all: remove some unused return parameters

As found by unparam. Picked the low-hanging fruit, consisting only of
errors that were always nil and results that were never used. Left out
those that were useful for consistency with other func signatures.

Change-Id: I06b52bbd3541f8a5d66659c909bd93cb3e172018
Reviewed-on: https://go-review.googlesource.com/102418
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/encoding/gob/decode.go

@@ -1070,14 +1070,14 @@ func (dec *Decoder) compileSingle(remoteId typeId, ut *userTypeInfo) (engine *de
 }
 
 // compileIgnoreSingle compiles the decoder engine for a non-struct top-level value that will be discarded.
-func (dec *Decoder) compileIgnoreSingle(remoteId typeId) (engine *decEngine, err error) {
-	engine = new(decEngine)
+func (dec *Decoder) compileIgnoreSingle(remoteId typeId) *decEngine {
+	engine := new(decEngine)
 	engine.instr = make([]decInstr, 1) // one item
 	op := dec.decIgnoreOpFor(remoteId, make(map[typeId]*decOp))
 	ovfl := overflow(dec.typeString(remoteId))
 	engine.instr[0] = decInstr{*op, 0, nil, ovfl}
 	engine.numInstr = 1
-	return
+	return engine
 }
 
 // compileDec compiles the decoder engine for a value. If the value is not a struct,
@@ -1168,7 +1168,7 @@ func (dec *Decoder) getIgnoreEnginePtr(wireId typeId) (enginePtr **decEngine, er
 		if wire != nil && wire.StructT != nil {
 			*enginePtr, err = dec.compileDec(wireId, userType(emptyStructType))
 		} else {
-			*enginePtr, err = dec.compileIgnoreSingle(wireId)
+			*enginePtr = dec.compileIgnoreSingle(wireId)
 		}
 		if err != nil {
 			delete(dec.ignorerCache, wireId)

src/internal/trace/parser.go

@@ -108,10 +108,7 @@ func parse(r io.Reader, bin string) (int, ParseResult, error) {
 	if err != nil {
 		return 0, ParseResult{}, err
 	}
-	events, err = removeFutile(events)
-	if err != nil {
-		return 0, ParseResult{}, err
-	}
+	events = removeFutile(events)
 	err = postProcessTrace(ver, events)
 	if err != nil {
 		return 0, ParseResult{}, err
@@ -505,7 +502,7 @@ func parseEvents(ver int, rawEvents []rawEvent, strings map[uint64]string) (even
 // ahead and acquired the mutex before the first goroutine is scheduled,
 // so the first goroutine has to block again. Such wakeups happen on buffered
 // channels and sync.Mutex, but are generally not interesting for end user.
-func removeFutile(events []*Event) ([]*Event, error) {
+func removeFutile(events []*Event) []*Event {
 	// Two non-trivial aspects:
 	// 1. A goroutine can be preempted during a futile wakeup and migrate to another P.
 	//	We want to remove all of that.
@@ -552,7 +549,7 @@ func removeFutile(events []*Event) ([]*Event, error) {
 			newEvents = append(newEvents, ev)
 		}
 	}
-	return newEvents, nil
+	return newEvents
 }
 
 // ErrTimeOrder is returned by Parse when the trace contains

src/regexp/syntax/prog.go

@@ -122,15 +122,13 @@ func (p *Prog) String() string {
 	return b.String()
 }
 
-// skipNop follows any no-op or capturing instructions
-// and returns the resulting pc.
-func (p *Prog) skipNop(pc uint32) (*Inst, uint32) {
+// skipNop follows any no-op or capturing instructions.
+func (p *Prog) skipNop(pc uint32) *Inst {
 	i := &p.Inst[pc]
 	for i.Op == InstNop || i.Op == InstCapture {
-		pc = i.Out
-		i = &p.Inst[pc]
+		i = &p.Inst[i.Out]
 	}
-	return i, pc
+	return i
 }
 
 // op returns i.Op but merges all the Rune special cases into InstRune
@@ -147,7 +145,7 @@ func (i *Inst) op() InstOp {
 // regexp must start with. Complete is true if the prefix
 // is the entire match.
 func (p *Prog) Prefix() (prefix string, complete bool) {
-	i, _ := p.skipNop(uint32(p.Start))
+	i := p.skipNop(uint32(p.Start))
 
 	// Avoid allocation of buffer if prefix is empty.
 	if i.op() != InstRune || len(i.Rune) != 1 {
@@ -158,7 +156,7 @@ func (p *Prog) Prefix() (prefix string, complete bool) {
 	var buf bytes.Buffer
 	for i.op() == InstRune && len(i.Rune) == 1 && Flags(i.Arg)&FoldCase == 0 {
 		buf.WriteRune(i.Rune[0])
-		i, _ = p.skipNop(i.Out)
+		i = p.skipNop(i.Out)
 	}
 	return buf.String(), i.Op == InstMatch
 }

src/runtime/pprof/proto.go

@@ -343,7 +343,7 @@ func (b *profileBuilder) addCPUData(data []uint64, tags []unsafe.Pointer) error
 }
 
 // build completes and returns the constructed profile.
-func (b *profileBuilder) build() error {
+func (b *profileBuilder) build() {
 	b.end = time.Now()
 
 	b.pb.int64Opt(tagProfile_TimeNanos, b.start.UnixNano())
@@ -396,7 +396,6 @@ func (b *profileBuilder) build() error {
 	b.pb.strings(tagProfile_StringTable, b.strings)
 	b.zw.Write(b.pb.data)
 	b.zw.Close()
-	return nil
 }
 
 // readMapping reads /proc/self/maps and writes mappings to b.pb.

src/time/format.go

@@ -1059,7 +1059,7 @@ func parse(layout, value string, defaultLocation, local *Location) (Time, error)
 
 		// Look for local zone with the given offset.
 		// If that zone was in effect at the given time, use it.
-		name, offset, _, _, _ := local.lookup(t.unixSec())
+		name, offset, _, _ := local.lookup(t.unixSec())
 		if offset == zoneOffset && (zoneName == "" || name == zoneName) {
 			t.setLoc(local)
 			return t, nil

src/time/time.go

@@ -445,7 +445,7 @@ func (t Time) abs() uint64 {
 		if l.cacheZone != nil && l.cacheStart <= sec && sec < l.cacheEnd {
 			sec += int64(l.cacheZone.offset)
 		} else {
-			_, offset, _, _, _ := l.lookup(sec)
+			_, offset, _, _ := l.lookup(sec)
 			sec += int64(offset)
 		}
 	}
@@ -466,7 +466,7 @@ func (t Time) locabs() (name string, offset int, abs uint64) {
 			name = l.cacheZone.name
 			offset = l.cacheZone.offset
 		} else {
-			name, offset, _, _, _ = l.lookup(sec)
+			name, offset, _, _ = l.lookup(sec)
 		}
 		sec += int64(offset)
 	} else {
@@ -1088,7 +1088,7 @@ func (t Time) Location() *Location {
 // Zone computes the time zone in effect at time t, returning the abbreviated
 // name of the zone (such as "CET") and its offset in seconds east of UTC.
 func (t Time) Zone() (name string, offset int) {
-	name, offset, _, _, _ = t.loc.lookup(t.unixSec())
+	name, offset, _, _ = t.loc.lookup(t.unixSec())
 	return
 }
 
@@ -1181,7 +1181,7 @@ func (t *Time) UnmarshalBinary(data []byte) error {
 
 	if offset == -1*60 {
 		t.setLoc(&utcLoc)
-	} else if _, localoff, _, _, _ := Local.lookup(t.unixSec()); offset == localoff {
+	} else if _, localoff, _, _ := Local.lookup(t.unixSec()); offset == localoff {
 		t.setLoc(Local)
 	} else {
 		t.setLoc(FixedZone("", offset))
@@ -1366,13 +1366,13 @@ func Date(year int, month Month, day, hour, min, sec, nsec int, loc *Location) T
 	// The lookup function expects UTC, so we pass t in the
 	// hope that it will not be too close to a zone transition,
 	// and then adjust if it is.
-	_, offset, _, start, end := loc.lookup(unix)
+	_, offset, start, end := loc.lookup(unix)
 	if offset != 0 {
 		switch utc := unix - int64(offset); {
 		case utc < start:
-			_, offset, _, _, _ = loc.lookup(start - 1)
+			_, offset, _, _ = loc.lookup(start - 1)
 		case utc >= end:
-			_, offset, _, _, _ = loc.lookup(end)
+			_, offset, _, _ = loc.lookup(end)
 		}
 		unix -= int64(offset)
 	}

src/time/zoneinfo.go

@@ -108,13 +108,12 @@ func FixedZone(name string, offset int) *Location {
 // the start and end times bracketing sec when that zone is in effect,
 // the offset in seconds east of UTC (such as -5*60*60), and whether
 // the daylight savings is being observed at that time.
-func (l *Location) lookup(sec int64) (name string, offset int, isDST bool, start, end int64) {
+func (l *Location) lookup(sec int64) (name string, offset int, start, end int64) {
 	l = l.get()
 
 	if len(l.zone) == 0 {
 		name = "UTC"
 		offset = 0
-		isDST = false
 		start = alpha
 		end = omega
 		return
@@ -123,7 +122,6 @@ func (l *Location) lookup(sec int64) (name string, offset int, isDST bool, start
 	if zone := l.cacheZone; zone != nil && l.cacheStart <= sec && sec < l.cacheEnd {
 		name = zone.name
 		offset = zone.offset
-		isDST = zone.isDST
 		start = l.cacheStart
 		end = l.cacheEnd
 		return
@@ -133,7 +131,6 @@ func (l *Location) lookup(sec int64) (name string, offset int, isDST bool, start
 		zone := &l.zone[l.lookupFirstZone()]
 		name = zone.name
 		offset = zone.offset
-		isDST = zone.isDST
 		start = alpha
 		if len(l.tx) > 0 {
 			end = l.tx[0].when
@@ -162,7 +159,6 @@ func (l *Location) lookup(sec int64) (name string, offset int, isDST bool, start
 	zone := &l.zone[tx[lo].index]
 	name = zone.name
 	offset = zone.offset
-	isDST = zone.isDST
 	start = tx[lo].when
 	// end = maintained during the search
 	return
@@ -235,7 +231,7 @@ func (l *Location) lookupName(name string, unix int64) (offset int, ok bool) {
 	for i := range l.zone {
 		zone := &l.zone[i]
 		if zone.name == name {
-			nam, offset, _, _, _ := l.lookup(unix - int64(zone.offset))
+			nam, offset, _, _ := l.lookup(unix - int64(zone.offset))
 			if nam == zone.name {
 				return offset, true
 			}