// Copyright 2009 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 scanner

import (
	"fmt"
	"go/token"
	"os"
	"path/filepath"
	"runtime"
	"slices"
	"strings"
	"testing"
)

var fset = token.NewFileSet()

const /* class */ (
	special = iota
	literal
	operator
	keyword
)

func tokenclass(tok token.Token) int {
	switch {
	case tok.IsLiteral():
		return literal
	case tok.IsOperator():
		return operator
	case tok.IsKeyword():
		return keyword
	}
	return special
}

type elt struct {
	tok   token.Token
	lit   string
	class int
}

var tokens = []elt{
	// Special tokens
	{token.COMMENT, "/* a comment */", special},
	{token.COMMENT, "// a comment \n", special},
	{token.COMMENT, "/*\r*/", special},
	{token.COMMENT, "/**\r/*/", special}, // issue 11151
	{token.COMMENT, "/**\r\r/*/", special},
	{token.COMMENT, "//\r\n", special},

	// Identifiers and basic type literals
	{token.IDENT, "foobar", literal},
	{token.IDENT, "a۰۱۸", literal},
	{token.IDENT, "foo६४", literal},
	{token.IDENT, "bar９８７６", literal},
	{token.IDENT, "ŝ", literal},    // was bug (issue 4000)
	{token.IDENT, "ŝfoo", literal}, // was bug (issue 4000)
	{token.INT, "0", literal},
	{token.INT, "1", literal},
	{token.INT, "123456789012345678890", literal},
	{token.INT, "01234567", literal},
	{token.INT, "0xcafebabe", literal},
	{token.FLOAT, "0.", literal},
	{token.FLOAT, ".0", literal},
	{token.FLOAT, "3.14159265", literal},
	{token.FLOAT, "1e0", literal},
	{token.FLOAT, "1e+100", literal},
	{token.FLOAT, "1e-100", literal},
	{token.FLOAT, "2.71828e-1000", literal},
	{token.IMAG, "0i", literal},
	{token.IMAG, "1i", literal},
	{token.IMAG, "012345678901234567889i", literal},
	{token.IMAG, "123456789012345678890i", literal},
	{token.IMAG, "0.i", literal},
	{token.IMAG, ".0i", literal},
	{token.IMAG, "3.14159265i", literal},
	{token.IMAG, "1e0i", literal},
	{token.IMAG, "1e+100i", literal},
	{token.IMAG, "1e-100i", literal},
	{token.IMAG, "2.71828e-1000i", literal},
	{token.CHAR, "'a'", literal},
	{token.CHAR, "'\\000'", literal},
	{token.CHAR, "'\\xFF'", literal},
	{token.CHAR, "'\\uff16'", literal},
	{token.CHAR, "'\\U0000ff16'", literal},
	{token.STRING, "`foobar`", literal},
	{token.STRING, "`" + `foo
	                        bar` +
		"`",
		literal,
	},
	{token.STRING, "`\r`", literal},
	{token.STRING, "`foo\r\nbar`", literal},

	// Operators and delimiters
	{token.ADD, "+", operator},
	{token.SUB, "-", operator},
	{token.MUL, "*", operator},
	{token.QUO, "/", operator},
	{token.REM, "%", operator},

	{token.AND, "&", operator},
	{token.OR, "|", operator},
	{token.XOR, "^", operator},
	{token.SHL, "<<", operator},
	{token.SHR, ">>", operator},
	{token.AND_NOT, "&^", operator},

	{token.ADD_ASSIGN, "+=", operator},
	{token.SUB_ASSIGN, "-=", operator},
	{token.MUL_ASSIGN, "*=", operator},
	{token.QUO_ASSIGN, "/=", operator},
	{token.REM_ASSIGN, "%=", operator},

	{token.AND_ASSIGN, "&=", operator},
	{token.OR_ASSIGN, "|=", operator},
	{token.XOR_ASSIGN, "^=", operator},
	{token.SHL_ASSIGN, "<<=", operator},
	{token.SHR_ASSIGN, ">>=", operator},
	{token.AND_NOT_ASSIGN, "&^=", operator},

	{token.LAND, "&&", operator},
	{token.LOR, "||", operator},
	{token.ARROW, "<-", operator},
	{token.INC, "++", operator},
	{token.DEC, "--", operator},

	{token.EQL, "==", operator},
	{token.LSS, "<", operator},
	{token.GTR, ">", operator},
	{token.ASSIGN, "=", operator},
	{token.NOT, "!", operator},

	{token.NEQ, "!=", operator},
	{token.LEQ, "<=", operator},
	{token.GEQ, ">=", operator},
	{token.DEFINE, ":=", operator},
	{token.ELLIPSIS, "...", operator},

	{token.LPAREN, "(", operator},
	{token.LBRACK, "[", operator},
	{token.LBRACE, "{", operator},
	{token.COMMA, ",", operator},
	{token.PERIOD, ".", operator},

	{token.RPAREN, ")", operator},
	{token.RBRACK, "]", operator},
	{token.RBRACE, "}", operator},
	{token.SEMICOLON, ";", operator},
	{token.COLON, ":", operator},
	{token.TILDE, "~", operator},

	// Keywords
	{token.BREAK, "break", keyword},
	{token.CASE, "case", keyword},
	{token.CHAN, "chan", keyword},
	{token.CONST, "const", keyword},
	{token.CONTINUE, "continue", keyword},

	{token.DEFAULT, "default", keyword},
	{token.DEFER, "defer", keyword},
	{token.ELSE, "else", keyword},
	{token.FALLTHROUGH, "fallthrough", keyword},
	{token.FOR, "for", keyword},

	{token.FUNC, "func", keyword},
	{token.GO, "go", keyword},
	{token.GOTO, "goto", keyword},
	{token.IF, "if", keyword},
	{token.IMPORT, "import", keyword},

	{token.INTERFACE, "interface", keyword},
	{token.MAP, "map", keyword},
	{token.PACKAGE, "package", keyword},
	{token.RANGE, "range", keyword},
	{token.RETURN, "return", keyword},

	{token.SELECT, "select", keyword},
	{token.STRUCT, "struct", keyword},
	{token.SWITCH, "switch", keyword},
	{token.TYPE, "type", keyword},
	{token.VAR, "var", keyword},
}

const whitespace = "  \t  \n\n\n" // to separate tokens

var source = func() []byte {
	var src []byte
	for _, t := range tokens {
		src = append(src, t.lit...)
		src = append(src, whitespace...)
	}
	return src
}()

func newlineCount(s string) int {
	n := 0
	for i := 0; i < len(s); i++ {
		if s[i] == '\n' {
			n++
		}
	}
	return n
}

func checkPos(t *testing.T, lit string, p token.Pos, expected token.Position) {
	pos := fset.Position(p)
	// Check cleaned filenames so that we don't have to worry about
	// different os.PathSeparator values.
	if pos.Filename != expected.Filename && filepath.Clean(pos.Filename) != filepath.Clean(expected.Filename) {
		t.Errorf("bad filename for %q: got %s, expected %s", lit, pos.Filename, expected.Filename)
	}
	if pos.Offset != expected.Offset {
		t.Errorf("bad position for %q: got %d, expected %d", lit, pos.Offset, expected.Offset)
	}
	if pos.Line != expected.Line {
		t.Errorf("bad line for %q: got %d, expected %d", lit, pos.Line, expected.Line)
	}
	if pos.Column != expected.Column {
		t.Errorf("bad column for %q: got %d, expected %d", lit, pos.Column, expected.Column)
	}
}

// Verify that calling Scan() provides the correct results.
func TestScan(t *testing.T) {
	whitespace_linecount := newlineCount(whitespace)

	// error handler
	eh := func(_ token.Position, msg string) {
		t.Errorf("error handler called (msg = %s)", msg)
	}

	// verify scan
	var s Scanner
	s.Init(fset.AddFile("", fset.Base(), len(source)), source, eh, ScanComments|dontInsertSemis)

	// set up expected position
	epos := token.Position{
		Filename: "",
		Offset:   0,
		Line:     1,
		Column:   1,
	}

	index := 0
	for {
		pos, tok, lit := s.Scan()

		// check position
		if tok == token.EOF {
			// correction for EOF
			epos.Line = newlineCount(string(source))
			epos.Column = 2
		}
		checkPos(t, lit, pos, epos)

		// check token
		e := elt{token.EOF, "", special}
		if index < len(tokens) {
			e = tokens[index]
			index++
		}
		if tok != e.tok {
			t.Errorf("bad token for %q: got %s, expected %s", lit, tok, e.tok)
		}

		// check token class
		if tokenclass(tok) != e.class {
			t.Errorf("bad class for %q: got %d, expected %d", lit, tokenclass(tok), e.class)
		}

		// check literal
		elit := ""
		switch e.tok {
		case token.COMMENT:
			// no CRs in comments
			elit = string(stripCR([]byte(e.lit), e.lit[1] == '*'))
			//-style comment literal doesn't contain newline
			if elit[1] == '/' {
				elit = elit[0 : len(elit)-1]
			}
		case token.IDENT:
			elit = e.lit
		case token.SEMICOLON:
			elit = ";"
		default:
			if e.tok.IsLiteral() {
				// no CRs in raw string literals
				elit = e.lit
				if elit[0] == '`' {
					elit = string(stripCR([]byte(elit), false))
				}
			} else if e.tok.IsKeyword() {
				elit = e.lit
			}
		}
		if lit != elit {
			t.Errorf("bad literal for %q: got %q, expected %q", lit, lit, elit)
		}

		if tok == token.EOF {
			break
		}

		// update position
		epos.Offset += len(e.lit) + len(whitespace)
		epos.Line += newlineCount(e.lit) + whitespace_linecount

	}

	if s.ErrorCount != 0 {
		t.Errorf("found %d errors", s.ErrorCount)
	}
}

func TestStripCR(t *testing.T) {
	for _, test := range []struct{ have, want string }{
		{"//\n", "//\n"},
		{"//\r\n", "//\n"},
		{"//\r\r\r\n", "//\n"},
		{"//\r*\r/\r\n", "//*/\n"},
		{"/**/", "/**/"},
		{"/*\r/*/", "/*/*/"},
		{"/*\r*/", "/**/"},
		{"/**\r/*/", "/**\r/*/"},
		{"/*\r/\r*\r/*/", "/*/*\r/*/"},
		{"/*\r\r\r\r*/", "/**/"},
	} {
		got := string(stripCR([]byte(test.have), len(test.have) >= 2 && test.have[1] == '*'))
		if got != test.want {
			t.Errorf("stripCR(%q) = %q; want %q", test.have, got, test.want)
		}
	}
}

func checkSemi(t *testing.T, input, want string, mode Mode) {
	if mode&ScanComments == 0 {
		want = strings.ReplaceAll(want, "COMMENT ", "")
		want = strings.ReplaceAll(want, " COMMENT", "") // if at end
		want = strings.ReplaceAll(want, "COMMENT", "")  // if sole token
	}

	file := fset.AddFile("TestSemis", fset.Base(), len(input))
	var scan Scanner
	scan.Init(file, []byte(input), nil, mode)
	var tokens []string
	for {
		pos, tok, lit := scan.Scan()
		if tok == token.EOF {
			break
		}
		if tok == token.SEMICOLON && lit != ";" {
			// Artificial semicolon:
			// assert that position is EOF or that of a newline.
			off := file.Offset(pos)
			if off != len(input) && input[off] != '\n' {
				t.Errorf("scanning <<%s>>, got SEMICOLON at offset %d, want newline or EOF", input, off)
			}
		}
		lit = tok.String() // "\n" => ";"
		tokens = append(tokens, lit)
	}
	if got := strings.Join(tokens, " "); got != want {
		t.Errorf("scanning <<%s>>, got [%s], want [%s]", input, got, want)
	}
}

var semicolonTests = [...]struct{ input, want string }{
	{"", ""},
	{"\ufeff;", ";"}, // first BOM is ignored
	{";", ";"},
	{"foo\n", "IDENT ;"},
	{"123\n", "INT ;"},
	{"1.2\n", "FLOAT ;"},
	{"'x'\n", "CHAR ;"},
	{`"x"` + "\n", "STRING ;"},
	{"`x`\n", "STRING ;"},

	{"+\n", "+"},
	{"-\n", "-"},
	{"*\n", "*"},
	{"/\n", "/"},
	{"%\n", "%"},

	{"&\n", "&"},
	{"|\n", "|"},
	{"^\n", "^"},
	{"<<\n", "<<"},
	{">>\n", ">>"},
	{"&^\n", "&^"},

	{"+=\n", "+="},
	{"-=\n", "-="},
	{"*=\n", "*="},
	{"/=\n", "/="},
	{"%=\n", "%="},

	{"&=\n", "&="},
	{"|=\n", "|="},
	{"^=\n", "^="},
	{"<<=\n", "<<="},
	{">>=\n", ">>="},
	{"&^=\n", "&^="},

	{"&&\n", "&&"},
	{"||\n", "||"},
	{"<-\n", "<-"},
	{"++\n", "++ ;"},
	{"--\n", "-- ;"},

	{"==\n", "=="},
	{"<\n", "<"},
	{">\n", ">"},
	{"=\n", "="},
	{"!\n", "!"},

	{"!=\n", "!="},
	{"<=\n", "<="},
	{">=\n", ">="},
	{":=\n", ":="},
	{"...\n", "..."},

	{"(\n", "("},
	{"[\n", "["},
	{"{\n", "{"},
	{",\n", ","},
	{".\n", "."},

	{")\n", ") ;"},
	{"]\n", "] ;"},
	{"}\n", "} ;"},
	{";\n", ";"},
	{":\n", ":"},

	{"break\n", "break ;"},
	{"case\n", "case"},
	{"chan\n", "chan"},
	{"const\n", "const"},
	{"continue\n", "continue ;"},

	{"default\n", "default"},
	{"defer\n", "defer"},
	{"else\n", "else"},
	{"fallthrough\n", "fallthrough ;"},
	{"for\n", "for"},

	{"func\n", "func"},
	{"go\n", "go"},
	{"goto\n", "goto"},
	{"if\n", "if"},
	{"import\n", "import"},

	{"interface\n", "interface"},
	{"map\n", "map"},
	{"package\n", "package"},
	{"range\n", "range"},
	{"return\n", "return ;"},

	{"select\n", "select"},
	{"struct\n", "struct"},
	{"switch\n", "switch"},
	{"type\n", "type"},
	{"var\n", "var"},

	{"foo//comment\n", "IDENT COMMENT ;"},
	{"foo//comment", "IDENT COMMENT ;"},
	{"foo/*comment*/\n", "IDENT COMMENT ;"},
	{"foo/*\n*/", "IDENT COMMENT ;"},
	{"foo/*comment*/    \n", "IDENT COMMENT ;"},
	{"foo/*\n*/    ", "IDENT COMMENT ;"},

	{"foo    // comment\n", "IDENT COMMENT ;"},
	{"foo    // comment", "IDENT COMMENT ;"},
	{"foo    /*comment*/\n", "IDENT COMMENT ;"},
	{"foo    /*\n*/", "IDENT COMMENT ;"},
	{"foo    /*  */ /* \n */ bar/**/\n", "IDENT COMMENT COMMENT ; IDENT COMMENT ;"},
	{"foo    /*0*/ /*1*/ /*2*/\n", "IDENT COMMENT COMMENT COMMENT ;"},

	{"foo    /*comment*/    \n", "IDENT COMMENT ;"},
	{"foo    /*0*/ /*1*/ /*2*/    \n", "IDENT COMMENT COMMENT COMMENT ;"},
	{"foo	/**/ /*-------------*/       /*----\n*/bar       /*  \n*/baa\n", "IDENT COMMENT COMMENT COMMENT ; IDENT COMMENT ; IDENT ;"},
	{"foo    /* an EOF terminates a line */", "IDENT COMMENT ;"},
	{"foo    /* an EOF terminates a line */ /*", "IDENT COMMENT COMMENT ;"},
	{"foo    /* an EOF terminates a line */ //", "IDENT COMMENT COMMENT ;"},

	{"package main\n\nfunc main() {\n\tif {\n\t\treturn /* */ }\n}\n", "package IDENT ; func IDENT ( ) { if { return COMMENT } ; } ;"},
	{"package main", "package IDENT ;"},
}

func TestSemicolons(t *testing.T) {
	for _, test := range semicolonTests {
		input, want := test.input, test.want
		checkSemi(t, input, want, 0)
		checkSemi(t, input, want, ScanComments)

		// if the input ended in newlines, the input must tokenize the
		// same with or without those newlines
		for i := len(input) - 1; i >= 0 && input[i] == '\n'; i-- {
			checkSemi(t, input[0:i], want, 0)
			checkSemi(t, input[0:i], want, ScanComments)
		}
	}
}

type segment struct {
	srcline      string // a line of source text
	filename     string // filename for current token; error message for invalid line directives
	line, column int    // line and column for current token; error position for invalid line directives
}

var segments = []segment{
	// exactly one token per line since the test consumes one token per segment
	{"  line1", "TestLineDirectives", 1, 3},
	{"\nline2", "TestLineDirectives", 2, 1},
	{"\nline3  //line File1.go:100", "TestLineDirectives", 3, 1}, // bad line comment, ignored
	{"\nline4", "TestLineDirectives", 4, 1},
	{"\n//line File1.go:100\n  line100", "File1.go", 100, 0},
	{"\n//line  \t :42\n  line1", " \t ", 42, 0},
	{"\n//line File2.go:200\n  line200", "File2.go", 200, 0},
	{"\n//line foo\t:42\n  line42", "foo\t", 42, 0},
	{"\n //line foo:42\n  line43", "foo\t", 44, 0}, // bad line comment, ignored (use existing, prior filename)
	{"\n//line foo 42\n  line44", "foo\t", 46, 0},  // bad line comment, ignored (use existing, prior filename)
	{"\n//line /bar:42\n  line45", "/bar", 42, 0},
	{"\n//line ./foo:42\n  line46", "foo", 42, 0},
	{"\n//line a/b/c/File1.go:100\n  line100", "a/b/c/File1.go", 100, 0},
	{"\n//line c:\\bar:42\n  line200", "c:\\bar", 42, 0},
	{"\n//line c:\\dir\\File1.go:100\n  line201", "c:\\dir\\File1.go", 100, 0},

	// tests for new line directive syntax
	{"\n//line :100\na1", "", 100, 0}, // missing filename means empty filename
	{"\n//line bar:100\nb1", "bar", 100, 0},
	{"\n//line :100:10\nc1", "bar", 100, 10}, // missing filename means current filename
	{"\n//line foo:100:10\nd1", "foo", 100, 10},

	{"\n/*line :100*/a2", "", 100, 0}, // missing filename means empty filename
	{"\n/*line bar:100*/b2", "bar", 100, 0},
	{"\n/*line :100:10*/c2", "bar", 100, 10}, // missing filename means current filename
	{"\n/*line foo:100:10*/d2", "foo", 100, 10},
	{"\n/*line foo:100:10*/    e2", "foo", 100, 14}, // line-directive relative column
	{"\n/*line foo:100:10*/\n\nf2", "foo", 102, 1},  // absolute column since on new line
}

var dirsegments = []segment{
	// exactly one token per line since the test consumes one token per segment
	{"  line1", "TestLineDir/TestLineDirectives", 1, 3},
	{"\n//line File1.go:100\n  line100", "TestLineDir/File1.go", 100, 0},
}

var dirUnixSegments = []segment{
	{"\n//line /bar:42\n  line42", "/bar", 42, 0},
}

var dirWindowsSegments = []segment{
	{"\n//line c:\\bar:42\n  line42", "c:\\bar", 42, 0},
}

// Verify that line directives are interpreted correctly.
func TestLineDirectives(t *testing.T) {
	testSegments(t, segments, "TestLineDirectives")
	testSegments(t, dirsegments, "TestLineDir/TestLineDirectives")
	if runtime.GOOS == "windows" {
		testSegments(t, dirWindowsSegments, "TestLineDir/TestLineDirectives")
	} else {
		testSegments(t, dirUnixSegments, "TestLineDir/TestLineDirectives")
	}
}

func testSegments(t *testing.T, segments []segment, filename string) {
	var src string
	for _, e := range segments {
		src += e.srcline
	}

	// verify scan
	var S Scanner
	file := fset.AddFile(filename, fset.Base(), len(src))
	S.Init(file, []byte(src), func(pos token.Position, msg string) { t.Error(Error{pos, msg}) }, dontInsertSemis)
	for _, s := range segments {
		p, _, lit := S.Scan()
		pos := file.Position(p)
		checkPos(t, lit, p, token.Position{
			Filename: s.filename,
			Offset:   pos.Offset,
			Line:     s.line,
			Column:   s.column,
		})
	}

	if S.ErrorCount != 0 {
		t.Errorf("got %d errors", S.ErrorCount)
	}
}

// The filename is used for the error message in these test cases.
// The first line directive is valid and used to control the expected error line.
var invalidSegments = []segment{
	{"\n//line :1:1\n//line foo:42 extra text\ndummy", "invalid line number: 42 extra text", 1, 12},
	{"\n//line :2:1\n//line foobar:\ndummy", "invalid line number: ", 2, 15},
	{"\n//line :5:1\n//line :0\ndummy", "invalid line number: 0", 5, 9},
	{"\n//line :10:1\n//line :1:0\ndummy", "invalid column number: 0", 10, 11},
	{"\n//line :1:1\n//line :foo:0\ndummy", "invalid line number: 0", 1, 13}, // foo is considered part of the filename
}

// Verify that invalid line directives get the correct error message.
func TestInvalidLineDirectives(t *testing.T) {
	// make source
	var src string
	for _, e := range invalidSegments {
		src += e.srcline
	}

	// verify scan
	var S Scanner
	var s segment // current segment
	file := fset.AddFile(filepath.Join("dir", "TestInvalidLineDirectives"), fset.Base(), len(src))
	S.Init(file, []byte(src), func(pos token.Position, msg string) {
		if msg != s.filename {
			t.Errorf("got error %q; want %q", msg, s.filename)
		}
		if pos.Line != s.line || pos.Column != s.column {
			t.Errorf("got position %d:%d; want %d:%d", pos.Line, pos.Column, s.line, s.column)
		}
	}, dontInsertSemis)
	for _, s = range invalidSegments {
		S.Scan()
	}

	if S.ErrorCount != len(invalidSegments) {
		t.Errorf("got %d errors; want %d", S.ErrorCount, len(invalidSegments))
	}
}

// Verify that initializing the same scanner more than once works correctly.
func TestInit(t *testing.T) {
	var s Scanner

	// 1st init
	src1 := "if true { }"
	f1 := fset.AddFile("src1", fset.Base(), len(src1))
	s.Init(f1, []byte(src1), nil, dontInsertSemis)
	if f1.Size() != len(src1) {
		t.Errorf("bad file size: got %d, expected %d", f1.Size(), len(src1))
	}
	s.Scan()              // if
	s.Scan()              // true
	_, tok, _ := s.Scan() // {
	if tok != token.LBRACE {
		t.Errorf("bad token: got %s, expected %s", tok, token.LBRACE)
	}

	// 2nd init
	src2 := "go true { ]"
	f2 := fset.AddFile("src2", fset.Base(), len(src2))
	s.Init(f2, []byte(src2), nil, dontInsertSemis)
	if f2.Size() != len(src2) {
		t.Errorf("bad file size: got %d, expected %d", f2.Size(), len(src2))
	}
	_, tok, _ = s.Scan() // go
	if tok != token.GO {
		t.Errorf("bad token: got %s, expected %s", tok, token.GO)
	}

	if s.ErrorCount != 0 {
		t.Errorf("found %d errors", s.ErrorCount)
	}
}

func TestStdErrorHandler(t *testing.T) {
	const src = "@\n" + // illegal character, cause an error
		"@ @\n" + // two errors on the same line
		"//line File2:20\n" +
		"@\n" + // different file, but same line
		"//line File2:1\n" +
		"@ @\n" + // same file, decreasing line number
		"//line File1:1\n" +
		"@ @ @" // original file, line 1 again

	var list ErrorList
	eh := func(pos token.Position, msg string) { list.Add(pos, msg) }

	var s Scanner
	s.Init(fset.AddFile("File1", fset.Base(), len(src)), []byte(src), eh, dontInsertSemis)
	for {
		if _, tok, _ := s.Scan(); tok == token.EOF {
			break
		}
	}

	if len(list) != s.ErrorCount {
		t.Errorf("found %d errors, expected %d", len(list), s.ErrorCount)
	}

	if len(list) != 9 {
		t.Errorf("found %d raw errors, expected 9", len(list))
		PrintError(os.Stderr, list)
	}

	list.Sort()
	if len(list) != 9 {
		t.Errorf("found %d sorted errors, expected 9", len(list))
		PrintError(os.Stderr, list)
	}

	list.RemoveMultiples()
	if len(list) != 4 {
		t.Errorf("found %d one-per-line errors, expected 4", len(list))
		PrintError(os.Stderr, list)
	}
}

type errorCollector struct {
	cnt int            // number of errors encountered
	msg string         // last error message encountered
	pos token.Position // last error position encountered
}

func checkError(t *testing.T, src string, tok token.Token, pos int, lit, err string) {
	var s Scanner
	var h errorCollector
	eh := func(pos token.Position, msg string) {
		h.cnt++
		h.msg = msg
		h.pos = pos
	}
	s.Init(fset.AddFile("", fset.Base(), len(src)), []byte(src), eh, ScanComments|dontInsertSemis)
	_, tok0, lit0 := s.Scan()
	if tok0 != tok {
		t.Errorf("%q: got %s, expected %s", src, tok0, tok)
	}
	if tok0 != token.ILLEGAL && lit0 != lit {
		t.Errorf("%q: got literal %q, expected %q", src, lit0, lit)
	}
	cnt := 0
	if err != "" {
		cnt = 1
	}
	if h.cnt != cnt {
		t.Errorf("%q: got cnt %d, expected %d", src, h.cnt, cnt)
	}
	if h.msg != err {
		t.Errorf("%q: got msg %q, expected %q", src, h.msg, err)
	}
	if h.pos.Offset != pos {
		t.Errorf("%q: got offset %d, expected %d", src, h.pos.Offset, pos)
	}
}

var errors = []struct {
	src string
	tok token.Token
	pos int
	lit string
	err string
}{
	{"\a", token.ILLEGAL, 0, "", "illegal character U+0007"},
	{`#`, token.ILLEGAL, 0, "", "illegal character U+0023 '#'"},
	{`…`, token.ILLEGAL, 0, "", "illegal character U+2026 '…'"},
	{"..", token.PERIOD, 0, "", ""}, // two periods, not invalid token (issue #28112)
	{`' '`, token.CHAR, 0, `' '`, ""},
	{`''`, token.CHAR, 0, `''`, "illegal rune literal"},
	{`'12'`, token.CHAR, 0, `'12'`, "illegal rune literal"},
	{`'123'`, token.CHAR, 0, `'123'`, "illegal rune literal"},
	{`'\0'`, token.CHAR, 3, `'\0'`, "illegal character U+0027 ''' in escape sequence"},
	{`'\07'`, token.CHAR, 4, `'\07'`, "illegal character U+0027 ''' in escape sequence"},
	{`'\8'`, token.CHAR, 2, `'\8'`, "unknown escape sequence"},
	{`'\08'`, token.CHAR, 3, `'\08'`, "illegal character U+0038 '8' in escape sequence"},
	{`'\x'`, token.CHAR, 3, `'\x'`, "illegal character U+0027 ''' in escape sequence"},
	{`'\x0'`, token.CHAR, 4, `'\x0'`, "illegal character U+0027 ''' in escape sequence"},
	{`'\x0g'`, token.CHAR, 4, `'\x0g'`, "illegal character U+0067 'g' in escape sequence"},
	{`'\u'`, token.CHAR, 3, `'\u'`, "illegal character U+0027 ''' in escape sequence"},
	{`'\u0'`, token.CHAR, 4, `'\u0'`, "illegal character U+0027 ''' in escape sequence"},
	{`'\u00'`, token.CHAR, 5, `'\u00'`, "illegal character U+0027 ''' in escape sequence"},
	{`'\u000'`, token.CHAR, 6, `'\u000'`, "illegal character U+0027 ''' in escape sequence"},
	{`'\u000`, token.CHAR, 6, `'\u000`, "escape sequence not terminated"},
	{`'\u0000'`, token.CHAR, 0, `'\u0000'`, ""},
	{`'\U'`, token.CHAR, 3, `'\U'`, "illegal character U+0027 ''' in escape sequence"},
	{`'\U0'`, token.CHAR, 4, `'\U0'`, "illegal character U+0027 ''' in escape sequence"},
	{`'\U00'`, token.CHAR, 5, `'\U00'`, "illegal character U+0027 ''' in escape sequence"},
	{`'\U000'`, token.CHAR, 6, `'\U000'`, "illegal character U+0027 ''' in escape sequence"},
	{`'\U0000'`, token.CHAR, 7, `'\U0000'`, "illegal character U+0027 ''' in escape sequence"},
	{`'\U00000'`, token.CHAR, 8, `'\U00000'`, "illegal character U+0027 ''' in escape sequence"},
	{`'\U000000'`, token.CHAR, 9, `'\U000000'`, "illegal character U+0027 ''' in escape sequence"},
	{`'\U0000000'`, token.CHAR, 10, `'\U0000000'`, "illegal character U+0027 ''' in escape sequence"},
	{`'\U0000000`, token.CHAR, 10, `'\U0000000`, "escape sequence not terminated"},
	{`'\U00000000'`, token.CHAR, 0, `'\U00000000'`, ""},
	{`'\Uffffffff'`, token.CHAR, 2, `'\Uffffffff'`, "escape sequence is invalid Unicode code point"},
	{`'`, token.CHAR, 0, `'`, "rune literal not terminated"},
	{`'\`, token.CHAR, 2, `'\`, "escape sequence not terminated"},
	{"'\n", token.CHAR, 0, "'", "rune literal not terminated"},
	{"'\n   ", token.CHAR, 0, "'", "rune literal not terminated"},
	{`""`, token.STRING, 0, `""`, ""},
	{`"abc`, token.STRING, 0, `"abc`, "string literal not terminated"},
	{"\"abc\n", token.STRING, 0, `"abc`, "string literal not terminated"},
	{"\"abc\n   ", token.STRING, 0, `"abc`, "string literal not terminated"},
	{"``", token.STRING, 0, "``", ""},
	{"`", token.STRING, 0, "`", "raw string literal not terminated"},
	{"/**/", token.COMMENT, 0, "/**/", ""},
	{"/*", token.COMMENT, 0, "/*", "comment not terminated"},
	{"077", token.INT, 0, "077", ""},
	{"078.", token.FLOAT, 0, "078.", ""},
	{"07801234567.", token.FLOAT, 0, "07801234567.", ""},
	{"078e0", token.FLOAT, 0, "078e0", ""},
	{"0E", token.FLOAT, 2, "0E", "exponent has no digits"}, // issue 17621
	{"078", token.INT, 2, "078", "invalid digit '8' in octal literal"},
	{"07090000008", token.INT, 3, "07090000008", "invalid digit '9' in octal literal"},
	{"0x", token.INT, 2, "0x", "hexadecimal literal has no digits"},
	{"\"abc\x00def\"", token.STRING, 4, "\"abc\x00def\"", "illegal character NUL"},
	{"\"abc\x80def\"", token.STRING, 4, "\"abc\x80def\"", "illegal UTF-8 encoding"},
	{"\ufeff\ufeff", token.ILLEGAL, 3, "\ufeff\ufeff", "illegal byte order mark"},                        // only first BOM is ignored
	{"//\ufeff", token.COMMENT, 2, "//\ufeff", "illegal byte order mark"},                                // only first BOM is ignored
	{"'\ufeff" + `'`, token.CHAR, 1, "'\ufeff" + `'`, "illegal byte order mark"},                         // only first BOM is ignored
	{`"` + "abc\ufeffdef" + `"`, token.STRING, 4, `"` + "abc\ufeffdef" + `"`, "illegal byte order mark"}, // only first BOM is ignored
	{"abc\x00def", token.IDENT, 3, "abc", "illegal character NUL"},
	{"abc\x00", token.IDENT, 3, "abc", "illegal character NUL"},
	{"“abc”", token.ILLEGAL, 0, "abc", `curly quotation mark '“' (use neutral '"')`},
}

func TestScanErrors(t *testing.T) {
	for _, e := range errors {
		checkError(t, e.src, e.tok, e.pos, e.lit, e.err)
	}
}

func TestUTF16(t *testing.T) {
	// This test doesn't fit within TestScanErrors because
	// the latter assumes that there was only one error.
	for _, src := range []string{
		"\xfe\xff\x00p\x00a\x00c\x00k\x00a\x00g\x00e\x00 \x00p", // BOM + "package p" encoded as UTF-16 BE
		"\xff\xfep\x00a\x00c\x00k\x00a\x00g\x00e\x00 \x00p\x00", // BOM + "package p" encoded as UTF-16 LE
	} {
		var got []string
		eh := func(posn token.Position, msg string) {
			got = append(got, fmt.Sprintf("#%d: %s", posn.Offset, msg))
		}
		var sc Scanner
		sc.Init(fset.AddFile("", fset.Base(), len(src)), []byte(src), eh, 0)
		sc.Scan()

		// We expect two errors:
		// one from the decoder, one from the scanner.
		want := []string{
			"#0: illegal UTF-8 encoding (got UTF-16)",
			"#0: illegal character U+FFFD '�'",
		}
		if !slices.Equal(got, want) {
			t.Errorf("Scan(%q) returned errors %q, want %q", src, got, want)
		}
	}
}

// Verify that no comments show up as literal values when skipping comments.
func TestIssue10213(t *testing.T) {
	const src = `
		var (
			A = 1 // foo
		)

		var (
			B = 2
			// foo
		)

		var C = 3 // foo

		var D = 4
		// foo

		func anycode() {
		// foo
		}
	`
	var s Scanner
	s.Init(fset.AddFile("", fset.Base(), len(src)), []byte(src), nil, 0)
	for {
		pos, tok, lit := s.Scan()
		class := tokenclass(tok)
		if lit != "" && class != keyword && class != literal && tok != token.SEMICOLON {
			t.Errorf("%s: tok = %s, lit = %q", fset.Position(pos), tok, lit)
		}
		if tok <= token.EOF {
			break
		}
	}
}

func TestIssue28112(t *testing.T) {
	const src = "... .. 0.. .." // make sure to have stand-alone ".." immediately before EOF to test EOF behavior
	tokens := []token.Token{token.ELLIPSIS, token.PERIOD, token.PERIOD, token.FLOAT, token.PERIOD, token.PERIOD, token.PERIOD, token.EOF}
	var s Scanner
	s.Init(fset.AddFile("", fset.Base(), len(src)), []byte(src), nil, 0)
	for _, want := range tokens {
		pos, got, lit := s.Scan()
		if got != want {
			t.Errorf("%s: got %s, want %s", fset.Position(pos), got, want)
		}
		// literals expect to have a (non-empty) literal string and we don't care about other tokens for this test
		if tokenclass(got) == literal && lit == "" {
			t.Errorf("%s: for %s got empty literal string", fset.Position(pos), got)
		}
	}
}

func BenchmarkScan(b *testing.B) {
	b.StopTimer()
	fset := token.NewFileSet()
	file := fset.AddFile("", fset.Base(), len(source))
	var s Scanner
	b.StartTimer()
	for i := 0; i < b.N; i++ {
		s.Init(file, source, nil, ScanComments)
		for {
			_, tok, _ := s.Scan()
			if tok == token.EOF {
				break
			}
		}
	}
}

func BenchmarkScanFiles(b *testing.B) {
	// Scan a few arbitrary large files, and one small one, to provide some
	// variety in benchmarks.
	for _, p := range []string{
		"go/types/expr.go",
		"go/parser/parser.go",
		"net/http/server.go",
		"go/scanner/errors.go",
	} {
		b.Run(p, func(b *testing.B) {
			b.StopTimer()
			filename := filepath.Join("..", "..", filepath.FromSlash(p))
			src, err := os.ReadFile(filename)
			if err != nil {
				b.Fatal(err)
			}
			fset := token.NewFileSet()
			file := fset.AddFile(filename, fset.Base(), len(src))
			b.SetBytes(int64(len(src)))
			var s Scanner
			b.StartTimer()
			for i := 0; i < b.N; i++ {
				s.Init(file, src, nil, ScanComments)
				for {
					_, tok, _ := s.Scan()
					if tok == token.EOF {
						break
					}
				}
			}
		})
	}
}

func TestNumbers(t *testing.T) {
	for _, test := range []struct {
		tok              token.Token
		src, tokens, err string
	}{
		// binaries
		{token.INT, "0b0", "0b0", ""},
		{token.INT, "0b1010", "0b1010", ""},
		{token.INT, "0B1110", "0B1110", ""},

		{token.INT, "0b", "0b", "binary literal has no digits"},
		{token.INT, "0b0190", "0b0190", "invalid digit '9' in binary literal"},
		{token.INT, "0b01a0", "0b01 a0", ""}, // only accept 0-9

		{token.FLOAT, "0b.", "0b.", "invalid radix point in binary literal"},
		{token.FLOAT, "0b.1", "0b.1", "invalid radix point in binary literal"},
		{token.FLOAT, "0b1.0", "0b1.0", "invalid radix point in binary literal"},
		{token.FLOAT, "0b1e10", "0b1e10", "'e' exponent requires decimal mantissa"},
		{token.FLOAT, "0b1P-1", "0b1P-1", "'P' exponent requires hexadecimal mantissa"},

		{token.IMAG, "0b10i", "0b10i", ""},
		{token.IMAG, "0b10.0i", "0b10.0i", "invalid radix point in binary literal"},

		// octals
		{token.INT, "0o0", "0o0", ""},
		{token.INT, "0o1234", "0o1234", ""},
		{token.INT, "0O1234", "0O1234", ""},

		{token.INT, "0o", "0o", "octal literal has no digits"},
		{token.INT, "0o8123", "0o8123", "invalid digit '8' in octal literal"},
		{token.INT, "0o1293", "0o1293", "invalid digit '9' in octal literal"},
		{token.INT, "0o12a3", "0o12 a3", ""}, // only accept 0-9

		{token.FLOAT, "0o.", "0o.", "invalid radix point in octal literal"},
		{token.FLOAT, "0o.2", "0o.2", "invalid radix point in octal literal"},
		{token.FLOAT, "0o1.2", "0o1.2", "invalid radix point in octal literal"},
		{token.FLOAT, "0o1E+2", "0o1E+2", "'E' exponent requires decimal mantissa"},
		{token.FLOAT, "0o1p10", "0o1p10", "'p' exponent requires hexadecimal mantissa"},

		{token.IMAG, "0o10i", "0o10i", ""},
		{token.IMAG, "0o10e0i", "0o10e0i", "'e' exponent requires decimal mantissa"},

		// 0-octals
		{token.INT, "0", "0", ""},
		{token.INT, "0123", "0123", ""},

		{token.INT, "08123", "08123", "invalid digit '8' in octal literal"},
		{token.INT, "01293", "01293", "invalid digit '9' in octal literal"},
		{token.INT, "0F.", "0 F .", ""}, // only accept 0-9
		{token.INT, "0123F.", "0123 F .", ""},
		{token.INT, "0123456x", "0123456 x", ""},

		// decimals
		{token.INT, "1", "1", ""},
		{token.INT, "1234", "1234", ""},

		{token.INT, "1f", "1 f", ""}, // only accept 0-9

		{token.IMAG, "0i", "0i", ""},
		{token.IMAG, "0678i", "0678i", ""},

		// decimal floats
		{token.FLOAT, "0.", "0.", ""},
		{token.FLOAT, "123.", "123.", ""},
		{token.FLOAT, "0123.", "0123.", ""},

		{token.FLOAT, ".0", ".0", ""},
		{token.FLOAT, ".123", ".123", ""},
		{token.FLOAT, ".0123", ".0123", ""},

		{token.FLOAT, "0.0", "0.0", ""},
		{token.FLOAT, "123.123", "123.123", ""},
		{token.FLOAT, "0123.0123", "0123.0123", ""},

		{token.FLOAT, "0e0", "0e0", ""},
		{token.FLOAT, "123e+0", "123e+0", ""},
		{token.FLOAT, "0123E-1", "0123E-1", ""},

		{token.FLOAT, "0.e+1", "0.e+1", ""},
		{token.FLOAT, "123.E-10", "123.E-10", ""},
		{token.FLOAT, "0123.e123", "0123.e123", ""},

		{token.FLOAT, ".0e-1", ".0e-1", ""},
		{token.FLOAT, ".123E+10", ".123E+10", ""},
		{token.FLOAT, ".0123E123", ".0123E123", ""},

		{token.FLOAT, "0.0e1", "0.0e1", ""},
		{token.FLOAT, "123.123E-10", "123.123E-10", ""},
		{token.FLOAT, "0123.0123e+456", "0123.0123e+456", ""},

		{token.FLOAT, "0e", "0e", "exponent has no digits"},
		{token.FLOAT, "0E+", "0E+", "exponent has no digits"},
		{token.FLOAT, "1e+f", "1e+ f", "exponent has no digits"},
		{token.FLOAT, "0p0", "0p0", "'p' exponent requires hexadecimal mantissa"},
		{token.FLOAT, "1.0P-1", "1.0P-1", "'P' exponent requires hexadecimal mantissa"},

		{token.IMAG, "0.i", "0.i", ""},
		{token.IMAG, ".123i", ".123i", ""},
		{token.IMAG, "123.123i", "123.123i", ""},
		{token.IMAG, "123e+0i", "123e+0i", ""},
		{token.IMAG, "123.E-10i", "123.E-10i", ""},
		{token.IMAG, ".123E+10i", ".123E+10i", ""},

		// hexadecimals
		{token.INT, "0x0", "0x0", ""},
		{token.INT, "0x1234", "0x1234", ""},
		{token.INT, "0xcafef00d", "0xcafef00d", ""},
		{token.INT, "0XCAFEF00D", "0XCAFEF00D", ""},

		{token.INT, "0x", "0x", "hexadecimal literal has no digits"},
		{token.INT, "0x1g", "0x1 g", ""},

		{token.IMAG, "0xf00i", "0xf00i", ""},

		// hexadecimal floats
		{token.FLOAT, "0x0p0", "0x0p0", ""},
		{token.FLOAT, "0x12efp-123", "0x12efp-123", ""},
		{token.FLOAT, "0xABCD.p+0", "0xABCD.p+0", ""},
		{token.FLOAT, "0x.0189P-0", "0x.0189P-0", ""},
		{token.FLOAT, "0x1.ffffp+1023", "0x1.ffffp+1023", ""},

		{token.FLOAT, "0x.", "0x.", "hexadecimal literal has no digits"},
		{token.FLOAT, "0x0.", "0x0.", "hexadecimal mantissa requires a 'p' exponent"},
		{token.FLOAT, "0x.0", "0x.0", "hexadecimal mantissa requires a 'p' exponent"},
		{token.FLOAT, "0x1.1", "0x1.1", "hexadecimal mantissa requires a 'p' exponent"},
		{token.FLOAT, "0x1.1e0", "0x1.1e0", "hexadecimal mantissa requires a 'p' exponent"},
		{token.FLOAT, "0x1.2gp1a", "0x1.2 gp1a", "hexadecimal mantissa requires a 'p' exponent"},
		{token.FLOAT, "0x0p", "0x0p", "exponent has no digits"},
		{token.FLOAT, "0xeP-", "0xeP-", "exponent has no digits"},
		{token.FLOAT, "0x1234PAB", "0x1234P AB", "exponent has no digits"},
		{token.FLOAT, "0x1.2p1a", "0x1.2p1 a", ""},

		{token.IMAG, "0xf00.bap+12i", "0xf00.bap+12i", ""},

		// separators
		{token.INT, "0b_1000_0001", "0b_1000_0001", ""},
		{token.INT, "0o_600", "0o_600", ""},
		{token.INT, "0_466", "0_466", ""},
		{token.INT, "1_000", "1_000", ""},
		{token.FLOAT, "1_000.000_1", "1_000.000_1", ""},
		{token.IMAG, "10e+1_2_3i", "10e+1_2_3i", ""},
		{token.INT, "0x_f00d", "0x_f00d", ""},
		{token.FLOAT, "0x_f00d.0p1_2", "0x_f00d.0p1_2", ""},

		{token.INT, "0b__1000", "0b__1000", "'_' must separate successive digits"},
		{token.INT, "0o60___0", "0o60___0", "'_' must separate successive digits"},
		{token.INT, "0466_", "0466_", "'_' must separate successive digits"},
		{token.FLOAT, "1_.", "1_.", "'_' must separate successive digits"},
		{token.FLOAT, "0._1", "0._1", "'_' must separate successive digits"},
		{token.FLOAT, "2.7_e0", "2.7_e0", "'_' must separate successive digits"},
		{token.IMAG, "10e+12_i", "10e+12_i", "'_' must separate successive digits"},
		{token.INT, "0x___0", "0x___0", "'_' must separate successive digits"},
		{token.FLOAT, "0x1.0_p0", "0x1.0_p0", "'_' must separate successive digits"},
	} {
		var s Scanner
		var err string
		s.Init(fset.AddFile("", fset.Base(), len(test.src)), []byte(test.src), func(_ token.Position, msg string) {
			if err == "" {
				err = msg
			}
		}, 0)
		for i, want := range strings.Split(test.tokens, " ") {
			err = ""
			_, tok, lit := s.Scan()

			// compute lit where for tokens where lit is not defined
			switch tok {
			case token.PERIOD:
				lit = "."
			case token.ADD:
				lit = "+"
			case token.SUB:
				lit = "-"
			}

			if i == 0 {
				if tok != test.tok {
					t.Errorf("%q: got token %s; want %s", test.src, tok, test.tok)
				}
				if err != test.err {
					t.Errorf("%q: got error %q; want %q", test.src, err, test.err)
				}
			}

			if lit != want {
				t.Errorf("%q: got literal %q (%s); want %s", test.src, lit, tok, want)
			}
		}

		// make sure we read all
		_, tok, _ := s.Scan()
		if tok == token.SEMICOLON {
			_, tok, _ = s.Scan()
		}
		if tok != token.EOF {
			t.Errorf("%q: got %s; want EOF", test.src, tok)
		}
	}
}

func TestScanReuseSemiInNewlineComment(t *testing.T) {
	fset := token.NewFileSet()

	const src = "identifier /*a\nb*/ + other"
	var s Scanner
	s.Init(fset.AddFile("test.go", -1, len(src)), []byte(src), func(pos token.Position, msg string) {
		t.Fatal(msg)
	}, ScanComments)

	s.Scan() // IDENT(identifier)

	_, tok, _ := s.Scan() // COMMENT(/*a\nb*/)
	if tok != token.COMMENT {
		t.Fatalf("tok = %v; want = token.SEMICOLON", tok)
	}

	s.Init(fset.AddFile("test.go", -1, len(src)), []byte(src), func(pos token.Position, msg string) {
		t.Fatal(msg)
	}, ScanComments)

	_, tok, _ = s.Scan()
	if tok != token.IDENT {
		t.Fatalf("tok = %v; want = token.IDENT", tok)
	}
}

func TestScannerEnd(t *testing.T) {
	type tok struct {
		tok   token.Token
		start token.Pos
		end   token.Pos
	}

	cases := []struct {
		name string
		src  string
		end  []tok
	}{
		{
			name: "operators",
			src:  "+ - / >> == =",
			end: []tok{
				{token.ADD, 1, 2},
				{token.SUB, 3, 4},
				{token.QUO, 5, 6},
				{token.SHR, 7, 9},
				{token.EQL, 10, 12},
				{token.ASSIGN, 13, 14},
				{token.EOF, 14, 14},
			},
		},
		{
			name: "braces",
			src:  "{([])}",
			end: []tok{
				{token.LBRACE, 1, 2},
				{token.LPAREN, 2, 3},
				{token.LBRACK, 3, 4},
				{token.RBRACK, 4, 5},
				{token.RPAREN, 5, 6},
				{token.RBRACE, 6, 7},
				{token.SEMICOLON, 7, 7},
				{token.EOF, 7, 7},
			},
		},
		{
			name: "literals",
			src:  `"foo" 123 1.23 0b11`,
			end: []tok{
				{token.STRING, 1, 6},
				{token.INT, 7, 10},
				{token.FLOAT, 11, 15},
				{token.INT, 16, 20},
				{token.SEMICOLON, 20, 20},
				{token.EOF, 20, 20},
			},
		},
		{
			name: "missing newline at the end of file",
			src:  "foo",
			end: []tok{
				{token.IDENT, 1, 4},
				{token.SEMICOLON, 4, 4},
				{token.EOF, 4, 4},
			},
		},
		{
			name: "newline at the end of file",
			src:  "foo\n",
			end: []tok{
				{token.IDENT, 1, 4},
				{token.SEMICOLON, 4, 5},
				{token.EOF, 5, 5},
			},
		},
		{
			name: "semicolon at the end of file",
			src:  "foo;",
			end: []tok{
				{token.IDENT, 1, 4},
				{token.SEMICOLON, 4, 5},
				{token.EOF, 5, 5},
			},
		},
		{
			name: "semicolon and newline at the end of file",
			src:  "foo;\n",
			end: []tok{
				{token.IDENT, 1, 4},
				{token.SEMICOLON, 4, 5},
				{token.EOF, 6, 6},
			},
		},
		{
			name: "newline in comment acting as semicolon",
			src:  "foo /*\n*/ bar",
			end: []tok{
				{token.IDENT, 1, 4},
				{token.COMMENT, 5, 10},
				{token.SEMICOLON, 7, 8},
				{token.IDENT, 11, 14},
				{token.SEMICOLON, 14, 14},
				{token.EOF, 14, 14},
			},
		},
		{
			name: "BOM",
			src:  "\uFEFFfoo",
			end: []tok{
				{token.IDENT, 4, 7},
				{token.SEMICOLON, 7, 7},
				{token.EOF, 7, 7},
			},
		},
	}

	for _, tt := range cases {
		t.Run(tt.name, func(t *testing.T) {
			fset := token.NewFileSet()

			var s Scanner
			errorHandler := func(_ token.Position, msg string) { t.Fatal(msg) }
			s.Init(fset.AddFile("test.go", -1, len(tt.src)), []byte(tt.src), errorHandler, ScanComments)

			if end := s.End(); end != token.NoPos {
				t.Errorf("after init: s.End() = %v; want token.NoPos", end)
			}

			var got []tok
			for {
				pos, tokTyp, _ := s.Scan()
				got = append(got, tok{tokTyp, pos, s.End()})
				if tokTyp == token.EOF {
					break
				}
			}

			if !slices.Equal(got, tt.end) {
				t.Fatalf("input %q: got = %v; want = %v", tt.src, got, tt.end)
			}
		})
	}
}

func TestScannerEndReuse(t *testing.T) {
	fset := token.NewFileSet()

	const src = "identifier /*a\nb*/ + other"
	var s Scanner
	s.Init(fset.AddFile("test.go", -1, len(src)), []byte(src), func(pos token.Position, msg string) {
		t.Fatal(msg)
	}, ScanComments)

	s.Scan() // IDENT(identifier)
	s.Scan() // COMMENT(/*a\n*b/)

	_, tok, _ := s.Scan() // SEMICOLON
	if tok != token.SEMICOLON {
		t.Fatalf("tok = %v; want = token.SEMICOLON", tok)
	}

	s.Init(fset.AddFile("test.go", -1, len(src)), []byte(src), func(pos token.Position, msg string) {
		t.Fatal(msg)
	}, ScanComments)

	if end := s.End(); end != token.NoPos {
		t.Errorf("s.End() = %v; want token.NoPos", end)
	}
}