all: remove public named return values when useless

Named returned values should only be used on public funcs and methods
when it contributes to the documentation.

Named return values should not be used if they're only saving the
programmer a few lines of code inside the body of the function,
especially if that means there's stutter in the documentation or it
was only there so the programmer could use a naked return
statement. (Naked returns should not be used except in very small
functions)

This change is a manual audit & cleanup of public func signatures.

Signatures were not changed if:

* the func was private (wouldn't be in public godoc)
* the documentation referenced it
* the named return value was an interesting name. (i.e. it wasn't
  simply stutter, repeating the name of the type)

There should be no changes in behavior. (At least: none intended)

Change-Id: I3472ef49619678fe786e5e0994bdf2d9de76d109
Reviewed-on: https://go-review.googlesource.com/20024
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Andrew Gerrand <adg@golang.org>

doc/effective_go.html

@@ -239,9 +239,9 @@ starts with the name being declared.
 </p>
 
 <pre>
-// Compile parses a regular expression and returns, if successful, a Regexp
-// object that can be used to match against text.
-func Compile(str string) (regexp *Regexp, err error) {
+// Compile parses a regular expression and returns, if successful,
+// a Regexp that can be used to match against text.
+func Compile(str string) (*Regexp, error) {
 </pre>
 
 <p>

src/archive/zip/reader.go

@@ -153,19 +153,18 @@ func (f *File) DataOffset() (offset int64, err error) {
 
 // Open returns a ReadCloser that provides access to the File's contents.
 // Multiple files may be read concurrently.
-func (f *File) Open() (rc io.ReadCloser, err error) {
+func (f *File) Open() (io.ReadCloser, error) {
 	bodyOffset, err := f.findBodyOffset()
 	if err != nil {
-		return
+		return nil, err
 	}
 	size := int64(f.CompressedSize64)
 	r := io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset, size)
 	dcomp := f.zip.decompressor(f.Method)
 	if dcomp == nil {
-		err = ErrAlgorithm
-		return
+		return nil, ErrAlgorithm
 	}
-	rc = dcomp(r)
+	var rc io.ReadCloser = dcomp(r)
 	var desr io.Reader
 	if f.hasDataDescriptor() {
 		desr = io.NewSectionReader(f.zipr, f.headerOffset+bodyOffset+size, dataDescriptorLen)
@@ -176,7 +175,7 @@ func (f *File) Open() (rc io.ReadCloser, err error) {
 		f:    f,
 		desr: desr,
 	}
-	return
+	return rc, nil
 }
 
 type checksumReader struct {

src/bufio/bufio.go

@@ -220,7 +220,7 @@ func (b *Reader) Read(p []byte) (n int, err error) {
 
 // ReadByte reads and returns a single byte.
 // If no byte is available, returns an error.
-func (b *Reader) ReadByte() (c byte, err error) {
+func (b *Reader) ReadByte() (byte, error) {
 	b.lastRuneSize = -1
 	for b.r == b.w {
 		if b.err != nil {
@@ -228,7 +228,7 @@ func (b *Reader) ReadByte() (c byte, err error) {
 		}
 		b.fill() // buffer is empty
 	}
-	c = b.buf[b.r]
+	c := b.buf[b.r]
 	b.r++
 	b.lastByte = int(c)
 	return c, nil
@@ -395,12 +395,12 @@ func (b *Reader) ReadLine() (line []byte, isPrefix bool, err error) {
 // ReadBytes returns err != nil if and only if the returned data does not end in
 // delim.
 // For simple uses, a Scanner may be more convenient.
-func (b *Reader) ReadBytes(delim byte) (line []byte, err error) {
+func (b *Reader) ReadBytes(delim byte) ([]byte, error) {
 	// Use ReadSlice to look for array,
 	// accumulating full buffers.
 	var frag []byte
 	var full [][]byte
-
+	var err error
 	for {
 		var e error
 		frag, e = b.ReadSlice(delim)
@@ -442,10 +442,9 @@ func (b *Reader) ReadBytes(delim byte) (line []byte, err error) {
 // ReadString returns err != nil if and only if the returned data does not end in
 // delim.
 // For simple uses, a Scanner may be more convenient.
-func (b *Reader) ReadString(delim byte) (line string, err error) {
+func (b *Reader) ReadString(delim byte) (string, error) {
 	bytes, err := b.ReadBytes(delim)
-	line = string(bytes)
-	return line, err
+	return string(bytes), err
 }
 
 // WriteTo implements io.WriterTo.

src/bytes/buffer.go

@@ -293,14 +293,14 @@ func (b *Buffer) Next(n int) []byte {
 
 // ReadByte reads and returns the next byte from the buffer.
 // If no byte is available, it returns error io.EOF.
-func (b *Buffer) ReadByte() (c byte, err error) {
+func (b *Buffer) ReadByte() (byte, error) {
 	b.lastRead = opInvalid
 	if b.off >= len(b.buf) {
 		// Buffer is empty, reset to recover space.
 		b.Truncate(0)
 		return 0, io.EOF
 	}
-	c = b.buf[b.off]
+	c := b.buf[b.off]
 	b.off++
 	b.lastRead = opRead
 	return c, nil

src/bytes/reader.go

@@ -63,14 +63,14 @@ func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
 	return
 }
 
-func (r *Reader) ReadByte() (b byte, err error) {
+func (r *Reader) ReadByte() (byte, error) {
 	r.prevRune = -1
 	if r.i >= int64(len(r.s)) {
 		return 0, io.EOF
 	}
-	b = r.s[r.i]
+	b := r.s[r.i]
 	r.i++
-	return
+	return b, nil
 }
 
 func (r *Reader) UnreadByte() error {

src/crypto/dsa/dsa.go

@@ -52,7 +52,7 @@ const numMRTests = 64
 
 // GenerateParameters puts a random, valid set of DSA parameters into params.
 // This function can take many seconds, even on fast machines.
-func GenerateParameters(params *Parameters, rand io.Reader, sizes ParameterSizes) (err error) {
+func GenerateParameters(params *Parameters, rand io.Reader, sizes ParameterSizes) error {
 	// This function doesn't follow FIPS 186-3 exactly in that it doesn't
 	// use a verification seed to generate the primes. The verification
 	// seed doesn't appear to be exported or used by other code and
@@ -87,9 +87,8 @@ func GenerateParameters(params *Parameters, rand io.Reader, sizes ParameterSizes
 
 GeneratePrimes:
 	for {
-		_, err = io.ReadFull(rand, qBytes)
-		if err != nil {
-			return
+		if _, err := io.ReadFull(rand, qBytes); err != nil {
+			return err
 		}
 
 		qBytes[len(qBytes)-1] |= 1
@@ -101,9 +100,8 @@ GeneratePrimes:
 		}
 
 		for i := 0; i < 4*L; i++ {
-			_, err = io.ReadFull(rand, pBytes)
-			if err != nil {
-				return
+			if _, err := io.ReadFull(rand, pBytes); err != nil {
+				return err
 			}
 
 			pBytes[len(pBytes)-1] |= 1
@@ -142,7 +140,7 @@ GeneratePrimes:
 		}
 
 		params.G = g
-		return
+		return nil
 	}
 }
 

src/crypto/ecdsa/ecdsa.go

@@ -96,17 +96,17 @@ func randFieldElement(c elliptic.Curve, rand io.Reader) (k *big.Int, err error)
 }
 
 // GenerateKey generates a public and private key pair.
-func GenerateKey(c elliptic.Curve, rand io.Reader) (priv *PrivateKey, err error) {
+func GenerateKey(c elliptic.Curve, rand io.Reader) (*PrivateKey, error) {
 	k, err := randFieldElement(c, rand)
 	if err != nil {
-		return
+		return nil, err
 	}
 
-	priv = new(PrivateKey)
+	priv := new(PrivateKey)
 	priv.PublicKey.Curve = c
 	priv.D = k
 	priv.PublicKey.X, priv.PublicKey.Y = c.ScalarBaseMult(k.Bytes())
-	return
+	return priv, nil
 }
 
 // hashToInt converts a hash value to an integer. There is some disagreement

src/crypto/rsa/pkcs1v15.go

@@ -24,31 +24,32 @@ type PKCS1v15DecryptOptions struct {
 	SessionKeyLen int
 }
 
-// EncryptPKCS1v15 encrypts the given message with RSA and the padding scheme from PKCS#1 v1.5.
-// The message must be no longer than the length of the public modulus minus 11 bytes.
+// EncryptPKCS1v15 encrypts the given message with RSA and the padding
+// scheme from PKCS#1 v1.5.  The message must be no longer than the
+// length of the public modulus minus 11 bytes.
 //
-// The rand parameter is used as a source of entropy to ensure that encrypting
-// the same message twice doesn't result in the same ciphertext.
+// The rand parameter is used as a source of entropy to ensure that
+// encrypting the same message twice doesn't result in the same
+// ciphertext.
 //
-// WARNING: use of this function to encrypt plaintexts other than session keys
-// is dangerous. Use RSA OAEP in new protocols.
-func EncryptPKCS1v15(rand io.Reader, pub *PublicKey, msg []byte) (out []byte, err error) {
+// WARNING: use of this function to encrypt plaintexts other than
+// session keys is dangerous. Use RSA OAEP in new protocols.
+func EncryptPKCS1v15(rand io.Reader, pub *PublicKey, msg []byte) ([]byte, error) {
 	if err := checkPub(pub); err != nil {
 		return nil, err
 	}
 	k := (pub.N.BitLen() + 7) / 8
 	if len(msg) > k-11 {
-		err = ErrMessageTooLong
-		return
+		return nil, ErrMessageTooLong
 	}
 
 	// EM = 0x00 || 0x02 || PS || 0x00 || M
 	em := make([]byte, k)
 	em[1] = 2
 	ps, mm := em[2:len(em)-len(msg)-1], em[len(em)-len(msg):]
-	err = nonZeroRandomBytes(ps, rand)
+	err := nonZeroRandomBytes(ps, rand)
 	if err != nil {
-		return
+		return nil, err
 	}
 	em[len(em)-len(msg)-1] = 0
 	copy(mm, msg)
@@ -57,8 +58,7 @@ func EncryptPKCS1v15(rand io.Reader, pub *PublicKey, msg []byte) (out []byte, er
 	c := encrypt(new(big.Int), pub, m)
 
 	copyWithLeftPad(em, c.Bytes())
-	out = em
-	return
+	return em, nil
 }
 
 // DecryptPKCS1v15 decrypts a plaintext using RSA and the padding scheme from PKCS#1 v1.5.
@@ -69,19 +69,18 @@ func EncryptPKCS1v15(rand io.Reader, pub *PublicKey, msg []byte) (out []byte, er
 // learn whether each instance returned an error then they can decrypt and
 // forge signatures as if they had the private key. See
 // DecryptPKCS1v15SessionKey for a way of solving this problem.
-func DecryptPKCS1v15(rand io.Reader, priv *PrivateKey, ciphertext []byte) (out []byte, err error) {
+func DecryptPKCS1v15(rand io.Reader, priv *PrivateKey, ciphertext []byte) ([]byte, error) {
 	if err := checkPub(&priv.PublicKey); err != nil {
 		return nil, err
 	}
 	valid, out, index, err := decryptPKCS1v15(rand, priv, ciphertext)
 	if err != nil {
-		return
+		return nil, err
 	}
 	if valid == 0 {
 		return nil, ErrDecryption
 	}
-	out = out[index:]
-	return
+	return out[index:], nil
 }
 
 // DecryptPKCS1v15SessionKey decrypts a session key using RSA and the padding scheme from PKCS#1 v1.5.
@@ -103,7 +102,7 @@ func DecryptPKCS1v15(rand io.Reader, priv *PrivateKey, ciphertext []byte) (out [
 // a random value was used (because it'll be different for the same ciphertext)
 // and thus whether the padding was correct. This defeats the point of this
 // function. Using at least a 16-byte key will protect against this attack.
-func DecryptPKCS1v15SessionKey(rand io.Reader, priv *PrivateKey, ciphertext []byte, key []byte) (err error) {
+func DecryptPKCS1v15SessionKey(rand io.Reader, priv *PrivateKey, ciphertext []byte, key []byte) error {
 	if err := checkPub(&priv.PublicKey); err != nil {
 		return err
 	}
@@ -114,7 +113,7 @@ func DecryptPKCS1v15SessionKey(rand io.Reader, priv *PrivateKey, ciphertext []by
 
 	valid, em, index, err := decryptPKCS1v15(rand, priv, ciphertext)
 	if err != nil {
-		return
+		return err
 	}
 
 	if len(em) != k {
@@ -125,7 +124,7 @@ func DecryptPKCS1v15SessionKey(rand io.Reader, priv *PrivateKey, ciphertext []by
 
 	valid &= subtle.ConstantTimeEq(int32(len(em)-index), int32(len(key)))
 	subtle.ConstantTimeCopy(valid, key, em[len(em)-len(key):])
-	return
+	return nil
 }
 
 // decryptPKCS1v15 decrypts ciphertext using priv and blinds the operation if
@@ -213,21 +212,23 @@ var hashPrefixes = map[crypto.Hash][]byte{
 	crypto.RIPEMD160: {0x30, 0x20, 0x30, 0x08, 0x06, 0x06, 0x28, 0xcf, 0x06, 0x03, 0x00, 0x31, 0x04, 0x14},
 }
 
-// SignPKCS1v15 calculates the signature of hashed using RSASSA-PKCS1-V1_5-SIGN from RSA PKCS#1 v1.5.
-// Note that hashed must be the result of hashing the input message using the
-// given hash function. If hash is zero, hashed is signed directly. This isn't
+// SignPKCS1v15 calculates the signature of hashed using
+// RSASSA-PKCS1-V1_5-SIGN from RSA PKCS#1 v1.5.  Note that hashed must
+// be the result of hashing the input message using the given hash
+// function. If hash is zero, hashed is signed directly. This isn't
 // advisable except for interoperability.
 //
-// If rand is not nil then RSA blinding will be used to avoid timing side-channel attacks.
+// If rand is not nil then RSA blinding will be used to avoid timing
+// side-channel attacks.
 //
-// This function is deterministic. Thus, if the set of possible messages is
-// small, an attacker may be able to build a map from messages to signatures
-// and identify the signed messages. As ever, signatures provide authenticity,
-// not confidentiality.
-func SignPKCS1v15(rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []byte) (s []byte, err error) {
+// This function is deterministic. Thus, if the set of possible
+// messages is small, an attacker may be able to build a map from
+// messages to signatures and identify the signed messages. As ever,
+// signatures provide authenticity, not confidentiality.
+func SignPKCS1v15(rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []byte) ([]byte, error) {
 	hashLen, prefix, err := pkcs1v15HashInfo(hash, len(hashed))
 	if err != nil {
-		return
+		return nil, err
 	}
 
 	tLen := len(prefix) + hashLen
@@ -248,12 +249,11 @@ func SignPKCS1v15(rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []b
 	m := new(big.Int).SetBytes(em)
 	c, err := decryptAndCheck(rand, priv, m)
 	if err != nil {
-		return
+		return nil, err
 	}
 
 	copyWithLeftPad(em, c.Bytes())
-	s = em
-	return
+	return em, nil
 }
 
 // VerifyPKCS1v15 verifies an RSA PKCS#1 v1.5 signature.
@@ -261,17 +261,16 @@ func SignPKCS1v15(rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []b
 // function and sig is the signature. A valid signature is indicated by
 // returning a nil error. If hash is zero then hashed is used directly. This
 // isn't advisable except for interoperability.
-func VerifyPKCS1v15(pub *PublicKey, hash crypto.Hash, hashed []byte, sig []byte) (err error) {
+func VerifyPKCS1v15(pub *PublicKey, hash crypto.Hash, hashed []byte, sig []byte) error {
 	hashLen, prefix, err := pkcs1v15HashInfo(hash, len(hashed))
 	if err != nil {
-		return
+		return err
 	}
 
 	tLen := len(prefix) + hashLen
 	k := (pub.N.BitLen() + 7) / 8
 	if k < tLen+11 {
-		err = ErrVerification
-		return
+		return ErrVerification
 	}
 
 	c := new(big.Int).SetBytes(sig)

src/crypto/rsa/pss.go

@@ -246,7 +246,7 @@ func (opts *PSSOptions) saltLength() int {
 // Note that hashed must be the result of hashing the input message using the
 // given hash function. The opts argument may be nil, in which case sensible
 // defaults are used.
-func SignPSS(rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []byte, opts *PSSOptions) (s []byte, err error) {
+func SignPSS(rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []byte, opts *PSSOptions) ([]byte, error) {
 	saltLength := opts.saltLength()
 	switch saltLength {
 	case PSSSaltLengthAuto:
@@ -260,8 +260,8 @@ func SignPSS(rand io.Reader, priv *PrivateKey, hash crypto.Hash, hashed []byte,
 	}
 
 	salt := make([]byte, saltLength)
-	if _, err = io.ReadFull(rand, salt); err != nil {
-		return
+	if _, err := io.ReadFull(rand, salt); err != nil {
+		return nil, err
 	}
 	return signPSSWithSalt(rand, priv, hash, hashed, salt)
 }

src/crypto/rsa/rsa.go

@@ -191,7 +191,7 @@ func (priv *PrivateKey) Validate() error {
 
 // GenerateKey generates an RSA keypair of the given bit size using the
 // random source random (for example, crypto/rand.Reader).
-func GenerateKey(random io.Reader, bits int) (priv *PrivateKey, err error) {
+func GenerateKey(random io.Reader, bits int) (*PrivateKey, error) {
 	return GenerateMultiPrimeKey(random, 2, bits)
 }
 
@@ -206,8 +206,8 @@ func GenerateKey(random io.Reader, bits int) (priv *PrivateKey, err error) {
 //
 // [1] US patent 4405829 (1972, expired)
 // [2] http://www.cacr.math.uwaterloo.ca/techreports/2006/cacr2006-16.pdf
-func GenerateMultiPrimeKey(random io.Reader, nprimes int, bits int) (priv *PrivateKey, err error) {
-	priv = new(PrivateKey)
+func GenerateMultiPrimeKey(random io.Reader, nprimes int, bits int) (*PrivateKey, error) {
+	priv := new(PrivateKey)
 	priv.E = 65537
 
 	if nprimes < 2 {
@@ -234,6 +234,7 @@ NextSetOfPrimes:
 			todo += (nprimes - 2) / 5
 		}
 		for i := 0; i < nprimes; i++ {
+			var err error
 			primes[i], err = rand.Prime(random, todo/(nprimes-i))
 			if err != nil {
 				return nil, err
@@ -283,7 +284,7 @@ NextSetOfPrimes:
 	}
 
 	priv.Precompute()
-	return
+	return priv, nil
 }
 
 // incCounter increments a four byte, big-endian counter.
@@ -348,15 +349,14 @@ func encrypt(c *big.Int, pub *PublicKey, m *big.Int) *big.Int {
 //
 // The message must be no longer than the length of the public modulus less
 // twice the hash length plus 2.
-func EncryptOAEP(hash hash.Hash, random io.Reader, pub *PublicKey, msg []byte, label []byte) (out []byte, err error) {
+func EncryptOAEP(hash hash.Hash, random io.Reader, pub *PublicKey, msg []byte, label []byte) ([]byte, error) {
 	if err := checkPub(pub); err != nil {
 		return nil, err
 	}
 	hash.Reset()
 	k := (pub.N.BitLen() + 7) / 8
 	if len(msg) > k-2*hash.Size()-2 {
-		err = ErrMessageTooLong
-		return
+		return nil, ErrMessageTooLong
 	}
 
 	hash.Write(label)
@@ -371,9 +371,9 @@ func EncryptOAEP(hash hash.Hash, random io.Reader, pub *PublicKey, msg []byte, l
 	db[len(db)-len(msg)-1] = 1
 	copy(db[len(db)-len(msg):], msg)
 
-	_, err = io.ReadFull(random, seed)
+	_, err := io.ReadFull(random, seed)
 	if err != nil {
-		return
+		return nil, err
 	}
 
 	mgf1XOR(db, hash, seed)
@@ -382,7 +382,7 @@ func EncryptOAEP(hash hash.Hash, random io.Reader, pub *PublicKey, msg []byte, l
 	m := new(big.Int)
 	m.SetBytes(em)
 	c := encrypt(new(big.Int), pub, m)
-	out = c.Bytes()
+	out := c.Bytes()
 
 	if len(out) < k {
 		// If the output is too small, we need to left-pad with zeros.
@@ -391,7 +391,7 @@ func EncryptOAEP(hash hash.Hash, random io.Reader, pub *PublicKey, msg []byte, l
 		out = t
 	}
 
-	return
+	return out, nil
 }
 
 // ErrDecryption represents a failure to decrypt a message.
@@ -562,22 +562,21 @@ func decryptAndCheck(random io.Reader, priv *PrivateKey, c *big.Int) (m *big.Int
 //
 // The label parameter must match the value given when encrypting. See
 // EncryptOAEP for details.
-func DecryptOAEP(hash hash.Hash, random io.Reader, priv *PrivateKey, ciphertext []byte, label []byte) (msg []byte, err error) {
+func DecryptOAEP(hash hash.Hash, random io.Reader, priv *PrivateKey, ciphertext []byte, label []byte) ([]byte, error) {
 	if err := checkPub(&priv.PublicKey); err != nil {
 		return nil, err
 	}
 	k := (priv.N.BitLen() + 7) / 8
 	if len(ciphertext) > k ||
 		k < hash.Size()*2+2 {
-		err = ErrDecryption
-		return
+		return nil, ErrDecryption
 	}
 
 	c := new(big.Int).SetBytes(ciphertext)
 
 	m, err := decrypt(random, priv, c)
 	if err != nil {
-		return
+		return nil, err
 	}
 
 	hash.Write(label)
@@ -625,12 +624,10 @@ func DecryptOAEP(hash hash.Hash, random io.Reader, priv *PrivateKey, ciphertext
 	}
 
 	if firstByteIsZero&lHash2Good&^invalid&^lookingForIndex != 1 {
-		err = ErrDecryption
-		return
+		return nil, ErrDecryption
 	}
 
-	msg = rest[index+1:]
-	return
+	return rest[index+1:], nil
 }
 
 // leftPad returns a new slice of length size. The contents of input are right

src/crypto/tls/tls.go

@@ -47,14 +47,13 @@ type listener struct {
 }
 
 // Accept waits for and returns the next incoming TLS connection.
-// The returned connection c is a *tls.Conn.
-func (l *listener) Accept() (c net.Conn, err error) {
-	c, err = l.Listener.Accept()
+// The returned connection is of type *Conn.
+func (l *listener) Accept() (net.Conn, error) {
+	c, err := l.Listener.Accept()
 	if err != nil {
-		return
+		return nil, err
 	}
-	c = Server(c, l.config)
-	return
+	return Server(c, l.config), nil
 }
 
 // NewListener creates a Listener which accepts connections from an inner

src/crypto/x509/pkcs1.go

@@ -36,15 +36,14 @@ type pkcs1AdditionalRSAPrime struct {
 }
 
 // ParsePKCS1PrivateKey returns an RSA private key from its ASN.1 PKCS#1 DER encoded form.
-func ParsePKCS1PrivateKey(der []byte) (key *rsa.PrivateKey, err error) {
+func ParsePKCS1PrivateKey(der []byte) (*rsa.PrivateKey, error) {
 	var priv pkcs1PrivateKey
 	rest, err := asn1.Unmarshal(der, &priv)
 	if len(rest) > 0 {
-		err = asn1.SyntaxError{Msg: "trailing data"}
-		return
+		return nil, asn1.SyntaxError{Msg: "trailing data"}
 	}
 	if err != nil {
-		return
+		return nil, err
 	}
 
 	if priv.Version > 1 {
@@ -55,7 +54,7 @@ func ParsePKCS1PrivateKey(der []byte) (key *rsa.PrivateKey, err error) {
 		return nil, errors.New("x509: private key contains zero or negative value")
 	}
 
-	key = new(rsa.PrivateKey)
+	key := new(rsa.PrivateKey)
 	key.PublicKey = rsa.PublicKey{
 		E: priv.E,
 		N: priv.N,
@@ -80,7 +79,7 @@ func ParsePKCS1PrivateKey(der []byte) (key *rsa.PrivateKey, err error) {
 	}
 	key.Precompute()
 
-	return
+	return key, nil
 }
 
 // MarshalPKCS1PrivateKey converts a private key to ASN.1 DER encoded form.

src/crypto/x509/sec1.go

@@ -29,7 +29,7 @@ type ecPrivateKey struct {
 }
 
 // ParseECPrivateKey parses an ASN.1 Elliptic Curve Private Key Structure.
-func ParseECPrivateKey(der []byte) (key *ecdsa.PrivateKey, err error) {
+func ParseECPrivateKey(der []byte) (*ecdsa.PrivateKey, error) {
 	return parseECPrivateKey(nil, der)
 }
 
@@ -41,8 +41,8 @@ func MarshalECPrivateKey(key *ecdsa.PrivateKey) ([]byte, error) {
 	}
 
 	privateKeyBytes := key.D.Bytes()
-	paddedPrivateKey := make([]byte, (key.Curve.Params().N.BitLen() + 7) / 8)
-	copy(paddedPrivateKey[len(paddedPrivateKey) - len(privateKeyBytes):], privateKeyBytes)
+	paddedPrivateKey := make([]byte, (key.Curve.Params().N.BitLen()+7)/8)
+	copy(paddedPrivateKey[len(paddedPrivateKey)-len(privateKeyBytes):], privateKeyBytes)
 
 	return asn1.Marshal(ecPrivateKey{
 		Version:       1,
@@ -84,7 +84,7 @@ func parseECPrivateKey(namedCurveOID *asn1.ObjectIdentifier, der []byte) (key *e
 	priv.Curve = curve
 	priv.D = k
 
-	privateKey := make([]byte, (curveOrder.BitLen() + 7) / 8)
+	privateKey := make([]byte, (curveOrder.BitLen()+7)/8)
 
 	// Some private keys have leading zero padding. This is invalid
 	// according to [SEC1], but this code will ignore it.
@@ -98,7 +98,7 @@ func parseECPrivateKey(namedCurveOID *asn1.ObjectIdentifier, der []byte) (key *e
 	// Some private keys remove all leading zeros, this is also invalid
 	// according to [SEC1] but since OpenSSL used to do this, we ignore
 	// this too.
-	copy(privateKey[len(privateKey) - len(privKey.PrivateKey):], privKey.PrivateKey)
+	copy(privateKey[len(privateKey)-len(privKey.PrivateKey):], privKey.PrivateKey)
 	priv.X, priv.Y = curve.ScalarBaseMult(privateKey)
 
 	return priv, nil

src/crypto/x509/x509.go

@@ -641,7 +641,7 @@ var entrustBrokenSPKI = []byte{
 
 // CheckSignatureFrom verifies that the signature on c is a valid signature
 // from parent.
-func (c *Certificate) CheckSignatureFrom(parent *Certificate) (err error) {
+func (c *Certificate) CheckSignatureFrom(parent *Certificate) error {
 	// RFC 5280, 4.2.1.9:
 	// "If the basic constraints extension is not present in a version 3
 	// certificate, or the extension is present but the cA boolean is not
@@ -669,7 +669,7 @@ func (c *Certificate) CheckSignatureFrom(parent *Certificate) (err error) {
 
 // CheckSignature verifies that signature is a valid signature over signed from
 // c's public key.
-func (c *Certificate) CheckSignature(algo SignatureAlgorithm, signed, signature []byte) (err error) {
+func (c *Certificate) CheckSignature(algo SignatureAlgorithm, signed, signature []byte) error {
 	return checkSignature(algo, signed, signature, c.PublicKey)
 }
 
@@ -737,7 +737,7 @@ func checkSignature(algo SignatureAlgorithm, signed, signature []byte, publicKey
 }
 
 // CheckCRLSignature checks that the signature in crl is from c.
-func (c *Certificate) CheckCRLSignature(crl *pkix.CertificateList) (err error) {
+func (c *Certificate) CheckCRLSignature(crl *pkix.CertificateList) error {
 	algo := getSignatureAlgorithmFromOID(crl.SignatureAlgorithm.Algorithm)
 	return c.CheckSignature(algo, crl.TBSCertList.Raw, crl.SignatureValue.RightAlign())
 }
@@ -1654,7 +1654,7 @@ var pemType = "X509 CRL"
 // encoded CRLs will appear where they should be DER encoded, so this function
 // will transparently handle PEM encoding as long as there isn't any leading
 // garbage.
-func ParseCRL(crlBytes []byte) (certList *pkix.CertificateList, err error) {
+func ParseCRL(crlBytes []byte) (*pkix.CertificateList, error) {
 	if bytes.HasPrefix(crlBytes, pemCRLPrefix) {
 		block, _ := pem.Decode(crlBytes)
 		if block != nil && block.Type == pemType {
@@ -1665,8 +1665,8 @@ func ParseCRL(crlBytes []byte) (certList *pkix.CertificateList, err error) {
 }
 
 // ParseDERCRL parses a DER encoded CRL from the given bytes.
-func ParseDERCRL(derBytes []byte) (certList *pkix.CertificateList, err error) {
-	certList = new(pkix.CertificateList)
+func ParseDERCRL(derBytes []byte) (*pkix.CertificateList, error) {
+	certList := new(pkix.CertificateList)
 	if rest, err := asn1.Unmarshal(derBytes, certList); err != nil {
 		return nil, err
 	} else if len(rest) != 0 {
@@ -2071,7 +2071,7 @@ func parseCertificateRequest(in *certificateRequest) (*CertificateRequest, error
 	return out, nil
 }
 
-// CheckSignature verifies that the signature on c is a valid signature
-func (c *CertificateRequest) CheckSignature() (err error) {
+// CheckSignature reports whether the signature on c is valid.
+func (c *CertificateRequest) CheckSignature() error {
 	return checkSignature(c.SignatureAlgorithm, c.RawTBSCertificateRequest, c.Signature, c.PublicKey)
 }

src/debug/macho/fat.go

@@ -122,18 +122,18 @@ func NewFatFile(r io.ReaderAt) (*FatFile, error) {
 
 // OpenFat opens the named file using os.Open and prepares it for use as a Mach-O
 // universal binary.
-func OpenFat(name string) (ff *FatFile, err error) {
+func OpenFat(name string) (*FatFile, error) {
 	f, err := os.Open(name)
 	if err != nil {
 		return nil, err
 	}
-	ff, err = NewFatFile(f)
+	ff, err := NewFatFile(f)
 	if err != nil {
 		f.Close()
 		return nil, err
 	}
 	ff.closer = f
-	return
+	return ff, nil
 }
 
 func (ff *FatFile) Close() error {

src/encoding/csv/writer.go

@@ -37,27 +37,28 @@ func NewWriter(w io.Writer) *Writer {
 
 // Writer writes a single CSV record to w along with any necessary quoting.
 // A record is a slice of strings with each string being one field.
-func (w *Writer) Write(record []string) (err error) {
+func (w *Writer) Write(record []string) error {
 	for n, field := range record {
 		if n > 0 {
-			if _, err = w.w.WriteRune(w.Comma); err != nil {
-				return
+			if _, err := w.w.WriteRune(w.Comma); err != nil {
+				return err
 			}
 		}
 
 		// If we don't have to have a quoted field then just
 		// write out the field and continue to the next field.
 		if !w.fieldNeedsQuotes(field) {
-			if _, err = w.w.WriteString(field); err != nil {
-				return
+			if _, err := w.w.WriteString(field); err != nil {
+				return err
 			}
 			continue
 		}
-		if err = w.w.WriteByte('"'); err != nil {
-			return
+		if err := w.w.WriteByte('"'); err != nil {
+			return err
 		}
 
 		for _, r1 := range field {
+			var err error
 			switch r1 {
 			case '"':
 				_, err = w.w.WriteString(`""`)
@@ -75,20 +76,21 @@ func (w *Writer) Write(record []string) (err error) {
 				_, err = w.w.WriteRune(r1)
 			}
 			if err != nil {
-				return
+				return err
 			}
 		}
 
-		if err = w.w.WriteByte('"'); err != nil {
-			return
+		if err := w.w.WriteByte('"'); err != nil {
+			return err
 		}
 	}
+	var err error
 	if w.UseCRLF {
 		_, err = w.w.WriteString("\r\n")
 	} else {
 		err = w.w.WriteByte('\n')
 	}
-	return
+	return err
 }
 
 // Flush writes any buffered data to the underlying io.Writer.
@@ -104,9 +106,9 @@ func (w *Writer) Error() error {
 }
 
 // WriteAll writes multiple CSV records to w using Write and then calls Flush.
-func (w *Writer) WriteAll(records [][]string) (err error) {
+func (w *Writer) WriteAll(records [][]string) error {
 	for _, record := range records {
-		err = w.Write(record)
+		err := w.Write(record)
 		if err != nil {
 			return err
 		}

src/encoding/xml/xml.go

@@ -237,10 +237,11 @@ func NewDecoder(r io.Reader) *Decoder {
 // set to the URL identifying its name space when known.
 // If Token encounters an unrecognized name space prefix,
 // it uses the prefix as the Space rather than report an error.
-func (d *Decoder) Token() (t Token, err error) {
+func (d *Decoder) Token() (Token, error) {
+	var t Token
+	var err error
 	if d.stk != nil && d.stk.kind == stkEOF {
-		err = io.EOF
-		return
+		return nil, io.EOF
 	}
 	if d.nextToken != nil {
 		t = d.nextToken
@@ -249,7 +250,7 @@ func (d *Decoder) Token() (t Token, err error) {
 		if err == io.EOF && d.stk != nil && d.stk.kind != stkEOF {
 			err = d.syntaxError("unexpected EOF")
 		}
-		return
+		return t, err
 	}
 
 	if !d.Strict {
@@ -292,7 +293,7 @@ func (d *Decoder) Token() (t Token, err error) {
 		}
 		t = t1
 	}
-	return
+	return t, err
 }
 
 const xmlURL = "http://www.w3.org/XML/1998/namespace"

src/fmt/print.go

@@ -38,7 +38,7 @@ const (
 // the flags and options for the operand's format specifier.
 type State interface {
 	// Write is the function to call to emit formatted output to be printed.
-	Write(b []byte) (ret int, err error)
+	Write(b []byte) (n int, err error)
 	// Width returns the value of the width option and whether it has been set.
 	Width() (wid int, ok bool)
 	// Precision returns the value of the precision option and whether it has been set.

src/go/ast/print.go

@@ -36,8 +36,11 @@ func NotNilFilter(_ string, v reflect.Value) bool {
 // struct fields for which f(fieldname, fieldvalue) is true are
 // printed; all others are filtered from the output. Unexported
 // struct fields are never printed.
-//
-func Fprint(w io.Writer, fset *token.FileSet, x interface{}, f FieldFilter) (err error) {
+func Fprint(w io.Writer, fset *token.FileSet, x interface{}, f FieldFilter) error {
+	return fprint(w, fset, x, f)
+}
+
+func fprint(w io.Writer, fset *token.FileSet, x interface{}, f FieldFilter) (err error) {
 	// setup printer
 	p := printer{
 		output: w,

src/go/build/build.go

@@ -87,11 +87,11 @@ type Context struct {
 	// ReadDir returns a slice of os.FileInfo, sorted by Name,
 	// describing the content of the named directory.
 	// If ReadDir is nil, Import uses ioutil.ReadDir.
-	ReadDir func(dir string) (fi []os.FileInfo, err error)
+	ReadDir func(dir string) ([]os.FileInfo, error)
 
 	// OpenFile opens a file (not a directory) for reading.
 	// If OpenFile is nil, Import uses os.Open.
-	OpenFile func(path string) (r io.ReadCloser, err error)
+	OpenFile func(path string) (io.ReadCloser, error)
 }
 
 // joinPath calls ctxt.JoinPath (if not nil) or else filepath.Join.

src/go/types/check.go

@@ -215,7 +215,9 @@ func (check *Checker) handleBailout(err *error) {
 }
 
 // Files checks the provided files as part of the checker's package.
-func (check *Checker) Files(files []*ast.File) (err error) {
+func (check *Checker) Files(files []*ast.File) error { return check.checkFiles(files) }
+
+func (check *Checker) checkFiles(files []*ast.File) (err error) {
 	defer check.handleBailout(&err)
 
 	check.initFiles(files)

src/go/types/eval.go

@@ -34,7 +34,7 @@ import (
 // level untyped constants will return an untyped type rather then the
 // respective context-specific type.
 //
-func Eval(fset *token.FileSet, pkg *Package, pos token.Pos, expr string) (tv TypeAndValue, err error) {
+func Eval(fset *token.FileSet, pkg *Package, pos token.Pos, expr string) (TypeAndValue, error) {
 	// determine scope
 	var scope *Scope
 	if pkg == nil {

src/io/io.go

@@ -226,7 +226,7 @@ type WriterAt interface {
 //
 // ReadByte reads and returns the next byte from the input.
 type ByteReader interface {
-	ReadByte() (c byte, err error)
+	ReadByte() (byte, error)
 }
 
 // ByteScanner is the interface that adds the UnreadByte method to the

src/log/syslog/syslog.go

@@ -103,7 +103,7 @@ type netConn struct {
 // New establishes a new connection to the system log daemon.  Each
 // write to the returned writer sends a log message with the given
 // priority and prefix.
-func New(priority Priority, tag string) (w *Writer, err error) {
+func New(priority Priority, tag string) (*Writer, error) {
 	return Dial("", "", priority, tag)
 }
 
@@ -187,57 +187,57 @@ func (w *Writer) Close() error {
 
 // Emerg logs a message with severity LOG_EMERG, ignoring the severity
 // passed to New.
-func (w *Writer) Emerg(m string) (err error) {
-	_, err = w.writeAndRetry(LOG_EMERG, m)
+func (w *Writer) Emerg(m string) error {
+	_, err := w.writeAndRetry(LOG_EMERG, m)
 	return err
 }
 
 // Alert logs a message with severity LOG_ALERT, ignoring the severity
 // passed to New.
-func (w *Writer) Alert(m string) (err error) {
-	_, err = w.writeAndRetry(LOG_ALERT, m)
+func (w *Writer) Alert(m string) error {
+	_, err := w.writeAndRetry(LOG_ALERT, m)
 	return err
 }
 
 // Crit logs a message with severity LOG_CRIT, ignoring the severity
 // passed to New.
-func (w *Writer) Crit(m string) (err error) {
-	_, err = w.writeAndRetry(LOG_CRIT, m)
+func (w *Writer) Crit(m string) error {
+	_, err := w.writeAndRetry(LOG_CRIT, m)
 	return err
 }
 
 // Err logs a message with severity LOG_ERR, ignoring the severity
 // passed to New.
-func (w *Writer) Err(m string) (err error) {
-	_, err = w.writeAndRetry(LOG_ERR, m)
+func (w *Writer) Err(m string) error {
+	_, err := w.writeAndRetry(LOG_ERR, m)
 	return err
 }
 
 // Warning logs a message with severity LOG_WARNING, ignoring the
 // severity passed to New.
-func (w *Writer) Warning(m string) (err error) {
-	_, err = w.writeAndRetry(LOG_WARNING, m)
+func (w *Writer) Warning(m string) error {
+	_, err := w.writeAndRetry(LOG_WARNING, m)
 	return err
 }
 
 // Notice logs a message with severity LOG_NOTICE, ignoring the
 // severity passed to New.
-func (w *Writer) Notice(m string) (err error) {
-	_, err = w.writeAndRetry(LOG_NOTICE, m)
+func (w *Writer) Notice(m string) error {
+	_, err := w.writeAndRetry(LOG_NOTICE, m)
 	return err
 }
 
 // Info logs a message with severity LOG_INFO, ignoring the severity
 // passed to New.
-func (w *Writer) Info(m string) (err error) {
-	_, err = w.writeAndRetry(LOG_INFO, m)
+func (w *Writer) Info(m string) error {
+	_, err := w.writeAndRetry(LOG_INFO, m)
 	return err
 }
 
 // Debug logs a message with severity LOG_DEBUG, ignoring the severity
 // passed to New.
-func (w *Writer) Debug(m string) (err error) {
-	_, err = w.writeAndRetry(LOG_DEBUG, m)
+func (w *Writer) Debug(m string) error {
+	_, err := w.writeAndRetry(LOG_DEBUG, m)
 	return err
 }
 

src/mime/multipart/formdata.go

@@ -20,7 +20,11 @@ import (
 // a Content-Disposition of "form-data".
 // It stores up to maxMemory bytes of the file parts in memory
 // and the remainder on disk in temporary files.
-func (r *Reader) ReadForm(maxMemory int64) (f *Form, err error) {
+func (r *Reader) ReadForm(maxMemory int64) (*Form, error) {
+	return r.readForm(maxMemory)
+}
+
+func (r *Reader) readForm(maxMemory int64) (_ *Form, err error) {
 	form := &Form{make(map[string][]string), make(map[string][]*FileHeader)}
 	defer func() {
 		if err != nil {

src/net/http/request.go

@@ -704,7 +704,9 @@ func putTextprotoReader(r *textproto.Reader) {
 }
 
 // ReadRequest reads and parses an incoming request from b.
-func ReadRequest(b *bufio.Reader) (req *Request, err error) { return readRequest(b, deleteHostHeader) }
+func ReadRequest(b *bufio.Reader) (*Request, error) {
+	return readRequest(b, deleteHostHeader)
+}
 
 // Constants for readRequest's deleteHostHeader parameter.
 const (

src/net/unixsock_posix.go

@@ -309,14 +309,14 @@ func (l *UnixListener) AcceptUnix() (*UnixConn, error) {
 	return newUnixConn(fd), nil
 }
 
-// Accept implements the Accept method in the Listener interface; it
-// waits for the next call and returns a generic Conn.
-func (l *UnixListener) Accept() (c Conn, err error) {
-	c1, err := l.AcceptUnix()
+// Accept implements the Accept method in the Listener interface.
+// Returned connections will be of type *UnixConn.
+func (l *UnixListener) Accept() (Conn, error) {
+	c, err := l.AcceptUnix()
 	if err != nil {
 		return nil, err
 	}
-	return c1, nil
+	return c, nil
 }
 
 // Close stops listening on the Unix address.  Already accepted

src/net/url/url.go

@@ -411,10 +411,11 @@ func split(s string, c string, cutc bool) (string, string) {
 
 // Parse parses rawurl into a URL structure.
 // The rawurl may be relative or absolute.
-func Parse(rawurl string) (url *URL, err error) {
+func Parse(rawurl string) (*URL, error) {
 	// Cut off #frag
 	u, frag := split(rawurl, "#", true)
-	if url, err = parse(u, false); err != nil {
+	url, err := parse(u, false)
+	if err != nil {
 		return nil, err
 	}
 	if frag == "" {
@@ -431,7 +432,7 @@ func Parse(rawurl string) (url *URL, err error) {
 // only as an absolute URI or an absolute path.
 // The string rawurl is assumed not to have a #fragment suffix.
 // (Web browsers strip #fragment before sending the URL to a web server.)
-func ParseRequestURI(rawurl string) (url *URL, err error) {
+func ParseRequestURI(rawurl string) (*URL, error) {
 	return parse(rawurl, true)
 }
 
@@ -744,10 +745,10 @@ func (v Values) Del(key string) {
 // ParseQuery always returns a non-nil map containing all the
 // valid query parameters found; err describes the first decoding error
 // encountered, if any.
-func ParseQuery(query string) (m Values, err error) {
-	m = make(Values)
-	err = parseQuery(m, query)
-	return
+func ParseQuery(query string) (Values, error) {
+	m := make(Values)
+	err := parseQuery(m, query)
+	return m, err
 }
 
 func parseQuery(m Values, query string) (err error) {

src/os/doc.go

@@ -112,7 +112,7 @@ func Hostname() (name string, err error) {
 // nil error. If it encounters an error before the end of the
 // directory, Readdir returns the FileInfo read until that point
 // and a non-nil error.
-func (f *File) Readdir(n int) (fi []FileInfo, err error) {
+func (f *File) Readdir(n int) ([]FileInfo, error) {
 	if f == nil {
 		return nil, ErrInvalid
 	}

src/os/exec/lp_windows.go

@@ -46,7 +46,7 @@ func findExecutable(file string, exts []string) (string, error) {
 			return f, nil
 		}
 	}
-	return ``, os.ErrNotExist
+	return "", os.ErrNotExist
 }
 
 // LookPath searches for an executable binary named file
@@ -55,9 +55,9 @@ func findExecutable(file string, exts []string) (string, error) {
 // LookPath also uses PATHEXT environment variable to match
 // a suitable candidate.
 // The result may be an absolute path or a path relative to the current directory.
-func LookPath(file string) (f string, err error) {
+func LookPath(file string) (string, error) {
 	x := os.Getenv(`PATHEXT`)
-	if x == `` {
+	if x == "" {
 		x = `.COM;.EXE;.BAT;.CMD`
 	}
 	exts := []string{}
@@ -71,22 +71,23 @@ func LookPath(file string) (f string, err error) {
 		exts = append(exts, e)
 	}
 	if strings.ContainsAny(file, `:\/`) {
-		if f, err = findExecutable(file, exts); err == nil {
-			return
+		if f, err := findExecutable(file, exts); err == nil {
+			return f, nil
+		} else {
+			return "", &Error{file, err}
 		}
-		return ``, &Error{file, err}
 	}
-	if f, err = findExecutable(`.\`+file, exts); err == nil {
-		return
+	if f, err := findExecutable(`.\`+file, exts); err == nil {
+		return f, nil
 	}
-	if pathenv := os.Getenv(`PATH`); pathenv != `` {
+	if pathenv := os.Getenv(`PATH`); pathenv != "" {
 		for _, dir := range splitList(pathenv) {
-			if f, err = findExecutable(dir+`\`+file, exts); err == nil {
-				return
+			if f, err := findExecutable(dir+`\`+file, exts); err == nil {
+				return f, nil
 			}
 		}
 	}
-	return ``, &Error{file, ErrNotFound}
+	return "", &Error{file, ErrNotFound}
 }
 
 func splitList(path string) []string {
@@ -115,7 +116,7 @@ func splitList(path string) []string {
 	// Remove quotes.
 	for i, s := range list {
 		if strings.Contains(s, `"`) {
-			list[i] = strings.Replace(s, `"`, ``, -1)
+			list[i] = strings.Replace(s, `"`, "", -1)
 		}
 	}
 

src/strconv/atob.go

@@ -7,7 +7,7 @@ package strconv
 // ParseBool returns the boolean value represented by the string.
 // It accepts 1, t, T, TRUE, true, True, 0, f, F, FALSE, false, False.
 // Any other value returns an error.
-func ParseBool(str string) (value bool, err error) {
+func ParseBool(str string) (bool, error) {
 	switch str {
 	case "1", "t", "T", "true", "TRUE", "True":
 		return true, nil

src/strconv/atof.go

@@ -528,11 +528,10 @@ func atof64(s string) (f float64, err error) {
 // If s is syntactically well-formed but is more than 1/2 ULP
 // away from the largest floating point number of the given size,
 // ParseFloat returns f = ±Inf, err.Err = ErrRange.
-func ParseFloat(s string, bitSize int) (f float64, err error) {
+func ParseFloat(s string, bitSize int) (float64, error) {
 	if bitSize == 32 {
-		f1, err1 := atof32(s)
-		return float64(f1), err1
+		f, err := atof32(s)
+		return float64(f), err
 	}
-	f1, err1 := atof64(s)
-	return f1, err1
+	return atof64(s)
 }

src/strconv/atoi.go

@@ -39,7 +39,9 @@ const IntSize = intSize
 const maxUint64 = (1<<64 - 1)
 
 // ParseUint is like ParseInt but for unsigned numbers.
-func ParseUint(s string, base int, bitSize int) (n uint64, err error) {
+func ParseUint(s string, base int, bitSize int) (uint64, error) {
+	var n uint64
+	var err error
 	var cutoff, maxVal uint64
 
 	if bitSize == 0 {
@@ -196,7 +198,7 @@ func ParseInt(s string, base int, bitSize int) (i int64, err error) {
 }
 
 // Atoi is shorthand for ParseInt(s, 10, 0).
-func Atoi(s string) (i int, err error) {
+func Atoi(s string) (int, error) {
 	i64, err := ParseInt(s, 10, 0)
 	return int(i64), err
 }

src/strconv/quote.go

@@ -347,7 +347,7 @@ func UnquoteChar(s string, quote byte) (value rune, multibyte bool, tail string,
 // that s quotes.  (If s is single-quoted, it would be a Go
 // character literal; Unquote returns the corresponding
 // one-character string.)
-func Unquote(s string) (t string, err error) {
+func Unquote(s string) (string, error) {
 	n := len(s)
 	if n < 2 {
 		return "", ErrSyntax

src/strings/reader.go

@@ -62,14 +62,14 @@ func (r *Reader) ReadAt(b []byte, off int64) (n int, err error) {
 	return
 }
 
-func (r *Reader) ReadByte() (b byte, err error) {
+func (r *Reader) ReadByte() (byte, error) {
 	r.prevRune = -1
 	if r.i >= int64(len(r.s)) {
 		return 0, io.EOF
 	}
-	b = r.s[r.i]
+	b := r.s[r.i]
 	r.i++
-	return
+	return b, nil
 }
 
 func (r *Reader) UnreadByte() error {

src/testing/quick/quick.go

@@ -262,24 +262,21 @@ func (s *CheckEqualError) Error() string {
 // 			t.Error(err)
 // 		}
 // 	}
-func Check(f interface{}, config *Config) (err error) {
+func Check(f interface{}, config *Config) error {
 	if config == nil {
 		config = &defaultConfig
 	}
 
 	fVal, fType, ok := functionAndType(f)
 	if !ok {
-		err = SetupError("argument is not a function")
-		return
+		return SetupError("argument is not a function")
 	}
 
 	if fType.NumOut() != 1 {
-		err = SetupError("function does not return one value")
-		return
+		return SetupError("function does not return one value")
 	}
 	if fType.Out(0).Kind() != reflect.Bool {
-		err = SetupError("function does not return a bool")
-		return
+		return SetupError("function does not return a bool")
 	}
 
 	arguments := make([]reflect.Value, fType.NumIn())
@@ -287,43 +284,39 @@ func Check(f interface{}, config *Config) (err error) {
 	maxCount := config.getMaxCount()
 
 	for i := 0; i < maxCount; i++ {
-		err = arbitraryValues(arguments, fType, config, rand)
+		err := arbitraryValues(arguments, fType, config, rand)
 		if err != nil {
-			return
+			return err
 		}
 
 		if !fVal.Call(arguments)[0].Bool() {
-			err = &CheckError{i + 1, toInterfaces(arguments)}
-			return
+			return &CheckError{i + 1, toInterfaces(arguments)}
 		}
 	}
 
-	return
+	return nil
 }
 
 // CheckEqual looks for an input on which f and g return different results.
 // It calls f and g repeatedly with arbitrary values for each argument.
 // If f and g return different answers, CheckEqual returns a *CheckEqualError
 // describing the input and the outputs.
-func CheckEqual(f, g interface{}, config *Config) (err error) {
+func CheckEqual(f, g interface{}, config *Config) error {
 	if config == nil {
 		config = &defaultConfig
 	}
 
 	x, xType, ok := functionAndType(f)
 	if !ok {
-		err = SetupError("f is not a function")
-		return
+		return SetupError("f is not a function")
 	}
 	y, yType, ok := functionAndType(g)
 	if !ok {
-		err = SetupError("g is not a function")
-		return
+		return SetupError("g is not a function")
 	}
 
 	if xType != yType {
-		err = SetupError("functions have different types")
-		return
+		return SetupError("functions have different types")
 	}
 
 	arguments := make([]reflect.Value, xType.NumIn())
@@ -331,21 +324,20 @@ func CheckEqual(f, g interface{}, config *Config) (err error) {
 	maxCount := config.getMaxCount()
 
 	for i := 0; i < maxCount; i++ {
-		err = arbitraryValues(arguments, xType, config, rand)
+		err := arbitraryValues(arguments, xType, config, rand)
 		if err != nil {
-			return
+			return err
 		}
 
 		xOut := toInterfaces(x.Call(arguments))
 		yOut := toInterfaces(y.Call(arguments))
 
 		if !reflect.DeepEqual(xOut, yOut) {
-			err = &CheckEqualError{CheckError{i + 1, toInterfaces(arguments)}, xOut, yOut}
-			return
+			return &CheckEqualError{CheckError{i + 1, toInterfaces(arguments)}, xOut, yOut}
 		}
 	}
 
-	return
+	return nil
 }
 
 // arbitraryValues writes Values to args such that args contains Values

src/text/tabwriter/tabwriter.go

@@ -462,8 +462,11 @@ func handlePanic(err *error, op string) {
 // that any data buffered in the Writer is written to output. Any
 // incomplete escape sequence at the end is considered
 // complete for formatting purposes.
-//
-func (b *Writer) Flush() (err error) {
+func (b *Writer) Flush() error {
+	return b.flush()
+}
+
+func (b *Writer) flush() (err error) {
 	defer b.reset() // even in the presence of errors
 	defer handlePanic(&err, "Flush")
 
@@ -478,8 +481,7 @@ func (b *Writer) Flush() (err error) {
 
 	// format contents of buffer
 	b.format(0, 0, len(b.lines))
-
-	return
+	return nil
 }
 
 var hbar = []byte("---\n")

src/text/template/exec.go

@@ -164,7 +164,11 @@ func (t *Template) ExecuteTemplate(wr io.Writer, name string, data interface{})
 // execution stops, but partial results may already have been written to
 // the output writer.
 // A template may be executed safely in parallel.
-func (t *Template) Execute(wr io.Writer, data interface{}) (err error) {
+func (t *Template) Execute(wr io.Writer, data interface{}) error {
+	return t.execute(wr, data)
+}
+
+func (t *Template) execute(wr io.Writer, data interface{}) (err error) {
 	defer errRecover(&err)
 	value := reflect.ValueOf(data)
 	state := &state{

src/text/template/parse/parse.go

@@ -48,12 +48,12 @@ func (t *Tree) Copy() *Tree {
 // templates described in the argument string. The top-level template will be
 // given the specified name. If an error is encountered, parsing stops and an
 // empty map is returned with the error.
-func Parse(name, text, leftDelim, rightDelim string, funcs ...map[string]interface{}) (treeSet map[string]*Tree, err error) {
-	treeSet = make(map[string]*Tree)
+func Parse(name, text, leftDelim, rightDelim string, funcs ...map[string]interface{}) (map[string]*Tree, error) {
+	treeSet := make(map[string]*Tree)
 	t := New(name)
 	t.text = text
-	_, err = t.Parse(text, leftDelim, rightDelim, treeSet, funcs...)
-	return
+	_, err := t.Parse(text, leftDelim, rightDelim, treeSet, funcs...)
+	return treeSet, err
 }
 
 // next returns the next token.

src/time/time.go

@@ -945,10 +945,11 @@ func (t Time) MarshalJSON() ([]byte, error) {
 
 // UnmarshalJSON implements the json.Unmarshaler interface.
 // The time is expected to be a quoted string in RFC 3339 format.
-func (t *Time) UnmarshalJSON(data []byte) (err error) {
+func (t *Time) UnmarshalJSON(data []byte) error {
 	// Fractional seconds are handled implicitly by Parse.
+	var err error
 	*t, err = Parse(`"`+RFC3339+`"`, string(data))
-	return
+	return err
 }
 
 // MarshalText implements the encoding.TextMarshaler interface.
@@ -964,10 +965,11 @@ func (t Time) MarshalText() ([]byte, error) {
 
 // UnmarshalText implements the encoding.TextUnmarshaler interface.
 // The time is expected to be in RFC 3339 format.
-func (t *Time) UnmarshalText(data []byte) (err error) {
+func (t *Time) UnmarshalText(data []byte) error {
 	// Fractional seconds are handled implicitly by Parse.
+	var err error
 	*t, err = Parse(RFC3339, string(data))
-	return
+	return err
 }
 
 // Unix returns the local Time corresponding to the given Unix time,