stride3d/stride · error · SyntaxErrorException

While scanning a block scalar, find a tab character where…

Error message

While scanning a block scalar, find a tab character where an intendation space is expected.

What it means

Inside a block scalar's body, indentation must consist of spaces only. ScanBlockScalar throws this SyntaxErrorException when it detects a tab character on a line whose column is before the required indentation (or while indentation is still 0), because tabs cannot count as indentation in YAML block scalars.

Solutions

1. Replace leading tabs with spaces in all lines of the block scalar.
2. Configure your editor to insert spaces for indentation in YAML files (editorconfig: indent_style = space).
3. Fix generator/serializer code to pad with spaces, e.g. new string(' ', indent) instead of '\t'.
4. Re-encode files: run expand -t 2 (or similar) over the YAML to convert tabs to spaces.
5. Add a pre-commit or CI check rejecting tab characters at line starts in YAML files.

Example fix

// before (tab indentation inside block scalar)
text: |
	line one

// after (spaces)
text: |
  line one

static bool NoLeadingTabs(string yamlContent) =>
    !yamlContent.Split('\n').Any(line => line.Length > 0 && (line[0] == '\t' || line.TrimEnd().StartsWith("\t")));

try
{
    var obj = deserializer.Deserialize<T>(input);
}
catch (YamlException ex)
{
    throw new FormatException($"Tab used for indentation at {ex.Start.Line}:{ex.Start.Column} — replace tabs with spaces", ex);
}

When it happens

Trigger: A multi-line block scalar whose continuation lines are indented with tab characters instead of spaces, e.g. 'text: |\n\tline'. Any parse of such content throws while scanning the block scalar body.

Common situations: Editors configured with tab indentation saving YAML files, code generators emitting '\t' prefixes for multi-line strings, and paste operations converting leading spaces to tabs.

Related errors

• Did not find expected
• Did not find expected <stream-start>.
• Expected ' ', got ' ' (at line , character ).
• The length must be positive.
• While parsing a block collection, did not find expected '-'…

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/772c031748015c89. Report an issue: GitHub.

Appendix: source

Thrown at sources/core/Stride.Core.Yaml/Scanner.cs:1518

            for (;;)
            {
                // Eat the intendation spaces.

                while ((currentIndent == 0 || mark.Column < currentIndent) && analyzer.IsSpace())
                {
                    Skip();
                }

                if (mark.Column > maxIndent)
                {
                    maxIndent = mark.Column;
                }

                // Check for a tab character messing the intendation.

                if ((currentIndent == 0 || mark.Column < currentIndent) && analyzer.IsTab())
                {
                    throw new SyntaxErrorException(start, mark, "While scanning a block scalar, find a tab character where an intendation space is expected.");
                }

                // Have we find a non-empty line?

                if (!analyzer.IsBreak())
                {
                    break;
                }

                // Consume the line break.

                ReadLine(breaks);

                end = mark;
            }

            // Determine the indentation level if needed.

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