What version of Go are you using (go version)?

$ go version
go version go1.12 linux/amd64

Does this issue reproduce with the latest release?

It does reproduce with Go versions 1.3 to 1.12 (latest at the time of writing), but it works as expected in Go version 1.2.

What operating system and processor architecture are you using (go env)?

$ go env
GOARCH="amd64"
GOBIN=""
GOCACHE="/root/.cache/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/go"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build610735870=/tmp/go-build -gno-record-gcc-switches"

What did you do?

I called the suffixarray FindAllIndex method with a regexp anchored both to the beginning and end of text (https://play.golang.org/p/TaXeqtHt4Iq):

func main() {
	idx := suffixarray.New([]byte("banana"))
	re := regexp.MustCompile("^a$")
	fmt.Println(idx.FindAllIndex(re, -1))
	// Output:
	// [[1 2] [3 4] [5 6]]
}

What did you expect to see?

I expected an empty result [], the same result as for the equivalent regexp method FindAllIndex (https://play.golang.org/p/PVThOv1EE8S):

func main() {
	re := regexp.MustCompile("^a$")
	fmt.Println(re.FindAllIndex([]byte("banana"), -1))
	// Output:
	// []
}

What did you see instead?

suffixarray FindAllIndex returned the following index pairs in "banana" for the regexp "^a$":

[[1 2] [3 4] [5 6]]

The FindAllIndex documentation reads:

FindAllIndex returns a sorted list of non-overlapping matches of the regular expression r, where a match is a pair of indices specifying the matched slice of x.Bytes(). If n < 0, all matches are returned in successive order. Otherwise, at most n matches are returned and they may not be successive. The result is nil if there are no matches, or if n == 0.

There are no matches for the expression "^a$" in the string "banana". Therefore the result should be empty, nil.

Go 1.2 produced the expected result. This is a regression in Go 1.3 where the behaviour of the regexp method LiteralPrefix changed. See the discussion in #30425.