internal/str: add package
Change-Id: Icb5ec1385be4d200f19613eebcd4d290b3b01642
diff --git a/internal/str/str.go b/internal/str/str.go
new file mode 100644
index 0000000..f8a44cb
--- /dev/null
+++ b/internal/str/str.go
@@ -0,0 +1,151 @@
+// Copyright 2018 The CUE Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package str provides string manipulation utilities.
+package str // import "cuelang.org/go/internal/str"
+
+import (
+ "bytes"
+ "fmt"
+ "unicode"
+ "unicode/utf8"
+)
+
+// StringList flattens its arguments into a single []string.
+// Each argument in args must have type string or []string.
+func StringList(args ...interface{}) []string {
+ var x []string
+ for _, arg := range args {
+ switch arg := arg.(type) {
+ case []string:
+ x = append(x, arg...)
+ case string:
+ x = append(x, arg)
+ default:
+ panic("stringList: invalid argument of type " + fmt.Sprintf("%T", arg))
+ }
+ }
+ return x
+}
+
+// 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.
+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()
+}
+
+// FoldDup reports a pair of strings from the list that are
+// equal according to strings.EqualFold.
+// It returns "", "" if there are no such strings.
+func FoldDup(list []string) (string, string) {
+ clash := map[string]string{}
+ for _, s := range list {
+ fold := ToFold(s)
+ if t := clash[fold]; t != "" {
+ if s > t {
+ s, t = t, s
+ }
+ return s, t
+ }
+ clash[fold] = s
+ }
+ return "", ""
+}
+
+// Contains reports whether x contains s.
+func Contains(x []string, s string) bool {
+ for _, t := range x {
+ if t == s {
+ return true
+ }
+ }
+ return false
+}
+
+func isSpaceByte(c byte) bool {
+ return c == ' ' || c == '\t' || c == '\n' || c == '\r'
+}
+
+// SplitQuotedFields splits s into a list of fields,
+// allowing single or double quotes around elements.
+// There is no unescaping or other processing within
+// quoted fields.
+func SplitQuotedFields(s string) ([]string, error) {
+ // Split fields allowing '' or "" around elements.
+ // Quotes further inside the string do not count.
+ var f []string
+ for len(s) > 0 {
+ for len(s) > 0 && isSpaceByte(s[0]) {
+ s = s[1:]
+ }
+ if len(s) == 0 {
+ break
+ }
+ // Accepted quoted string. No unescaping inside.
+ if s[0] == '"' || s[0] == '\'' {
+ quote := s[0]
+ s = s[1:]
+ i := 0
+ for i < len(s) && s[i] != quote {
+ i++
+ }
+ if i >= len(s) {
+ return nil, fmt.Errorf("unterminated %c string", quote)
+ }
+ f = append(f, s[:i])
+ s = s[i+1:]
+ continue
+ }
+ i := 0
+ for i < len(s) && !isSpaceByte(s[i]) {
+ i++
+ }
+ f = append(f, s[:i])
+ s = s[i:]
+ }
+ return f, nil
+}
