fix: sentinel errors should not have stack traces (#2042)

## Problem

While debugging a program which is using badger I noticed that stack
traces returned from my code (which uses errors with stack traces) are
useless. I found the reason: badger uses sentinel errors (great!) but it
creates them with stack traces at the "global init time" (e.g., `var
ErrFoo = errors.New(...)`) and not at "return from function time".
Because of that I was seeing stack traces like:

```
github.com/dgraph-io/badger/v4.init
	/go/pkg/mod/github.com/dgraph-io/badger/[email protected]/compaction.go:41
runtime.doInit1
	/usr/local/go/src/runtime/proc.go:6740
runtime.doInit
	/usr/local/go/src/runtime/proc.go:6707
runtime.main
	/usr/local/go/src/runtime/proc.go:249
runtime.goexit
	/usr/local/go/src/runtime/asm_amd64.s:1650
```

Instead of a stack trace which would show me where the call which is
returning sentinel error is made.

## Solution

Ideally, one would create all sentinel errors without stack traces
(standard errors package works great for that) and then when the error
happens in a function, you return `errors.WithStack(ErrFoobar)` instead
of just `ErrFoobar`. This means that sentinel error is then annotated
with a stack trace at the place where the error happens. But if you do
that, then you have to check for sentinel errors with `errors.Is`
instead of just comparing errors with equality (`==`). That might be a
breaking change for people who are not using `errors.Is` as they should.
Because badger's own codebase uses equality instead of `errors.Is` I
decided to not do this in this PR, but instead:

Just make sentinel errors without stack traces. This allows me to
annotate with a stack trace inside my program (otherwise my program does
not do so because if finds an existing stack trace and assumes it is a
deeper one) and I get at least that part of the stack trace. Equality
still works as usual.

I suggest this is merged this way and in v5 of badger `errors.WithStack`
and required `errors.Is` are introduced.

## Side note

Some time ago [I made this errors package for
Go](https://gitlab.com/tozd/go/errors) which fixes various issues in
`github.com/pkg/errors` and also has direct support for sentinel (in
that package called "base") errors. It also has some features badger has
in its `y` package for dealing with errors. You could consider adopting
that package to have a comprehensive errors handling in badger.

badger/cmd/bank.go

@@ -20,6 +20,7 @@ import (
 	"bytes"
 	"context"
 	"errors"
+	stderrors "errors"
 	"fmt"
 	"log"
 	"math"
@@ -148,7 +149,7 @@ func min(a, b uint64) uint64 {
 	return b
 }
 
-var errAbandoned = errors.New("Transaction abandonded due to insufficient balance")
+var errAbandoned = stderrors.New("Transaction abandonded due to insufficient balance")
 
 func moveMoney(db *badger.DB, from, to int) error {
 	return db.Update(func(txn *badger.Txn) error {

db.go

@@ -20,6 +20,7 @@ import (
 	"bytes"
 	"context"
 	"encoding/binary"
+	stderrors "errors"
 	"expvar"
 	"fmt"
 	"math"
@@ -1015,7 +1016,7 @@ func (db *DB) batchSetAsync(entries []*Entry, f func(error)) error {
 	return nil
 }
 
-var errNoRoom = errors.New("No room for write")
+var errNoRoom = stderrors.New("No room for write")
 
 // ensureRoomForWrite is always called serially.
 func (db *DB) ensureRoomForWrite() error {

errors.go

@@ -17,9 +17,8 @@
 package badger
 
 import (
+	stderrors "errors"
 	"math"
-
-	"github.com/pkg/errors"
 )
 
 const (
@@ -30,97 +29,97 @@ const (
 var (
 	// ErrValueLogSize is returned when opt.ValueLogFileSize option is not within the valid
 	// range.
-	ErrValueLogSize = errors.New("Invalid ValueLogFileSize, must be in range [1MB, 2GB)")
+	ErrValueLogSize = stderrors.New("Invalid ValueLogFileSize, must be in range [1MB, 2GB)")
 
 	// ErrKeyNotFound is returned when key isn't found on a txn.Get.
-	ErrKeyNotFound = errors.New("Key not found")
+	ErrKeyNotFound = stderrors.New("Key not found")
 
 	// ErrTxnTooBig is returned if too many writes are fit into a single transaction.
-	ErrTxnTooBig = errors.New("Txn is too big to fit into one request")
+	ErrTxnTooBig = stderrors.New("Txn is too big to fit into one request")
 
 	// ErrConflict is returned when a transaction conflicts with another transaction. This can
 	// happen if the read rows had been updated concurrently by another transaction.
-	ErrConflict = errors.New("Transaction Conflict. Please retry")
+	ErrConflict = stderrors.New("Transaction Conflict. Please retry")
 
 	// ErrReadOnlyTxn is returned if an update function is called on a read-only transaction.
-	ErrReadOnlyTxn = errors.New("No sets or deletes are allowed in a read-only transaction")
+	ErrReadOnlyTxn = stderrors.New("No sets or deletes are allowed in a read-only transaction")
 
 	// ErrDiscardedTxn is returned if a previously discarded transaction is re-used.
-	ErrDiscardedTxn = errors.New("This transaction has been discarded. Create a new one")
+	ErrDiscardedTxn = stderrors.New("This transaction has been discarded. Create a new one")
 
 	// ErrEmptyKey is returned if an empty key is passed on an update function.
-	ErrEmptyKey = errors.New("Key cannot be empty")
+	ErrEmptyKey = stderrors.New("Key cannot be empty")
 
 	// ErrInvalidKey is returned if the key has a special !badger! prefix,
 	// reserved for internal usage.
-	ErrInvalidKey = errors.New("Key is using a reserved !badger! prefix")
+	ErrInvalidKey = stderrors.New("Key is using a reserved !badger! prefix")
 
 	// ErrBannedKey is returned if the read/write key belongs to any banned namespace.
-	ErrBannedKey = errors.New("Key is using the banned prefix")
+	ErrBannedKey = stderrors.New("Key is using the banned prefix")
 
 	// ErrThresholdZero is returned if threshold is set to zero, and value log GC is called.
 	// In such a case, GC can't be run.
-	ErrThresholdZero = errors.New(
+	ErrThresholdZero = stderrors.New(
 		"Value log GC can't run because threshold is set to zero")
 
 	// ErrNoRewrite is returned if a call for value log GC doesn't result in a log file rewrite.
-	ErrNoRewrite = errors.New(
+	ErrNoRewrite = stderrors.New(
 		"Value log GC attempt didn't result in any cleanup")
 
 	// ErrRejected is returned if a value log GC is called either while another GC is running, or
 	// after DB::Close has been called.
-	ErrRejected = errors.New("Value log GC request rejected")
+	ErrRejected = stderrors.New("Value log GC request rejected")
 
 	// ErrInvalidRequest is returned if the user request is invalid.
-	ErrInvalidRequest = errors.New("Invalid request")
+	ErrInvalidRequest = stderrors.New("Invalid request")
 
 	// ErrManagedTxn is returned if the user tries to use an API which isn't
 	// allowed due to external management of transactions, when using ManagedDB.
-	ErrManagedTxn = errors.New(
+	ErrManagedTxn = stderrors.New(
 		"Invalid API request. Not allowed to perform this action using ManagedDB")
 
 	// ErrNamespaceMode is returned if the user tries to use an API which is allowed only when
 	// NamespaceOffset is non-negative.
-	ErrNamespaceMode = errors.New(
+	ErrNamespaceMode = stderrors.New(
 		"Invalid API request. Not allowed to perform this action when NamespaceMode is not set.")
 
 	// ErrInvalidDump if a data dump made previously cannot be loaded into the database.
-	ErrInvalidDump = errors.New("Data dump cannot be read")
+	ErrInvalidDump = stderrors.New("Data dump cannot be read")
 
 	// ErrZeroBandwidth is returned if the user passes in zero bandwidth for sequence.
-	ErrZeroBandwidth = errors.New("Bandwidth must be greater than zero")
+	ErrZeroBandwidth = stderrors.New("Bandwidth must be greater than zero")
 
 	// ErrWindowsNotSupported is returned when opt.ReadOnly is used on Windows
-	ErrWindowsNotSupported = errors.New("Read-only mode is not supported on Windows")
+	ErrWindowsNotSupported = stderrors.New("Read-only mode is not supported on Windows")
 
 	// ErrPlan9NotSupported is returned when opt.ReadOnly is used on Plan 9
-	ErrPlan9NotSupported = errors.New("Read-only mode is not supported on Plan 9")
+	ErrPlan9NotSupported = stderrors.New("Read-only mode is not supported on Plan 9")
 
 	// ErrTruncateNeeded is returned when the value log gets corrupt, and requires truncation of
 	// corrupt data to allow Badger to run properly.
-	ErrTruncateNeeded = errors.New(
+	ErrTruncateNeeded = stderrors.New(
 		"Log truncate required to run DB. This might result in data loss")
 
 	// ErrBlockedWrites is returned if the user called DropAll. During the process of dropping all
 	// data from Badger, we stop accepting new writes, by returning this error.
-	ErrBlockedWrites = errors.New("Writes are blocked, possibly due to DropAll or Close")
+	ErrBlockedWrites = stderrors.New("Writes are blocked, possibly due to DropAll or Close")
 
 	// ErrNilCallback is returned when subscriber's callback is nil.
-	ErrNilCallback = errors.New("Callback cannot be nil")
+	ErrNilCallback = stderrors.New("Callback cannot be nil")
 
 	// ErrEncryptionKeyMismatch is returned when the storage key is not
 	// matched with the key previously given.
-	ErrEncryptionKeyMismatch = errors.New("Encryption key mismatch")
+	ErrEncryptionKeyMismatch = stderrors.New("Encryption key mismatch")
 
 	// ErrInvalidDataKeyID is returned if the datakey id is invalid.
-	ErrInvalidDataKeyID = errors.New("Invalid datakey id")
+	ErrInvalidDataKeyID = stderrors.New("Invalid datakey id")
 
 	// ErrInvalidEncryptionKey is returned if length of encryption keys is invalid.
-	ErrInvalidEncryptionKey = errors.New("Encryption key's length should be" +
+	ErrInvalidEncryptionKey = stderrors.New("Encryption key's length should be" +
 		"either 16, 24, or 32 bytes")
 	// ErrGCInMemoryMode is returned when db.RunValueLogGC is called in in-memory mode.
-	ErrGCInMemoryMode = errors.New("Cannot run value log GC when DB is opened in InMemory mode")
+	ErrGCInMemoryMode = stderrors.New("Cannot run value log GC when DB is opened in InMemory mode")
 
 	// ErrDBClosed is returned when a get operation is performed after closing the DB.
-	ErrDBClosed = errors.New("DB Closed")
+	ErrDBClosed = stderrors.New("DB Closed")
 )

levels.go

@@ -20,6 +20,7 @@ import (
 	"bytes"
 	"context"
 	"encoding/hex"
+	stderrors "errors"
 	"fmt"
 	"math"
 	"math/rand"
@@ -1512,7 +1513,7 @@ func tablesToString(tables []*table.Table) []string {
 	return res
 }
 
-var errFillTables = errors.New("Unable to fill tables")
+var errFillTables = stderrors.New("Unable to fill tables")
 
 // doCompact picks some table on level l and compacts it away to the next level.
 func (s *levelsController) doCompact(id int, p compactionPriority) error {

manifest.go

@@ -20,6 +20,7 @@ import (
 	"bufio"
 	"bytes"
 	"encoding/binary"
+	stderrors "errors"
 	"fmt"
 	"hash/crc32"
 	"io"
@@ -352,8 +353,8 @@ func (r *countingReader) ReadByte() (b byte, err error) {
 }
 
 var (
-	errBadMagic    = errors.New("manifest has bad magic")
-	errBadChecksum = errors.New("manifest has checksum mismatch")
+	errBadMagic    = stderrors.New("manifest has bad magic")
+	errBadChecksum = stderrors.New("manifest has checksum mismatch")
 )
 
 // ReplayManifestFile reads the manifest file and constructs two manifest objects.  (We need one

merge.go

@@ -17,11 +17,10 @@
 package badger
 
 import (
+	stderrors "errors"
 	"sync"
 	"time"
 
-	"github.com/pkg/errors"
-
 	"github.com/dgraph-io/badger/v4/y"
 	"github.com/dgraph-io/ristretto/z"
 )
@@ -58,7 +57,7 @@ func (db *DB) GetMergeOperator(key []byte,
 	return op
 }
 
-var errNoMerge = errors.New("No need for merge")
+var errNoMerge = stderrors.New("No need for merge")
 
 func (op *MergeOperator) iterateAndMerge() (newVal []byte, latest uint64, err error) {
 	txn := op.db.NewTransaction(false)

value.go

@@ -19,6 +19,7 @@ package badger
 import (
 	"bytes"
 	"context"
+	stderrors "errors"
 	"fmt"
 	"hash"
 	"hash/crc32"
@@ -63,8 +64,8 @@ const (
 	vlogHeaderSize = 20
 )
 
-var errStop = errors.New("Stop iteration")
-var errTruncate = errors.New("Do truncate")
+var errStop = stderrors.New("Stop iteration")
+var errTruncate = stderrors.New("Do truncate")
 
 type logEntry func(e Entry, vp valuePointer) error
 

y/checksum.go

@@ -17,16 +17,16 @@
 package y
 
 import (
+	stderrors "errors"
 	"hash/crc32"
 
 	"github.com/cespare/xxhash/v2"
-	"github.com/pkg/errors"
 
 	"github.com/dgraph-io/badger/v4/pb"
 )
 
 // ErrChecksumMismatch is returned at checksum mismatch.
-var ErrChecksumMismatch = errors.New("checksum mismatch")
+var ErrChecksumMismatch = stderrors.New("checksum mismatch")
 
 // CalculateChecksum calculates checksum for data using ct checksum type.
 func CalculateChecksum(data []byte, ct pb.Checksum_Algorithm) uint64 {

y/y.go

@@ -19,6 +19,7 @@ package y
 import (
 	"bytes"
 	"encoding/binary"
+	stderrors "errors"
 	"fmt"
 	"hash/crc32"
 	"io"
@@ -30,20 +31,18 @@ import (
 	"time"
 	"unsafe"
 
-	"github.com/pkg/errors"
-
 	"github.com/dgraph-io/badger/v4/pb"
 	"github.com/dgraph-io/ristretto/z"
 )
 
 var (
 	// ErrEOF indicates an end of file when trying to read from a memory mapped file
 	// and encountering the end of slice.
-	ErrEOF = errors.New("ErrEOF: End of file")
+	ErrEOF = stderrors.New("ErrEOF: End of file")
 
 	// ErrCommitAfterFinish indicates that write batch commit was called after
 	// finish
-	ErrCommitAfterFinish = errors.New("Batch commit not permitted after finish")
+	ErrCommitAfterFinish = stderrors.New("Batch commit not permitted after finish")
 )
 
 type Flags int