internal/lsp: find references to package

Update References to detect if the package is referenced and a regtest to test within and external package references.

Updates golang/go#41567

Change-Id: I607a47bf15f1c9f8236336f795fcef081db49d6a
Reviewed-on: https://go-review.googlesource.com/c/tools/+/408714
Reviewed-by: Robert Findley <rfindley@google.com>
Run-TryBot: Dylan Le <dungtuanle@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>

gopls/internal/regtest/misc/references_test.go

@@ -5,6 +5,8 @@
 package misc
 
 import (
+	"fmt"
+	"strings"
 	"testing"
 
 	. "golang.org/x/tools/internal/lsp/regtest"
@@ -81,3 +83,89 @@ func _() {
 		}
 	})
 }
+
+func TestPackageReferences(t *testing.T) {
+	tests := []struct {
+		packageName  string
+		wantRefCount int
+		wantFiles    []string
+	}{
+		{
+			"lib1",
+			3,
+			[]string{
+				"main.go",
+				"lib1/a.go",
+				"lib1/b.go",
+			},
+		},
+		{
+			"lib2",
+			2,
+			[]string{
+				"main.go",
+				"lib2/a.go",
+			},
+		},
+	}
+
+	const files = `
+-- go.mod --
+module mod.com
+
+go 1.18
+-- lib1/a.go --
+package lib1
+
+const A = 1
+
+-- lib1/b.go --
+package lib1
+
+const B = 1
+
+-- lib2/a.go --
+package lib2
+
+const C = 1
+
+-- main.go --
+package main
+
+import (
+	"mod.com/lib1"
+	"mod.com/lib2"
+)
+
+func main() {
+	println("Hello")
+}
+`
+	Run(t, files, func(t *testing.T, env *Env) {
+		for _, test := range tests {
+			f := fmt.Sprintf("%s/a.go", test.packageName)
+			env.OpenFile(f)
+			pos := env.RegexpSearch(f, test.packageName)
+			refs := env.References(fmt.Sprintf("%s/a.go", test.packageName), pos)
+			if len(refs) != test.wantRefCount {
+				t.Fatalf("got %v reference(s), want %d", len(refs), test.wantRefCount)
+			}
+			var refURIs []string
+			for _, ref := range refs {
+				refURIs = append(refURIs, string(ref.URI))
+			}
+			for _, base := range test.wantFiles {
+				hasBase := false
+				for _, ref := range refURIs {
+					if strings.HasSuffix(ref, base) {
+						hasBase = true
+						break
+					}
+				}
+				if !hasBase {
+					t.Fatalf("got [%v], want reference ends with \"%v\"", strings.Join(refURIs, ","), base)
+				}
+			}
+		}
+	})
+}

internal/lsp/source/references.go

@@ -9,12 +9,15 @@ import (
 	"errors"
 	"fmt"
 	"go/ast"
+
 	"go/token"
 	"go/types"
 	"sort"
+	"strconv"
 
 	"golang.org/x/tools/internal/event"
 	"golang.org/x/tools/internal/lsp/protocol"
+	"golang.org/x/tools/internal/lsp/safetoken"
 	"golang.org/x/tools/internal/span"
 )
 
@@ -34,6 +37,63 @@ func References(ctx context.Context, s Snapshot, f FileHandle, pp protocol.Posit
 	ctx, done := event.Start(ctx, "source.References")
 	defer done()
 
+	// Find position of the package name declaration
+	pgf, err := s.ParseGo(ctx, f, ParseFull)
+	if err != nil {
+		return nil, err
+	}
+
+	cursorOffset, err := pgf.Mapper.Offset(pp)
+	if err != nil {
+		return nil, err
+	}
+
+	packageNameStart, err := safetoken.Offset(pgf.Tok, pgf.File.Name.Pos())
+	if err != nil {
+		return nil, err
+	}
+
+	packageNameEnd, err := safetoken.Offset(pgf.Tok, pgf.File.Name.End())
+	if err != nil {
+		return nil, err
+	}
+
+	if packageNameStart <= cursorOffset && cursorOffset < packageNameEnd {
+		renamingPkg, err := s.PackageForFile(ctx, f.URI(), TypecheckAll, NarrowestPackage)
+		if err != nil {
+			return nil, err
+		}
+
+		// Find external references to the package.
+		rdeps, err := s.GetReverseDependencies(ctx, renamingPkg.ID())
+		if err != nil {
+			return nil, err
+		}
+		var refs []*ReferenceInfo
+		for _, dep := range rdeps {
+			for _, f := range dep.CompiledGoFiles() {
+				for _, imp := range f.File.Imports {
+					if path, err := strconv.Unquote(imp.Path.Value); err == nil && path == renamingPkg.PkgPath() {
+						refs = append(refs, &ReferenceInfo{
+							Name:        pgf.File.Name.Name,
+							MappedRange: NewMappedRange(s.FileSet(), f.Mapper, imp.Pos(), imp.End()),
+						})
+					}
+				}
+			}
+		}
+
+		// Find internal references to the package within the package itself
+		for _, f := range renamingPkg.CompiledGoFiles() {
+			refs = append(refs, &ReferenceInfo{
+				Name:        pgf.File.Name.Name,
+				MappedRange: NewMappedRange(s.FileSet(), f.Mapper, f.File.Name.Pos(), f.File.Name.End()),
+			})
+		}
+
+		return refs, nil
+	}
+
 	qualifiedObjs, err := qualifiedObjsAtProtocolPos(ctx, s, f.URI(), pp)
 	// Don't return references for builtin types.
 	if errors.Is(err, errBuiltin) {