go/printer: predict the position of the '.' in SelectorExpr #70982

Original file line number	Diff line number	Diff line change
Expand Up		@@ -1156,6 +1156,14 @@ func (p *printer) possibleSelectorExpr(expr ast.Expr, prec1, depth int) bool {
		// multiple lines.
		func (p printer) selectorExpr(x ast.SelectorExpr, depth int, isMethod bool) bool {
		p.expr1(x.X, token.HighestPrec, depth)

	// We don't have the position of the dot, so we have to predict it,
	// to avoid issues with comment handling.
	// See https://go.dev/issue/70978 and TestIssue70978 for more details.
	if x.Sel.Pos().IsValid() && p.pos.Offset > p.posFor(x.Sel.Pos()).Offset {
	p.setPos(x.Sel.Pos())
	}

		p.print(token.PERIOD)
		if line := p.lineFor(x.Sel.Pos()); p.pos.IsValid() && p.pos.Line < line {
		p.print(indent, newline)
Expand Down

75 changes: 75 additions & 0 deletions src/go/printer/printer_test.go

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -16,6 +16,7 @@ import (
		"io"
		"os"
		"path/filepath"
	"strings"
		"testing"
		"time"
		)
Expand Down Expand Up		@@ -863,3 +864,77 @@ func TestEmptyDecl(t *testing.T) { // issue 63566
		}
		}
		}

	func TestIssue70978(t *testing.T) {
	cases := []struct {
	src string
	want string
	newName string
	}{
	{
	newName: "someotherfmtpackage",
	src: `package main

	func main() {
	// comment

	fmt.Println() // Comment
	}
	`,
	want: `package main

	func main() {
	// comment

	someotherfmtpackage.Println() // Comment
	}
	`,
	},
	{
	newName: "someotherfmtpkg",
	src: `package main

	func main() {
	// comment

	fmt.Println() // Comment
	}
	`,
	want: `package main

	func main() {
	// comment

	someotherfmtpkg.Println() // Comment
	}
	`,
	},
	}

	for _, tt := range cases {
	fset := token.NewFileSet()
	f, err := parser.ParseFile(fset, "test.go", tt.src, parser.SkipObjectResolution\|parser.ParseComments)
	if err != nil {
	t.Fatal(err)
	}

	ast.Inspect(f, func(n ast.Node) bool {
	switch n := n.(type) {
	case *ast.SelectorExpr:
	switch x := n.X.(type) {
	case *ast.Ident:
	x.Name = tt.newName
	}
	}
	return true
	})

	var b strings.Builder
	config := Config{Mode: UseSpaces \| TabIndent, Tabwidth: 8}
	config.Fprint(&b, fset, f)
	got := b.String()
	if got != tt.want {
	t.Errorf("unexpected Fprint output:\n%s\nwant:\n%s", got, tt.want)
	}
	}
	}

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