propagate_errors());
+    url.set_host(hostname == "localhost" ? String {} : String::from_deprecated_string(hostname).release_value_but_fixme_should_propagate_errors());
 
     url.set_paths(lexical_path.parts());
     if (path.ends_with('/'))
         url.append_slash();
-    if (!fragment.is_null())
+    if (!fragment.is_empty())
         url.set_fragment(String::from_deprecated_string(fragment).release_value_but_fixme_should_propagate_errors());
     return url;
 }