Make Type Params carry pre inference variance info instead of post inference info

Summary:
We are constructing type parameters in the class definition, function definitions and type aliases constructions.

We don't need post inference variance information there as we can see from this diff (I think we don't need variance info at all there).

We need variance info for the subtype check.

In this diff, I am using preinfence variance everywhere, because at all those places we mentioned above, we don't have enough info to infer variance.  And when it's time to do the subtyping check, I convert the representation.

Things to look into:
1- I need to find a way to somehow thread a variance map to the subtyping check, where I can query the specific parameter I want by supplying the class name and the parameter I need. Right now, I don't see the class info there, so that's the next thing to look into

2- Do we need the variance info at all in TParam and TParamInfo? my guess is no, but I can't get rid of it until I figure out item #1.

Reviewed By: rchen152

Differential Revision: D75485457

fbshipit-source-id: bcf530a1a61661e38dfb8c972b6ab2c6fa90a6ae

Author: migeed-z

pyrefly/lib/alt/class/typed_dict.rs

@@ -37,8 +37,8 @@ use crate::types::class::Class;
 use crate::types::class::Substitution;
 use crate::types::literal::Lit;
 use crate::types::quantified::Quantified;
+use crate::types::type_var::PreInferenceVariance;
 use crate::types::type_var::Restriction;
-use crate::types::type_var::Variance;
 use crate::types::typed_dict::TypedDict;
 use crate::types::typed_dict::TypedDictField;
 use crate::types::types::Forall;
@@ -261,7 +261,7 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
 
                 let tparams = vec![TParam {
                     quantified: q.clone(),
-                    variance: Variance::Invariant,
+                    variance: PreInferenceVariance::PInvariant,
                 }];
 
                 literal_signatures.push(OverloadType::Forall(Forall {

pyrefly/lib/alt/solve.rs

@@ -29,7 +29,6 @@ use crate::alt::answers::AnswersSolver;
 use crate::alt::answers::LookupAnswer;
 use crate::alt::callable::CallArg;
 use crate::alt::class::class_field::ClassField;
-use crate::alt::class::variance_inference::pre_to_post_variance;
 use crate::alt::types::class_metadata::ClassMetadata;
 use crate::alt::types::class_metadata::ClassSynthesizedFields;
 use crate::alt::types::decorated_function::DecoratedFunction;
@@ -1018,7 +1017,7 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
                 quantified: tparam.quantified,
                 // Classes set the variance before getting here. For functions and aliases, the variance isn't meaningful;
                 // it doesn't matter what we set it to as long as we make it non-None to indicate that it's not missing.
-                variance: pre_to_post_variance(tparam.variance),
+                variance: tparam.variance,
             });
         }
 

pyrefly/lib/solver/subset.rs

@@ -16,6 +16,7 @@ use ruff_python_ast::name::Name;
 use starlark_map::small_map::SmallMap;
 
 use crate::alt::answers::LookupAnswer;
+use crate::alt::class::variance_inference::pre_to_post_variance;
 use crate::dunder;
 use crate::solver::solver::Subset;
 use crate::types::callable::Callable;
@@ -1012,7 +1013,8 @@ impl<'a, Ans: LookupAnswer> Subset<'a, Ans> {
             let result = if param.quantified.kind() == QuantifiedKind::TypeVarTuple {
                 self.is_equal(got_arg, want_arg)
             } else {
-                match param.variance {
+                let param_variance = pre_to_post_variance(param.variance);
+                match param_variance {
                     Variance::Covariant => self.is_subset_eq(got_arg, want_arg),
                     Variance::Contravariant => self.is_subset_eq(want_arg, got_arg),
                     Variance::Invariant => self.is_equal(got_arg, want_arg),

pyrefly/lib/types/display.rs

@@ -364,7 +364,6 @@ pub mod tests {
     use crate::types::type_var::PreInferenceVariance;
     use crate::types::type_var::Restriction;
     use crate::types::type_var::TypeVar;
-    use crate::types::type_var::Variance;
     use crate::types::typed_dict::TypedDict;
     use crate::types::types::TParam;
     use crate::types::types::TParams;
@@ -396,7 +395,7 @@ pub mod tests {
                     default: None,
                 },
             ),
-            variance: Variance::Invariant,
+            variance: PreInferenceVariance::PInvariant,
         }
     }
 

pyrefly/lib/types/equality.rs

@@ -273,8 +273,8 @@ mod tests {
     use crate::types::quantified::Quantified;
     use crate::types::quantified::QuantifiedInfo;
     use crate::types::quantified::QuantifiedKind;
+    use crate::types::type_var::PreInferenceVariance;
     use crate::types::type_var::Restriction;
-    use crate::types::type_var::Variance;
     use crate::types::types::Forallable;
     use crate::types::types::TParam;
     use crate::types::types::TParams;
@@ -362,7 +362,7 @@ mod tests {
 
             let tparams = TParams::new(vec![TParam {
                 quantified: q.clone(),
-                variance: Variance::Invariant,
+                variance: PreInferenceVariance::PInvariant,
             }]);
 
             Forallable::Function(Function {

pyrefly/lib/types/types.rs

@@ -47,7 +47,6 @@ use crate::types::tuple::Tuple;
 use crate::types::type_var::PreInferenceVariance;
 use crate::types::type_var::Restriction;
 use crate::types::type_var::TypeVar;
-use crate::types::type_var::Variance;
 use crate::types::type_var_tuple::TypeVarTuple;
 use crate::types::typed_dict::TypedDict;
 
@@ -87,7 +86,7 @@ pub struct TParamInfo {
 #[derive(Visit, VisitMut, TypeEq)]
 pub struct TParam {
     pub quantified: Quantified,
-    pub variance: Variance,
+    pub variance: PreInferenceVariance,
 }
 
 impl Display for TParam {