src

Go monorepo.
git clone git://code.dwrz.net/src
Log | Files | Refs

version.go (3005B)

      1 // Copyright 2024 The Go Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style
      3 // license that can be found in the LICENSE file.
      4 
      5 package pkgbits
      6 
      7 // Version indicates a version of a unified IR bitstream.
      8 // Each Version indicates the addition, removal, or change of
      9 // new data in the bitstream.
     10 //
     11 // These are serialized to disk and the interpretation remains fixed.
     12 type Version uint32
     13 
     14 const (
     15 	// V0: initial prototype.
     16 	//
     17 	// All data that is not assigned a Field is in version V0
     18 	// and has not been deprecated.
     19 	V0 Version = iota
     20 
     21 	// V1: adds the Flags uint32 word
     22 	V1
     23 
     24 	// V2: removes unused legacy fields and supports type parameters for aliases.
     25 	// - remove the legacy "has init" bool from the public root
     26 	// - remove obj's "derived func instance" bool
     27 	// - add a TypeParamNames field to ObjAlias
     28 	// - remove derived info "needed" bool
     29 	V2
     30 
     31 	// V3: introduces a more compact format for composite literal element lists
     32 	// - negative lengths indicate that (some) elements may have keys
     33 	// - positive lengths indicate that no element has a key
     34 	// - a negative struct field index indicates an embedded field
     35 	V3
     36 
     37 	// V4: encodes generic methods as standalone function objects
     38 	V4
     39 
     40 	numVersions = iota
     41 )
     42 
     43 // Field denotes a unit of data in the serialized unified IR bitstream.
     44 // It is conceptually a like field in a structure.
     45 //
     46 // We only really need Fields when the data may or may not be present
     47 // in a stream based on the Version of the bitstream.
     48 //
     49 // Unlike much of pkgbits, Fields are not serialized and
     50 // can change values as needed.
     51 type Field int
     52 
     53 const (
     54 	// Flags in a uint32 in the header of a bitstream
     55 	// that is used to indicate whether optional features are enabled.
     56 	Flags Field = iota
     57 
     58 	// Deprecated: HasInit was a bool indicating whether a package
     59 	// has any init functions.
     60 	HasInit
     61 
     62 	// Deprecated: DerivedFuncInstance was a bool indicating
     63 	// whether an object was a function instance.
     64 	DerivedFuncInstance
     65 
     66 	// ObjAlias has a list of TypeParamNames.
     67 	AliasTypeParamNames
     68 
     69 	// Deprecated: DerivedInfoNeeded was a bool indicating
     70 	// whether a type was a derived type.
     71 	DerivedInfoNeeded
     72 
     73 	// Composite literals use a more compact format for element lists.
     74 	CompactCompLiterals
     75 
     76 	// Generic methods may appear as standalone function objects.
     77 	GenericMethods
     78 
     79 	numFields = iota
     80 )
     81 
     82 // introduced is the version a field was added.
     83 var introduced = [numFields]Version{
     84 	Flags:               V1,
     85 	AliasTypeParamNames: V2,
     86 	CompactCompLiterals: V3,
     87 	GenericMethods:      V4,
     88 }
     89 
     90 // removed is the version a field was removed in or 0 for fields
     91 // that have not yet been deprecated.
     92 // (So removed[f]-1 is the last version it is included in.)
     93 var removed = [numFields]Version{
     94 	HasInit:             V2,
     95 	DerivedFuncInstance: V2,
     96 	DerivedInfoNeeded:   V2,
     97 }
     98 
     99 // Has reports whether field f is present in a bitstream at version v.
    100 func (v Version) Has(f Field) bool {
    101 	return introduced[f] <= v && (v < removed[f] || removed[f] == V0)
    102 }