std: pass bytes.Buffer and strings.Builder by pointer

This CL fixes a number of (all true positive) findings of vet's
copylock analyzer patched to treat the Bu{ff,uild}er types
as non-copyable after first use.

This does require imposing an additional indirection
between noder.writer and Encoder since the field is
embedded by value but its constructor now returns a pointer.

Updates golang/go#25907
Updates golang/go#47276

Change-Id: I0b4d77ac12bcecadf06a91709e695365da10766c
Reviewed-on: https://go-review.googlesource.com/c/go/+/635339
Reviewed-by: Robert Findley <rfindley@google.com>
Commit-Queue: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Alan Donovan <adonovan@google.com>

src/bytes/buffer_test.go

@@ -354,7 +354,7 @@ func TestWriteAppend(t *testing.T) {
 		got.Write(b)
 	}
 	if !Equal(got.Bytes(), want) {
-		t.Fatalf("Bytes() = %q, want %q", got, want)
+		t.Fatalf("Bytes() = %q, want %q", &got, want)
 	}
 
 	// With a sufficiently sized buffer, there should be no allocations.

src/cmd/compile/internal/noder/linker.go

@@ -84,7 +84,7 @@ func (l *linker) relocIdx(pr *pkgReader, k pkgbits.SectionKind, idx index) index
 		// if we do external relocations.
 
 		w := l.pw.NewEncoderRaw(k)
-		l.relocCommon(pr, &w, k, idx)
+		l.relocCommon(pr, w, k, idx)
 		newidx = w.Idx
 	}
 
@@ -168,9 +168,9 @@ func (l *linker) relocObj(pr *pkgReader, idx index) index {
 	assert(wname.Idx == w.Idx)
 	assert(wdict.Idx == w.Idx)
 
-	l.relocCommon(pr, &w, pkgbits.SectionObj, idx)
+	l.relocCommon(pr, w, pkgbits.SectionObj, idx)
-	l.relocCommon(pr, &wname, pkgbits.SectionName, idx)
+	l.relocCommon(pr, wname, pkgbits.SectionName, idx)
-	l.relocCommon(pr, &wdict, pkgbits.SectionObjDict, idx)
+	l.relocCommon(pr, wdict, pkgbits.SectionObjDict, idx)
 
 	// Generic types and functions won't have definitions, and imported
 	// objects may not either.
@@ -181,15 +181,15 @@ func (l *linker) relocObj(pr *pkgReader, idx index) index {
 		wext.Sync(pkgbits.SyncObject1)
 		switch tag {
 		case pkgbits.ObjFunc:
-			l.relocFuncExt(&wext, obj)
+			l.relocFuncExt(wext, obj)
 		case pkgbits.ObjType:
-			l.relocTypeExt(&wext, obj)
+			l.relocTypeExt(wext, obj)
 		case pkgbits.ObjVar:
-			l.relocVarExt(&wext, obj)
+			l.relocVarExt(wext, obj)
 		}
 		wext.Flush()
 	} else {
-		l.relocCommon(pr, &wext, pkgbits.SectionObjExt, idx)
+		l.relocCommon(pr, wext, pkgbits.SectionObjExt, idx)
 	}
 
 	// Check if we need to export the inline bodies for functions and

src/cmd/compile/internal/noder/writer.go

@@ -174,7 +174,7 @@ func (pw *pkgWriter) typeOf(expr syntax.Expr) types2.Type {
 type writer struct {
 	p *pkgWriter
 
-	pkgbits.Encoder
+	*pkgbits.Encoder
 
 	// sig holds the signature for the current function body, if any.
 	sig *types2.Signature

src/compress/flate/inflate_test.go

@@ -35,7 +35,7 @@ func TestReset(t *testing.T) {
 
 	for i, s := range ss {
 		if s != inflated[i].String() {
-			t.Errorf("inflated[%d]:\ngot  %q\nwant %q", i, inflated[i], s)
+			t.Errorf("inflated[%d]:\ngot  %q\nwant %q", i, &inflated[i], s)
 		}
 	}
 }
@@ -92,7 +92,7 @@ func TestResetDict(t *testing.T) {
 
 	for i, s := range ss {
 		if s != inflated[i].String() {
-			t.Errorf("inflated[%d]:\ngot  %q\nwant %q", i, inflated[i], s)
+			t.Errorf("inflated[%d]:\ngot  %q\nwant %q", i, &inflated[i], s)
 		}
 	}
 }

src/internal/pkgbits/encoder.go

@@ -121,7 +121,7 @@ func (pw *PkgEncoder) StringIdx(s string) RelIndex {
 // NewEncoder returns an Encoder for a new element within the given
 // section, and encodes the given SyncMarker as the start of the
 // element bitstream.
-func (pw *PkgEncoder) NewEncoder(k SectionKind, marker SyncMarker) Encoder {
+func (pw *PkgEncoder) NewEncoder(k SectionKind, marker SyncMarker) *Encoder {
 	e := pw.NewEncoderRaw(k)
 	e.Sync(marker)
 	return e
@@ -131,11 +131,11 @@ func (pw *PkgEncoder) NewEncoder(k SectionKind, marker SyncMarker) Encoder {
 // section.
 //
 // Most callers should use NewEncoder instead.
-func (pw *PkgEncoder) NewEncoderRaw(k SectionKind) Encoder {
+func (pw *PkgEncoder) NewEncoderRaw(k SectionKind) *Encoder {
 	idx := RelIndex(len(pw.elems[k]))
 	pw.elems[k] = append(pw.elems[k], "") // placeholder
 
-	return Encoder{
+	return &Encoder{
 		p:   pw,
 		k:   k,
 		Idx: idx,

src/runtime/pprof/pprof_test.go

@@ -465,7 +465,7 @@ func testCPUProfile(t *testing.T, matches profileMatchFunc, f func(dur time.Dura
 		f(duration)
 		StopCPUProfile()
 
-		if p, ok := profileOk(t, matches, prof, duration); ok {
+		if p, ok := profileOk(t, matches, &prof, duration); ok {
 			return p
 		}
 
@@ -515,7 +515,7 @@ func stackContains(spec string, count uintptr, stk []*profile.Location, labels m
 
 type sampleMatchFunc func(spec string, count uintptr, stk []*profile.Location, labels map[string][]string) bool
 
-func profileOk(t *testing.T, matches profileMatchFunc, prof bytes.Buffer, duration time.Duration) (_ *profile.Profile, ok bool) {
+func profileOk(t *testing.T, matches profileMatchFunc, prof *bytes.Buffer, duration time.Duration) (_ *profile.Profile, ok bool) {
 	ok = true
 
 	var samples uintptr