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go/types: simplify Named.under

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This is a straighforward port of CL 341857 to go/types.

Change-Id: I3407676232b595662c1470627771a13263703061
Reviewed-on: https://go-review.googlesource.com/c/go/+/342479
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
This commit is contained in:
Robert Findley 2021-08-16 13:20:29 -04:00
parent 56a919f17f
commit d1ba047edf
1 changed files with 19 additions and 33 deletions
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52
src/go/types/named.go
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@ -170,18 +170,13 @@ func (t *Named) String() string { return TypeString(t, nil) }
// is detected, the result is Typ[Invalid]. If a cycle is detected and
// n0.check != nil, the cycle is reported.
func (n0 *Named) under() Type {
n0.expand(nil)
u := n0.load().underlying
if u == Typ[Invalid] {
return u
}
u := n0.Underlying()
// If the underlying type of a defined type is not a defined
// (incl. instance) type, then that is the desired underlying
// type.
switch u.(type) {
var n1 *Named
switch u1 := u.(type) {
case nil:
return Typ[Invalid]
default:
@ -189,6 +184,7 @@ func (n0 *Named) under() Type {
return u
case *Named:
// handled below
n1 = u1
}
if n0.check == nil {
@ -198,43 +194,33 @@ func (n0 *Named) under() Type {
// Invariant: after this point n0 as well as any named types in its
// underlying chain should be set up when this function exits.
check := n0.check
n := n0
// If we can't expand u at this point, it is invalid.
n := asNamed(u)
if n == nil {
n0.underlying = Typ[Invalid]
return n0.underlying
}
seen := make(map[*Named]int) // types that need their underlying resolved
var path []Object // objects encountered, for cycle reporting
// Otherwise, follow the forward chain.
seen := map[*Named]int{n0: 0}
path := []Object{n0.obj}
loop:
for {
u = n.load().underlying
if u == nil {
u = Typ[Invalid]
break
}
var n1 *Named
switch u1 := u.(type) {
case *Named:
u1.expand(nil)
n1 = u1
}
if n1 == nil {
break // end of chain
}
seen[n] = len(seen)
path = append(path, n.obj)
n = n1
if i, ok := seen[n]; ok {
// cycle
check.cycleError(path[i:])
u = Typ[Invalid]
break
}
u = n.Underlying()
switch u1 := u.(type) {
case nil:
u = Typ[Invalid]
break loop
default:
break loop
case *Named:
// Continue collecting *Named types in the chain.
n1 = u1
}
}
for n := range seen {