feat: set filename

Signed-off-by: Ian Lewis <ian@ianlewis.org>

Author: ianlewis

custom.go

@@ -21,6 +21,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"os"
 	"strings"
 
 	"github.com/ianlewis/runeio"
@@ -87,25 +88,34 @@ type CustomLexer struct {
 // NewCustomLexer creates a new Lexer initialized with the given starting
 // [LexState]. The Lexer takes ownership of the tokens channel and closes it
 // when lexing is completed.
-func NewCustomLexer(r io.Reader, startingState LexState) *CustomLexer {
+func NewCustomLexer(reader io.Reader, startingState LexState) *CustomLexer {
+	var fileName string
+
+	file, isFile := reader.(*os.File)
+	if isFile {
+		fileName = file.Name()
+	}
+
 	customLexer := &CustomLexer{
 		state: startingState,
 		pos: Position{
-			Offset: 0,
-			Line:   1,
-			Column: 1,
+			Filename: fileName,
+			Offset:   0,
+			Line:     1,
+			Column:   1,
 		},
 		cursor: Position{
-			Offset: 0,
-			Line:   1,
-			Column: 1,
+			Filename: fileName,
+			Offset:   0,
+			Line:     1,
+			Column:   1,
 		},
 	}
 
 	// If already a *bufio.Reader, use it directly.
-	br, ok := r.(*bufio.Reader)
-	if !ok {
-		br = bufio.NewReader(r)
+	br, isBufReader := reader.(*bufio.Reader)
+	if !isBufReader {
+		br = bufio.NewReader(reader)
 	}
 
 	customLexer.r = runeio.NewReader(br)
@@ -464,3 +474,9 @@ func (l *CustomLexer) setErr(err error) {
 		l.err = err
 	}
 }
+
+// SetFilename sets the filename in the lexer's positional information.
+func (l *CustomLexer) SetFilename(name string) {
+	l.pos.Filename = name
+	l.cursor.Filename = name
+}

custom_test.go

@@ -953,3 +953,36 @@ func TestCustomLexer_NextToken(t *testing.T) {
 		}
 	})
 }
+
+func TestCustomLexer_SetFilename(t *testing.T) {
+	t.Parallel()
+
+	t.Run("SetFilename", func(t *testing.T) {
+		t.Parallel()
+
+		customLexer := NewCustomLexer(strings.NewReader("Hello World!"), &lexWordState{})
+		customLexer.SetFilename("testfile.txt")
+
+		expectedPos := Position{
+			Offset:   0,
+			Line:     1,
+			Column:   1,
+			Filename: "testfile.txt",
+		}
+
+		if diff := cmp.Diff(expectedPos, customLexer.Pos()); diff != "" {
+			t.Errorf("Pos (-want +got):\n%s", diff)
+		}
+
+		expectedCursor := Position{
+			Offset:   0,
+			Line:     1,
+			Column:   1,
+			Filename: "testfile.txt",
+		}
+
+		if diff := cmp.Diff(expectedCursor, customLexer.Cursor()); diff != "" {
+			t.Errorf("Cursor (-want +got):\n%s", diff)
+		}
+	})
+}

scanner.go

@@ -19,6 +19,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"os"
 	"text/scanner"
 )
 
@@ -62,13 +63,23 @@ type ScanningLexer struct {
 // NewScanningLexer creates a new ScanningLexer that reads from the given
 // [io.Reader].
 func NewScanningLexer(r io.Reader) *ScanningLexer {
+	var fileName string
+
+	file, ok := r.(*os.File)
+	if ok {
+		fileName = file.Name()
+	}
+
 	l := ScanningLexer{}
 	l.s = &scanner.Scanner{
 		Error: func(s *scanner.Scanner, msg string) {
 			if l.err == nil {
 				l.err = fmt.Errorf("%w: %s: %s", errScanner, s.Position, msg)
 			}
 		},
+		Position: scanner.Position{
+			Filename: fileName,
+		},
 	}
 	l.s = l.s.Init(r)
 	// Configure the scanner to be more generic and to not skip Go comments.
@@ -102,3 +113,8 @@ func (l *ScanningLexer) newToken(typ TokenType) *Token {
 		End:   Position(l.s.Pos()),
 	}
 }
+
+// SetFilename sets the filename in the lexer's positional information.
+func (l *ScanningLexer) SetFilename(name string) {
+	l.s.Filename = name
+}

scanner_test.go

@@ -160,3 +160,37 @@ func TestScannerLexer_NextToken(t *testing.T) {
 		})
 	}
 }
+
+func TestScanningLexer_SetFilename(t *testing.T) {
+	t.Parallel()
+
+	t.Run("SetFilename", func(t *testing.T) {
+		t.Parallel()
+
+		customLexer := NewScanningLexer(strings.NewReader("Hello World!"))
+		customLexer.SetFilename("testfile.txt")
+
+		expectedToken := &Token{
+			Type:  TokenType(scanner.Ident),
+			Value: "Hello",
+			Start: Position{
+				Offset:   0,
+				Line:     1,
+				Column:   1,
+				Filename: "testfile.txt",
+			},
+			End: Position{
+				Offset:   5,
+				Line:     1,
+				Column:   6,
+				Filename: "testfile.txt",
+			},
+		}
+
+		token := customLexer.NextToken(context.Background())
+
+		if diff := cmp.Diff(expectedToken, token); diff != "" {
+			t.Errorf("Pos (-want +got):\n%s", diff)
+		}
+	})
+}