golang/dep

// Copyright 2017 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package gps

import (
    "bytes"
    "unicode"
    "unicode/utf8"
)

// toFold returns a string with the property that strings.EqualFold(s, t) iff
// ToFold(s) == ToFold(t) This lets us test a large set of strings for
// fold-equivalent duplicates without making a quadratic number of calls to
// EqualFold. Note that strings.ToUpper and strings.ToLower do not have the
// desired property in some corner cases.
//
// This is hoisted from toolchain internals: src/cmd/go/internal/str/str.go
func toFold(s string) string {
    // Fast path: all ASCII, no upper case.
    // Most paths look like this already.
    for i := 0; i < len(s); i++ {
        c := s[i]
        if c >= utf8.RuneSelf || 'A' <= c && c <= 'Z' {
            goto Slow
        }
    }
    return s

Slow:
    var buf bytes.Buffer
    for _, r := range s {
        // SimpleFold(x) cycles to the next equivalent rune > x
        // or wraps around to smaller values. Iterate until it wraps,
        // and we've found the minimum value.
        for {
            r0 := r
            r = unicode.SimpleFold(r0)
            if r <= r0 {
                break
            }
        }
        // Exception to allow fast path above: A-Z => a-z
        if 'A' <= r && r <= 'Z' {
            r += 'a' - 'A'
        }
        buf.WriteRune(r)
    }
    return buf.String()
}