[red-knot] Fix panic for tuple[x[y]] string annotation (#17787)

## Summary

closes #17775

## Test Plan

Added corpus regression test

Author: sharkdp

crates/red_knot_project/resources/test/corpus/95_annotation_string_tuple.py

@@ -0,0 +1 @@
+t: "tuple[list[int]]"

crates/red_knot_python_semantic/resources/primer/bad.txt

@@ -1,35 +1,30 @@
 Expression  # cycle panic (signature_)
 Tanjun  # cycle panic (signature_)
-aiohttp  # missing expression ID
-alerta  # missing expression ID
 altair  # cycle panics (try_metaclass_)
 antidote  # hangs / slow
 artigraph  # cycle panics (value_type_)
 colour  # cycle panics (try_metaclass_)
 core  # cycle panics (value_type_)
-cpython  # missing expression ID, access to field whilst being initialized, too many cycle iterations
+cpython  # access to field whilst being initialized, too many cycle iterations
 discord.py  # some kind of hang, only when multi-threaded?
 freqtrade  # cycle panics (try_metaclass_)
 hydpy  # cycle panics (try_metaclass_)
 ibis  # cycle panics (try_metaclass_)
 manticore  # stack overflow
 materialize  # stack overflow
-meson  # missing expression ID
 mypy  # cycle panic (signature_)
 pandas  # slow
 pandas-stubs  # cycle panics (try_metaclass_)
 pandera  # cycle panics (try_metaclass_)
 prefect # slow
-pytest  # cycle panics (signature_), missing expression ID
+pytest  # cycle panics (signature_)
 pywin32  # bad use-def map (binding with definitely-visible unbound)
 schemathesis  # cycle panics (signature_)
 scikit-learn  # success, but mypy-primer hangs processing the output
-scipy  # missing expression ID
+scipy  # missing expression type ("expression should belong to this TypeInference region")
 spack  # success, but mypy-primer hangs processing the output
 spark  # cycle panics (try_metaclass_)
-sphinx  # missing expression ID
-steam.py  # missing expression ID
+steam.py  # cycle panics (try_metaclass_), often hangs when multi-threaded
 streamlit  # cycle panic (signature_)
 sympy  # stack overflow
-trio  # missing expression ID
 xarray  # cycle panics (try_metaclass_)

crates/red_knot_python_semantic/resources/primer/good.txt

@@ -2,10 +2,12 @@ AutoSplit
 PyGithub
 PyWinCtl
 SinbadCogs
+aiohttp
 aiohttp-devtools
 aioredis
 aiortc
 alectryon
+alerta
 anyio
 apprise
 arviz
@@ -47,6 +49,7 @@ jinja
 koda-validate
 kopf
 kornia
+meson
 mitmproxy
 mkdocs
 mkosi
@@ -92,11 +95,13 @@ scrapy
 setuptools
 sockeye
 speedrun.com_global_scoreboard_webapp
+sphinx
 starlette
 static-frame
 stone
 strawberry
 tornado
+trio
 twine
 typeshed-stats
 urllib3

crates/red_knot_python_semantic/src/types/infer.rs

@@ -7615,7 +7615,7 @@ impl<'db> TypeInferenceBuilder<'db> {
         fn element_could_alter_type_of_whole_tuple(
             element: &ast::Expr,
             element_ty: Type,
-            builder: &TypeInferenceBuilder,
+            builder: &mut TypeInferenceBuilder,
         ) -> bool {
             if !element_ty.is_todo() {
                 return false;
@@ -7624,10 +7624,15 @@ impl<'db> TypeInferenceBuilder<'db> {
             match element {
                 ast::Expr::EllipsisLiteral(_) | ast::Expr::Starred(_) => true,
                 ast::Expr::Subscript(ast::ExprSubscript { value, .. }) => {
-                    matches!(
-                        builder.expression_type(value),
-                        Type::KnownInstance(KnownInstanceType::Unpack)
-                    )
+                    let value_ty = if builder.deferred_state.in_string_annotation() {
+                        // Using `.expression_type` does not work in string annotations, because
+                        // we do not store types for sub-expressions. Re-infer the type here.
+                        builder.infer_expression(value)
+                    } else {
+                        builder.expression_type(value)
+                    };
+
+                    matches!(value_ty, Type::KnownInstance(KnownInstanceType::Unpack))
                 }
                 _ => false,
             }