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// Copyright 2024 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 pkgbits
// Version indicates a version of a unified IR bitstream.
// Each Version indicates the addition, removal, or change of
// new data in the bitstream.
//
// These are serialized to disk and the interpretation remains fixed.
type Version uint32
const (
// V0: initial prototype.
//
// All data that is not assigned a Field is in version V0
// and has not been deprecated.
V0 Version = iota
// V1: adds the Flags uint32 word
V1
// V2: removes unused legacy fields and supports type parameters for aliases.
// - remove the legacy "has init" bool from the public root
// - remove obj's "derived func instance" bool
// - add a TypeParamNames field to ObjAlias
// - remove derived info "needed" bool
V2
numVersions = iota
)
// Field denotes a unit of data in the serialized unified IR bitstream.
// It is conceptually a like field in a structure.
//
// We only really need Fields when the data may or may not be present
// in a stream based on the Version of the bitstream.
//
// Unlike much of pkgbits, Fields are not serialized and
// can change values as needed.
type Field int
const (
// Flags in a uint32 in the header of a bitstream
// that is used to indicate whether optional features are enabled.
Flags Field = iota
// Deprecated: HasInit was a bool indicating whether a package
// has any init functions.
HasInit
// Deprecated: DerivedFuncInstance was a bool indicating
// whether an object was a function instance.
DerivedFuncInstance
// ObjAlias has a list of TypeParamNames.
AliasTypeParamNames
// Deprecated: DerivedInfoNeeded was a bool indicating
// whether a type was a derived type.
DerivedInfoNeeded
numFields = iota
)
// introduced is the version a field was added.
var introduced = [numFields]Version{
Flags: V1,
AliasTypeParamNames: V2,
}
// removed is the version a field was removed in or 0 for fields
// that have not yet been deprecated.
// (So removed[f]-1 is the last version it is included in.)
var removed = [numFields]Version{
HasInit: V2,
DerivedFuncInstance: V2,
DerivedInfoNeeded: V2,
}
// Has reports whether field f is present in a bitstream at version v.
func (v Version) Has(f Field) bool {
return introduced[f] <= v && (v < removed[f] || removed[f] == V0)
}
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