--- /dev/null
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package parser
+
+import (
+ "fmt"
+ "go/ast"
+ "go/scanner"
+ "go/token"
+ "os"
+ "path/filepath"
+ "strings"
+ "testing"
+)
+
+// TestResolution checks that identifiers are resolved to the declarations
+// annotated in the source, by comparing the positions of the resulting
+// Ident.Obj.Decl to positions marked in the source via special comments.
+//
+// In the test source, any comment prefixed with '=' or '@' (or both) marks the
+// previous token position as the declaration ('=') or a use ('@') of an
+// identifier. The text following '=' and '@' in the comment string is the
+// label to use for the location. Declaration labels must be unique within the
+// file, and use labels must refer to an existing declaration label. It's OK
+// for a comment to denote both the declaration and use of a label (e.g.
+// '=@foo'). Leading and trailing whitespace is ignored. Any comment not
+// beginning with '=' or '@' is ignored.
+func TestResolution(t *testing.T) {
+ dir := filepath.Join("testdata", "resolution")
+ fis, err := os.ReadDir(dir)
+ if err != nil {
+ t.Fatal(err)
+ }
+
+ for _, fi := range fis {
+ t.Run(fi.Name(), func(t *testing.T) {
+ fset := token.NewFileSet()
+ path := filepath.Join(dir, fi.Name())
+ src := readFile(path) // panics on failure
+ file, err := ParseFile(fset, path, src, 0)
+ if err != nil {
+ t.Fatal(err)
+ }
+
+ // Compare the positions of objects resolved during parsing (fromParser)
+ // to those annotated in source comments (fromComments).
+
+ handle := fset.File(file.Package)
+ fromParser := declsFromParser(file)
+ fromComments := declsFromComments(handle, src)
+
+ pos := func(pos token.Pos) token.Position {
+ p := handle.Position(pos)
+ // The file name is implied by the subtest, so remove it to avoid
+ // clutter in error messages.
+ p.Filename = ""
+ return p
+ }
+ for k, want := range fromComments {
+ if got := fromParser[k]; got != want {
+ t.Errorf("%s resolved to %s, want %s", pos(k), pos(got), pos(want))
+ }
+ delete(fromParser, k)
+ }
+ // What remains in fromParser are unexpected resolutions.
+ for k, got := range fromParser {
+ t.Errorf("%s resolved to %s, want no object", pos(k), pos(got))
+ }
+ })
+ }
+}
+
+// declsFromParser walks the file and collects the map associating an
+// identifier position with its declaration position.
+func declsFromParser(file *ast.File) map[token.Pos]token.Pos {
+ objmap := map[token.Pos]token.Pos{}
+ ast.Inspect(file, func(node ast.Node) bool {
+ if ident, _ := node.(*ast.Ident); ident != nil && ident.Obj != nil {
+ objmap[ident.Pos()] = ident.Obj.Pos()
+ }
+ return true
+ })
+ return objmap
+}
+
+// declsFromComments looks at comments annotating uses and declarations, and
+// maps each identifier use to its corresponding declaration. See the
+// description of these annotations in the documentation for TestResolution.
+func declsFromComments(handle *token.File, src []byte) map[token.Pos]token.Pos {
+ decls, uses := positionMarkers(handle, src)
+
+ objmap := make(map[token.Pos]token.Pos)
+ // Join decls and uses on name, to build the map of use->decl.
+ for name, posns := range uses {
+ declpos, ok := decls[name]
+ if !ok {
+ panic(fmt.Sprintf("missing declaration for %s", name))
+ }
+ for _, pos := range posns {
+ objmap[pos] = declpos
+ }
+ }
+ return objmap
+}
+
+// positionMarkers extracts named positions from the source denoted by comments
+// prefixed with '=' (declarations) and '@' (uses): for example '@foo' or
+// '=@bar'. It returns a map of name->position for declarations, and
+// name->position(s) for uses.
+func positionMarkers(handle *token.File, src []byte) (decls map[string]token.Pos, uses map[string][]token.Pos) {
+ var s scanner.Scanner
+ s.Init(handle, src, nil, scanner.ScanComments)
+ decls = make(map[string]token.Pos)
+ uses = make(map[string][]token.Pos)
+ var prev token.Pos // position of last non-comment, non-semicolon token
+
+scanFile:
+ for {
+ pos, tok, lit := s.Scan()
+ switch tok {
+ case token.EOF:
+ break scanFile
+ case token.COMMENT:
+ name, decl, use := annotatedObj(lit)
+ if len(name) > 0 {
+ if decl {
+ if _, ok := decls[name]; ok {
+ panic(fmt.Sprintf("duplicate declaration markers for %s", name))
+ }
+ decls[name] = prev
+ }
+ if use {
+ uses[name] = append(uses[name], prev)
+ }
+ }
+ case token.SEMICOLON:
+ // ignore automatically inserted semicolon
+ if lit == "\n" {
+ continue scanFile
+ }
+ fallthrough
+ default:
+ prev = pos
+ }
+ }
+ return decls, uses
+}
+
+func annotatedObj(lit string) (name string, decl, use bool) {
+ if lit[1] == '*' {
+ lit = lit[:len(lit)-2] // strip trailing */
+ }
+ lit = strings.TrimSpace(lit[2:])
+
+scanLit:
+ for idx, r := range lit {
+ switch r {
+ case '=':
+ decl = true
+ case '@':
+ use = true
+ default:
+ name = lit[idx:]
+ break scanLit
+ }
+ }
+ return
+}