go.tools/go/types: add Scope.comment as a debugging aid.

e.g. file foo.go scope {...}
     package math scope {...}
     function f scope {...}
     if scope {...}

LGTM=gri
R=gri
CC=golang-codereviews
https://golang.org/cl/74320043

go/types/check.go

@@ -7,6 +7,7 @@
 package types
 
 import (
+	"fmt"
 	"go/ast"
 	"go/token"
 
@@ -164,7 +165,7 @@ func (check *checker) initFiles(files []*ast.File) {
 
 	// determine package name, files, and set up file scopes, dotImports maps
 	pkg := check.pkg
-	for _, file := range files {
+	for i, file := range files {
 		switch name := file.Name.Name; pkg.name {
 		case "":
 			pkg.name = name
@@ -172,7 +173,13 @@ func (check *checker) initFiles(files []*ast.File) {
 
 		case name:
 			check.files = append(check.files, file)
-			fileScope := NewScope(pkg.scope)
+			var comment string
+			if pos := file.Pos(); pos.IsValid() {
+				comment = "file " + check.fset.File(pos).Name()
+			} else {
+				comment = fmt.Sprintf("file[%d]", i)
+			}
+			fileScope := NewScope(pkg.scope, comment)
 			check.recordScope(file, fileScope)
 			check.fileScopes = append(check.fileScopes, fileScope)
 			check.dotImports = append(check.dotImports, nil) // element (map) is lazily allocated

go/types/labels.go

@@ -12,7 +12,7 @@ import (
 // labels checks correct label use in body.
 func (check *checker) labels(body *ast.BlockStmt) {
 	// set of all labels in this body
-	all := NewScope(nil)
+	all := NewScope(nil, "label")
 
 	fwdJumps := check.blockBranches(all, nil, nil, body.List)
 

go/types/package.go

@@ -19,7 +19,8 @@ type Package struct {
 // NewPackage returns a new Package for the given package path and name.
 // The package is not complete and contains no explicit imports.
 func NewPackage(path, name string) *Package {
-	return &Package{path: path, name: name, scope: NewScope(Universe)}
+	scope := NewScope(Universe, fmt.Sprintf("package %q", path))
+	return &Package{path: path, name: name, scope: scope}
 }
 
 // Path returns the package path.

go/types/scope.go

@@ -24,13 +24,14 @@ import (
 type Scope struct {
 	parent   *Scope
 	children []*Scope
+	comment  string            // for debugging only
 	elems    map[string]Object // lazily allocated
 }
 
 // NewScope returns a new, empty scope contained in the given parent
-// scope, if any.
+// scope, if any.  The comment is for debugging only.
-func NewScope(parent *Scope) *Scope {
+func NewScope(parent *Scope, comment string) *Scope {
-	s := &Scope{parent: parent}
+	s := &Scope{parent: parent, comment: comment}
 	// don't add children to Universe scope!
 	if parent != nil && parent != Universe {
 		parent.children = append(parent.children, s)
@@ -118,12 +119,13 @@ func (s *Scope) WriteTo(w io.Writer, n int, recurse bool) {
 	const ind = ".  "
 	indn := strings.Repeat(ind, n)
 
+	fmt.Fprintf(w, "%s%s scope %p {", indn, s.comment, s)
 	if len(s.elems) == 0 {
-		fmt.Fprintf(w, "%sscope %p {}\n", indn, s)
+		fmt.Fprintf(w, "}\n")
 		return
 	}
 
-	fmt.Fprintf(w, "%sscope %p {\n", indn, s)
+	fmt.Fprintln(w)
 	indn1 := indn + ind
 	for _, name := range s.Names() {
 		fmt.Fprintf(w, "%s%s\n", indn1, s.elems[name])

go/types/stmt.go

@@ -118,8 +118,8 @@ func (check *checker) multipleDefaults(list []ast.Stmt) {
 	}
 }
 
-func (check *checker) openScope(s ast.Stmt) {
+func (check *checker) openScope(s ast.Stmt, comment string) {
-	scope := NewScope(check.scope)
+	scope := NewScope(check.scope, comment)
 	check.recordScope(s, scope)
 	check.scope = scope
 }
@@ -366,13 +366,13 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 		}
 
 	case *ast.BlockStmt:
-		check.openScope(s)
+		check.openScope(s, "block")
 		defer check.closeScope()
 
 		check.stmtList(inner, s.List)
 
 	case *ast.IfStmt:
-		check.openScope(s)
+		check.openScope(s, "if")
 		defer check.closeScope()
 
 		check.initStmt(s.Init)
@@ -388,7 +388,7 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 
 	case *ast.SwitchStmt:
 		inner |= inBreakable
-		check.openScope(s)
+		check.openScope(s, "switch")
 		defer check.closeScope()
 
 		check.initStmt(s.Init)
@@ -415,7 +415,7 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 			if x.mode != invalid {
 				check.caseValues(x, clause.List)
 			}
-			check.openScope(clause)
+			check.openScope(clause, "case")
 			inner := inner
 			if i+1 < len(s.Body.List) {
 				inner |= fallthroughOk
@@ -426,7 +426,7 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 
 	case *ast.TypeSwitchStmt:
 		inner |= inBreakable
-		check.openScope(s)
+		check.openScope(s, "type switch")
 		defer check.closeScope()
 
 		check.initStmt(s.Init)
@@ -493,7 +493,7 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 			}
 			// Check each type in this type switch case.
 			T := check.caseTypes(&x, xtyp, clause.List, seen)
-			check.openScope(clause)
+			check.openScope(clause, "case")
 			// If lhs exists, declare a corresponding variable in the case-local scope.
 			if lhs != nil {
 				// spec: "The TypeSwitchGuard may include a short variable declaration.
@@ -567,7 +567,7 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 				continue
 			}
 
-			check.openScope(s)
+			check.openScope(s, "case")
 			defer check.closeScope()
 			if clause.Comm != nil {
 				check.stmt(inner, clause.Comm)
@@ -577,7 +577,7 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 
 	case *ast.ForStmt:
 		inner |= inBreakable | inContinuable
-		check.openScope(s)
+		check.openScope(s, "for")
 		defer check.closeScope()
 
 		check.initStmt(s.Init)
@@ -593,7 +593,7 @@ func (check *checker) stmt(ctxt stmtContext, s ast.Stmt) {
 
 	case *ast.RangeStmt:
 		inner |= inBreakable | inContinuable
-		check.openScope(s)
+		check.openScope(s, "for")
 		defer check.closeScope()
 
 		// check expression to iterate over

go/types/typexpr.go

@@ -141,7 +141,7 @@ func (check *checker) typ(e ast.Expr) Type {
 
 // funcType type-checks a function or method type and returns its signature.
 func (check *checker) funcType(sig *Signature, recv *ast.FieldList, ftyp *ast.FuncType) *Signature {
-	scope := NewScope(check.scope)
+	scope := NewScope(check.scope, "function")
 	check.recordScope(ftyp, scope)
 
 	recv_, _ := check.collectParams(scope, recv, false)

go/types/universe.go

@@ -177,7 +177,7 @@ func DefPredeclaredTestFuncs() {
 }
 
 func init() {
-	Universe = NewScope(nil)
+	Universe = NewScope(nil, "universe")
 	Unsafe = NewPackage("unsafe", "unsafe")
 	Unsafe.complete = true