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Report a block whose aliases form a cycle or expand too far as unreadable [patch] - #191
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…able [patch] YamlDotNet resolves an alias to the same object as its anchor, so an alias inside its own anchor (`a: &x [1, *x]`) produced a cyclic value, and ConvertValue copied it recursively until the stack overflowed and the host process died. Nested aliases were also expanded in full at every use, so a 350-byte block grew to a million values. ConvertValue now tracks the containers on the path it is converting and counts the values it has produced. A cycle, or more than 100,000 values, throws InvalidOperationException, which TryParseYamlObject already reports as an unreadable block, so the document is left unchanged. Fixes #159 Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Hnw6WDDjwQ8HvxinnWS9CF
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This was referenced Oct 7, 2026
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Fixes #159
Before: an alias inside its own anchor, for example
a: &x [1, *x]ora: &x {b: *x}, madeYamlSerializer.ConvertValuerecurse until the stack overflowed. The test host died with exit code 134 andStack overflow., which no caller can catch. Nested aliases were also expanded in full at every use. A six-level, roughly 350-byte block grew to a million values, andCombineFrontmatterwrote out a 15-million-character header.After:
ConvertValuekeeps track of the containers on the path it is converting, comparing them by reference, and counts how many values it has produced. A cycle, or more thanMaxExpandedValues(100,000) values, throwsInvalidOperationException.TryParseYamlObjectalready catches that exception and reports the block as unreadable, soExtractFrontmatterreturns null andCombineFrontmatterreturns the document unchanged. An alias that is used more than once without a cycle still expands as before.ReferenceEqualityComparerisn't available on netstandard2.0/2.1, so a small private reference comparer takes its place.DeepCloneValueneeds no guard, because it only ever sees the bounded, acyclic tree thatConvertValuereturns.Tests: added
YamlAliasTests, which covers a self-referencing sequence and mapping through bothTryParseYamlObjectand the public API, the six-level alias bomb, and a non-cyclic alias used twice. With the fix reverted, the self-referencing tests crash the host (exit 134, stack overflow) and both bomb tests fail. With the fix in place, the full suite passes: 260 of 260.🤖 Generated with Claude Code
https://claude.ai/code/session_01Hnw6WDDjwQ8HvxinnWS9CF
Generated by Claude Code