gopls/internal/lsp/source: reinstate equalOrigin for references check

This logic was dropped in CL 464902, but is necessary for correctly
resolving references to variables.

Fixes golang/go#61618

Change-Id: Iebe46339e5f6ac0230f7376e742d786bae2a7438
Reviewed-on: https://go-review.googlesource.com/c/tools/+/513780
Run-TryBot: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>

gopls/internal/lsp/source/references.go

@@ -580,9 +580,12 @@ func localReferences(pkg Package, targets map[types.Object]bool, correspond bool
 	// matches reports whether obj either is or corresponds to a target.
 	// (Correspondence is defined as usual for interface methods.)
 	matches := func(obj types.Object) bool {
-		if targets[obj] {
-			return true
-		} else if methodRecvs != nil && obj.Name() == methodName {
+		for target := range targets {
+			if equalOrigin(obj, target) {
+				return true
+			}
+		}
+		if methodRecvs != nil && obj.Name() == methodName {
 			if orecv := effectiveReceiver(obj); orecv != nil {
 				for _, mrecv := range methodRecvs {
 					if concreteImplementsIntf(orecv, mrecv) {
@@ -608,6 +611,13 @@ func localReferences(pkg Package, targets map[types.Object]bool, correspond bool
 	return nil
 }
 
+// equalOrigin reports whether obj1 and obj2 have equivalent origin object.
+// This may be the case even if obj1 != obj2, if one or both of them is
+// instantiated.
+func equalOrigin(obj1, obj2 types.Object) bool {
+	return obj1.Pkg() == obj2.Pkg() && obj1.Pos() == obj2.Pos() && obj1.Name() == obj2.Name()
+}
+
 // effectiveReceiver returns the effective receiver type for method-set
 // comparisons for obj, if it is a method, or nil otherwise.
 func effectiveReceiver(obj types.Object) types.Type {

gopls/internal/regtest/marker/testdata/references/issue61618.txt

@@ -0,0 +1,39 @@
+Regression test for 'references' bug golang/go#61618:
+references to instantiated fields were missing.
+
+-- flags --
+-min_go=go1.18
+
+-- go.mod --
+module example.com
+go 1.18
+
+-- a.go --
+package a
+
+// This file is adapted from the example in the issue.
+
+type builder[S ~[]F, F ~string] struct {
+	name string
+	elements S //@loc(def, "elements"), refs(def, def, assign, use)
+	elemData map[F][]ElemData[F]
+}
+
+type ElemData[F ~string] struct {
+  Name F
+}
+
+type BuilderImpl[S ~[]F, F ~string] struct{ builder[S, F] }
+
+func NewBuilderImpl[S ~[]F, F ~string](name string)  *BuilderImpl[S, F] {
+  impl := &BuilderImpl[S,F]{
+	builder[S, F]{
+	  name: name,
+	  elements: S{}, //@loc(assign, "elements"), refs(assign, def, assign, use)
+	  elemData: map[F][]ElemData[F]{},
+	},
+  }
+
+  _ = impl.elements //@loc(use, "elements"), refs(use, def, assign, use)
+  return impl
+}