UBiDi and UText Enhancements Roll-up

This ticket is a roll-up of outstanding Tickets that are related to supporting UText functionality in UBidi.

In other functions within the ICU library, the UText abstraction facility is used to allow any text storage and encoding provider to be used, however, UBiDi currently does not support UText. One of the reasons for the lack of support is the ubidi_writeReordered() and ubidi_writeReverse() functions which write to the provided UChar arrays. The implementation of the UChar UText Provider currently does not support write operations.

In making changes to the ubidi_writeReordered() and ubidi_writeReverse() functions, the deficiencies of the existing UText UChar Provider need to be addressed. At the same time a general review of the current implementations for UChar arrays (UTF-16), uint8_t arrays (UTF-8) can be completed.

The following new API functions are Proposed for UBidi to support UText:

void ubidi_setUContext(UBiDi *pBiDi,
UText *prologueUt,
UText *epilogueUt,
UErrorCode *pErrorCode);

void ubidi_setUPara(UBiDi *pBiDi, UText *pText,
UBiDiLevel paraLevel, UBiDiLevel *embeddingLevels,
UErrorCode *pErrorCode);

UBiDiDirection ubidi_getUBaseDirection(UText *ut);

const UText * ubidi_getUText(const UBiDi *pBiDi);

int32_t ubidi_writeUReordered(UBiDi *pBiDi,
UText *dstUt,
uint16_t options,
UErrorCode *pErrorCode);

int32_t ubidi_writeUReverse(UText *srcUt,
UText *dstUt,
uint16_t options,
UErrorCode *pErrorCode);

The following new API function is Proposed to test if a UText is valid:

UBool utext_isValid(const UText* ut);

The following new API functions are Proposed to provide a consistent entry for creating internal array-based UText Providers:

UText * utext_openConstU16(UText *ut,
const UChar *s, int64_t length, int64_t capacity,
UErrorCode *status);

UText * utext_openU16(UText *ut,
UChar *s, int64_t length, int64_t capacity,
UErrorCode *status);

UText * utext_openConstU8(UText *ut,
const uint8_t *s, int64_t length, int64_t capacity,
UErrorCode *status);

UText * utext_openU8(UText *ut,
uint8_t *s, int64_t length, int64_t capacity,
UErrorCode *status);

UText * utext_openConstU32(UText *ut,
const UChar32 *s, int64_t length, int64_t capacity,
UErrorCode *status);

UText * utext_openU32(UText *ut,
UChar32 *s, int64_t length, int64_t capacity,
UErrorCode *status);

The following new API function is Proposed as a help function to UText Provider developers:

UText *utext_shallowClone(UText *dest, const UText *src, UErrorCode *status);

A discussion of the general approach is available here: https://werbicki.github.io/c++/2018/12/29/icu-ubidi-utext-enhancements.html