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fix: throw clear errors when constant instantiation is performed through YAML directly #5271

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fix: throw clear errors when constant instantiation is performed through YAML directly #5271

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37 changes: 26 additions & 11 deletions alchemist-loading/src/main/kotlin/it/unibo/alchemist/boundary/loader/SimulationModel.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -382,18 +382,33 @@ internal object SimulationModel {
}

private fun visitConstant(name: String, context: Context, root: Any?): Result<Constant<*>>? {
val constant: Result<Constant<*>>? =
when (root) {
is Map<*, *> -> {
visitDependentVariable(name, context, root)
?.mapCatching { it.getWith(context.constants) }
?.onFailure {
logger.debug("Evaluation failed at {}, context {}:\n{}", root, context, it.message)
}?.onSuccess { context.registerConstant(name, root, it) }
?.map { Constant(it) }
}
else -> null
fun unsupportedConstantInstantiation(): Nothing = throw IllegalArgumentException(
"""
Constant creation failed: '$name' with value '$root'.
Direct constant instantiation from YAML is not supported, please consult the Alchemist YAML spec at:
> https://alchemistsimulator.github.io/reference/yaml/index.html#variable
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Copilot AI Apr 14, 2026

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The exception message links to .../reference/yaml/index.html#variable, but the docs in this repo reference the variables section as /reference/yaml/#variables (e.g., site/content/howtos/simulation/variables/_index.md:10). Please update the URL/anchor so the guidance doesn’t send users to a dead/incorrect page.

Suggested change
> https://alchemistsimulator.github.io/reference/yaml/index.html#variable
> https://alchemistsimulator.github.io/reference/yaml/#variables

Copilot uses AI. Check for mistakes.
Likely workaround:
```yaml
$name:
formula: >
$root
```
""".trimIndent(),
)
Comment on lines +385 to +397
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Copilot AI Apr 14, 2026

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The suggested workaround snippet uses formula: > $root, but visitDependentVariable treats String formulas as JSR-223 code (not string literals). If $root is a YAML String, following this advice will likely evaluate as an identifier and fail unless it’s quoted as a language literal. Consider tailoring the message by type (e.g., numeric/list constants can use a non-string formula, while string constants need explicit quoting guidance).

Suggested change
fun unsupportedConstantInstantiation(): Nothing = throw IllegalArgumentException(
"""
Constant creation failed: '$name' with value '$root'.
Direct constant instantiation from YAML is not supported, please consult the Alchemist YAML spec at:
> https://alchemistsimulator.github.io/reference/yaml/index.html#variable
Likely workaround:
```yaml
$name:
formula: >
$root
```
""".trimIndent(),
)
fun formulaLiteral(value: Any?): String = when (value) {
is String -> "\"" + value.replace("\\", "\\\\").replace("\"", "\\\"") + "\""
else -> value.toString()
}
fun unsupportedConstantInstantiation(): Nothing {
val suggestedFormula = formulaLiteral(root)
throw IllegalArgumentException(
"""
Constant creation failed: '$name' with value '$root'.
Direct constant instantiation from YAML is not supported, please consult the Alchemist YAML spec at:
> https://alchemistsimulator.github.io/reference/yaml/index.html#variable
Likely workaround:
```yaml
$name:
formula: >
$suggestedFormula
```
""".trimIndent(),
)
}

Copilot uses AI. Check for mistakes.
val constant: Result<Constant<*>>? = when (root) {
is Number -> unsupportedConstantInstantiation()
is String -> unsupportedConstantInstantiation()
is Boolean -> unsupportedConstantInstantiation()
Comment on lines +398 to +401
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Copilot AI Apr 14, 2026

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This change introduces a new hard failure for scalar entries under variables (Number/String/Boolean). There are existing YAML-loading regression tests for variables/constants (e.g., alchemist-loading/src/test/kotlin/it/unibo/alchemist/test/TestKtVariable.kt); please add a regression test that loads a YAML with variables: { someConst: 3 } (and/or a scalar string/boolean) and asserts that the thrown exception is the new, user-friendly one.

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is Map<*, *> -> {
visitDependentVariable(name, context, root)
?.mapCatching { it.getWith(context.constants) }
?.onFailure {
logger.debug("Evaluation failed at {}, context {}:\n{}", root, context, it.message)
}?.onSuccess { context.registerConstant(name, root, it) }
?.map { Constant(it) }
}
else -> null
}
constant?.onSuccess {
logger.debug("Variable {}, evaluated from {} as constant, returned {}", name, root, it.value)
check(!context.constants.containsKey(name) || context.constants[name] == it.value) {
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