diff options
Diffstat (limited to 'vendor/github.com/rivo/uniseg/line.go')
-rw-r--r-- | vendor/github.com/rivo/uniseg/line.go | 129 |
1 files changed, 129 insertions, 0 deletions
diff --git a/vendor/github.com/rivo/uniseg/line.go b/vendor/github.com/rivo/uniseg/line.go new file mode 100644 index 000000000..03d1928c0 --- /dev/null +++ b/vendor/github.com/rivo/uniseg/line.go @@ -0,0 +1,129 @@ +package uniseg + +import "unicode/utf8" + +// FirstLineSegment returns the prefix of the given byte slice after which a +// decision to break the string over to the next line can or must be made, +// according to the rules of Unicode Standard Annex #14. This is used to +// implement line breaking. +// +// Line breaking, also known as word wrapping, is the process of breaking a +// section of text into lines such that it will fit in the available width of a +// page, window or other display area. +// +// The returned "segment" may not be broken into smaller parts, unless no other +// breaking opportunities present themselves, in which case you may break by +// grapheme clusters (using the FirstGraphemeCluster() function to determine the +// grapheme clusters). +// +// The "mustBreak" flag indicates whether you MUST break the line after the +// given segment (true), for example after newline characters, or you MAY break +// the line after the given segment (false). +// +// This function can be called continuously to extract all non-breaking sub-sets +// from a byte slice, as illustrated in the example below. +// +// If you don't know the current state, for example when calling the function +// for the first time, you must pass -1. For consecutive calls, pass the state +// and rest slice returned by the previous call. +// +// The "rest" slice is the sub-slice of the original byte slice "b" starting +// after the last byte of the identified line segment. If the length of the +// "rest" slice is 0, the entire byte slice "b" has been processed. The +// "segment" byte slice is the sub-slice of the input slice containing the +// identified line segment. +// +// Given an empty byte slice "b", the function returns nil values. +// +// Note that in accordance with UAX #14 LB3, the final segment will end with +// "mustBreak" set to true. You can choose to ignore this by checking if the +// length of the "rest" slice is 0 and calling [HasTrailingLineBreak] or +// [HasTrailingLineBreakInString] on the last rune. +// +// Note also that this algorithm may break within grapheme clusters. This is +// addressed in Section 8.2 Example 6 of UAX #14. To avoid this, you can use +// the Step() function instead. +func FirstLineSegment(b []byte, state int) (segment, rest []byte, mustBreak bool, newState int) { + // An empty byte slice returns nothing. + if len(b) == 0 { + return + } + + // Extract the first rune. + r, length := utf8.DecodeRune(b) + if len(b) <= length { // If we're already past the end, there is nothing else to parse. + return b, nil, true, lbAny // LB3. + } + + // If we don't know the state, determine it now. + if state < 0 { + state, _ = transitionLineBreakState(state, r, b[length:], "") + } + + // Transition until we find a boundary. + var boundary int + for { + r, l := utf8.DecodeRune(b[length:]) + state, boundary = transitionLineBreakState(state, r, b[length+l:], "") + + if boundary != LineDontBreak { + return b[:length], b[length:], boundary == LineMustBreak, state + } + + length += l + if len(b) <= length { + return b, nil, true, lbAny // LB3 + } + } +} + +// FirstLineSegmentInString is like FirstLineSegment() but its input and outputs +// are strings. +func FirstLineSegmentInString(str string, state int) (segment, rest string, mustBreak bool, newState int) { + // An empty byte slice returns nothing. + if len(str) == 0 { + return + } + + // Extract the first rune. + r, length := utf8.DecodeRuneInString(str) + if len(str) <= length { // If we're already past the end, there is nothing else to parse. + return str, "", true, lbAny // LB3. + } + + // If we don't know the state, determine it now. + if state < 0 { + state, _ = transitionLineBreakState(state, r, nil, str[length:]) + } + + // Transition until we find a boundary. + var boundary int + for { + r, l := utf8.DecodeRuneInString(str[length:]) + state, boundary = transitionLineBreakState(state, r, nil, str[length+l:]) + + if boundary != LineDontBreak { + return str[:length], str[length:], boundary == LineMustBreak, state + } + + length += l + if len(str) <= length { + return str, "", true, lbAny // LB3. + } + } +} + +// HasTrailingLineBreak returns true if the last rune in the given byte slice is +// one of the hard line break code points as defined in LB4 and LB5 of UAX #14. +func HasTrailingLineBreak(b []byte) bool { + r, _ := utf8.DecodeLastRune(b) + property, _ := propertyWithGenCat(lineBreakCodePoints, r) + return property == lbBK || property == lbCR || property == lbLF || property == lbNL +} + +// HasTrailingLineBreakInString is like [HasTrailingLineBreak] but for a string. +func HasTrailingLineBreakInString(str string) bool { + r, _ := utf8.DecodeLastRuneInString(str) + property, _ := propertyWithGenCat(lineBreakCodePoints, r) + return property == lbBK || property == lbCR || property == lbLF || property == lbNL +} |