internal/lsp: include declaration for references

A client can specify "IncludeDeclaration" in its ReferenceParams.
When they do so, we want to include the declaration, even if it was not
in the scope we searched for references.

Additionally, we also return the location of the declaration first in
the result array when it is included in the results.

Updates golang/go#32572

Change-Id: I12837cd98102ee8d531f0f4bac2fb7bded2564c0
Reviewed-on: https://go-review.googlesource.com/c/tools/+/184723
Run-TryBot: Suzy Mueller <suzmue@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>

internal/lsp/references.go

@@ -36,6 +36,18 @@ func (s *Server) references(ctx context.Context, params *protocol.ReferenceParam
 	if err != nil {
 		view.Session().Logger().Errorf(ctx, "no references for %s: %v", ident.Name, err)
 	}
+	if params.Context.IncludeDeclaration {
+		// The declaration of this identifier may not be in the
+		// scope that we search for references, so make sure
+		// it is added to the beginning of the list if IncludeDeclaration
+		// was specified.
+		references = append([]*source.ReferenceInfo{
+			&source.ReferenceInfo{
+				Range: ident.DeclarationRange(),
+			},
+		}, references...)
+	}
+
 	// Get the location of each reference to return as the result.
 	locations := make([]protocol.Location, 0, len(references))
 	seen := make(map[span.Span]bool)

internal/lsp/source/references.go

@@ -23,7 +23,7 @@ type ReferenceInfo struct {
 }
 
 // References returns a list of references for a given identifier within the packages
-// containing i.File.
+// containing i.File. Declarations appear first in the result.
 func (i *IdentifierInfo) References(ctx context.Context) ([]*ReferenceInfo, error) {
 	var references []*ReferenceInfo
 
@@ -57,13 +57,14 @@ func (i *IdentifierInfo) References(ctx context.Context) ([]*ReferenceInfo, erro
 			if obj == nil || obj.Pos() != i.decl.obj.Pos() {
 				continue
 			}
-			references = append(references, &ReferenceInfo{
+			// Add the declarations at the beginning of the references list.
+			references = append([]*ReferenceInfo{&ReferenceInfo{
 				Name:          ident.Name,
 				Range:         span.NewRange(i.File.FileSet(), ident.Pos(), ident.End()),
 				ident:         ident,
 				obj:           obj,
 				isDeclaration: true,
-			})
+			}}, references...)
 		}
 		for ident, obj := range info.Uses {
 			if obj == nil || obj.Pos() != i.decl.obj.Pos() {