This is a temporary mechanism while LibUnicode is in an in-between state
where some symbols are weakly linked and others are dynamically loaded.
The latter require an asm() label to be loaded.
Currently, we load the generated Unicode symbols with dlopen at runtime.
This is unnecessary as of 565a880ce5.
Applications that want Unicode data now link directly against the shared
library holding that data. So the same functionality can be achieved
with weak symbols.
ECMA-402 now supports short-offset, long-offset, short-generic, and
long-generic time zone name formatting. For example, in the en-US locale
the America/Eastern time zone would be formatted as:
short-offset: GMT-5
long-offset: GMT-05:00
short-generic: ET
long-generic: Eastern Time
We currently only support the UTC time zone, however. Therefore, this
very minimal implementation does not consider GMT offset or generic
display names. Instead, the CLDR defines specific strings for UTC.
The generated data for libunicodedata.so is quite large, and loading it
is a price paid by nearly every application by way of depending on
LibRegex. In order to defer this cost until an application actually uses
one of the surrounding APIs, dynamically load the generated symbols.
To be able to load the symbols dynamically, the generated methods must
have demangled names. Typically, this is accomplished with `extern "C"`
blocks. The clang toolchain complains about this here because the types
returned from the generators are strictly C++ types. So to demangle the
names, we use the asm() compiler directive to manually define a symbol
name; the caveat is that we *must* be sure the symbols are unique. As an
extra precaution, we prefix each symbol name with "unicode_". For more
details, see: https://gcc.gnu.org/onlinedocs/gcc/Asm-Labels.html
This symbol loader used in this implementation provides the additional
benefit of removing many [[maybe_unused]] attributes from the LibUnicode
methods. Internally, if ENABLE_UNICODE_DATABASE_DOWNLOAD is OFF, the
loader is able to stub out the function pointers it returns.
Note that as of this commit, LibUnicode is still directly linked against
LibUnicodeData. This commit is just a first step towards removing that.
The variable `s_time_zone_list_index_type` seems to be unused (detected
when compiling with clang), and it seems logical to bind it even it if
it is not used for now.
Similar to commit 2a7f36b392, this change moves the generated
CalendarSymbol enumeration to the public LibUnicode/NumberFormat.h
header with a pre-defined set of symbols that we need. This is to
prepare for uniquely generating the CalendarSymbols structure.
Each of the 374 generated calendars include 4 sets of symbols, each of
which have 3 lists of symbols (narrow, short, long). Of these 4488
lists, only 819 are unique.
There are 443 number system objects generated, each of which held an
array of number system symbols. Of those 443 arrays, only 39 are unique.
To uniquely store these, this change moves the generated NumericSymbol
enumeration to the public LibUnicode/NumberFormat.h header with a pre-
defined set of symbols that we need. This is to ensure the generated,
unique arrays are created in a known order with known symbols. While it
is unfortunate to no longer discover these symbols at generation time,
it does allow us to ignore unwanted symbols and perform less string-to-
enumeration conversions at lookup time.
The evolution of UniqueStorage has been as follows:
1. It was created as UniqueStringStorage to ensure only one copy of each
unique string is generated. Interested parties stored an index into
a unique string list, rather than the string itself.
Commits: f9e605397c and 04e6b43f05
2. It became apparent that non-string structures could also be de-
duplicated to reduce the size of libunicode.so. UniqueStringStorage
was generalized to UniqueStorage for this purpose.
Commit: d8e6beb14f
It's now also apparent that there's heavy duplication of lists of
structures. For example, the NumberFormat generator stores 4 lists of
NumberFormat objects. In total, we currently generate nearly 2,000 lists
of these objects, of which 275 are unique.
This change updates UniqueStorage to support storing lists. The only
change is how the storage is generated - we generate each stored list
individually, then an array storing spans of those lists.
In the CLDR, there aren't "night" values, there are "night1" & "night2"
values. This is for locales which use a different name for nighttime
depending on the hour. For example, the ja locale uses "夜" between the
hours of 19:00 and 23:00, and "夜中" between the hours of 23:00 and
04:00. Our CLDR parser is currently ignoring "night2", so this rename
is to prepare for that.
We could probably come up with better names, but in the end, the API in
LibUnicode will be such that outside callers won't even see Night1, etc.
Pattern skeletons are more or less the "key" of format patterns. Every
format pattern is assigned a skeleton. Interval patterns (which are not
yet parsed) are also assigned a skeleton - this is used to match them to
an "owning" format pattern. So we will use the skeleton generated here
to match format patterns at runtime with their available interval
patterns.
An alternative approach would be to append interval patterns directly to
their owning format pattern, but this has some draw backs:
1. Skeletons aren't totally unique. A skeleton may appear in both
the "dateFormats" and "availableFormats" objects, in which case
the same interval formats would be generated more than once.
2. Otherwise unique format patterns may only differ by the interval
patterns assigned to them. This would cause the UniqueStorage for
the format patterns to increase in size, impacting both compile
times and libunicode.so size.
The parsing in parse_calendar_symbols() might be a bit more verbose than
it really needs to be, but it is to ensure the symbols are generated in
a known order that we can control with enumerations.
TR-35's Matching Skeleton algorithm dictates how user requests including
fractional second digits should be handled when the CLDR format pattern
does not include that field. When the format pattern contains {second},
but does not contain {fractionalSecondDigits}, generate a second pattern
which appends "{decimal}{fractionalSecondDigits}" to the {second} field.
TR-35 does define lengths for {ampm}, but they are unused by ECMA-402.
To the contrary, defining the day_period length for this segment will
prevent BasicFormatMatcher from ever selecting a pattern that contains
this segment. Instead, ECMA-402 will only use the short length for
{ampm} segments.
TR-35 describes how to combine date, time, and available formats with
date-time format patterns to generate more available format patterns:
https://unicode.org/reports/tr35/tr35-dates.html#Missing_Skeleton_Fields
Use these steps to generate ~400 new patterns for each calendar. These
are required for ECMA-402's BasicFormatMatcher to produce reasonable
results.
