antlr/antlr4 · error · ArgumentException

the interval extends past the end of the stream

Error message

the interval extends past the end of the stream

What it means

If UnbufferedCharStream's buffer already ends with EOF, GetText knows the true end of input. It rejects intervals whose start plus length extends beyond that end. In short, the requested text range reaches past EOF.

Source

Thrown at runtime/CSharp/src/UnbufferedCharStream.cs:437

                {
                    return IntStreamConstants.UnknownSourceName;
                }
                return name;
            }
        }

        public virtual string GetText(Interval interval)
        {
            if (interval.a < 0 || interval.b < interval.a - 1)
            {
                throw new ArgumentException("invalid interval");
            }
            int bufferStartIndex = BufferStartIndex;
            if (n > 0 && data[n - 1] == IntStreamConstants.EOF)
            {
                if (interval.a + interval.Length > bufferStartIndex + n)
                {
                    throw new ArgumentException("the interval extends past the end of the stream");
                }
            }
            if (interval.a < bufferStartIndex || interval.b >= bufferStartIndex + n)
            {
                throw new NotSupportedException("interval " + interval + " outside buffer: " + bufferStartIndex + ".." + (bufferStartIndex + n - 1));
            }
            // convert from absolute to local index
            int i = interval.a - bufferStartIndex;
            // build a UTF-16 string from the Unicode code points in data
            var sb = new StringBuilder(interval.Length);
            for (int offset = 0; offset < interval.Length; offset++) {
                sb.Append(Char.ConvertFromUtf32(data[i + offset]));
            }
            return sb.ToString();
        }

        protected internal int BufferStartIndex
        {

View on GitHub (pinned to 7d5770395b)

Solutions

1. Clamp the stop index to the last valid character index before calling GetText.
2. Use the exact start/stop character indexes from tokens.
3. Avoid sentinel values such as int.MaxValue for ranges on unbuffered input.

Example fix

// before
string text = chars.GetText(Interval.Of(start, int.MaxValue));

// after
int last = chars.Index - 1; // valid once EOF has been read
string text = last >= start ? chars.GetText(Interval.Of(start, last)) : string.Empty;

int last = chars.Index - 1; // meaningful after EOF has been reached
if (interval.a > last) text = string.Empty;
else text = chars.GetText(Interval.Of(interval.a, Math.Min(interval.b, last)));

try { text = chars.GetText(interval); }
catch (ArgumentException ex) when (ex.Message == "the interval extends past the end of the stream") { /* clamp stop index and retry */ }

When it happens

Trigger: Calling GetText with a stop index beyond EOF; passing an oversized interval such as Interval.Of(0, int.MaxValue); or using stale/overlarge token character indexes after recovery at EOF.

Common situations: Error-recovery tokens with invalid stop indexes; code that uses a sentinel end index; or generic range extraction copied from a fully buffered implementation.

Related errors

• cannot consume EOF
• invalid interval
• interval ${interval} outside buffer: ${bufferStartIndex}..${
• cannot consume EOF
• cannot consume EOF

AI-assisted analysis of antlr/antlr4@7d5770395b (2026-08-14). Data as JSON: /api/errors/c0f1f82a40205876. Report an issue: GitHub.