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[dev.typeparams] go/types: recursive substitution must terminate (bug fix)

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This is a port of CL 333383 to go/types.

Change-Id: I7ff68116cbe63337dbcc834c473a2a5588274e36
Reviewed-on: https://go-review.googlesource.com/c/go/+/335115
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:
Rob Findley 2021-07-16 14:30:15 -04:00 committed by Robert Findley
parent c7c13ae432
commit 43ad1ffa99
2 changed files with 45 additions and 16 deletions
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23
src/go/types/api_test.go
View File

@ -1817,3 +1817,26 @@ func f(x T) T { return foo.F(x) }
}
}
}
func TestInstantiate(t *testing.T) {
// eventually we like more tests but this is a start
const src = genericPkg + "p; type T[P any] *T[P]"
pkg, err := pkgFor(".", src, nil)
if err != nil {
t.Fatal(err)
}
// type T should have one type parameter
T := pkg.Scope().Lookup("T").Type().(*Named)
if n := len(T.TParams()); n != 1 {
t.Fatalf("expected 1 type parameter; found %d", n)
}
// instantiation should succeed (no endless recursion)
res := Instantiate(token.NoPos, T, []Type{Typ[Int]})
// instantiated type should point to itself
if res.Underlying().(*Pointer).Elem() != res {
t.Fatalf("unexpected result type: %s", res)
}
}

38
src/go/types/subst.go
View File

@ -237,15 +237,27 @@ func (check *Checker) subst(pos token.Pos, typ Type, smap *substMap) Type {
}
// general case
subst := subster{check, pos, make(map[Type]Type), smap}
var subst subster
subst.pos = pos
subst.smap = smap
if check != nil {
subst.check = check
subst.typMap = check.typMap
} else {
// If we don't have a *Checker and its global type map,
// use a local version. Besides avoiding duplicate work,
// the type map prevents infinite recursive substitution
// for recursive types (example: type T[P any] *T[P]).
subst.typMap = make(map[string]*Named)
}
return subst.typ(typ)
}
type subster struct {
check *Checker
pos token.Pos
cache map[Type]Type
smap *substMap
pos token.Pos
smap *substMap
check *Checker // nil if called via Instantiate
typMap map[string]*Named
}
func (subst *subster) typ(typ Type) Type {
@ -390,22 +402,16 @@ func (subst *subster) typ(typ Type) Type {
// before creating a new named type, check if we have this one already
h := instantiatedHash(t, newTargs)
dump(">>> new type hash: %s", h)
if subst.check != nil {
if named, found := subst.check.typMap[h]; found {
dump(">>> found %s", named)
subst.cache[t] = named
return named
}
if named, found := subst.typMap[h]; found {
dump(">>> found %s", named)
return named
}
// create a new named type and populate caches to avoid endless recursion
// create a new named type and populate typMap to avoid endless recursion
tname := NewTypeName(subst.pos, t.obj.pkg, t.obj.name, nil)
named := subst.check.newNamed(tname, t, t.Underlying(), t.TParams(), t.methods) // method signatures are updated lazily
named.targs = newTargs
if subst.check != nil {
subst.check.typMap[h] = named
}
subst.cache[t] = named
subst.typMap[h] = named
// do the substitution
dump(">>> subst %s with %s (new: %s)", t.underlying, subst.smap, newTargs)