fix str.join with and/or expression narrowing #2875

crates/pyrefly_types/src/types.rs

@@ -1851,6 +1851,7 @@ impl Type {
             Type::Literal(lit) if let Lit::Int(x) = &lit.value => Some(x.as_bool()),
             Type::Literal(lit) if let Lit::Bytes(x) = &lit.value => Some(!x.is_empty()),
             Type::Literal(lit) if let Lit::Str(x) = &lit.value => Some(!x.is_empty()),
+            Type::Type(_) => Some(true),
             Type::None => Some(false),
             Type::Tuple(Tuple::Concrete(elements)) => Some(!elements.is_empty()),
             Type::Union(box Union { members, .. }) => {

pyrefly/lib/alt/expr.rs

@@ -77,6 +77,7 @@ use crate::binding::binding::Key;
 use crate::binding::binding::KeyYield;
 use crate::binding::binding::KeyYieldFrom;
 use crate::binding::binding::LambdaParamId;
+use crate::binding::narrow::AtomicNarrowOp;
 use crate::binding::narrow::int_from_slice;
 use crate::config::error_kind::ErrorKind;
 use crate::error::collector::ErrorCollector;
@@ -89,7 +90,6 @@ use crate::types::callable::Params;
 use crate::types::callable::Required;
 use crate::types::class::Class;
 use crate::types::facet::FacetKind;
-use crate::types::lit_int::LitInt;
 use crate::types::literal::Lit;
 use crate::types::param_spec::ParamSpec;
 use crate::types::quantified::Quantified;
@@ -1231,6 +1231,10 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
             BoolOp::And => false,
             BoolOp::Or => true,
         };
+        let result_narrow = match op {
+            BoolOp::And => AtomicNarrowOp::IsFalsy,
+            BoolOp::Or => AtomicNarrowOp::IsTruthy,
+        };
         let should_shortcircuit =
             |t: &Type, r: TextRange| self.as_bool(t, r, errors) == Some(target);
         let should_discard = |t: &Type, r: TextRange| self.as_bool(t, r, errors) == Some(!target);
@@ -1264,21 +1268,8 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
                         None => t.clone(),
                         Some(acc) => self.union(acc, t.clone()),
                     });
-                    // Narrow the type for the result of the boolop
-                    let t = if i != last_index
-                        && t == self.heap.mk_class_type(self.stdlib.bool().clone())
-                    {
-                        Lit::Bool(target).to_implicit_type()
-                    } else if i != last_index
-                        && t == self.heap.mk_class_type(self.stdlib.int().clone())
-                        && !target
-                    {
-                        LitInt::new(0).to_implicit_type()
-                    } else if i != last_index
-                        && t == self.heap.mk_class_type(self.stdlib.str().clone())
-                        && !target
-                    {
-                        Lit::Str(Default::default()).to_implicit_type()
+                    let t = if i != last_index {
+                        self.atomic_narrow(&t, &result_narrow, value.range(), errors)
                     } else {
                         t
                     };

pyrefly/lib/alt/narrow.rs

@@ -885,7 +885,7 @@ impl<'a, Ans: LookupAnswer> AnswersSolver<'a, Ans> {
         }
     }
 
-    fn atomic_narrow(
+    pub(crate) fn atomic_narrow(
         &self,
         ty: &Type,
         op: &AtomicNarrowOp,

pyrefly/lib/test/literal.rs

@@ -378,6 +378,18 @@ def f(x1: list[str], x2: list[LiteralString]):
     "#,
 );
 
+testcase!(
+    test_str_join_boolop_narrowing,
+    r#"
+from typing import assert_type
+
+def format_types(types: set[type | None]) -> str:
+    values = sorted((e and e.__name__) or "None" for e in types)
+    assert_type(values, list[str])
+    return ", ".join(values)
+    "#,
+);
+
 testcase!(
     test_giant_literal_string,
     r#"

pyrefly/lib/test/lsp/lsp_interaction/pytorch_benchmark.rs

@@ -48,7 +48,7 @@ fn test_pytorch_error_propagation_latency() {
     };
     // Use all available cores for realistic benchmarking
     let mut interaction =
-        LspInteraction::new_with_args(args, NoTelemetry, Some(ThreadCount::AllThreads));
+        LspInteraction::new_with_args(args, NoTelemetry, Some(ThreadCount::AllThreads), None);
     interaction.set_root(pytorch_root.clone());
 
     interaction