expand: resolve the two remaining TODOs

The main point of hasGlob in older v2 versions was to avoid doing
globbing work for many more directories than needed, since we'd perform
globbing on filepath.Join($PWD, field).

However, newer versions glob only on the field relative to PWD, so we
already skip that extra work without the need for this piece of code.

As for the binary search, it can be implemented in just a few lines
thanks to sort.SearchStrings.

expand/environ.go

@@ -170,15 +170,14 @@ func listEnvironWithUpper(upper bool, pairs ...string) Environ {
 	return listEnviron(list)
 }
 
+// listEnviron is a sorted list of "name=value" strings.
 type listEnviron []string
 
 func (l listEnviron) Get(name string) Variable {
-	// TODO: binary search
 	prefix := name + "="
-	for _, pair := range l {
-		if val := strings.TrimPrefix(pair, prefix); val != pair {
-			return Variable{Exported: true, Value: val}
-		}
+	i := sort.SearchStrings(l, prefix)
+	if i < len(l) && strings.HasPrefix(l[i], prefix) {
+		return Variable{Exported: true, Value: strings.TrimPrefix(l[i], prefix)}
 	}
 	return Variable{}
 }
@@ -187,7 +186,7 @@ func (l listEnviron) Each(fn func(name string, vr Variable) bool) {
 	for _, pair := range l {
 		i := strings.IndexByte(pair, '=')
 		if i < 0 {
-			// can't happen; see above
+			// should never happen; see listEnvironWithUpper
 			panic("expand.listEnviron: did not expect malformed name-value pair: " + pair)
 		}
 		name, value := pair[:i], pair[i+1:]

expand/expand.go

@@ -11,7 +11,6 @@ import (
 	"os/user"
 	"path/filepath"
 	"regexp"
-	"runtime"
 	"strconv"
 	"strings"
 
@@ -583,16 +582,6 @@ func findAllIndex(pattern, name string, n int) [][]int {
 	return rx.FindAllStringIndex(name, n)
 }
 
-// TODO: use this again to optimize globbing; see
-// https://github.com/mvdan/sh/issues/213
-func hasGlob(path string) bool {
-	magicChars := `*?[`
-	if runtime.GOOS != "windows" {
-		magicChars = `*?[\`
-	}
-	return strings.ContainsAny(path, magicChars)
-}
-
 var rxGlobStar = regexp.MustCompile(".*")
 
 // pathJoin2 is a simpler version of filepath.Join without cleaning the result,