sort, internal/reflectlite: flesh out reflectlite enough for use by sort

Now the net package is back to no longer depending on unicode. And lock that in
with a test.

Fixes #30440

Change-Id: I18b89b02f7d96488783adc07308da990f505affd
Reviewed-on: https://go-review.googlesource.com/c/go/+/169137
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/go_test.go

@@ -1888,7 +1888,7 @@ func TestGoListTest(t *testing.T) {
 	tg.grepStdout(`^runtime/cgo$`, "missing runtime/cgo")
 
 	tg.run("list", "-deps", "-f", "{{if .DepOnly}}{{.ImportPath}}{{end}}", "sort")
-	tg.grepStdout(`^reflect$`, "missing reflect")
+	tg.grepStdout(`^internal/reflectlite$`, "missing internal/reflectlite")
 	tg.grepStdoutNot(`^sort`, "unexpected sort")
 }
 

src/cmd/go/internal/load/pkg.go

@@ -969,6 +969,13 @@ func disallowInternal(srcDir string, importer *Package, importerPath string, p *
 		return p
 	}
 
+	// The sort package depends on internal/reflectlite, but during bootstrap
+	// the path rewriting causes the normal internal checks to fail.
+	// Instead, just ignore the internal rules during bootstrap.
+	if p.Standard && strings.HasPrefix(importerPath, "bootstrap/") {
+		return p
+	}
+
 	// The stack includes p.ImportPath.
 	// If that's the only thing on the stack, we started
 	// with a name given on the command line, not an

src/go/build/deps_test.go

@@ -120,7 +120,7 @@ var pkgDeps = map[string][]string{
 	"image/color/palette":    {"L2", "image/color"},
 	"internal/fmtsort":       {"reflect", "sort"},
 	"reflect":                {"L2"},
-	"sort":                   {"reflect"},
+	"sort":                   {"internal/reflectlite"},
 
 	"L3": {
 		"L2",
@@ -563,11 +563,12 @@ func TestDependencies(t *testing.T) {
 	// these dependency paths:
 	badPaths := []struct{ from, to string }{
 		{"net", "unicode"},
+		{"os", "unicode"},
 	}
 
 	for _, path := range badPaths {
 		if how := depPath(path.from, path.to); how != "" {
-			t.Logf("TODO(issue 30440): policy violation: %s", how)
+			t.Errorf("policy violation: %s", how)
 		}
 	}
 
@@ -585,6 +586,11 @@ func findImports(pkg string) ([]string, error) {
 	var haveImport = map[string]bool{}
 	for _, file := range files {
 		name := file.Name()
+		if name == "slice_pre113.go" {
+			// This file is ignored by build tags which aren't
+			// handled by this findImports func.
+			continue
+		}
 		if !strings.HasSuffix(name, ".go") || strings.HasSuffix(name, "_test.go") {
 			continue
 		}

src/internal/reflectlite/swapper.go

@@ -0,0 +1,74 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package reflectlite
+
+import "unsafe"
+
+// Swapper returns a function that swaps the elements in the provided
+// slice.
+//
+// Swapper panics if the provided interface is not a slice.
+func Swapper(slice interface{}) func(i, j int) {
+	v := ValueOf(slice)
+	if v.Kind() != Slice {
+		panic(&ValueError{Method: "Swapper", Kind: v.Kind()})
+	}
+	// Fast path for slices of size 0 and 1. Nothing to swap.
+	switch v.Len() {
+	case 0:
+		return func(i, j int) { panic("reflect: slice index out of range") }
+	case 1:
+		return func(i, j int) {
+			if i != 0 || j != 0 {
+				panic("reflect: slice index out of range")
+			}
+		}
+	}
+
+	typ := v.Type().Elem().(*rtype)
+	size := typ.Size()
+	hasPtr := typ.ptrdata != 0
+
+	// Some common & small cases, without using memmove:
+	if hasPtr {
+		if size == ptrSize {
+			ps := *(*[]unsafe.Pointer)(v.ptr)
+			return func(i, j int) { ps[i], ps[j] = ps[j], ps[i] }
+		}
+		if typ.Kind() == String {
+			ss := *(*[]string)(v.ptr)
+			return func(i, j int) { ss[i], ss[j] = ss[j], ss[i] }
+		}
+	} else {
+		switch size {
+		case 8:
+			is := *(*[]int64)(v.ptr)
+			return func(i, j int) { is[i], is[j] = is[j], is[i] }
+		case 4:
+			is := *(*[]int32)(v.ptr)
+			return func(i, j int) { is[i], is[j] = is[j], is[i] }
+		case 2:
+			is := *(*[]int16)(v.ptr)
+			return func(i, j int) { is[i], is[j] = is[j], is[i] }
+		case 1:
+			is := *(*[]int8)(v.ptr)
+			return func(i, j int) { is[i], is[j] = is[j], is[i] }
+		}
+	}
+
+	s := (*sliceHeader)(v.ptr)
+	tmp := unsafe_New(typ) // swap scratch space
+
+	return func(i, j int) {
+		if uint(i) >= uint(s.Len) || uint(j) >= uint(s.Len) {
+			panic("reflect: slice index out of range")
+		}
+		val1 := arrayAt(s.Data, i, size, "i < s.Len")
+		val2 := arrayAt(s.Data, j, size, "j < s.Len")
+		typedmemmove(typ, tmp, val1)
+		typedmemmove(typ, val1, val2)
+		typedmemmove(typ, val2, tmp)
+	}
+}

src/internal/reflectlite/type.go

@@ -35,6 +35,10 @@ type Type interface {
 	// will be the empty string.
 	PkgPath() string
 
+	// Size returns the number of bytes needed to store
+	// a value of the given type; it is analogous to unsafe.Sizeof.
+	Size() uintptr
+
 	// Kind returns the specific kind of this type.
 	Kind() Kind
 
@@ -482,8 +486,12 @@ func (t *rtype) String() string {
 	return s
 }
 
+func (t *rtype) Size() uintptr { return t.size }
+
 func (t *rtype) Kind() Kind { return Kind(t.kind & kindMask) }
 
+func (t *rtype) pointers() bool { return t.ptrdata != 0 }
+
 func (t *rtype) common() *rtype { return t }
 
 func (t *rtype) exportedMethods() []method {

src/internal/reflectlite/value.go

@@ -9,6 +9,8 @@ import (
 	"unsafe"
 )
 
+const ptrSize = 4 << (^uintptr(0) >> 63) // unsafe.Sizeof(uintptr(0)) but an ideal const
+
 // Value is the reflection interface to a Go value.
 //
 // Not all methods apply to all kinds of values. Restrictions,
@@ -84,6 +86,18 @@ func (f flag) ro() flag {
 	return 0
 }
 
+// pointer returns the underlying pointer represented by v.
+// v.Kind() must be Ptr, Map, Chan, Func, or UnsafePointer
+func (v Value) pointer() unsafe.Pointer {
+	if v.typ.size != ptrSize || !v.typ.pointers() {
+		panic("can't call pointer on a non-pointer Value")
+	}
+	if v.flag&flagIndir != 0 {
+		return *(*unsafe.Pointer)(v.ptr)
+	}
+	return v.ptr
+}
+
 // packEface converts v to the empty interface.
 func packEface(v Value) interface{} {
 	t := v.typ
@@ -316,6 +330,32 @@ func (v Value) Kind() Kind {
 	return v.kind()
 }
 
+// implemented in runtime:
+func chanlen(unsafe.Pointer) int
+func maplen(unsafe.Pointer) int
+
+// Len returns v's length.
+// It panics if v's Kind is not Array, Chan, Map, Slice, or String.
+func (v Value) Len() int {
+	k := v.kind()
+	switch k {
+	case Array:
+		tt := (*arrayType)(unsafe.Pointer(v.typ))
+		return int(tt.len)
+	case Chan:
+		return chanlen(v.pointer())
+	case Map:
+		return maplen(v.pointer())
+	case Slice:
+		// Slice is bigger than a word; assume flagIndir.
+		return (*sliceHeader)(v.ptr).Len
+	case String:
+		// String is bigger than a word; assume flagIndir.
+		return (*stringHeader)(v.ptr).Len
+	}
+	panic(&ValueError{"reflect.Value.Len", v.kind()})
+}
+
 // NumMethod returns the number of exported methods in the value's method set.
 func (v Value) numMethod() int {
 	if v.typ == nil {
@@ -427,6 +467,17 @@ func (v Value) assignTo(context string, dst *rtype, target unsafe.Pointer) Value
 	panic(context + ": value of type " + v.typ.String() + " is not assignable to type " + dst.String())
 }
 
+// arrayAt returns the i-th element of p,
+// an array whose elements are eltSize bytes wide.
+// The array pointed at by p must have at least i+1 elements:
+// it is invalid (but impossible to check here) to pass i >= len,
+// because then the result will point outside the array.
+// whySafe must explain why i < len. (Passing "i < len" is fine;
+// the benefit is to surface this assumption at the call site.)
+func arrayAt(p unsafe.Pointer, i int, eltSize uintptr, whySafe string) unsafe.Pointer {
+	return add(p, uintptr(i)*eltSize, "i < len")
+}
+
 func ifaceE2I(t *rtype, src interface{}, dst unsafe.Pointer)
 
 // typedmemmove copies a value of type t to dst from src.

src/runtime/chan.go

@@ -678,6 +678,14 @@ func reflect_chanlen(c *hchan) int {
 	return int(c.qcount)
 }
 
+//go:linkname reflectlite_chanlen internal/reflectlite.chanlen
+func reflectlite_chanlen(c *hchan) int {
+	if c == nil {
+		return 0
+	}
+	return int(c.qcount)
+}
+
 //go:linkname reflect_chancap reflect.chancap
 func reflect_chancap(c *hchan) int {
 	if c == nil {

src/runtime/map.go

@@ -1371,6 +1371,18 @@ func reflect_maplen(h *hmap) int {
 	return h.count
 }
 
+//go:linkname reflectlite_maplen internal/reflectlite.maplen
+func reflectlite_maplen(h *hmap) int {
+	if h == nil {
+		return 0
+	}
+	if raceenabled {
+		callerpc := getcallerpc()
+		racereadpc(unsafe.Pointer(h), callerpc, funcPC(reflect_maplen))
+	}
+	return h.count
+}
+
 //go:linkname reflect_ismapkey reflect.ismapkey
 func reflect_ismapkey(t *_type) bool {
 	return ismapkey(t)

src/sort/slice.go

@@ -2,11 +2,13 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !compiler_bootstrap go1.8
+// +build !compiler_bootstrap go1.13
 
 package sort
 
-import "reflect"
+import (
+	"internal/reflectlite"
+)
 
 // Slice sorts the provided slice given the provided less function.
 //
@@ -15,8 +17,8 @@ import "reflect"
 //
 // The function panics if the provided interface is not a slice.
 func Slice(slice interface{}, less func(i, j int) bool) {
-	rv := reflect.ValueOf(slice)
-	swap := reflect.Swapper(slice)
+	rv := reflectlite.ValueOf(slice)
+	swap := reflectlite.Swapper(slice)
 	length := rv.Len()
 	quickSort_func(lessSwap{less, swap}, 0, length, maxDepth(length))
 }
@@ -26,8 +28,8 @@ func Slice(slice interface{}, less func(i, j int) bool) {
 //
 // The function panics if the provided interface is not a slice.
 func SliceStable(slice interface{}, less func(i, j int) bool) {
-	rv := reflect.ValueOf(slice)
-	swap := reflect.Swapper(slice)
+	rv := reflectlite.ValueOf(slice)
+	swap := reflectlite.Swapper(slice)
 	stable_func(lessSwap{less, swap}, rv.Len())
 }
 
@@ -35,7 +37,7 @@ func SliceStable(slice interface{}, less func(i, j int) bool) {
 //
 // The function panics if the provided interface is not a slice.
 func SliceIsSorted(slice interface{}, less func(i, j int) bool) bool {
-	rv := reflect.ValueOf(slice)
+	rv := reflectlite.ValueOf(slice)
 	n := rv.Len()
 	for i := n - 1; i > 0; i-- {
 		if less(i, i-1) {

src/sort/slice_pre113.go

@@ -0,0 +1,46 @@
+// Copyright 2017 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build go1.8,!go1.13
+
+package sort
+
+import "reflect"
+
+// Slice sorts the provided slice given the provided less function.
+//
+// The sort is not guaranteed to be stable. For a stable sort, use
+// SliceStable.
+//
+// The function panics if the provided interface is not a slice.
+func Slice(slice interface{}, less func(i, j int) bool) {
+	rv := reflect.ValueOf(slice)
+	swap := reflect.Swapper(slice)
+	length := rv.Len()
+	quickSort_func(lessSwap{less, swap}, 0, length, maxDepth(length))
+}
+
+// SliceStable sorts the provided slice given the provided less
+// function while keeping the original order of equal elements.
+//
+// The function panics if the provided interface is not a slice.
+func SliceStable(slice interface{}, less func(i, j int) bool) {
+	rv := reflect.ValueOf(slice)
+	swap := reflect.Swapper(slice)
+	stable_func(lessSwap{less, swap}, rv.Len())
+}
+
+// SliceIsSorted tests whether a slice is sorted.
+//
+// The function panics if the provided interface is not a slice.
+func SliceIsSorted(slice interface{}, less func(i, j int) bool) bool {
+	rv := reflect.ValueOf(slice)
+	n := rv.Len()
+	for i := n - 1; i > 0; i-- {
+		if less(i, i-1) {
+			return false
+		}
+	}
+	return true
+}