go/token: add (*File).End method

Also, use it in a number of places.

+ test, api, relnote

Fixes #75849

Change-Id: I44acf5b8190b964fd3975009aa407d7c82cee19b
Reviewed-on: https://go-review.googlesource.com/c/go/+/720061
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Robert Griesemer <gri@google.com>

api/next/75849.txt

@@ -0,0 +1 @@
+pkg go/token, method (*File) End() Pos #75849

doc/next/6-stdlib/99-minor/go/token/75849.md

@@ -0,0 +1 @@
+The new [File.End] convenience method returns the file's end position.

src/go/ast/issues_test.go

@@ -30,10 +30,10 @@ func TestIssue33649(t *testing.T) {
 			tf = f
 			return true
 		})
-		tfEnd := tf.Base() + tf.Size()
+		tfEnd := tf.End()
 
 		fd := f.Decls[len(f.Decls)-1].(*ast.FuncDecl)
-		fdEnd := int(fd.End())
+		fdEnd := fd.End()
 
 		if fdEnd != tfEnd {
 			t.Errorf("%q: got fdEnd = %d; want %d (base = %d, size = %d)", src, fdEnd, tfEnd, tf.Base(), tf.Size())

src/go/parser/interface.go

@@ -120,7 +120,7 @@ func ParseFile(fset *token.FileSet, filename string, src any, mode Mode) (f *ast
 		// Ensure the start/end are consistent,
 		// whether parsing succeeded or not.
 		f.FileStart = token.Pos(file.Base())
-		f.FileEnd = token.Pos(file.Base() + file.Size())
+		f.FileEnd = file.End()
 
 		p.errors.Sort()
 		err = p.errors.Err()

src/go/token/position.go

@@ -127,6 +127,11 @@ func (f *File) Size() int {
 	return f.size
 }
 
+// End returns the end position of file f as registered with AddFile.
+func (f *File) End() Pos {
+	return Pos(f.base + f.size)
+}
+
 // LineCount returns the number of lines in file f.
 func (f *File) LineCount() int {
 	f.mutex.Lock()

src/go/token/position_test.go

@@ -572,7 +572,7 @@ func fsetString(fset *FileSet) string {
 	buf.WriteRune('{')
 	sep := ""
 	fset.Iterate(func(f *File) bool {
-		fmt.Fprintf(&buf, "%s%s:%d-%d", sep, f.Name(), f.Base(), f.Base()+f.Size())
+		fmt.Fprintf(&buf, "%s%s:%d-%d", sep, f.Name(), f.Base(), f.End())
 		sep = " "
 		return true
 	})
@@ -643,3 +643,11 @@ func TestRemovedFileFileReturnsNil(t *testing.T) {
 		}
 	}
 }
+
+func TestFile_End(t *testing.T) {
+	f := NewFileSet().AddFile("a.go", 100, 42)
+	got := fmt.Sprintf("%d, %d", f.Base(), f.End())
+	if want := "100, 142"; got != want {
+		t.Errorf("Base, End = %s, want %s", got, want)
+	}
+}

src/go/token/tree.go

@@ -313,8 +313,8 @@ func (t *tree) add(file *File) {
 	}
 	if prev := (*pos).file; prev != file {
 		panic(fmt.Sprintf("file %s (%d-%d) overlaps with file %s (%d-%d)",
-			prev.Name(), prev.Base(), prev.Base()+prev.Size(),
+			prev.Name(), prev.Base(), prev.End(),
-			file.Name(), file.Base(), file.Base()+file.Size()))
+			file.Name(), file.Base(), file.End()))
 	}
 }
 

src/go/types/resolver.go

@@ -247,7 +247,7 @@ func (check *Checker) collectObjects() {
 		// Be conservative and use the *ast.File extent if we don't have a *token.File.
 		pos, end := file.Pos(), file.End()
 		if f := check.fset.File(file.Pos()); f != nil {
-			pos, end = token.Pos(f.Base()), token.Pos(f.Base()+f.Size())
+			pos, end = token.Pos(f.Base()), f.End()
 		}
 		fileScope := NewScope(pkg.scope, pos, end, check.filename(fileNo))
 		fileScopes[fileNo] = fileScope