Fix formatter adding extra space at end of line without trailing newline

internal/format/api_test.go

@@ -66,6 +66,54 @@ func TestFormat(t *testing.T) {
 	})
 }
 
+func TestFormatNoTrailingNewline(t *testing.T) {
+	t.Parallel()
+	// Issue: Formatter adds extra space at end of line
+	// When formatting a file that has content "1;" with no trailing newline,
+	// an extra space should NOT be added at the end of the line
+
+	testCases := []struct {
+		name string
+		text string
+	}{
+		{"simple statement without trailing newline", "1;"},
+		{"function call without trailing newline", "console.log('hello');"},
+		{"variable declaration without trailing newline", "const x = 1;"},
+		{"multiple statements without trailing newline", "const x = 1;\nconst y = 2;"},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			ctx := format.WithFormatCodeSettings(t.Context(), &format.FormatCodeSettings{
+				EditorSettings: format.EditorSettings{
+					TabSize:                4,
+					IndentSize:             4,
+					BaseIndentSize:         4,
+					NewLineCharacter:       "\n",
+					ConvertTabsToSpaces:    true,
+					IndentStyle:            format.IndentStyleSmart,
+					TrimTrailingWhitespace: true,
+				},
+			}, "\n")
+			sourceFile := parser.ParseSourceFile(ast.SourceFileParseOptions{
+				FileName: "/test.ts",
+				Path:     "/test.ts",
+			}, tc.text, core.ScriptKindTS)
+			edits := format.FormatDocument(ctx, sourceFile)
+			newText := applyBulkEdits(tc.text, edits)
+
+			// The formatted text should not add extra space at the end
+			// It may add proper spacing within the code, but not after the last character
+			assert.Assert(t, !strings.HasSuffix(newText, " "), "Formatter should not add trailing space")
+			// Also check that no space was added at EOF position if text didn't end with newline
+			if !strings.HasSuffix(tc.text, "\n") {
+				assert.Assert(t, !strings.HasSuffix(newText, " "), "Formatter should not add space before EOF")
+			}
+		})
+	}
+}
+
 func BenchmarkFormat(b *testing.B) {
 	ctx := format.WithFormatCodeSettings(b.Context(), &format.FormatCodeSettings{
 		EditorSettings: format.EditorSettings{

internal/format/rules.go

@@ -9,7 +9,9 @@ import (
 func getAllRules() []ruleSpec {
 	allTokens := make([]ast.Kind, 0, ast.KindLastToken-ast.KindFirstToken+1)
 	for token := ast.KindFirstToken; token <= ast.KindLastToken; token++ {
-		allTokens = append(allTokens, token)
+		if token != ast.KindEndOfFile {
+			allTokens = append(allTokens, token)
+		}
 	}
 
 	anyTokenExcept := func(tokens ...ast.Kind) tokenRange {

internal/scanner/scanner.go

@@ -2438,14 +2438,31 @@ func GetECMALineAndCharacterOfPosition(sourceFile ast.SourceFileLike, pos int) (
 }
 
 func GetECMAEndLinePosition(sourceFile *ast.SourceFile, line int) int {
-	pos := int(GetECMALineStarts(sourceFile)[line])
-	for {
-		ch, size := utf8.DecodeRuneInString(sourceFile.Text()[pos:])
-		if size == 0 || stringutil.IsLineBreak(ch) {
-			return pos
+	lineStarts := GetECMALineStarts(sourceFile)
+	text := sourceFile.Text()
+
+	// If this is the last line, return the index of the last character (or -1 for empty file)
+	if line+1 == len(lineStarts) {
+		if len(text) == 0 {
+			return -1
 		}
-		pos += size
+		return len(text) - 1
 	}
+
+	// For other lines, get the start of the next line and walk backwards to skip line breaks
+	start := int(lineStarts[line])
+	pos := int(lineStarts[line+1]) - 1
+
+	// Walk backwards while we're on line breaks, stopping at the beginning of the current line
+	for start <= pos {
+		ch, _ := utf8.DecodeLastRuneInString(text[:pos+1])
+		if !stringutil.IsLineBreak(ch) {
+			break
+		}
+		pos--
+	}
+
+	return pos
 }
 
 func GetECMAPositionOfLineAndCharacter(sourceFile *ast.SourceFile, line int, character int) int {