go/types: mark implicit interfaces as such

This is a straightforward port of CL 353396 to go/types.

For #48424

Change-Id: I3040c2ad3a8c9573026277de01deb9c47953cec8
Reviewed-on: https://go-review.googlesource.com/c/go/+/354991
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>

diff --git a/src/go/types/decl.go b/src/go/types/decl.go
index c8cac0f1483fb0cb94df30f475e1605372f1a85a..f97fa252cbf23bfcabde28cedbc057cbb0a3e821 100644 (file)
--- a/src/go/types/decl.go
+++ b/src/go/types/decl.go
@@ -715,11 +715,13 @@ func (check *Checker) bound(x ast.Expr) Type {
                wrap = op.Op == token.OR
        }
        if wrap {
-               // TODO(gri) Should mark this interface as "implicit" somehow
-               //           (and propagate the info to types2.Interface) so
-               //           that we can elide the interface again in error
-               //           messages. Could use a sentinel name for the field.
                x = &ast.InterfaceType{Methods: &ast.FieldList{List: []*ast.Field{{Type: x}}}}
+               t := check.typ(x)
+               // mark t as implicit interface if all went well
+               if t, _ := t.(*Interface); t != nil {
+                       t.implicit = true
+               }
+               return t
        }
        return check.typ(x)
 }

diff --git a/src/go/types/interface.go b/src/go/types/interface.go
index 866a3427ca18c26b2e034e2919aff1dbdf0ce81d..2f4f10d45fa19cadb44a3eeb1afe0ea5d2f4d00e 100644 (file)
--- a/src/go/types/interface.go
+++ b/src/go/types/interface.go
@@ -19,6 +19,7 @@ type Interface struct {
        methods   []*Func      // ordered list of explicitly declared methods
        embeddeds []Type       // ordered list of explicitly embedded elements
        embedPos  *[]token.Pos // positions of embedded elements; or nil (for error messages) - use pointer to save space
+       implicit  bool         // interface is wrapper for type set literal (non-interface T, ~T, or A|B)
        complete  bool         // indicates that obj, methods, and embeddeds are set and type set can be computed
 
        tset *_TypeSet // type set described by this interface, computed lazily
@@ -108,6 +109,9 @@ func (t *Interface) IsComparable() bool { return t.typeSet().IsComparable() }
 // set.
 func (t *Interface) IsMethodSet() bool { return t.typeSet().IsMethodSet() }
 
+// IsImplicit reports whether the interface t is a wrapper for a type set literal.
+func (t *Interface) IsImplicit() bool { return t.implicit }
+
 // Complete computes the interface's type set. It must be called by users of
 // NewInterfaceType and NewInterface after the interface's embedded types are
 // fully defined and before using the interface type in any way other than to
@@ -143,7 +147,6 @@ func (check *Checker) interfaceType(ityp *Interface, iface *ast.InterfaceType, d
 
        for _, f := range iface.Methods.List {
                if len(f.Names) == 0 {
-                       // We have an embedded type; possibly a union of types.
                        addEmbedded(f.Type.Pos(), parseUnion(check, flattenUnion(nil, f.Type)))
                        continue
                }

diff --git a/src/go/types/testdata/examples/typesets.go2 b/src/go/types/testdata/examples/typesets.go2
index 0a1b0f5cfc0d7e22ceed175825400c0a6f36809f..cf01072d8cb06003ea8a8e7a0a5a19fd86c716ff 100644 (file)
--- a/src/go/types/testdata/examples/typesets.go2
+++ b/src/go/types/testdata/examples/typesets.go2
@@ -46,3 +46,13 @@ func _() *int {
 // A type parameter may not be embedded in an interface;
 // so it can also not be used as a constraint.
 func _[A any, B A /* ERROR cannot use a type parameter as constraint */ ]() {}
+
+// Error messages refer to the type constraint as it appears in the source.
+// (No implicit interface should be exposed.)
+func _[T string](x T) T {
+       return x /* ERROR constrained by string */ * x
+}
+
+func _[T int|string](x T) T {
+       return x /* ERROR constrained by int|string */ * x
+}

diff --git a/src/go/types/typeparam.go b/src/go/types/typeparam.go
index 51bedc2b7d801bf1f3fe5b332c2cc6c02d043f7a..e2755cbbda2040ad237d0e9748fd11bdc04590db 100644 (file)
--- a/src/go/types/typeparam.go
+++ b/src/go/types/typeparam.go
@@ -108,6 +108,7 @@ func (t *TypeParam) iface() *Interface {
        // TODO(gri) mark it as implicit - see comment in Checker.bound
        if ityp == nil {
                ityp = NewInterfaceType(nil, []Type{bound})
+               ityp.implicit = true
                t.bound = ityp // update t.bound for next time (optimization)
        }
 

diff --git a/src/go/types/typestring.go b/src/go/types/typestring.go
index 4a087c4ed17af7994b6ce5c3a91c7bacc3fc9902..a0c78e8cc354aaae3a2779697f288ac8734e2ae7 100644 (file)
--- a/src/go/types/typestring.go
+++ b/src/go/types/typestring.go
@@ -191,6 +191,15 @@ func (w *typeWriter) typ(typ Type) {
                }
 
        case *Interface:
+               if t.implicit {
+                       if len(t.methods) == 0 && len(t.embeddeds) == 1 {
+                               w.typ(t.embeddeds[0])
+                               break
+                       }
+                       // Something's wrong with the implicit interface.
+                       // Print it as such and continue.
+                       w.string("/* implicit */ ")
+               }
                w.string("interface{")
                first := true
                for _, m := range t.methods {

diff --git a/src/go/types/universe.go b/src/go/types/universe.go
index 4d52242e6138e9cf2119b2b94dededaee7cd9d9d..519cf0b7078705900a30890bd0ce0eba2599b5e0 100644 (file)
--- a/src/go/types/universe.go
+++ b/src/go/types/universe.go
@@ -89,7 +89,7 @@ func defPredeclaredTypes() {
                res := NewVar(token.NoPos, nil, "", Typ[String])
                sig := NewSignatureType(nil, nil, nil, nil, NewTuple(res), false)
                err := NewFunc(token.NoPos, nil, "Error", sig)
-               ityp := &Interface{nil, obj, []*Func{err}, nil, nil, true, nil}
+               ityp := &Interface{nil, obj, []*Func{err}, nil, nil, false, true, nil}
                computeInterfaceTypeSet(nil, token.NoPos, ityp) // prevent races due to lazy computation of tset
                typ := NewNamed(obj, ityp, nil)
                sig.recv = NewVar(token.NoPos, nil, "", typ)
@@ -100,7 +100,7 @@ func defPredeclaredTypes() {
        {
                obj := NewTypeName(token.NoPos, nil, "comparable", nil)
                obj.setColor(black)
-               ityp := &Interface{nil, obj, nil, nil, nil, true, &_TypeSet{true, nil, allTermlist}}
+               ityp := &Interface{nil, obj, nil, nil, nil, false, true, &_TypeSet{true, nil, allTermlist}}
                NewNamed(obj, ityp, nil)
                def(obj)
        }