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cmd/compile/internal/syntax: allow eliding interface in constraint literals

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This CL permits an arbitrary type as well as the type sets  ~T and A|B
in constraint position, without the need of a surrrounding interface.
For instance, the type parameter list

	[P interface{ ~map[K]V }, K comparable, V interface{ ~string }]

may be written as

	[P ~map[K]V, K comparable, V ~string]

The feature must be enabled explicitly with the AllowTypeSets mode
and is only available if AllowGenerics is set as well.

For #48424.

Change-Id: Ic70bb97a49ff75e67e040853eac10e6aed0fef1a
Reviewed-on: https://go-review.googlesource.com/c/go/+/353133
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
This commit is contained in:
Robert Griesemer 2021-09-29 11:14:05 -07:00
parent f19b2d50c6
commit 5279e534b5
6 changed files with 133 additions and 22 deletions
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68
src/cmd/compile/internal/syntax/parser.go
View file

@ -87,6 +87,8 @@ func (p *parser) init(file *PosBase, r io.Reader, errh ErrorHandler, pragh Pragm
p.indent = nil
}
func (p *parser) allowGenerics() bool { return p.mode&AllowGenerics != 0 }
// takePragma returns the current parsed pragmas
// and clears them from the parser state.
func (p *parser) takePragma() Pragma {
@ -597,7 +599,7 @@ func (p *parser) typeDecl(group *Group) Decl {
p.xnest++
x := p.expr()
p.xnest--
if name0, ok := x.(*Name); p.mode&AllowGenerics != 0 && ok && p.tok != _Rbrack {
if name0, ok := x.(*Name); p.allowGenerics() && ok && p.tok != _Rbrack {
// generic type
d.TParamList = p.paramList(name0, _Rbrack, true)
pos := p.pos()
@ -687,7 +689,7 @@ func (p *parser) funcDeclOrNil() *FuncDecl {
}
f.Name = p.name()
if p.mode&AllowGenerics != 0 && p.got(_Lbrack) {
if p.allowGenerics() && p.got(_Lbrack) {
if p.tok == _Rbrack {
p.syntaxError("empty type parameter list")
p.next()
@ -1425,7 +1427,7 @@ func (p *parser) interfaceType() *InterfaceType {
switch p.tok {
case _Name:
f := p.methodDecl()
if f.Name == nil && p.mode&AllowGenerics != 0 {
if f.Name == nil && p.allowGenerics() {
f = p.embeddedElem(f)
}
typ.MethodList = append(typ.MethodList, f)
@ -1443,14 +1445,14 @@ func (p *parser) interfaceType() *InterfaceType {
return false
case _Operator:
if p.op == Tilde && p.mode&AllowGenerics != 0 {
if p.op == Tilde && p.allowGenerics() {
typ.MethodList = append(typ.MethodList, p.embeddedElem(nil))
return false
}
case _Type:
// TODO(gri) remove TypeList syntax if we accept #45346
if p.mode&AllowGenerics != 0 && p.mode&AllowTypeLists != 0 {
if p.allowGenerics() && p.mode&AllowTypeLists != 0 {
type_ := NewName(p.pos(), "type") // cannot have a method named "type"
p.next()
if p.tok != _Semi && p.tok != _Rbrace {
@ -1473,7 +1475,7 @@ func (p *parser) interfaceType() *InterfaceType {
}
default:
if p.mode&AllowGenerics != 0 {
if p.allowGenerics() {
pos := p.pos()
if t := p.typeOrNil(); t != nil {
f := new(Field)
@ -1485,7 +1487,7 @@ func (p *parser) interfaceType() *InterfaceType {
}
}
if p.mode&AllowGenerics != 0 {
if p.allowGenerics() {
if p.mode&AllowTypeLists != 0 {
p.syntaxError("expecting method, type list, or embedded element")
p.advance(_Semi, _Rbrace, _Type)
@ -1570,7 +1572,7 @@ func (p *parser) fieldDecl(styp *StructType) {
// Careful dance: We don't know if we have an embedded instantiated
// type T[P1, P2, ...] or a field T of array/slice type [P]E or []E.
if p.mode&AllowGenerics != 0 && len(names) == 1 && p.tok == _Lbrack {
if p.allowGenerics() && len(names) == 1 && p.tok == _Lbrack {
typ = p.arrayOrTArgs()
if typ, ok := typ.(*IndexExpr); ok {
// embedded type T[P1, P2, ...]
@ -1708,7 +1710,7 @@ func (p *parser) methodDecl() *Field {
f.Type = p.funcType()
case _Lbrack:
if p.mode&AllowGenerics != 0 {
if p.allowGenerics() {
// Careful dance: We don't know if we have a generic method m[T C](x T)
// or an embedded instantiated type T[P1, P2] (we accept generic methods
// for generality and robustness of parsing).
@ -1846,38 +1848,60 @@ func (p *parser) paramDeclOrNil(name *Name, follow token) *Field {
defer p.trace("paramDecl")()
}
f := new(Field)
// type set notation is ok in type parameter lists
typeSetsOk := p.mode&AllowTypeSets != 0 && follow == _Rbrack
pos := p.pos()
if name != nil {
f.pos = name.pos
} else {
f.pos = p.pos()
pos = name.pos
} else if typeSetsOk && p.tok == _Operator && p.op == Tilde {
// "~" ...
return p.embeddedElem(nil)
}
f := new(Field)
f.pos = pos
if p.tok == _Name || name != nil {
// name
if name == nil {
name = p.name()
}
if p.mode&AllowGenerics != 0 && p.tok == _Lbrack {
if p.allowGenerics() && p.tok == _Lbrack {
// name "[" ...
f.Type = p.arrayOrTArgs()
if typ, ok := f.Type.(*IndexExpr); ok {
// name "[" ... "]"
typ.X = name
} else {
// name "[" n "]" E
f.Name = name
}
return f
}
if p.tok == _Dot {
// name_or_type
// name "." ...
f.Type = p.qualifiedName(name)
if typeSetsOk && p.tok == _Operator && p.op == Or {
// name "." name "|" ...
f = p.embeddedElem(f)
}
return f
}
if typeSetsOk && p.tok == _Operator && p.op == Or {
// name "|" ...
f.Type = name
return p.embeddedElem(f)
}
f.Name = name
}
if p.tok == _DotDotDot {
// [name] "..." ...
t := new(DotsType)
t.pos = p.pos()
p.next()
@ -1890,7 +1914,17 @@ func (p *parser) paramDeclOrNil(name *Name, follow token) *Field {
return f
}
if typeSetsOk && p.tok == _Operator && p.op == Tilde {
// [name] "~" ...
f.Type = p.embeddedElem(nil).Type
return f
}
f.Type = p.typeOrNil()
if typeSetsOk && p.tok == _Operator && p.op == Or && f.Type != nil {
// [name] type "|"
f = p.embeddedElem(f)
}
if f.Name != nil || f.Type != nil {
return f
}
@ -1952,7 +1986,7 @@ func (p *parser) paramList(name *Name, close token, requireNames bool) (list []*
if par.Type != nil {
typ = par.Type
if par.Name == nil {
pos = typ.Pos()
pos = StartPos(typ)
par.Name = NewName(pos, "_")
}
} else if typ != nil {
@ -2654,7 +2688,7 @@ func (p *parser) qualifiedName(name *Name) Expr {
x = s
}
if p.mode&AllowGenerics != 0 && p.tok == _Lbrack {
if p.allowGenerics() && p.tok == _Lbrack {
x = p.typeInstance(x)
}