Warnings & Limits

The compiler returns diagnostic information that does not stop compilation through the warnings array. Each warning object has these fields:

type LuisCompileWarning = {
  code: string
  line: number
  message: string
}

Policy

There are two policies: fail-closed and fail-soft.

Policy	Behavior on limit exceeded
`fail-closed`	Produces a compile error and stops compilation
`fail-soft`	Produces a `resource-limit` warning and compilation continues

The default policy is fail-closed. When debug: true is provided, the default policy switches to fail-soft.

Code	Trigger Scenario
`missing-semicolon`	A `;` is missing after a declaration or composition line
`invalid-syntax`	Invalid `.luis` syntax — present in the type definition; these scenarios are generally error-path behavior and are not emitted as warnings

Code	Trigger Scenario
`invalid-directive-order`	Directives like `@charset`, `@layer` are written in the wrong order
`invalid-directive-position`	A directive is used in a disallowed position

Code	Trigger Scenario
`unsupported-import`	Import format not supported by the compiler, or a `.luis` import exists when `importResolver` is not defined
`import-not-found`	`importResolver` returned `null` — import could not be resolved
`import-cycle`	Two or more `.luis` files import each other
`invalid-import-url`	Unsafe or unsupported URL used (`javascript:`, etc.)
`duplicate-import-variable`	The same variable was defined more than once from different imports

Code	Trigger Scenario
`invalid-array-range-unit`	Start and end units differ in an array range (`[1px-3rem]` etc.)
`invalid-object-loop-access`	Object key access was attempted on a non-object value in a `@for` loop

Code	Trigger Scenario
`invalid-function-syntax`	Function definition syntax is invalid
`invalid-function-name`	Function name contains invalid characters
`duplicate-function`	Two functions with the same name were defined
`unknown-function-call`	An undefined function was called
`invalid-function-call`	A function call was made in an invalid form
`function-argument-mismatch`	The argument count in the call does not match the definition
`function-recursion`	A function calls itself

Code	Trigger Scenario
`resource-limit`	`fail-soft` mode only: a resource limit was exceeded

Limit	Default	Description
`maxForIterationsPerLoop`	`2,000`	Maximum iteration count in a single `@for` loop
`maxNestedLoopProduct`	`100,000`	Iteration product limit in nested loops (`i × j × k…`)
`maxExpandedRules`	`50,000`	Maximum number of rules that can be produced in compilation
`maxOutputCssChars`	`3,000,000`	Maximum character count of the final CSS output
`maxImportDepth`	`64`	Maximum depth allowed in an import chain
`maxImportCount`	`2,000`	Total number of imports that can be resolved during compilation
`maxImportedBytes`	`4,000,000`	Total imported source character/byte budget

Limit	Default	Description
`maxObservedRules`	`5,000`	Total observed rule count that can be accepted during compilation
`maxObservedActiveRules`	`1,000`	Number of observed rules that can be active at the same time at runtime
`maxObservedRuleKeysPerToken`	`300`	Maximum rule key count that can be held for a single token in the runtime index
`maxMutationBatchTokens`	`1,500`	Number of tokens that can be processed in a single mutation batch at runtime
`maxObservedReevalPerTick`	`500`	Number of observed rules that can be re-evaluated in a single tick at runtime

When resourcePolicy: 'fail-soft' is active, the compilation state and generated output for each error type:

Error Type	Output	Warning Code
Missing `;`	Rule is generated as-is	`missing-semicolon`
Invalid selector	No general warning is produced; selector text is generally emitted as-is. Some observed suffix errors fall back to static selector. Structural syntax errors stop compilation with an error.	—
Invalid `${...}` expression	Not converted to a warning; throws `Invalid .luis syntax ...` error and stops compilation. Not converted to an empty string.	—
Unknown `@fun` call	Call is skipped	`unknown-function-call`
Argument count mismatch	Call is not expanded	`function-argument-mismatch`
Unsafe or unsupported `@import` URL	Import is skipped	`invalid-import-url`
Import depth / count / imported-bytes limit exceeded	`resource-limit` warning is produced; the branch that exceeds the limit is cut	`resource-limit`
Loop / nested loop limit exceeded	`resource-limit` warning is produced; the loop block that exceeds the limit is skipped	`resource-limit`
Expanded rule limit exceeded	`resource-limit` warning is produced; extra rules are cut to the limit	`resource-limit`
Observed rule limit exceeded	`resource-limit` warning is produced; non-observed rules are preserved, observed rules are filtered to the limit	`resource-limit`
Final CSS size limit exceeded	`resource-limit` warning is produced; CSS output is returned as-is, not truncated	`resource-limit`

In fail-soft mode, the behavior on exceeding each limit differs:

Limit Exceeded	Behavior
Import depth / count / imported-bytes limit	`resource-limit` warning is produced; the branch that exceeds the limit is cut at resolution
Loop iteration / nested loop product limit	`resource-limit` warning is produced; the loop block that exceeds the limit is skipped
Expanded rule limit	`resource-limit` warning is produced; extra rules are cut to the limit
Observed rule limit (`maxObservedRules`)	`resource-limit` warning is produced; non-observed rules are preserved, observed rules are filtered to the limit
Final CSS size limit	`resource-limit` warning is produced; CSS output is returned as-is, not truncated
Mutation batch limit (`maxMutationBatchTokens`)	`resource-limit` warning is produced; the token set to be processed is cut to the limit
Observed reevaluation limit (`maxObservedReevalPerTick`)	`resource-limit` warning is produced; the rule key set to be re-evaluated is cut to the limit
Active observed rule limit (`maxObservedActiveRules`)	`resource-limit` warning is produced; the active rule key set is cut to the limit