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// Package spell file defines a simple spelling checker for use in attribute errors
// such as "no such field .foo; did you mean .food?".
package spell
import (
"strings"
"unicode"
)
// Nearest returns the element of candidates
// nearest to x using the Levenshtein metric,
// or "" if none were promising.
func Nearest(x string, candidates []string) string {
// Ignore underscores and case when matching.
fold := func(s string) string {
return strings.Map(func(r rune) rune {
if r == '_' {
return -1
}
return unicode.ToLower(r)
}, s)
}
x = fold(x)
var best string
bestD := (len(x) + 1) / 2 // allow up to 50% typos
for _, c := range candidates {
d := levenshtein(x, fold(c), bestD)
if d < bestD {
bestD = d
best = c
}
}
return best
}
// levenshtein returns the non-negative Levenshtein edit distance
// between the byte strings x and y.
//
// If the computed distance exceeds max,
// the function may return early with an approximate value > max.
func levenshtein(x, y string, max int) int {
// This implementation is derived from one by Laurent Le Brun in
// Bazel that uses the single-row space efficiency trick
// described at bitbucket.org/clearer/iosifovich.
// Let x be the shorter string.
if len(x) > len(y) {
x, y = y, x
}
// Remove common prefix.
for i := 0; i < len(x); i++ {
if x[i] != y[i] {
x = x[i:]
y = y[i:]
break
}
}
if x == "" {
return len(y)
}
if d := abs(len(x) - len(y)); d > max {
return d // excessive length divergence
}
row := make([]int, len(y)+1)
for i := range row {
row[i] = i
}
for i := 1; i <= len(x); i++ {
row[0] = i
best := i
prev := i - 1
for j := 1; j <= len(y); j++ {
a := prev + b2i(x[i-1] != y[j-1]) // substitution
b := 1 + row[j-1] // deletion
c := 1 + row[j] // insertion
k := min(a, min(b, c))
prev, row[j] = row[j], k
best = min(best, k)
}
if best > max {
return best
}
}
return row[len(y)]
}
func b2i(b bool) int {
if b {
return 1
} else {
return 0
}
}
func min(x, y int) int {
if x < y {
return x
} else {
return y
}
}
func abs(x int) int {
if x >= 0 {
return x
} else {
return -x
}
}
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