[red-knot] add support for typing_extensions.reveal_type (#13397)

Before `typing.reveal_type` existed, there was
`typing_extensions.reveal_type`. We should support both.

Also adds a test to verify that we can handle aliasing of `reveal_type`
to a different name.

Adds a bit of code to ensure that if we have a union of different
`reveal_type` functions (e.g. a union containing both
`typing_extensions.reveal_type` and `typing.reveal_type`) we still emit
the reveal-type diagnostic only once. This is probably unlikely in
practice, but it doesn't hurt to handle it smoothly. (It comes up now
because we don't support `version_info` checks yet, so
`typing_extensions.reveal_type` is actually that union.)

---------

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

crates/red_knot_python_semantic/src/types.rs

@@ -762,12 +762,25 @@ impl<'db> CallOutcome<'db> {
             } => {
                 let mut not_callable = vec![];
                 let mut union_builder = UnionBuilder::new(db);
+                let mut revealed = false;
                 for outcome in &**outcomes {
-                    let return_ty = if let Self::NotCallable { not_callable_ty } = outcome {
-                        not_callable.push(*not_callable_ty);
-                        Type::Unknown
-                    } else {
-                        outcome.unwrap_with_diagnostic(db, node, builder)
+                    let return_ty = match outcome {
+                        Self::NotCallable { not_callable_ty } => {
+                            not_callable.push(*not_callable_ty);
+                            Type::Unknown
+                        }
+                        Self::RevealType {
+                            return_ty,
+                            revealed_ty: _,
+                        } => {
+                            if revealed {
+                                *return_ty
+                            } else {
+                                revealed = true;
+                                outcome.unwrap_with_diagnostic(db, node, builder)
+                            }
+                        }
+                        _ => outcome.unwrap_with_diagnostic(db, node, builder),
                     };
                     union_builder = union_builder.add(return_ty);
                 }
@@ -841,6 +854,15 @@ impl<'db> FunctionType<'db> {
             })
     }
 
+    /// Return true if this is a symbol with given name from `typing` or `typing_extensions`.
+    pub(crate) fn is_typing_symbol(self, db: &'db dyn Db, name: &str) -> bool {
+        name == self.name(db)
+            && file_to_module(db, self.definition(db).file(db)).is_some_and(|module| {
+                module.search_path().is_standard_library()
+                    && matches!(&**module.name(), "typing" | "typing_extensions")
+            })
+    }
+
     pub fn has_decorator(self, db: &dyn Db, decorator: Type<'_>) -> bool {
         self.decorators(db).contains(&decorator)
     }

crates/red_knot_python_semantic/src/types/infer.rs

@@ -705,7 +705,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         }
 
         let function_type = FunctionType::new(self.db, name.id.clone(), definition, decorator_tys);
-        let function_ty = if function_type.is_stdlib_symbol(self.db, "typing", "reveal_type") {
+        let function_ty = if function_type.is_typing_symbol(self.db, "reveal_type") {
             Type::RevealTypeFunction(function_type)
         } else {
             Type::Function(function_type)
@@ -2761,6 +2761,44 @@ mod tests {
         Ok(())
     }
 
+    #[test]
+    fn reveal_type_aliased() -> anyhow::Result<()> {
+        let mut db = setup_db();
+
+        db.write_dedented(
+            "/src/a.py",
+            "
+            from typing import reveal_type as rt
+
+            x = 1
+            rt(x)
+            ",
+        )?;
+
+        assert_file_diagnostics(&db, "/src/a.py", &["Revealed type is 'Literal[1]'."]);
+
+        Ok(())
+    }
+
+    #[test]
+    fn reveal_type_typing_extensions() -> anyhow::Result<()> {
+        let mut db = setup_db();
+
+        db.write_dedented(
+            "/src/a.py",
+            "
+            import typing_extensions
+
+            x = 1
+            typing_extensions.reveal_type(x)
+            ",
+        )?;
+
+        assert_file_diagnostics(&db, "/src/a.py", &["Revealed type is 'Literal[1]'."]);
+
+        Ok(())
+    }
+
     #[test]
     fn follow_import_to_class() -> anyhow::Result<()> {
         let mut db = setup_db();