1 files changed, 242 insertions, 0 deletions
diff --git a/vendor/github.com/rivo/uniseg/step.go b/vendor/github.com/rivo/uniseg/step.go
new file mode 100644
index 000000000..9b72c5e59
--- /dev/null
+++ b/vendor/github.com/rivo/uniseg/step.go
@@ -0,0 +1,242 @@
+package uniseg
+
+import "unicode/utf8"
+
+// The bit masks used to extract boundary information returned by [Step].
+const (
+	MaskLine     = 3
+	MaskWord     = 4
+	MaskSentence = 8
+)
+
+// The number of bits to shift the boundary information returned by [Step] to
+// obtain the monospace width of the grapheme cluster.
+const ShiftWidth = 4
+
+// The bit positions by which boundary flags are shifted by the [Step] function.
+// These must correspond to the Mask constants.
+const (
+	shiftWord     = 2
+	shiftSentence = 3
+	// shiftwWidth is ShiftWidth above. No mask as these are always the remaining bits.
+)
+
+// The bit positions by which states are shifted by the [Step] function. These
+// values must ensure state values defined for each of the boundary algorithms
+// don't overlap (and that they all still fit in a single int). These must
+// correspond to the Mask constants.
+const (
+	shiftWordState     = 4
+	shiftSentenceState = 9
+	shiftLineState     = 13
+	shiftPropState     = 21 // No mask as these are always the remaining bits.
+)
+
+// The bit mask used to extract the state returned by the [Step] function, after
+// shifting. These values must correspond to the shift constants.
+const (
+	maskGraphemeState = 0xf
+	maskWordState     = 0x1f
+	maskSentenceState = 0xf
+	maskLineState     = 0xff
+)
+
+// Step returns the first grapheme cluster (user-perceived character) found in
+// the given byte slice. It also returns information about the boundary between
+// that grapheme cluster and the one following it as well as the monospace width
+// of the grapheme cluster. There are three types of boundary information: word
+// boundaries, sentence boundaries, and line breaks. This function is therefore
+// a combination of [FirstGraphemeCluster], [FirstWord], [FirstSentence], and
+// [FirstLineSegment].
+//
+// The "boundaries" return value can be evaluated as follows:
+//
+//   - boundaries&MaskWord != 0: The boundary is a word boundary.
+//   - boundaries&MaskWord == 0: The boundary is not a word boundary.
+//   - boundaries&MaskSentence != 0: The boundary is a sentence boundary.
+//   - boundaries&MaskSentence == 0: The boundary is not a sentence boundary.
+//   - boundaries&MaskLine == LineDontBreak: You must not break the line at the
+//     boundary.
+//   - boundaries&MaskLine == LineMustBreak: You must break the line at the
+//     boundary.
+//   - boundaries&MaskLine == LineCanBreak: You may or may not break the line at
+//     the boundary.
+//   - boundaries >> ShiftWidth: The width of the grapheme cluster for most
+//     monospace fonts where a value of 1 represents one character cell.
+//
+// This function can be called continuously to extract all grapheme clusters
+// from a byte slice, as illustrated in the examples below.
+//
+// If you don't know which state to pass, 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 grapheme cluster. If the length of the
+// "rest" slice is 0, the entire byte slice "b" has been processed. The
+// "cluster" byte slice is the sub-slice of the input slice containing the
+// first identified grapheme cluster.
+//
+// Given an empty byte slice "b", the function returns nil values.
+//
+// While slightly less convenient than using the Graphemes class, this function
+// has much better performance and makes no allocations. It lends itself well to
+// large byte slices.
+//
+// Note that in accordance with [UAX #14 LB3], the final segment will end with
+// a mandatory line break (boundaries&MaskLine == LineMustBreak). 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.
+//
+// [UAX #14 LB3]: https://www.unicode.org/reports/tr14/#Algorithm
+func Step(b []byte, state int) (cluster, rest []byte, boundaries int, 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.
+		var prop int
+		if state < 0 {
+			prop = propertyGraphemes(r)
+		} else {
+			prop = state >> shiftPropState
+		}
+		return b, nil, LineMustBreak | (1 << shiftWord) | (1 << shiftSentence) | (runeWidth(r, prop) << ShiftWidth), grAny | (wbAny << shiftWordState) | (sbAny << shiftSentenceState) | (lbAny << shiftLineState) | (prop << shiftPropState)
+	}
+
+	// If we don't know the state, determine it now.
+	var graphemeState, wordState, sentenceState, lineState, firstProp int
+	remainder := b[length:]
+	if state < 0 {
+		graphemeState, firstProp, _ = transitionGraphemeState(state, r)
+		wordState, _ = transitionWordBreakState(state, r, remainder, "")
+		sentenceState, _ = transitionSentenceBreakState(state, r, remainder, "")
+		lineState, _ = transitionLineBreakState(state, r, remainder, "")
+	} else {
+		graphemeState = state & maskGraphemeState
+		wordState = (state >> shiftWordState) & maskWordState
+		sentenceState = (state >> shiftSentenceState) & maskSentenceState
+		lineState = (state >> shiftLineState) & maskLineState
+		firstProp = state >> shiftPropState
+	}
+
+	// Transition until we find a grapheme cluster boundary.
+	width := runeWidth(r, firstProp)
+	for {
+		var (
+			graphemeBoundary, wordBoundary, sentenceBoundary bool
+			lineBreak, prop                                  int
+		)
+
+		r, l := utf8.DecodeRune(remainder)
+		remainder = b[length+l:]
+
+		graphemeState, prop, graphemeBoundary = transitionGraphemeState(graphemeState, r)
+		wordState, wordBoundary = transitionWordBreakState(wordState, r, remainder, "")
+		sentenceState, sentenceBoundary = transitionSentenceBreakState(sentenceState, r, remainder, "")
+		lineState, lineBreak = transitionLineBreakState(lineState, r, remainder, "")
+
+		if graphemeBoundary {
+			boundary := lineBreak | (width << ShiftWidth)
+			if wordBoundary {
+				boundary |= 1 << shiftWord
+			}
+			if sentenceBoundary {
+				boundary |= 1 << shiftSentence
+			}
+			return b[:length], b[length:], boundary, graphemeState | (wordState << shiftWordState) | (sentenceState << shiftSentenceState) | (lineState << shiftLineState) | (prop << shiftPropState)
+		}
+
+		if firstProp == prExtendedPictographic {
+			if r == vs15 {
+				width = 1
+			} else if r == vs16 {
+				width = 2
+			}
+		} else if firstProp != prRegionalIndicator && firstProp != prL {
+			width += runeWidth(r, prop)
+		}
+
+		length += l
+		if len(b) <= length {
+			return b, nil, LineMustBreak | (1 << shiftWord) | (1 << shiftSentence) | (width << ShiftWidth), grAny | (wbAny << shiftWordState) | (sbAny << shiftSentenceState) | (lbAny << shiftLineState) | (prop << shiftPropState)
+		}
+	}
+}
+
+// StepString is like [Step] but its input and outputs are strings.
+func StepString(str string, state int) (cluster, rest string, boundaries int, 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.
+		prop := propertyGraphemes(r)
+		return str, "", LineMustBreak | (1 << shiftWord) | (1 << shiftSentence) | (runeWidth(r, prop) << ShiftWidth), grAny | (wbAny << shiftWordState) | (sbAny << shiftSentenceState) | (lbAny << shiftLineState)
+	}
+
+	// If we don't know the state, determine it now.
+	var graphemeState, wordState, sentenceState, lineState, firstProp int
+	remainder := str[length:]
+	if state < 0 {
+		graphemeState, firstProp, _ = transitionGraphemeState(state, r)
+		wordState, _ = transitionWordBreakState(state, r, nil, remainder)
+		sentenceState, _ = transitionSentenceBreakState(state, r, nil, remainder)
+		lineState, _ = transitionLineBreakState(state, r, nil, remainder)
+	} else {
+		graphemeState = state & maskGraphemeState
+		wordState = (state >> shiftWordState) & maskWordState
+		sentenceState = (state >> shiftSentenceState) & maskSentenceState
+		lineState = (state >> shiftLineState) & maskLineState
+		firstProp = state >> shiftPropState
+	}
+
+	// Transition until we find a grapheme cluster boundary.
+	width := runeWidth(r, firstProp)
+	for {
+		var (
+			graphemeBoundary, wordBoundary, sentenceBoundary bool
+			lineBreak, prop                                  int
+		)
+
+		r, l := utf8.DecodeRuneInString(remainder)
+		remainder = str[length+l:]
+
+		graphemeState, prop, graphemeBoundary = transitionGraphemeState(graphemeState, r)
+		wordState, wordBoundary = transitionWordBreakState(wordState, r, nil, remainder)
+		sentenceState, sentenceBoundary = transitionSentenceBreakState(sentenceState, r, nil, remainder)
+		lineState, lineBreak = transitionLineBreakState(lineState, r, nil, remainder)
+
+		if graphemeBoundary {
+			boundary := lineBreak | (width << ShiftWidth)
+			if wordBoundary {
+				boundary |= 1 << shiftWord
+			}
+			if sentenceBoundary {
+				boundary |= 1 << shiftSentence
+			}
+			return str[:length], str[length:], boundary, graphemeState | (wordState << shiftWordState) | (sentenceState << shiftSentenceState) | (lineState << shiftLineState) | (prop << shiftPropState)
+		}
+
+		if firstProp == prExtendedPictographic {
+			if r == vs15 {
+				width = 1
+			} else if r == vs16 {
+				width = 2
+			}
+		} else if firstProp != prRegionalIndicator && firstProp != prL {
+			width += runeWidth(r, prop)
+		}
+
+		length += l
+		if len(str) <= length {
+			return str, "", LineMustBreak | (1 << shiftWord) | (1 << shiftSentence) | (width << ShiftWidth), grAny | (wbAny << shiftWordState) | (sbAny << shiftSentenceState) | (lbAny << shiftLineState) | (prop << shiftPropState)
+		}
+	}
+}