[ty] Add support for PEP 750 t-strings (#20085)

This PR attempts to adds support for inferring`string.templatelib.Template` for t-string literals.

crates/ty_python_semantic/resources/mdtest/t_strings.md

@@ -0,0 +1,20 @@
+# Template strings
+
+(NB: `black` does not support Python 3.14 at the time of this writing)
+
+<!-- blacken-docs:off -->
+
+```toml
+[environment]
+python-version = "3.14"
+```
+
+Template strings, or t-strings, were added in Python 3.14.
+
+They may be specified as literals and are objects of type `string.templatelib.Template`.
+
+## Empty template string
+
+```py
+reveal_type(t"")  # revealed: Template
+```

crates/ty_python_semantic/src/module_resolver/module.rs

@@ -270,6 +270,8 @@ pub enum KnownModule {
     Dataclasses,
     Collections,
     Inspect,
+    #[strum(serialize = "string.templatelib")]
+    Templatelib,
     #[strum(serialize = "_typeshed._type_checker_internals")]
     TypeCheckerInternals,
     TyExtensions,
@@ -305,6 +307,7 @@ impl KnownModule {
             Self::UnittestMock => "unittest.mock",
             #[cfg(test)]
             Self::Uuid => "uuid",
+            Self::Templatelib => "string.templatelib",
         }
     }
 

crates/ty_python_semantic/src/types/class.rs

@@ -3540,6 +3540,8 @@ pub enum KnownClass {
     NamedTupleFallback,
     NamedTupleLike,
     TypedDictFallback,
+    // string.templatelib
+    Template,
 }
 
 impl KnownClass {
@@ -3582,7 +3584,8 @@ impl KnownClass {
             | Self::GeneratorType
             | Self::AsyncGeneratorType
             | Self::MethodWrapperType
-            | Self::CoroutineType => Some(Truthiness::AlwaysTrue),
+            | Self::CoroutineType
+            | Self::Template => Some(Truthiness::AlwaysTrue),
 
             Self::NoneType => Some(Truthiness::AlwaysFalse),
 
@@ -3716,7 +3719,8 @@ impl KnownClass {
             | KnownClass::InitVar
             | KnownClass::NamedTupleFallback
             | KnownClass::NamedTupleLike
-            | KnownClass::TypedDictFallback => false,
+            | KnownClass::TypedDictFallback
+            | KnownClass::Template => false,
         }
     }
 
@@ -3792,7 +3796,8 @@ impl KnownClass {
             | KnownClass::InitVar
             | KnownClass::NamedTupleFallback
             | KnownClass::NamedTupleLike
-            | KnownClass::TypedDictFallback => false,
+            | KnownClass::TypedDictFallback
+            | KnownClass::Template => false,
         }
     }
 
@@ -3867,7 +3872,8 @@ impl KnownClass {
             | KnownClass::InitVar
             | KnownClass::TypedDictFallback
             | KnownClass::NamedTupleLike
-            | KnownClass::NamedTupleFallback => false,
+            | KnownClass::NamedTupleFallback
+            | KnownClass::Template => false,
         }
     }
 
@@ -3955,7 +3961,8 @@ impl KnownClass {
             | Self::KwOnly
             | Self::InitVar
             | Self::NamedTupleFallback
-            | Self::TypedDictFallback => false,
+            | Self::TypedDictFallback
+            | Self::Template => false,
         }
     }
 
@@ -4051,6 +4058,7 @@ impl KnownClass {
             Self::NamedTupleFallback => "NamedTupleFallback",
             Self::NamedTupleLike => "NamedTupleLike",
             Self::TypedDictFallback => "TypedDictFallback",
+            Self::Template => "Template",
         }
     }
 
@@ -4315,6 +4323,7 @@ impl KnownClass {
             Self::Field | Self::KwOnly | Self::InitVar => KnownModule::Dataclasses,
             Self::NamedTupleFallback | Self::TypedDictFallback => KnownModule::TypeCheckerInternals,
             Self::NamedTupleLike => KnownModule::TyExtensions,
+            Self::Template => KnownModule::Templatelib,
         }
     }
 
@@ -4392,7 +4401,8 @@ impl KnownClass {
             | Self::Iterator
             | Self::NamedTupleFallback
             | Self::NamedTupleLike
-            | Self::TypedDictFallback => Some(false),
+            | Self::TypedDictFallback
+            | Self::Template => Some(false),
 
             Self::Tuple => None,
         }
@@ -4473,7 +4483,8 @@ impl KnownClass {
             | Self::Iterator
             | Self::NamedTupleFallback
             | Self::NamedTupleLike
-            | Self::TypedDictFallback => false,
+            | Self::TypedDictFallback
+            | Self::Template => false,
         }
     }
 
@@ -4563,6 +4574,7 @@ impl KnownClass {
             "NamedTupleFallback" => Self::NamedTupleFallback,
             "NamedTupleLike" => Self::NamedTupleLike,
             "TypedDictFallback" => Self::TypedDictFallback,
+            "Template" => Self::Template,
             _ => return None,
         };
 
@@ -4629,7 +4641,8 @@ impl KnownClass {
             | Self::TypedDictFallback
             | Self::NamedTupleLike
             | Self::Awaitable
-            | Self::Generator => module == self.canonical_module(db),
+            | Self::Generator
+            | Self::Template => module == self.canonical_module(db),
             Self::NoneType => matches!(module, KnownModule::Typeshed | KnownModule::Types),
             Self::SpecialForm
             | Self::TypeVar
@@ -5095,7 +5108,13 @@ mod tests {
 
     #[test]
     fn known_class_roundtrip_from_str() {
-        let db = setup_db();
+        let mut db = setup_db();
+        Program::get(&db)
+            .set_python_version_with_source(&mut db)
+            .to(PythonVersionWithSource {
+                version: PythonVersion::latest_preview(),
+                source: PythonVersionSource::default(),
+            });
         for class in KnownClass::iter() {
             let class_name = class.name(&db);
             let class_module = resolve_module(&db, &class.canonical_module(&db).name()).unwrap();
@@ -5124,6 +5143,14 @@ mod tests {
             });
 
         for class in KnownClass::iter() {
+            // Until the latest supported version is bumped to Python 3.14
+            // we need to skip template strings here.
+            // The assertion below should remind the developer to
+            // remove this exception once we _do_ bump `latest_ty`
+            assert_ne!(PythonVersion::latest_ty(), PythonVersion::PY314);
+            if matches!(class, KnownClass::Template) {
+                continue;
+            }
             assert_ne!(
                 class.to_instance(&db),
                 Type::unknown(),
@@ -5143,6 +5170,7 @@ mod tests {
         let mut classes: Vec<(KnownClass, PythonVersion)> = KnownClass::iter()
             .map(|class| {
                 let version_added = match class {
+                    KnownClass::Template => PythonVersion::PY314,
                     KnownClass::UnionType => PythonVersion::PY310,
                     KnownClass::BaseExceptionGroup | KnownClass::ExceptionGroup => {
                         PythonVersion::PY311

crates/ty_python_semantic/src/types/infer.rs

@@ -5744,7 +5744,7 @@ impl<'db, 'ast> TypeInferenceBuilder<'db, 'ast> {
                 }
             }
         }
-        todo_type!("Template")
+        KnownClass::Template.to_instance(self.db())
     }
 
     fn infer_ellipsis_literal_expression(