stride3d/stride · error · SemanticErrorException

While parsing a block collection, did not find expected '-'…

Error message

While parsing a block collection, did not find expected '-' indicator.

What it means

In the block-sequence state, the parser expects each entry to begin with a BLOCK-ENTRY token ('-'). When it encounters any other token, ParseBlockSequenceEntry throws SemanticErrorException at that token's span, indicating the sequence is malformed at that point.

Solutions

Ensure every item at the sequence indentation level starts with '-'
Fix inconsistent indentation so sequence items align and are more indented than the parent key
Replace tabs with spaces — YAML forbids tabs for indentation

Example fix

// before
list:
- a
b: c
// after
list:
- a
other: c

Defensive patterns

Strategy: try-catch

Validate before calling

// reject tabs and flag items at sequence level lacking '-'
if (text.Contains('\t')) throw new InvalidDataException("Tabs are not allowed in YAML indentation");

Try / catch

try { stream.Load(reader); } catch (SemanticErrorException ex) when (ex.Message.Contains("'-' indicator")) { throw new YamlConfigException($"Malformed block sequence near {ex.Start}", ex); }

Prevention

Use spaces, never tabs, for YAML indentation
Keep '-' items aligned at the same column
Lint YAML before loading user-edited files

When it happens

Trigger: Mixing indentation and '-' incorrectly, e.g. a non-'-' token at the sequence's indentation level: "list:\n- a\nb: c" where 'b: c' appears at sequence-entry column; or inconsistent indentation of '-' items.

Common situations: Hand-edited lists where an item lost its leading '- ', tab/space indentation mismatches, converting between flow and block styles partially.

Related errors

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/16a8765645922dbb. Report an issue: GitHub.

Appendix: source

Thrown at sources/core/Stride.Core.Yaml/Parser.cs:632

                else
                {
                    state = ParserState.YAML_PARSE_BLOCK_SEQUENCE_ENTRY_STATE;
                    return ProcessEmptyScalar(mark);
                }
            }

            else if (GetCurrentToken() is BlockEnd)
            {
                state = states.Pop();
                Event evt = new Events.SequenceEnd(GetCurrentToken().Start, GetCurrentToken().End);
                Skip();
                return evt;
            }

            else
            {
                var current = GetCurrentToken();
                throw new SemanticErrorException(current.Start, current.End, "While parsing a block collection, did not find expected '-' indicator.");
            }
        }

        /// <summary>
        /// Parse the productions:
        /// indentless_sequence  ::= (BLOCK-ENTRY block_node?)+
        ///                           *********** *
        /// </summary>
        private Event ParseIndentlessSequenceEntry()
        {
            if (GetCurrentToken() is BlockEntry)
            {
                Mark mark = GetCurrentToken().End;
                Skip();

                if (!(GetCurrentToken() is BlockEntry || GetCurrentToken() is Key || GetCurrentToken() is Value || GetCurrentToken() is BlockEnd))
                {
                    states.Push(ParserState.YAML_PARSE_INDENTLESS_SEQUENCE_ENTRY_STATE);

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