go/types, go/constant: remove backward-compatibility files (cleanup)

Not needed anymore since go/types is always built against the current
standard library.

Fixes #11538.

Change-Id: I2f07d73703f4e5661c4b5df5d487939dcf530b43
Reviewed-on: https://go-review.googlesource.com/13897Reviewed-by: Alan Donovan <adonovan@google.com>

src/go/constant/go13.go

-// Copyright 2014 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 !go1.4
-
-package constant
-
-import (
-	"math"
-	"math/big"
-)
-
-func ratToFloat32(x *big.Rat) (float32, bool) {
-	// Before 1.4, there's no Rat.Float32.
-	// Emulate it, albeit at the cost of
-	// imprecision in corner cases.
-	x64, exact := x.Float64()
-	x32 := float32(x64)
-	if math.IsInf(float64(x32), 0) {
-		exact = false
-	}
-	return x32, exact
-}

src/go/constant/go14.go

-// Copyright 2014 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 go1.4
-
-package constant
-
-import "math/big"
-
-func ratToFloat32(x *big.Rat) (float32, bool) {
-	return x.Float32()
-}

src/go/constant/value.go

@@ -258,9 +258,9 @@ func Float32Val(x Value) (float32, bool) {
 		f := float32(x)
 		return f, int64Val(f) == x
 	case intVal:
-		return ratToFloat32(new(big.Rat).SetFrac(x.val, int1))
+		return new(big.Rat).SetFrac(x.val, int1).Float32()
 	case floatVal:
-		return ratToFloat32(x.val)
+		return x.val.Float32()
 	case unknownVal:
 		return 0, false
 	}

src/go/types/expr.go

@@ -1256,7 +1256,7 @@ func (check *Checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 		switch typ := x.typ.Underlying().(type) {
 		case *Basic:
 			if isString(typ) {
-				if slice3(e) {
+				if e.Slice3 {
 					check.invalidOp(x.pos(), "3-index slice of string")
 					goto Error
 				}
@@ -1300,14 +1300,14 @@ func (check *Checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
 		x.mode = value
 
 		// spec: "Only the first index may be omitted; it defaults to 0."
-		if slice3(e) && (e.High == nil || sliceMax(e) == nil) {
+		if e.Slice3 && (e.High == nil || e.Max == nil) {
 			check.error(e.Rbrack, "2nd and 3rd index required in 3-index slice")
 			goto Error
 		}
 
 		// check indices
 		var ind [3]int64
-		for i, expr := range []ast.Expr{e.Low, e.High, sliceMax(e)} {
+		for i, expr := range []ast.Expr{e.Low, e.High, e.Max} {
 			x := int64(-1)
 			switch {
 			case expr != nil:

src/go/types/go11.go

-// Copyright 2013 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 !go1.2
-
-package types
-
-import "go/ast"
-
-func slice3(x *ast.SliceExpr) bool {
-	return false
-}
-
-func sliceMax(x *ast.SliceExpr) ast.Expr {
-	return nil
-}

src/go/types/go12.go

-// Copyright 2013 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 go1.2
-
-package types
-
-import "go/ast"
-
-func slice3(x *ast.SliceExpr) bool {
-	return x.Slice3
-}
-
-func sliceMax(x *ast.SliceExpr) ast.Expr {
-	return x.Max
-}