std: remove unused bits of code all over the place

Some were never used, and some haven't been used for years.

One exception is net/http's readerAndCloser, which was only used in a
test. Move it to a test file.

While at it, remove a check in regexp that could never fire; the field
is an uint32, so it can never be negative.

Change-Id: Ia2200f6afa106bae4034045ea8233b452f38747b
Reviewed-on: https://go-review.googlesource.com/c/go/+/192621
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/database/sql/ctxutil.go

@@ -94,8 +94,6 @@ func ctxDriverStmtQuery(ctx context.Context, si driver.Stmt, nvdargs []driver.Na
 	return si.Query(dargs)
 }
 
-var errLevelNotSupported = errors.New("sql: selected isolation level is not supported")
-
 func ctxDriverBegin(ctx context.Context, opts *TxOptions, ci driver.Conn) (driver.Tx, error) {
 	if ciCtx, is := ci.(driver.ConnBeginTx); is {
 		dopts := driver.TxOptions{}

src/encoding/json/decode_test.go

@@ -1744,41 +1744,6 @@ type NullTest struct {
 	Struct struct{}
 }
 
-type NullTestStrings struct {
-	Bool      bool              `json:",string"`
-	Int       int               `json:",string"`
-	Int8      int8              `json:",string"`
-	Int16     int16             `json:",string"`
-	Int32     int32             `json:",string"`
-	Int64     int64             `json:",string"`
-	Uint      uint              `json:",string"`
-	Uint8     uint8             `json:",string"`
-	Uint16    uint16            `json:",string"`
-	Uint32    uint32            `json:",string"`
-	Uint64    uint64            `json:",string"`
-	Float32   float32           `json:",string"`
-	Float64   float64           `json:",string"`
-	String    string            `json:",string"`
-	PBool     *bool             `json:",string"`
-	Map       map[string]string `json:",string"`
-	Slice     []string          `json:",string"`
-	Interface interface{}       `json:",string"`
-
-	PRaw    *RawMessage           `json:",string"`
-	PTime   *time.Time            `json:",string"`
-	PBigInt *big.Int              `json:",string"`
-	PText   *MustNotUnmarshalText `json:",string"`
-	PBuffer *bytes.Buffer         `json:",string"`
-	PStruct *struct{}             `json:",string"`
-
-	Raw    RawMessage           `json:",string"`
-	Time   time.Time            `json:",string"`
-	BigInt big.Int              `json:",string"`
-	Text   MustNotUnmarshalText `json:",string"`
-	Buffer bytes.Buffer         `json:",string"`
-	Struct struct{}             `json:",string"`
-}
-
 // JSON null values should be ignored for primitives and string values instead of resulting in an error.
 // Issue 2540
 func TestUnmarshalNulls(t *testing.T) {

src/encoding/xml/marshal_test.go

@@ -392,7 +392,6 @@ func stringptr(x string) *string {
 
 type T1 struct{}
 type T2 struct{}
-type T3 struct{}
 
 type IndirComment struct {
 	T1      T1

src/internal/reflectlite/value.go

@@ -179,19 +179,6 @@ type emptyInterface struct {
 	word unsafe.Pointer
 }
 
-// nonEmptyInterface is the header for an interface value with methods.
-type nonEmptyInterface struct {
-	// see ../runtime/iface.go:/Itab
-	itab *struct {
-		ityp *rtype // static interface type
-		typ  *rtype // dynamic concrete type
-		hash uint32 // copy of typ.hash
-		_    [4]byte
-		fun  [100000]unsafe.Pointer // method table
-	}
-	word unsafe.Pointer
-}
-
 // mustBeExported panics if f records that the value was obtained using
 // an unexported field.
 func (f flag) mustBeExported() {

src/net/http/response_test.go

@@ -636,6 +636,11 @@ var readResponseCloseInMiddleTests = []struct {
 	{true, true},
 }
 
+type readerAndCloser struct {
+	io.Reader
+	io.Closer
+}
+
 // TestReadResponseCloseInMiddle tests that closing a body after
 // reading only part of its contents advances the read to the end of
 // the request, right up until the next request.

src/net/http/transport.go

@@ -743,7 +743,6 @@ var (
 	errCloseIdleConns     = errors.New("http: CloseIdleConnections called")
 	errReadLoopExiting    = errors.New("http: persistConn.readLoop exiting")
 	errIdleConnTimeout    = errors.New("http: idle connection timeout")
-	errNotCachingH2Conn   = errors.New("http: not caching alternate protocol's connections")
 
 	// errServerClosedIdle is not seen by users for idempotent requests, but may be
 	// seen by a user if the server shuts down an idle connection and sends its FIN
@@ -1350,19 +1349,6 @@ func (t *Transport) decConnsPerHost(key connectMethodKey) {
 	}
 }
 
-// The connect method and the transport can both specify a TLS
-// Host name.  The transport's name takes precedence if present.
-func chooseTLSHost(cm connectMethod, t *Transport) string {
-	tlsHost := ""
-	if t.TLSClientConfig != nil {
-		tlsHost = t.TLSClientConfig.ServerName
-	}
-	if tlsHost == "" {
-		tlsHost = cm.tlsHost()
-	}
-	return tlsHost
-}
-
 // Add TLS to a persistent connection, i.e. negotiate a TLS session. If pconn is already a TLS
 // tunnel, this function establishes a nested TLS session inside the encrypted channel.
 // The remote endpoint's name may be overridden by TLSClientConfig.ServerName.
@@ -2625,11 +2611,6 @@ func (gz *gzipReader) Close() error {
 	return gz.body.Close()
 }
 
-type readerAndCloser struct {
-	io.Reader
-	io.Closer
-}
-
 type tlsHandshakeTimeoutError struct{}
 
 func (tlsHandshakeTimeoutError) Timeout() bool   { return true }

src/os/user/cgo_lookup_unix.go

@@ -129,10 +129,6 @@ func buildUser(pwd *C.struct_passwd) *User {
 	return u
 }
 
-func currentGroup() (*Group, error) {
-	return lookupUnixGid(syscall.Getgid())
-}
-
 func lookupGroup(groupname string) (*Group, error) {
 	var grp C.struct_group
 	var result *C.struct_group

src/reflect/type.go

@@ -527,11 +527,6 @@ func (n name) pkgPath() string {
 	return pkgPathName.name()
 }
 
-// round n up to a multiple of a.  a must be a power of 2.
-func round(n, a uintptr) uintptr {
-	return (n + a - 1) &^ (a - 1)
-}
-
 func newName(n, tag string, exported bool) name {
 	if len(n) > 1<<16-1 {
 		panic("reflect.nameFrom: name too long: " + n)
@@ -867,10 +862,6 @@ func (t *rtype) PkgPath() string {
 	return t.nameOff(ut.pkgPath).name()
 }
 
-func hasPrefix(s, prefix string) bool {
-	return len(s) >= len(prefix) && s[:len(prefix)] == prefix
-}
-
 func (t *rtype) hasName() bool {
 	return t.tflag&tflagNamed != 0
 }

src/regexp/backtrack.go

@@ -247,7 +247,7 @@ func (re *Regexp) tryBacktrack(b *bitState, i input, pc uint32, pos int) bool {
 				b.cap[inst.Arg] = pos
 				continue
 			} else {
-				if 0 <= inst.Arg && inst.Arg < uint32(len(b.cap)) {
+				if inst.Arg < uint32(len(b.cap)) {
 					// Capture pos to register, but save old value.
 					b.push(re, pc, b.cap[inst.Arg], true) // come back when we're done.
 					b.cap[inst.Arg] = pos