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go/types: ensure that constructed type parameters are immutable

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TypeParam.iface may mutate TypeParam.bound in the event that the type
parameter bound is not an interface.

Ensure that iface() is called before the type-checking pass returns, and
before NewTypeParam or TypeParam.SetConstraint exits.

Fixes #49788

Change-Id: I72279acf5f0223161671c04887bc2c3df4158927
Reviewed-on: https://go-review.googlesource.com/c/go/+/367614
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Robert Findley 2021-11-29 14:52:54 -05:00
parent c402d64f37
commit 186f375ecf
2 changed files with 32 additions and 3 deletions
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17
src/cmd/compile/internal/types2/typeparam.go
View file

@ -21,7 +21,7 @@ type TypeParam struct {
id uint64 // unique id, for debugging only
obj *TypeName // corresponding type name
index int // type parameter index in source order, starting at 0
bound Type // any type, but eventually an *Interface for correct programs (see TypeParam.iface)
bound Type // any type, but underlying is eventually *Interface for correct programs (see TypeParam.iface)
}
// Obj returns the type name for the type parameter t.
@ -47,6 +47,15 @@ func (check *Checker) newTypeParam(obj *TypeName, constraint Type) *TypeParam {
if obj.typ == nil {
obj.typ = typ
}
// iface may mutate typ.bound, so we must ensure that iface() is called
// at least once before the resulting TypeParam escapes.
if check != nil {
check.later(func() {
typ.iface()
})
} else if constraint != nil {
typ.iface()
}
return typ
}
@ -62,11 +71,17 @@ func (t *TypeParam) Constraint() Type {
}
// SetConstraint sets the type constraint for t.
//
// SetConstraint should not be called concurrently, but once SetConstraint
// returns the receiver t is safe for concurrent use.
func (t *TypeParam) SetConstraint(bound Type) {
if bound == nil {
panic("nil constraint")
}
t.bound = bound
// iface may mutate t.bound (if bound is not an interface), so ensure that
// this is done before returning.
t.iface()
}
func (t *TypeParam) Underlying() Type {

18
src/go/types/typeparam.go
View file

@ -24,7 +24,7 @@ type TypeParam struct {
id uint64 // unique id, for debugging only
obj *TypeName // corresponding type name
index int // type parameter index in source order, starting at 0
bound Type // any type, but eventually an *Interface for correct programs (see TypeParam.iface)
bound Type // any type, but underlying is eventually *Interface for correct programs (see TypeParam.iface)
}
// NewTypeParam returns a new TypeParam. Type parameters may be set on a Named
@ -47,6 +47,15 @@ func (check *Checker) newTypeParam(obj *TypeName, constraint Type) *TypeParam {
if obj.typ == nil {
obj.typ = typ
}
// iface may mutate typ.bound, so we must ensure that iface() is called
// at least once before the resulting TypeParam escapes.
if check != nil {
check.later(func() {
typ.iface()
})
} else if constraint != nil {
typ.iface()
}
return typ
}
@ -65,11 +74,17 @@ func (t *TypeParam) Constraint() Type {
}
// SetConstraint sets the type constraint for t.
//
// SetConstraint should not be called concurrently, but once SetConstraint
// returns the receiver t is safe for concurrent use.
func (t *TypeParam) SetConstraint(bound Type) {
if bound == nil {
panic("nil constraint")
}
t.bound = bound
// iface may mutate t.bound (if bound is not an interface), so ensure that
// this is done before returning.
t.iface()
}
func (t *TypeParam) Underlying() Type {
@ -104,7 +119,6 @@ func (t *TypeParam) iface() *Interface {
}
// If we don't have an interface, wrap constraint into an implicit interface.
// TODO(gri) mark it as implicit - see comment in Checker.bound
if ityp == nil {
ityp = NewInterfaceType(nil, []Type{bound})
ityp.implicit = true