go/internal/gcimporter: allow reusing empty interfaces on the RHS of

type decls This is a port of CL 367851 to x/tools. The test set-up is slightly different; I added a TODO to converge. Updates golang/go#49888 Change-Id: I31a63c1fc8f9a78526d8eea05fd01dae35770b5f Reviewed-on: https://go-review.googlesource.com/c/tools/+/368354 Trust: Robert Findley <[email protected]> Run-TryBot: Robert Findley <[email protected]> gopls-CI: kokoro <[email protected]> TryBot-Result: Go Bot <[email protected]> Reviewed-by: Robert Griesemer <[email protected]>
golang · Dec 1, 2021 · df48029 · df48029
1 parent d99d6fa
commit df48029
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Showing 2 changed files with 23 additions and 2 deletions.
diff --git a/go/internal/gcimporter/iexport_go118_test.go b/go/internal/gcimporter/iexport_go118_test.go
@@ -23,10 +23,13 @@ import (
 	"golang.org/x/tools/go/internal/gcimporter"
 )
 
+// TODO(rfindley): migrate this to testdata, as has been done in the standard library.
 func TestGenericExport(t *testing.T) {
 	const src = `
 package generic
 
+type Any any
+
 type T[A, B any] struct { Left A; Right B }
 
 var X T[int, string] = T[int, string]{1, "hi"}

diff --git a/go/internal/gcimporter/iimport.go b/go/internal/gcimporter/iimport.go
@@ -331,7 +331,7 @@ func (p *iimporter) pkgAt(off uint64) *types.Package {
 }
 
 func (p *iimporter) typAt(off uint64, base *types.Named) types.Type {
-	if t, ok := p.typCache[off]; ok && (base == nil || !isInterface(t)) {
+	if t, ok := p.typCache[off]; ok && canReuse(base, t) {
 		return t
 	}
 
@@ -343,12 +343,30 @@ func (p *iimporter) typAt(off uint64, base *types.Named) types.Type {
 	r.declReader.Reset(p.declData[off-predeclReserved:])
 	t := r.doType(base)
 
-	if base == nil || !isInterface(t) {
+	if canReuse(base, t) {
 		p.typCache[off] = t
 	}
 	return t
 }
 
+// canReuse reports whether the type rhs on the RHS of the declaration for def
+// may be re-used.
+//
+// Specifically, if def is non-nil and rhs is an interface type with methods, it
+// may not be re-used because we have a convention of setting the receiver type
+// for interface methods to def.
+func canReuse(def *types.Named, rhs types.Type) bool {
+	if def == nil {
+		return true
+	}
+	iface, _ := rhs.(*types.Interface)
+	if iface == nil {
+		return true
+	}
+	// Don't use iface.Empty() here as iface may not be complete.
+	return iface.NumEmbeddeds() == 0 && iface.NumExplicitMethods() == 0
+}
+
 type importReader struct {
 	p          *iimporter
 	declReader bytes.Reader