There are a couple of differences here due to using ICU:
1. Titlecasing behaves slightly differently. We previously transformed
"123dollars" to "123Dollars", as we would use word segmentation to
split a string into words, then transform the first cased character
to titlecase. ICU doesn't go quite that far, and leaves the string
as "123dollars". While this is a behavior change, the only user of
this API is the `text-transform: capitalize;` CSS rule, and we now
match the behavior of other browsers.
2. There isn't an API to compare strings with case insensitivity without
allocating case-folded strings for both the left- and right-hand-side
strings. Our implementation was previously allocation-free; however,
in a benchmark, ICU is still ~1.4x faster.
Now that ""_string is infallible, the only benefit of explicitly
constructing a short string is the ability to do it at compile-time. But
we never do that, so let's simplify the API and remove this
implementation detail from it.
Similar to POSIX read, the basic read and write functions of AK::Stream
do not have a lower limit of how much data they read or write (apart
from "none at all").
Rename the functions to "read some [data]" and "write some [data]" (with
"data" being omitted, since everything here is reading and writing data)
to make them sufficiently distinct from the functions that ensure to
use the entire buffer (which should be the go-to function for most
usages).
No functional changes, just a lot of new FIXMEs.
We currently fully casefold the left- and right-hand sides to compare
two strings with case-insensitivity. Now, we casefold one code point at
a time, storing the result in a view for comparison, until we exhaust
both strings.
For example the words "can't" and "32.3" should not have boundaries
detected on the "'" and "." code points, respectively.
The String test cases fixed here are because "b'ar" is now considered
one word.
In cases where we know a string literal will fit in the short string
storage, we can do so at compile time without needing to handle error
propagation. If the provided string literal is too long, a compilation
error will be emitted due to the failed VERIFY statement being a non-
constant expression.
The Unicode spec defines much more complicated caseless matching
algorithms in its Collation spec. This implements the "basic" case
folding comparison.
Since AK can't refer to LibUnicode directly, the strategy here is that
if you need case transformations, you can link LibUnicode and receive
them. If you try to use either of these methods without linking it, then
you'll of course get a linker error (note we don't do any fallbacks to
e.g. ASCII case transformations). If you don't need these methods, you
don't have to link LibUnicode.
DeprecatedString (formerly String) has been with us since the start,
and it has served us well. However, it has a number of shortcomings
that I'd like to address.
Some of these issues are hard if not impossible to solve incrementally
inside of DeprecatedString, so instead of doing that, let's build a new
String class and then incrementally move over to it instead.
Problems in DeprecatedString:
- It assumes string allocation never fails. This makes it impossible
to use in allocation-sensitive contexts, and is the reason we had to
ban DeprecatedString from the kernel entirely.
- The awkward null state. DeprecatedString can be null. It's different
from the empty state, although null strings are considered empty.
All code is immediately nicer when using Optional<DeprecatedString>
but DeprecatedString came before Optional, which is how we ended up
like this.
- The encoding of the underlying data is ambiguous. For the most part,
we use it as if it's always UTF-8, but there have been cases where
we pass around strings in other encodings (e.g ISO8859-1)
- operator[] and length() are used to iterate over DeprecatedString one
byte at a time. This is done all over the codebase, and will *not*
give the right results unless the string is all ASCII.
How we solve these issues in the new String:
- Functions that may allocate now return ErrorOr<String> so that ENOMEM
errors can be passed to the caller.
- String has no null state. Use Optional<String> when needed.
- String is always UTF-8. This is validated when constructing a String.
We may need to add a bypass for this in the future, for cases where
you have a known-good string, but for now: validate all the things!
- There is no operator[] or length(). You can get the underlying data
with bytes(), but for iterating over code points, you should be using
an UTF-8 iterator.
Furthermore, it has two nifty new features:
- String implements a small string optimization (SSO) for strings that
can fit entirely within a pointer. This means up to 3 bytes on 32-bit
platforms, and 7 bytes on 64-bit platforms. Such small strings will
not be heap-allocated.
- String can create substrings without making a deep copy of the
substring. Instead, the superstring gets +1 refcount from the
substring, and it acts like a view into the superstring. To make
substrings like this, use the substring_with_shared_superstring() API.
One caveat:
- String does not guarantee that the underlying data is null-terminated
like DeprecatedString does today. While this was nifty in a handful of
places where we were calling C functions, it did stand in the way of
shared-superstring substrings.
We have a new, improved string type coming up in AK (OOM aware, no null
state), and while it's going to use UTF-8, the name UTF8String is a
mouthful - so let's free up the String name by renaming the existing
class.
Making the old one have an annoying name will hopefully also help with
quick adoption :^)
Each of these strings would previously rely on StringView's char const*
constructor overload, which would call __builtin_strlen on the string.
Since we now have operator ""sv, we can replace these with much simpler
versions. This opens the door to being able to remove
StringView(char const*).
No functional changes.
This commit has no behavior changes.
In particular, this does not fix any of the wrong uses of the previous
default parameter (which used to be 'false', meaning "only replace the
first occurence in the string"). It simply replaces the default uses by
String::replace(..., ReplaceMode::FirstOnly), leaving them incorrect.
This test doesn't test AK::String, but LibC's sprintf instead, so it
does not belong in `Tests/AK`. This also means this test won't be ran on
Lagom using the host OS's printf implementation.
Fixes a deprecated declaration warning when compiling with macOS SDK 13.
This removes the awkward String::replace API which was the only String
API which mutated the String and replaces it with a new immutable
version that returns a new String with the replacements applied. This
also fixes a couple of UAFs that were caused by the use of this API.
As an optimization an equivalent StringView::replace API was also added
to remove an unnecessary String allocations in the format of:
`String { view }.replace(...);`
This adds a test case for String::find and String::find_all with empty
needles. The expected behavior is in line with what the C++ standard
library (and other languages standard libraries) expect.
We had two functions for doing mostly the same thing. Combine both
of them into String::find() and use that everywhere.
Also add some tests to cover basic behavior.
