[ty] Only calculate information for unresolved-reference subdiagnostic if we know we'll emit the diagnostic (#18465)

## Summary

This optimizes some of the logic added in
https://github.com/astral-sh/ruff/pull/18444. In general, we only
calculate information for subdiagnostics if we know we'll actually emit
the diagnostic. The check to see whether we'll emit the diagnostic is
work we'll definitely have to do whereas the the work to gather
information for a subdiagnostic isn't work we necessarily have to do if
the diagnostic isn't going to be emitted at all.

This PR makes us lazier about gathering the information we need for the
subdiagnostic, and moves all the subdiagnostic logic into one function
rather than having some `unresolved-reference` subdiagnostic logic in
`infer.rs` and some in `diagnostic.rs`.

## Test Plan

`cargo test -p ty_python_semantic`

crates/ty_python_semantic/src/types/diagnostic.rs

@@ -19,7 +19,6 @@ use crate::{Db, Module, ModuleName, Program, declare_lint};
 use itertools::Itertools;
 use ruff_db::diagnostic::{Annotation, Diagnostic, Severity, SubDiagnostic};
 use ruff_python_ast::{self as ast, AnyNodeRef};
-use ruff_python_stdlib::builtins::version_builtin_was_added;
 use ruff_text_size::{Ranged, TextRange};
 use rustc_hash::FxHashSet;
 use std::fmt::Formatter;
@@ -1778,35 +1777,6 @@ pub(super) fn report_possibly_unbound_attribute(
     ));
 }
 
-pub(super) fn report_unresolved_reference(
-    context: &InferContext,
-    expr_name_node: &ast::ExprName,
-    attribute_exists: bool,
-) {
-    let Some(builder) = context.report_lint(&UNRESOLVED_REFERENCE, expr_name_node) else {
-        return;
-    };
-
-    let ast::ExprName { id, .. } = expr_name_node;
-    let mut diagnostic = builder.into_diagnostic(format_args!("Name `{id}` used when not defined"));
-    if let Some(version_added_to_builtins) = version_builtin_was_added(id) {
-        diagnostic.info(format_args!(
-            "`{id}` was added as a builtin in Python 3.{version_added_to_builtins}"
-        ));
-        add_inferred_python_version_hint_to_diagnostic(
-            context.db(),
-            &mut diagnostic,
-            "resolving types",
-        );
-    }
-
-    if attribute_exists {
-        diagnostic.info(format_args!(
-            "An attribute `{id}` is available, consider using `self.{id}`"
-        ));
-    }
-}
-
 pub(super) fn report_invalid_exception_caught(context: &InferContext, node: &ast::Expr, ty: Type) {
     let Some(builder) = context.report_lint(&INVALID_EXCEPTION_CAUGHT, node) else {
         return;

crates/ty_python_semantic/src/types/infer.rs

@@ -39,6 +39,7 @@ use ruff_db::files::File;
 use ruff_db::parsed::parsed_module;
 use ruff_python_ast::visitor::{Visitor, walk_expr};
 use ruff_python_ast::{self as ast, AnyNodeRef, ExprContext, PythonVersion};
+use ruff_python_stdlib::builtins::version_builtin_was_added;
 use ruff_text_size::{Ranged, TextRange};
 use rustc_hash::{FxHashMap, FxHashSet};
 use salsa;
@@ -75,8 +76,8 @@ use crate::types::diagnostic::{
     INVALID_GENERIC_CLASS, INVALID_LEGACY_TYPE_VARIABLE, INVALID_PARAMETER_DEFAULT,
     INVALID_TYPE_ALIAS_TYPE, INVALID_TYPE_FORM, INVALID_TYPE_VARIABLE_CONSTRAINTS,
     POSSIBLY_UNBOUND_IMPLICIT_CALL, POSSIBLY_UNBOUND_IMPORT, TypeCheckDiagnostics,
-    UNDEFINED_REVEAL, UNRESOLVED_ATTRIBUTE, UNRESOLVED_IMPORT, UNSUPPORTED_OPERATOR,
-    report_implicit_return_type, report_invalid_arguments_to_annotated,
+    UNDEFINED_REVEAL, UNRESOLVED_ATTRIBUTE, UNRESOLVED_IMPORT, UNRESOLVED_REFERENCE,
+    UNSUPPORTED_OPERATOR, report_implicit_return_type, report_invalid_arguments_to_annotated,
     report_invalid_arguments_to_callable, report_invalid_assignment,
     report_invalid_attribute_assignment, report_invalid_generator_function_return_type,
     report_invalid_return_type, report_possibly_unbound_attribute,
@@ -112,7 +113,6 @@ use super::diagnostic::{
     report_invalid_type_checking_constant, report_non_subscriptable,
     report_possibly_unresolved_reference,
     report_runtime_check_against_non_runtime_checkable_protocol, report_slice_step_size_zero,
-    report_unresolved_reference,
 };
 use super::generics::LegacyGenericBase;
 use super::slots::check_class_slots;
@@ -5901,22 +5901,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         symbol
             .unwrap_with_diagnostic(|lookup_error| match lookup_error {
                 LookupError::Unbound(qualifiers) => {
-                    if self.is_reachable(name_node) {
-                        let attribute_exists =
-                            if let Some(class) = self.class_context_of_current_method() {
-                                let symbol = Type::instance(db, class.default_specialization(db))
-                                    .member(db, symbol_name)
-                                    .symbol;
-                                match symbol {
-                                    Symbol::Type(..) => true,
-                                    Symbol::Unbound => false,
-                                }
-                            } else {
-                                false
-                            };
-
-                        report_unresolved_reference(&self.context, name_node, attribute_exists);
-                    }
+                    self.report_unresolved_reference(name_node);
                     TypeAndQualifiers::new(Type::unknown(), qualifiers)
                 }
                 LookupError::PossiblyUnbound(type_when_bound) => {
@@ -5929,6 +5914,50 @@ impl<'db> TypeInferenceBuilder<'db> {
             .inner_type()
     }
 
+    pub(super) fn report_unresolved_reference(&self, expr_name_node: &ast::ExprName) {
+        if !self.is_reachable(expr_name_node) {
+            return;
+        }
+
+        let Some(builder) = self
+            .context
+            .report_lint(&UNRESOLVED_REFERENCE, expr_name_node)
+        else {
+            return;
+        };
+
+        let ast::ExprName { id, .. } = expr_name_node;
+        let mut diagnostic =
+            builder.into_diagnostic(format_args!("Name `{id}` used when not defined"));
+
+        if let Some(version_added_to_builtins) = version_builtin_was_added(id) {
+            diagnostic.info(format_args!(
+                "`{id}` was added as a builtin in Python 3.{version_added_to_builtins}"
+            ));
+            add_inferred_python_version_hint_to_diagnostic(
+                self.db(),
+                &mut diagnostic,
+                "resolving types",
+            );
+        }
+
+        let attribute_exists = self
+            .class_context_of_current_method()
+            .and_then(|class| {
+                Type::instance(self.db(), class.default_specialization(self.db()))
+                    .member(self.db(), id)
+                    .symbol
+                    .ignore_possibly_unbound()
+            })
+            .is_some();
+
+        if attribute_exists {
+            diagnostic.info(format_args!(
+                "An attribute `{id}` is available: consider using `self.{id}`"
+            ));
+        }
+    }
+
     fn infer_name_expression(&mut self, name: &ast::ExprName) -> Type<'db> {
         match name.ctx {
             ExprContext::Load => self.infer_name_load(name),