// with a "[" as in: P []E. In that case, simply parsing
// an expression would lead to an error: P[] is invalid.
// But since index or slice expressions are never constant
- // and thus invalid array length expressions, if we see a
- // "[" following a name it must be the start of an array
- // or slice constraint. Only if we don't see a "[" do we
- // need to parse a full expression.
+ // and thus invalid array length expressions, if the name
+ // is followed by "[" it must be the start of an array or
+ // slice constraint. Only if we don't see a "[" do we
+ // need to parse a full expression. Notably, name <- x
+ // is not a concern because name <- x is a statement and
+ // not an expression.
var x Expr = p.name()
if p.tok != _Lbrack {
// To parse the expression starting with name, expand
x = p.binaryExpr(p.pexpr(x, false), 0)
p.xnest--
}
-
- // analyze the cases
- var pname *Name // pname != nil means pname is the type parameter name
- var ptype Expr // ptype != nil means ptype is the type parameter type; pname != nil in this case
- switch t := x.(type) {
- case *Name:
- // Unless we see a "]", we are at the start of a type parameter list.
- if p.tok != _Rbrack {
- // d.Name "[" name ...
- pname = t
- // no ptype
- }
- case *Operation:
- // If we have an expression of the form name*T, and T is a (possibly
- // parenthesized) type literal or the next token is a comma, we are
- // at the start of a type parameter list.
- if name, _ := t.X.(*Name); name != nil {
- if t.Op == Mul && (isTypeLit(t.Y) || p.tok == _Comma) {
- // d.Name "[" name "*" t.Y
- // d.Name "[" name "*" t.Y ","
- t.X, t.Y = t.Y, nil // convert t into unary *t.Y
- pname = name
- ptype = t
- }
- }
- case *CallExpr:
- // If we have an expression of the form name(T), and T is a (possibly
- // parenthesized) type literal or the next token is a comma, we are
- // at the start of a type parameter list.
- if name, _ := t.Fun.(*Name); name != nil {
- if len(t.ArgList) == 1 && !t.HasDots && (isTypeLit(t.ArgList[0]) || p.tok == _Comma) {
- // d.Name "[" name "(" t.ArgList[0] ")"
- // d.Name "[" name "(" t.ArgList[0] ")" ","
- pname = name
- ptype = t.ArgList[0]
- }
- }
- }
-
- if pname != nil {
+ // Analyze expression x. If we can split x into a type parameter
+ // name, possibly followed by a type parameter type, we consider
+ // this the start of a type parameter list, with some caveats:
+ // a single name followed by "]" tilts the decision towards an
+ // array declaration; a type parameter type that could also be
+ // an ordinary expression but which is followed by a comma tilts
+ // the decision towards a type parameter list.
+ if pname, ptype := extractName(x, p.tok == _Comma); pname != nil && (ptype != nil || p.tok != _Rbrack) {
// d.Name "[" pname ...
// d.Name "[" pname ptype ...
// d.Name "[" pname ptype "," ...
- d.TParamList = p.paramList(pname, ptype, _Rbrack, true)
+ d.TParamList = p.paramList(pname, ptype, _Rbrack, true) // ptype may be nil
d.Alias = p.gotAssign()
d.Type = p.typeOrNil()
} else {
+ // d.Name "[" pname "]" ...
// d.Name "[" x ...
d.Type = p.arrayType(pos, x)
}
return d
}
-// isTypeLit reports whether x is a (possibly parenthesized) type literal.
-func isTypeLit(x Expr) bool {
+// extractName splits the expression x into (name, expr) if syntactically
+// x can be written as name expr. The split only happens if expr is a type
+// element (per the isTypeElem predicate) or if force is set.
+// If x is just a name, the result is (name, nil). If the split succeeds,
+// the result is (name, expr). Otherwise the result is (nil, x).
+// Examples:
+//
+// x force name expr
+// ------------------------------------
+// P*[]int T/F P *[]int
+// P*E T P *E
+// P*E F nil P*E
+// P([]int) T/F P []int
+// P(E) T P E
+// P(E) F nil P(E)
+// P*E|F|~G T/F P *E|F|~G
+// P*E|F|G T P *E|F|G
+// P*E|F|G F nil P*E|F|G
+func extractName(x Expr, force bool) (*Name, Expr) {
+ switch x := x.(type) {
+ case *Name:
+ return x, nil
+ case *Operation:
+ if x.Y == nil {
+ break // unary expr
+ }
+ switch x.Op {
+ case Mul:
+ if name, _ := x.X.(*Name); name != nil && (isTypeElem(x.Y) || force) {
+ // x = name *x.Y
+ op := *x
+ op.X, op.Y = op.Y, nil // change op into unary *op.Y
+ return name, &op
+ }
+ case Or:
+ if name, lhs := extractName(x.X, isTypeElem(x.Y) || force); name != nil && lhs != nil { // note: lhs should never be nil
+ // x = name lhs|x.Y
+ op := *x
+ op.X = lhs
+ return name, &op
+ }
+ }
+ case *CallExpr:
+ if name, _ := x.Fun.(*Name); name != nil {
+ if len(x.ArgList) == 1 && !x.HasDots && (isTypeElem(x.ArgList[0]) || force) {
+ // x = name "(" x.ArgList[0] ")"
+ return name, x.ArgList[0]
+ }
+ }
+ }
+ return nil, x
+}
+
+// isTypeElem reports whether x is a (possibly parenthesized) type element expression.
+// The result is false if x could be a type element OR an ordinary (value) expression.
+func isTypeElem(x Expr) bool {
switch x := x.(type) {
case *ArrayType, *StructType, *FuncType, *InterfaceType, *SliceType, *MapType, *ChanType:
return true
case *Operation:
- // *T may be a pointer dereferenciation.
- // Only consider *T as type literal if T is a type literal.
- return x.Op == Mul && x.Y == nil && isTypeLit(x.X)
+ return isTypeElem(x.X) || (x.Y != nil && isTypeElem(x.Y)) || x.Op == Tilde
case *ParenExpr:
- return isTypeLit(x.X)
+ return isTypeElem(x.X)
}
return false
}
}
p.print(n.Name)
if n.TParamList != nil {
- p.printParameterList(n.TParamList, true)
+ p.printParameterList(n.TParamList, _Type)
}
p.print(blank)
if n.Alias {
}
p.print(n.Name)
if n.TParamList != nil {
- p.printParameterList(n.TParamList, true)
+ p.printParameterList(n.TParamList, _Func)
}
p.printSignature(n.Type)
if n.Body != nil {
}
func (p *printer) printSignature(sig *FuncType) {
- p.printParameterList(sig.ParamList, false)
+ p.printParameterList(sig.ParamList, 0)
if list := sig.ResultList; list != nil {
p.print(blank)
if len(list) == 1 && list[0].Name == nil {
p.printNode(list[0].Type)
} else {
- p.printParameterList(list, false)
+ p.printParameterList(list, 0)
}
}
}
-func (p *printer) printParameterList(list []*Field, types bool) {
+// If tok != 0 print a type parameter list: tok == _Type means
+// a type parameter list for a type, tok == _Func means a type
+// parameter list for a func.
+func (p *printer) printParameterList(list []*Field, tok token) {
open, close := _Lparen, _Rparen
- if types {
+ if tok != 0 {
open, close = _Lbrack, _Rbrack
}
p.print(open)
}
p.printNode(unparen(f.Type)) // no need for (extra) parentheses around parameter types
}
- // A type parameter list [P *T] where T is not a type literal requires a comma as in [P *T,]
+ // A type parameter list [P *T] where T is not a type element requires a comma as in [P *T,]
// so that it's not parsed as [P*T].
- if types && len(list) == 1 {
- if t, _ := list[0].Type.(*Operation); t != nil && t.Op == Mul && t.Y == nil && !isTypeLit(t.X) {
+ if tok == _Type && len(list) == 1 {
+ if t, _ := list[0].Type.(*Operation); t != nil && !isTypeElem(t) {
p.print(_Comma)
}
}
dup("package p"),
dup("package p; type _ int; type T1 = struct{}; type ( _ *struct{}; T2 = float32 )"),
- // generic type declarations
+ // generic type declarations (given type separated with blank from LHS)
dup("package p; type _[T any] struct{}"),
dup("package p; type _[A, B, C interface{m()}] struct{}"),
dup("package p; type _[T any, A, B, C interface{m()}, X, Y, Z interface{~int}] struct{}"),
+ dup("package p; type _[P *struct{}] struct{}"),
dup("package p; type _[P *T,] struct{}"),
dup("package p; type _[P *T, _ any] struct{}"),
{"package p; type _[P (*T),] struct{}", "package p; type _[P *T,] struct{}"},
{"package p; type _[P (T),] struct{}", "package p; type _[P T] struct{}"},
{"package p; type _[P (T), _ any] struct{}", "package p; type _[P T, _ any] struct{}"},
- dup("package p; type _[P *struct{}] struct{}"),
{"package p; type _[P (*struct{})] struct{}", "package p; type _[P *struct{}] struct{}"},
{"package p; type _[P ([]int)] struct{}", "package p; type _[P []int] struct{}"},
-
- dup("package p; type _ [P(T)]struct{}"),
- dup("package p; type _ [P((T))]struct{}"),
- dup("package p; type _ [P * *T]struct{}"),
- dup("package p; type _ [P * T]struct{}"),
- dup("package p; type _ [P(*T)]struct{}"),
- dup("package p; type _ [P(**T)]struct{}"),
- dup("package p; type _ [P * T - T]struct{}"),
-
- // array type declarations
- dup("package p; type _ [P * T]struct{}"),
- dup("package p; type _ [P * T - T]struct{}"),
+ {"package p; type _[P ([]int) | int] struct{}", "package p; type _[P []int | int] struct{}"},
+
+ // a type literal in an |-expression indicates a type parameter list (blank after type parameter list and type)
+ dup("package p; type _[P *[]int] struct{}"),
+ dup("package p; type _[P *T | T, Q T] struct{}"),
+ dup("package p; type _[P *[]T | T] struct{}"),
+ dup("package p; type _[P *T | T | T | T | ~T] struct{}"),
+ dup("package p; type _[P *T | T | T | ~T | T] struct{}"),
+ dup("package p; type _[P *T | T | struct{} | T] struct{}"),
+ dup("package p; type _[P <-chan int] struct{}"),
+ dup("package p; type _[P *T | struct{} | T] struct{}"),
+
+ // a trailing comma always indicates a type parameter list (blank after type parameter list and type)
+ dup("package p; type _[P *T,] struct{}"),
+ dup("package p; type _[P *T | T,] struct{}"),
+ dup("package p; type _[P *T | <-T | T,] struct{}"),
+
+ // slice/array type declarations (no blank between array length and element type)
+ dup("package p; type _ []byte"),
+ dup("package p; type _ [n]byte"),
+ dup("package p; type _ [P(T)]byte"),
+ dup("package p; type _ [P((T))]byte"),
+ dup("package p; type _ [P * *T]byte"),
+ dup("package p; type _ [P * T]byte"),
+ dup("package p; type _ [P(*T)]byte"),
+ dup("package p; type _ [P(**T)]byte"),
+ dup("package p; type _ [P * T - T]byte"),
+ dup("package p; type _ [P * T - T]byte"),
+ dup("package p; type _ [P * T | T]byte"),
+ dup("package p; type _ [P * T | <-T | T]byte"),
// generic function declarations
dup("package p; func _[T any]()"),
dup("package p; func _[A, B, C interface{m()}]()"),
dup("package p; func _[T any, A, B, C interface{m()}, X, Y, Z interface{~int}]()"),
+ // generic functions with elided interfaces in type constraints
+ dup("package p; func _[P *T]() {}"),
+ dup("package p; func _[P *T | T | T | T | ~T]() {}"),
+ dup("package p; func _[P *T | T | struct{} | T]() {}"),
+ dup("package p; func _[P ~int, Q int | string]() {}"),
+ dup("package p; func _[P struct{f int}, Q *P]() {}"),
+
// methods with generic receiver types
dup("package p; func (R[T]) _()"),
dup("package p; func (*R[A, B, C]) _()"),
dup("package p; func (_ *R[A, B, C]) _()"),
- // type constraint literals with elided interfaces
- dup("package p; func _[P ~int, Q int | string]() {}"),
- dup("package p; func _[P struct{f int}, Q *P]() {}"),
-
// channels
dup("package p; type _ chan chan int"),
dup("package p; type _ chan (<-chan int)"),
func f[a t, b t, c /* ERROR missing type constraint */ ]()
func f[a b, /* ERROR expecting ] */ 0] ()
+
+// issue #49482
+type (
+ t[a *[]int] struct{}
+ t[a *t,] struct{}
+ t[a *t|[]int] struct{}
+ t[a *t|t,] struct{}
+ t[a *t|~t,] struct{}
+ t[a *struct{}|t] struct{}
+ t[a *t|struct{}] struct{}
+ t[a *struct{}|~t] struct{}
+)
+
+// issue #51488
+type (
+ t[a *t|t,] struct{}
+ t[a *t|t, b t] struct{}
+ t[a *t|t] struct{}
+ t[a *[]t|t] struct{}
+ t[a ([]t)] struct{}
+ t[a ([]t)|t] struct{}
+)
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
-// This file is tested when running "go test -run Manual"
-// without source arguments. Use for one-off debugging.
-
package p
// The following is OK, per the special handling for type literals discussed in issue #49482.
const P = 2 // declare P to avoid noisy 'undeclared name' errors below.
-// The following parse as invalid array types.
-type _[P *int /* ERROR "int \(type\) is not an expression" */ ] int
-type _[P /* ERROR non-function P */ (*int)] int
+// The following parse as invalid array types due to parsing ambiguitiues.
+type _ [P *int /* ERROR "int \(type\) is not an expression" */ ]int
+type _ [P /* ERROR non-function P */ (*int)]int
-// The following should be parsed as a generic type, but is instead parsed as an array type.
-type _[P *struct /* ERROR "not an expression" */ {}| int /* ERROR "not an expression" */ ] struct{}
+// Adding a trailing comma or an enclosing interface resolves the ambiguity.
+type _[P *int,] int
+type _[P (*int),] int
+type _[P interface{*int}] int
+type _[P interface{(*int)}] int
-// The following fails to parse, due to the '~'
-type _[P *struct /* ERROR "not an expression" */ {}|~int /* ERROR "not an expression" */ ] struct{}
+// The following parse correctly as valid generic types.
+type _[P *struct{} | int] struct{}
+type _[P *struct{} | ~int] struct{}