internal: simplify GetPackageInfo into an *ast.Package getter

The Index field was only used by the export package when obtaining
the attributes attached to the declarations to export.
We can use the length of ast.Package.Preamble instead.

The Name field reflected ast.Package.Name.Name when the package
was non-nil; so we can do that directly in the callers.
The resulting code is no more complex than before.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: I9e5c291bc01687fd2f9472638748f8abef417588
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1200971
Unity-Result: CUE porcuepine <[email protected]>
Reviewed-by: Roger Peppe <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>

Author: mvdan

Diff for: cmd/cue/cmd/orphans.go

@@ -274,8 +274,8 @@ func placeOrphans(b *buildPlan, d *encoding.Decoder, pkg string, objs ...*ast.Fi
 		} else {
 			field := &ast.Field{Label: labels[0]}
 			f.Decls = append(f.Decls, field)
-			if p := internal.GetPackageInfo(file).Package; p != nil {
-				astutil.CopyComments(field, p)
+			if pkg := internal.Package(file); pkg != nil {
+				astutil.CopyComments(field, pkg)
 			}
 			for _, e := range labels[1:] {
 				newField := &ast.Field{Label: e}

Diff for: cue/marshal.go

@@ -151,13 +151,12 @@ func (r *Runtime) Marshal(values ...InstanceOrValue) (b []byte, err error) {
 		})
 
 		if inst.PkgName != "" {
-			pi := internal.GetPackageInfo(file)
-			if pi.Package == nil {
+			if pkg := internal.Package(file); pkg == nil {
 				pkg := &ast.Package{Name: ast.NewIdent(inst.PkgName)}
 				file.Decls = append([]ast.Decl{pkg}, file.Decls...)
-			} else if pi.Name != inst.PkgName {
+			} else if pkg.Name.Name != inst.PkgName {
 				// pi is guaranteed to be generated by Def, so it is "safe" to modify.
-				pi.Package.Name = ast.NewIdent(inst.PkgName)
+				pkg.Name = ast.NewIdent(inst.PkgName)
 			}
 		}
 

Diff for: internal/core/export/extract.go

@@ -179,8 +179,7 @@ func extractDeclAttrs(attrs []*ast.Attribute, n ast.Node) []*ast.Attribute {
 	switch x := n.(type) {
 	case nil:
 	case *ast.File:
-		info := internal.GetPackageInfo(x)
-		attrs = appendDeclAttrs(attrs, x.Decls[info.Index:])
+		attrs = appendDeclAttrs(attrs, x.Decls[len(x.Preamble()):])
 	case *ast.StructLit:
 		attrs = appendDeclAttrs(attrs, x.Elts)
 	}

Diff for: internal/internal.go

@@ -132,36 +132,31 @@ func ListEllipsis(n *ast.ListLit) (elts []ast.Expr, e *ast.Ellipsis) {
 	return elts, e
 }
 
-type PkgInfo struct {
-	Package *ast.Package
-	Index   int // position in File.Decls
-	Name    string
-}
-
-func GetPackageInfo(f *ast.File) PkgInfo {
-	for i, d := range f.Decls {
-		switch x := d.(type) {
+// Package finds the package declaration from the preamble of a file.
+func Package(f *ast.File) *ast.Package {
+	for _, d := range f.Decls {
+		switch d := d.(type) {
 		case *ast.CommentGroup:
 		case *ast.Attribute:
 		case *ast.Package:
-			if x.Name == nil {
-				return PkgInfo{}
+			if d.Name == nil { // malformed package declaration
+				return nil
 			}
-			return PkgInfo{x, i, x.Name.Name}
+			return d
 		default:
-			return PkgInfo{}
+			return nil
 		}
 	}
-	return PkgInfo{}
+	return nil
 }
 
 func SetPackage(f *ast.File, name string, overwrite bool) {
-	if pi := GetPackageInfo(f); pi.Package != nil {
-		if !overwrite || pi.Name == name {
+	if pkg := Package(f); pkg != nil {
+		if !overwrite || pkg.Name.Name == name {
 			return
 		}
 		ident := ast.NewIdent(name)
-		astutil.CopyMeta(ident, pi.Package.Name)
+		astutil.CopyMeta(ident, pkg.Name)
 		return
 	}
 
@@ -223,7 +218,7 @@ func NewComment(isDoc bool, s string) *ast.CommentGroup {
 
 func FileComment(f *ast.File) *ast.CommentGroup {
 	var cgs []*ast.CommentGroup
-	if pkg := GetPackageInfo(f).Package; pkg != nil {
+	if pkg := Package(f); pkg != nil {
 		cgs = pkg.Comments()
 	} else if cgs = f.Comments(); len(cgs) > 0 {
 		// Use file comment.