Config

How many recursive calls to findMember are performed before logging names starts Note: this threshold has to be chosen carefully. Too large, and programs like tests/pos/IterableSelfRec go into polynomial (or even exponential?) compile time slowdown. Too small and normal programs will cause the compiler to do inefficient operations on findMember. The current value is determined so that (1) IterableSelfRec still compiles in reasonable time (< 10sec) (2) Compiling dotty itself only causes small pending names lists to be generated (we measured at max 6 elements) and these lists are never searched with contains.

How many recursive calls to isSubType are performed before logging starts.

How many recursive calls to NamedType#underlying are performed before logging starts.

If this flag is set, and we compute T1[X1] & T2[X2] as a new upper bound of a constrained parameter, try to align the arguments by computing S1 =:= S2 (which might instantiate type parameters). This rule is contentious because it cuts the constraint set.

For more info, see the comment in TypeComparer#glbArgs.

Check that atoms-based comparisons match regular comparisons that do not take atoms into account. The two have to give the same results, since atoms comparison is intended to be just an optimization.

Check that Name#toString is not called directly from backend by analyzing the stack trace of each toString call on names. This is very expensive, so not suitable for continuous testing. But it can be used to find a problem when running a specific test.

If a constraint is over a type lambda tl and tvar is one of the type variables associated with tl in the constraint, check that the origin of tvar is a parameter of tl.

Check that reverse dependencies in constraints are correct and complete. Can also be enabled using -Ycheck-constraint-deps.

When updating a constraint bound, check that the constrained parameter does not appear at the top-level of either of its bounds.

Check that each constraint is fully propagated. i.e. If P <: Q then the upper bound of P is a subtype of the upper bound of Q and the lower bound of Q is a subtype of the lower bound of P.

Check that each constraint resulting from a subtype test is satisfiable. Also check that a type variable instantiation satisfies its constraints. Note that this can fail when bad bounds are in scope, like in tests/neg/i4721a.scala.

If this flag is set, higher-kinded applications are checked for validity

Check that variances of lambda arguments match the variance of the underlying lambda class.

If checkLevelsOnConstraints is true, check levels of type variables and create fresh ones as needed when bounds are first entered intot he constraint. If checkLevelsOnInstantiation is true, allow level-incorrect constraints but fix levels on type variable instantiation.

If this flag is set, method types are checked for valid parameter references

Check that no type appearing as the info of a SymDenotation contains skolem types.

Check that constraint bounds do not contain wildcard types

Check positions for consistency after parsing

Check that typed trees don't point to untyped ones

Check that re-used type comparers are in their initialization state

If this flag is set, it is checked that class type parameters are only references with NoPrefix or ThisTypes as prefixes. This option is usually disabled, because there are still some legitimate cases where this can arise (e.g. for pos/Map.scala, in LambdaType.integrate).

If this flag is set, it is checked that TypeRefs don't refer directly to themselves.

Check that certain types cannot be created in erasedTypes phases. Note: Turning this option on will get some false negatives, since it is possible that And/Or types are still created during erasure as the result of some operation on an existing type.

If this flag is set, we check that types assigned to trees are error types only if some error was already reported. There are complicicated scenarios where this is not true. An example is TestNonCyclic in posTwice. If we remove the first (unused) import import dotty.tools.dotc.core.Types.Type in CompilationUnit, we end up assigning a CyclicReference error type to an import expression annotation before the cyclic reference is reported. What happens is that the error was reported as a result of a completion in a not-yet committed typerstate. So we cannot enforce this in all circumstances. But since it is almost always true it is useful to keep the Config option for debugging.

Check that constraints of globally committable typer states are closed. NOTE: When enabled, the check can cause CyclicReference errors because it traverses all elements of a type. Such failures were observed when compiling all of dotty together (source seems to be in GenBCode which accesses javac's settings.)

It is recommended to turn this option on only when chasing down a TypeParamRef instantiation error. See comment in Types.TypeVar.instantiate.

Assume -indent by default

Type comparer will fail with an assert if the upper bound of a constrained parameter becomes Nothing. This should be turned on only for specific debugging as normally instantiation to Nothing is not an error condition.

If this flag is set, take the fast path when comparing same-named type-aliases and types

If set, method results that are context functions are flattened by adding the parameters of the context function results to the methods themselves. This is an optimization that reduces closure allocations.

When in IDE, turn StaleSymbol errors into warnings instead of crashing

Initial capacity of the uniques HashMap. Note: This should be a power of two to work with util.HashSet

If true, the runWithOwner operation uses a re-usable context, similar to explore. This requires that the context does not escape the call. If false, runWithOwner runs its operation argument in a fresh context.

If true, Denotation#asSeenFrom is allowed to return an existing SymDenotation instead of allocating a new SingleDenotation if the two would only differ in their prefix (SymDenotation always have NoPrefix as their prefix). This is done for performance reasons: when compiling Dotty itself this reduces the number of allocated denotations by ~50%.

If set, prints a trace of all symbol completions

If set, show variable/variable reverse dependencies when printing constraints.

If this flag is on, always rewrite an application S[Ts] where S is an alias for [Xs] -> U to [Xs := Ts]U. Turning this flag on was observed to give a ~6% speedup on the JUnit test suite.

In derivedSelect, rewrite

(S & T)#A  -->  S#A & T#A
(S | T)#A  -->  S#A | T#A

Not sure whether this is useful. Preliminary measurements show a slowdown of about 7% for the build when this option is enabled.

The recursion depth for showing a summarized string

Show subtype traces for all deep subtype recursions

If set, enables tracing

When explaining subtypes and this flag is set, also show the classes of the compared types.