ssssssss-team/spider-flow · error · IndexOutOfBoundsException

Start must be >= 0.

Error message

Start must be >= 0.

What it means

The Span(String,int,int) constructor validates that the start offset is non-negative and throws IndexOutOfBoundsException("Start must be >= 0.") when a negative start is passed. Spans mark a character range inside a source string, so a negative start is meaningless. This is a fail-fast guard against programmer error in the caller.

Solutions

1. Check the start offset before constructing: ensure start >= 0.
2. Fix the offset computation that produced a negative value (e.g. an indexOf that returned -1).
3. Clamp negative offsets to 0 if that is semantically valid for the caller.
4. Use the single-argument Span(source) constructor when the span should cover the whole source.

Example fix

// before
int idx = source.indexOf('=');
Span span = new Span(source, idx, source.length());
// after
int idx = source.indexOf('=');
if (idx < 0) throw new IllegalArgumentException("'=' not found in source");
Span span = new Span(source, idx, source.length());

if (source == null) throw new IllegalArgumentException("source is null");
if (start < 0 || start > end || end > source.length()) throw new IllegalArgumentException("invalid span range [" + start + "," + end + "] for source of length " + source.length());

boolean isValidSpan(String source, int start, int end) {
    return source != null && start >= 0 && start <= end && end <= source.length() && start < source.length();
}

try {
    Span span = new Span(source, start, end);
} catch (IndexOutOfBoundsException | IllegalArgumentException e) {
    // log start/end/source.length() and fall back to a full-source span
    Span span = new Span(source);
}

When it happens

Trigger: Calling new Span(source, start, end) with a start value below 0, e.g. a computed offset that went negative due to subtraction on an empty or short string.

Common situations: Off-by-one arithmetic when slicing expressions, passing -1 as a default sentinel start, or computing substring offsets with charAt/indexOf results that returned -1 (not found).

Related errors

• Start outside of string.
• End outside of string.
• Start must be >= 0.
• Start must be <= end.
• The two spans do not reference the same source.

AI-assisted analysis of ssssssss-team/spider-flow@c799cca99c (2026-09-08). Data as JSON: /api/errors/1cd64674aa84b670. Report an issue: GitHub.

Appendix: source

Thrown at spider-flow-core/src/main/java/org/spiderflow/core/expression/parsing/Span.java:24

	/** the source string this span refers to **/
	private final String source;

	/** start index in source string, starting at 0 **/
	private int start;

	/** end index in source string, exclusive, starting at 0 **/
	private int end;

	/** Cached String instance to reduce pressure on GC **/
	private final String cachedText;

	public Span (String source) {
		this(source, 0, source.length());
	}

	public Span (String source, int start, int end) {
		if (start > end) throw new IllegalArgumentException("Start must be <= end.");
		if (start < 0) throw new IndexOutOfBoundsException("Start must be >= 0.");
		if (start > source.length() - 1) 
			throw new IndexOutOfBoundsException("Start outside of string.");
		if (end >source.length()) throw new IndexOutOfBoundsException("End outside of string.");

		this.source = source;
		this.start = start;
		this.end = end;
		this.cachedText = source.substring(start, end);
	}

	public Span (Span start, Span end) {
		if (!start.source.equals(end.source)) throw new IllegalArgumentException("The two spans do not reference the same source.");
		if (start.start > end.end) throw new IllegalArgumentException("Start must be <= end.");
		if (start.start < 0) throw new IndexOutOfBoundsException("Start must be >= 0.");
		if (start.start > start.source.length() - 1) throw new IndexOutOfBoundsException("Start outside of string.");
		if (end.end > start.source.length()) throw new IndexOutOfBoundsException("End outside of string.");

		this.source = start.source;

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