Cursor.Last() index out of range

[tv42]

This bug was introduced in 7214e08

func TestCursorLast(t *testing.T) {
    withOpenDB(func(db *DB, path string) {
        db.CreateBucket("widgets")
        db.Do(func(txn *RWTransaction) error {
            c := txn.Bucket("widgets").Cursor()
            _, _ = c.Last()
            return nil
        })
    })
}

[0 tv@brute ((7214e08...)) ~/go/src/github.com/boltdb/bolt]$ git checkout 1eb9e0902824fff3e7a943d421e83c7d30f43176
Previous HEAD position was 7214e08... Merge pull request #57 from benbjohnson/node-aware-cursors
HEAD is now at 1eb9e09... Merge branch 'master' of https://github.com/boltdb/bolt
[0 tv@brute ((1eb9e09...)) ~/go/src/github.com/boltdb/bolt]$ go test -run=TestCursorLast
seed: 64196
quick settings: count=5, items=1000, ksize=1024, vsize=1024
PASS
ok      github.com/boltdb/bolt  0.007s
[0 tv@brute ((1eb9e09...)) ~/go/src/github.com/boltdb/bolt]$ git checkout 7214e089c0f78fce8fb1e00f09f7d2b54c88bdbe
Previous HEAD position was 1eb9e09... Merge branch 'master' of https://github.com/boltdb/bolt
HEAD is now at 7214e08... Merge pull request #57 from benbjohnson/node-aware-cursors
[0 tv@brute ((7214e08...)) ~/go/src/github.com/boltdb/bolt]$ go test -run=TestCursorLast
seed: 87363
quick settings: count=5, items=1000, ksize=1024, vsize=1024
--- FAIL: TestCursorLast (0.00 seconds)
panic: runtime error: index out of range [recovered]
    panic: runtime error: index out of range

goroutine 19 [running]:
runtime.panic(0x5cd580, 0x766da3)
    /home/tv/src/go/src/pkg/runtime/panic.c:249 +0xba
testing.func·006()
    /home/tv/src/go/src/pkg/testing/testing.go:416 +0x15d
runtime.panic(0x5cd580, 0x766da3)
    /home/tv/src/go/src/pkg/runtime/panic.c:232 +0x116
github.com/boltdb/bolt.(*Cursor).keyValue(0xc208031d70, 0x0, 0x0, 0x0, 0x0, ...)
    /home/tv/go/src/github.com/boltdb/bolt/cursor.go:249 +0x30d
github.com/boltdb/bolt.(*Cursor).Last(0xc208031d70, 0x0, 0x0, 0x0, 0x0, ...)
    /home/tv/go/src/github.com/boltdb/bolt/cursor.go:35 +0x26e
github.com/boltdb/bolt.func·047(0xc208028050, 0x0, 0x0)
    /home/tv/go/src/github.com/boltdb/bolt/bug_test.go:11 +0xef
github.com/boltdb/bolt.(*DB).Do(0xc20805e000, 0x6ac508, 0x0, 0x0)
    /home/tv/go/src/github.com/boltdb/bolt/db.go:354 +0x82
github.com/boltdb/bolt.func·048(0xc20805e000, 0xc20800dec0, 0x1b)
    /home/tv/go/src/github.com/boltdb/bolt/bug_test.go:13 +0x53
github.com/boltdb/bolt.func·075(0xc20805e000, 0xc20800dec0, 0x1b)
    /home/tv/go/src/github.com/boltdb/bolt/db_test.go:372 +0x132
github.com/boltdb/bolt.withDB(0x7ff0c96fdf38)
    /home/tv/go/src/github.com/boltdb/bolt/db_test.go:353 +0xfc
github.com/boltdb/bolt.withOpenDB(0x6ac510)
    /home/tv/go/src/github.com/boltdb/bolt/db_test.go:373 +0x5c
github.com/boltdb/bolt.TestCursorLast(0xc208052120)
    /home/tv/go/src/github.com/boltdb/bolt/bug_test.go:14 +0x27
testing.tRunner(0xc208052120, 0x7691a0)
    /home/tv/src/go/src/pkg/testing/testing.go:422 +0x9d
created by testing.RunTests
    /home/tv/src/go/src/pkg/testing/testing.go:503 +0x8d9

goroutine 16 [chan receive]:
testing.RunTests(0x6ac570, 0x768fc0, 0x54, 0x54, 0x1)
    /home/tv/src/go/src/pkg/testing/testing.go:504 +0x909
testing.Main(0x6ac570, 0x768fc0, 0x54, 0x54, 0x76a9a0, ...)
    /home/tv/src/go/src/pkg/testing/testing.go:435 +0x9e
main.main()
    /home/tv/tmp/go-build690133294/github.com/boltdb/bolt/_test/_testmain.go:229 +0x9c
exit status 2
FAIL    github.com/boltdb/bolt  0.009s
[1 tv@brute ((7214e08...)) ~/go/src/github.com/boltdb/bolt]$ 

[benbjohnson]

@tv42 Thanks for finding this and providing a test. It was just a simple lower bounds checking bug.