[ty] Add tests for implicit submodule references (#21793)

## Summary

I realized we don't really test `DefinitionKind::ImportFromSubmodule` in
the IDE at all, so here's a bunch of them, just recording our current
behaviour.

## Test Plan

*stares at the camera*

crates/ty_ide/src/find_references.rs

@@ -1906,4 +1906,211 @@ func<CURSOR>_alias()
           |
         ");
     }
+
+    #[test]
+    fn references_submodule_import_from_use() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg.submod import val
+
+                x = sub<CURSOR>pkg
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // TODO(submodule-imports): this should light up both instances of `subpkg`
+        assert_snapshot!(test.references(), @r"
+        info[references]: Reference 1
+         --> mypackage/__init__.py:4:5
+          |
+        2 | from .subpkg.submod import val
+        3 |
+        4 | x = subpkg
+          |     ^^^^^^
+          |
+        ");
+    }
+
+    #[test]
+    fn references_submodule_import_from_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .sub<CURSOR>pkg.submod import val
+
+                x = subpkg
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // TODO(submodule-imports): this should light up both instances of `subpkg`
+        assert_snapshot!(test.references(), @"No references found");
+    }
+
+    #[test]
+    fn references_submodule_import_from_wrong_use() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg.submod import val
+
+                x = sub<CURSOR>mod
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // No references is actually correct (or it should only see itself)
+        assert_snapshot!(test.references(), @"No references found");
+    }
+
+    #[test]
+    fn references_submodule_import_from_wrong_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg.sub<CURSOR>mod import val
+
+                x = submod
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // No references is actually correct (or it should only see itself)
+        assert_snapshot!(test.references(), @"No references found");
+    }
+
+    #[test]
+    fn references_submodule_import_from_confusing_shadowed_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .sub<CURSOR>pkg import subpkg
+
+                x = subpkg
+                "#,
+            )
+            .source(
+                "mypackage/subpkg/__init__.py",
+                r#"
+                subpkg: int = 10
+                "#,
+            )
+            .build();
+
+        // No references is actually correct (or it should only see itself)
+        assert_snapshot!(test.references(), @"No references found");
+    }
+
+    #[test]
+    fn references_submodule_import_from_confusing_real_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg import sub<CURSOR>pkg
+
+                x = subpkg
+                "#,
+            )
+            .source(
+                "mypackage/subpkg/__init__.py",
+                r#"
+                subpkg: int = 10
+                "#,
+            )
+            .build();
+
+        assert_snapshot!(test.references(), @r"
+        info[references]: Reference 1
+         --> mypackage/__init__.py:2:21
+          |
+        2 | from .subpkg import subpkg
+          |                     ^^^^^^
+        3 |
+        4 | x = subpkg
+          |
+
+        info[references]: Reference 2
+         --> mypackage/__init__.py:4:5
+          |
+        2 | from .subpkg import subpkg
+        3 |
+        4 | x = subpkg
+          |     ^^^^^^
+          |
+
+        info[references]: Reference 3
+         --> mypackage/subpkg/__init__.py:2:1
+          |
+        2 | subpkg: int = 10
+          | ^^^^^^
+          |
+        ");
+    }
+
+    #[test]
+    fn references_submodule_import_from_confusing_use() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg import subpkg
+
+                x = sub<CURSOR>pkg
+                "#,
+            )
+            .source(
+                "mypackage/subpkg/__init__.py",
+                r#"
+                subpkg: int = 10
+                "#,
+            )
+            .build();
+
+        // TODO: this should also highlight the RHS subpkg in the import
+        assert_snapshot!(test.references(), @r"
+        info[references]: Reference 1
+         --> mypackage/__init__.py:4:5
+          |
+        2 | from .subpkg import subpkg
+        3 |
+        4 | x = subpkg
+          |     ^^^^^^
+          |
+        ");
+    }
 }

crates/ty_ide/src/goto_declaration.rs

@@ -2602,6 +2602,298 @@ def ab(a: int, *, c: int): ...
         ");
     }
 
+    #[test]
+    fn goto_declaration_submodule_import_from_use() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg.submod import val
+
+                x = sub<CURSOR>pkg
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // TODO(submodule-imports): this should only highlight `subpkg` in the import statement
+        // This happens because DefinitionKind::ImportFromSubmodule claims the entire ImportFrom node,
+        // which is correct but unhelpful. Unfortunately even if it only claimed the LHS identifier it
+        // would highlight `subpkg.submod` which is strictly better but still isn't what we want.
+        assert_snapshot!(test.goto_declaration(), @r"
+        info[goto-declaration]: Declaration
+         --> mypackage/__init__.py:2:1
+          |
+        2 | from .subpkg.submod import val
+          | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+        3 |
+        4 | x = subpkg
+          |
+        info: Source
+         --> mypackage/__init__.py:4:5
+          |
+        2 | from .subpkg.submod import val
+        3 |
+        4 | x = subpkg
+          |     ^^^^^^
+          |
+        ");
+    }
+
+    #[test]
+    fn goto_declaration_submodule_import_from_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .sub<CURSOR>pkg.submod import val
+
+                x = subpkg
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // TODO(submodule-imports): I don't *think* this is what we want..?
+        // It's a bit confusing because this symbol is essentially the LHS *and* RHS of
+        // `subpkg = mypackage.subpkg`. As in, it's both defining a local `subpkg` and
+        // loading the module `mypackage.subpkg`, so, it's understandable to get confused!
+        assert_snapshot!(test.goto_declaration(), @r"
+        info[goto-declaration]: Declaration
+        --> mypackage/subpkg/__init__.py:1:1
+         |
+         |
+        info: Source
+         --> mypackage/__init__.py:2:7
+          |
+        2 | from .subpkg.submod import val
+          |       ^^^^^^
+        3 |
+        4 | x = subpkg
+          |
+        ");
+    }
+
+    #[test]
+    fn goto_declaration_submodule_import_from_wrong_use() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg.submod import val
+
+                x = sub<CURSOR>mod
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // No result is correct!
+        assert_snapshot!(test.goto_declaration(), @"No goto target found");
+    }
+
+    #[test]
+    fn goto_declaration_submodule_import_from_wrong_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg.sub<CURSOR>mod import val
+
+                x = submod
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // Going to the submod module is correct!
+        assert_snapshot!(test.goto_declaration(), @r"
+        info[goto-declaration]: Declaration
+         --> mypackage/subpkg/submod.py:1:1
+          |
+        1 |
+          | ^
+        2 | val: int = 0
+          |
+        info: Source
+         --> mypackage/__init__.py:2:14
+          |
+        2 | from .subpkg.submod import val
+          |              ^^^^^^
+        3 |
+        4 | x = submod
+          |
+        ");
+    }
+
+    #[test]
+    fn goto_declaration_submodule_import_from_confusing_shadowed_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .sub<CURSOR>pkg import subpkg
+
+                x = subpkg
+                "#,
+            )
+            .source(
+                "mypackage/subpkg/__init__.py",
+                r#"
+                subpkg: int = 10
+                "#,
+            )
+            .build();
+
+        // Going to the subpkg module is correct!
+        assert_snapshot!(test.goto_declaration(), @r"
+        info[goto-declaration]: Declaration
+         --> mypackage/subpkg/__init__.py:1:1
+          |
+        1 |
+          | ^
+        2 | subpkg: int = 10
+          |
+        info: Source
+         --> mypackage/__init__.py:2:7
+          |
+        2 | from .subpkg import subpkg
+          |       ^^^^^^
+        3 |
+        4 | x = subpkg
+          |
+        ");
+    }
+
+    #[test]
+    fn goto_declaration_submodule_import_from_confusing_real_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg import sub<CURSOR>pkg
+
+                x = subpkg
+                "#,
+            )
+            .source(
+                "mypackage/subpkg/__init__.py",
+                r#"
+                subpkg: int = 10
+                "#,
+            )
+            .build();
+
+        // Going to the subpkg `int` is correct!
+        assert_snapshot!(test.goto_declaration(), @r"
+        info[goto-declaration]: Declaration
+         --> mypackage/subpkg/__init__.py:2:1
+          |
+        2 | subpkg: int = 10
+          | ^^^^^^
+          |
+        info: Source
+         --> mypackage/__init__.py:2:21
+          |
+        2 | from .subpkg import subpkg
+          |                     ^^^^^^
+        3 |
+        4 | x = subpkg
+          |
+        ");
+    }
+
+    #[test]
+    fn goto_declaration_submodule_import_from_confusing_use() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg import subpkg
+
+                x = sub<CURSOR>pkg
+                "#,
+            )
+            .source(
+                "mypackage/subpkg/__init__.py",
+                r#"
+                subpkg: int = 10
+                "#,
+            )
+            .build();
+
+        // TODO(submodule-imports): Ok this one is FASCINATING and it's kinda right but confusing!
+        //
+        // So there's 3 relevant definitions here:
+        //
+        // * `subpkg: int = 10` in the other file is in fact the original definition
+        //
+        // *  the LHS `subpkg` in the import is an instance of `subpkg = ...`
+        //    because it's a `DefinitionKind::ImportFromSubmodle`.
+        //    This is the span that covers the entire import.
+        //
+        // * `the RHS `subpkg` in the import is a second instance of `subpkg = ...`
+        //    that *immediately* overwrites the `ImportFromSubmodule`'s definition
+        //    This span seemingly doesn't appear at all!? Is it getting hidden by the LHS span?
+        assert_snapshot!(test.goto_declaration(), @r"
+        info[goto-declaration]: Declaration
+         --> mypackage/__init__.py:2:1
+          |
+        2 | from .subpkg import subpkg
+          | ^^^^^^^^^^^^^^^^^^^^^^^^^^
+        3 |
+        4 | x = subpkg
+          |
+        info: Source
+         --> mypackage/__init__.py:4:5
+          |
+        2 | from .subpkg import subpkg
+        3 |
+        4 | x = subpkg
+          |     ^^^^^^
+          |
+
+        info[goto-declaration]: Declaration
+         --> mypackage/subpkg/__init__.py:2:1
+          |
+        2 | subpkg: int = 10
+          | ^^^^^^
+          |
+        info: Source
+         --> mypackage/__init__.py:4:5
+          |
+        2 | from .subpkg import subpkg
+        3 |
+        4 | x = subpkg
+          |     ^^^^^^
+          |
+        ");
+    }
+
     impl CursorTest {
         fn goto_declaration(&self) -> String {
             let Some(targets) = goto_declaration(&self.db, self.cursor.file, self.cursor.offset)

crates/ty_ide/src/goto_type_definition.rs

@@ -1672,6 +1672,283 @@ def function():
         "#);
     }
 
+    #[test]
+    fn goto_type_submodule_import_from_use() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg.submod import val
+
+                x = sub<CURSOR>pkg
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // The module is the correct type definition
+        assert_snapshot!(test.goto_type_definition(), @r"
+        info[goto-type-definition]: Type definition
+        --> mypackage/subpkg/__init__.py:1:1
+         |
+         |
+        info: Source
+         --> mypackage/__init__.py:4:5
+          |
+        2 | from .subpkg.submod import val
+        3 |
+        4 | x = subpkg
+          |     ^^^^^^
+          |
+        ");
+    }
+
+    #[test]
+    fn goto_type_submodule_import_from_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .sub<CURSOR>pkg.submod import val
+
+                x = subpkg
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // The module is the correct type definition
+        assert_snapshot!(test.goto_type_definition(), @r"
+        info[goto-type-definition]: Type definition
+        --> mypackage/subpkg/__init__.py:1:1
+         |
+         |
+        info: Source
+         --> mypackage/__init__.py:2:7
+          |
+        2 | from .subpkg.submod import val
+          |       ^^^^^^
+        3 |
+        4 | x = subpkg
+          |
+        ");
+    }
+
+    #[test]
+    fn goto_type_submodule_import_from_wrong_use() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg.submod import val
+
+                x = sub<CURSOR>mod
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // Unknown is correct, `submod` is not in scope
+        assert_snapshot!(test.goto_type_definition(), @r"
+        info[goto-type-definition]: Type definition
+          --> stdlib/ty_extensions.pyi:20:1
+           |
+        19 | # Types
+        20 | Unknown = object()
+           | ^^^^^^^
+        21 | AlwaysTruthy = object()
+        22 | AlwaysFalsy = object()
+           |
+        info: Source
+         --> mypackage/__init__.py:4:5
+          |
+        2 | from .subpkg.submod import val
+        3 |
+        4 | x = submod
+          |     ^^^^^^
+          |
+        ");
+    }
+
+    #[test]
+    fn goto_type_submodule_import_from_wrong_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg.sub<CURSOR>mod import val
+
+                x = submod
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // The module is correct
+        assert_snapshot!(test.goto_type_definition(), @r"
+        info[goto-type-definition]: Type definition
+         --> mypackage/subpkg/submod.py:1:1
+          |
+        1 | /
+        2 | | val: int = 0
+          | |_____________^
+          |
+        info: Source
+         --> mypackage/__init__.py:2:14
+          |
+        2 | from .subpkg.submod import val
+          |              ^^^^^^
+        3 |
+        4 | x = submod
+          |
+        ");
+    }
+
+    #[test]
+    fn goto_type_submodule_import_from_confusing_shadowed_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .sub<CURSOR>pkg import subpkg
+
+                x = subpkg
+                "#,
+            )
+            .source(
+                "mypackage/subpkg/__init__.py",
+                r#"
+                subpkg: int = 10
+                "#,
+            )
+            .build();
+
+        // The module is correct
+        assert_snapshot!(test.goto_type_definition(), @r"
+        info[goto-type-definition]: Type definition
+         --> mypackage/subpkg/__init__.py:1:1
+          |
+        1 | /
+        2 | | subpkg: int = 10
+          | |_________________^
+          |
+        info: Source
+         --> mypackage/__init__.py:2:7
+          |
+        2 | from .subpkg import subpkg
+          |       ^^^^^^
+        3 |
+        4 | x = subpkg
+          |
+        ");
+    }
+
+    #[test]
+    fn goto_type_submodule_import_from_confusing_real_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg import sub<CURSOR>pkg
+
+                x = subpkg
+                "#,
+            )
+            .source(
+                "mypackage/subpkg/__init__.py",
+                r#"
+                subpkg: int = 10
+                "#,
+            )
+            .build();
+
+        // `int` is correct
+        assert_snapshot!(test.goto_type_definition(), @r#"
+        info[goto-type-definition]: Type definition
+           --> stdlib/builtins.pyi:348:7
+            |
+        347 | @disjoint_base
+        348 | class int:
+            |       ^^^
+        349 |     """int([x]) -> integer
+        350 |     int(x, base=10) -> integer
+            |
+        info: Source
+         --> mypackage/__init__.py:2:21
+          |
+        2 | from .subpkg import subpkg
+          |                     ^^^^^^
+        3 |
+        4 | x = subpkg
+          |
+        "#);
+    }
+
+    #[test]
+    fn goto_type_submodule_import_from_confusing_use() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg import subpkg
+
+                x = sub<CURSOR>pkg
+                "#,
+            )
+            .source(
+                "mypackage/subpkg/__init__.py",
+                r#"
+                subpkg: int = 10
+                "#,
+            )
+            .build();
+
+        // `int` is correct
+        assert_snapshot!(test.goto_type_definition(), @r#"
+        info[goto-type-definition]: Type definition
+           --> stdlib/builtins.pyi:348:7
+            |
+        347 | @disjoint_base
+        348 | class int:
+            |       ^^^
+        349 |     """int([x]) -> integer
+        350 |     int(x, base=10) -> integer
+            |
+        info: Source
+         --> mypackage/__init__.py:4:5
+          |
+        2 | from .subpkg import subpkg
+        3 |
+        4 | x = subpkg
+          |     ^^^^^^
+          |
+        "#);
+    }
+
     impl CursorTest {
         fn goto_type_definition(&self) -> String {
             let Some(targets) =

crates/ty_ide/src/hover.rs

@@ -3321,6 +3321,297 @@ def function():
         ");
     }
 
+    #[test]
+    fn hover_submodule_import_from_use() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg.submod import val
+
+                x = sub<CURSOR>pkg
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // The module is correct
+        assert_snapshot!(test.hover(), @r"
+        <module 'mypackage.subpkg'>
+        ---------------------------------------------
+        ```python
+        <module 'mypackage.subpkg'>
+        ```
+        ---------------------------------------------
+        info[hover]: Hovered content is
+         --> mypackage/__init__.py:4:5
+          |
+        2 | from .subpkg.submod import val
+        3 |
+        4 | x = subpkg
+          |     ^^^-^^
+          |     |  |
+          |     |  Cursor offset
+          |     source
+          |
+        ");
+    }
+
+    #[test]
+    fn hover_submodule_import_from_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .sub<CURSOR>pkg.submod import val
+
+                x = subpkg
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // The module is correct
+        assert_snapshot!(test.hover(), @r"
+        <module 'mypackage.subpkg'>
+        ---------------------------------------------
+        ```python
+        <module 'mypackage.subpkg'>
+        ```
+        ---------------------------------------------
+        info[hover]: Hovered content is
+         --> mypackage/__init__.py:2:7
+          |
+        2 | from .subpkg.submod import val
+          |       ^^^-^^
+          |       |  |
+          |       |  Cursor offset
+          |       source
+        3 |
+        4 | x = subpkg
+          |
+        ");
+    }
+
+    #[test]
+    fn hover_submodule_import_from_wrong_use() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg.submod import val
+
+                x = sub<CURSOR>mod
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // Unknown is correct
+        assert_snapshot!(test.hover(), @r"
+        Unknown
+        ---------------------------------------------
+        ```python
+        Unknown
+        ```
+        ---------------------------------------------
+        info[hover]: Hovered content is
+         --> mypackage/__init__.py:4:5
+          |
+        2 | from .subpkg.submod import val
+        3 |
+        4 | x = submod
+          |     ^^^-^^
+          |     |  |
+          |     |  Cursor offset
+          |     source
+          |
+        ");
+    }
+
+    #[test]
+    fn hover_submodule_import_from_wrong_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg.sub<CURSOR>mod import val
+
+                x = submod
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // The submodule is correct
+        assert_snapshot!(test.hover(), @r"
+        <module 'mypackage.subpkg.submod'>
+        ---------------------------------------------
+        ```python
+        <module 'mypackage.subpkg.submod'>
+        ```
+        ---------------------------------------------
+        info[hover]: Hovered content is
+         --> mypackage/__init__.py:2:14
+          |
+        2 | from .subpkg.submod import val
+          |              ^^^-^^
+          |              |  |
+          |              |  Cursor offset
+          |              source
+        3 |
+        4 | x = submod
+          |
+        ");
+    }
+
+    #[test]
+    fn hover_submodule_import_from_confusing_shadowed_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .sub<CURSOR>pkg import subpkg
+
+                x = subpkg
+                "#,
+            )
+            .source(
+                "mypackage/subpkg/__init__.py",
+                r#"
+                subpkg: int = 10
+                "#,
+            )
+            .build();
+
+        // The module is correct
+        assert_snapshot!(test.hover(), @r"
+        <module 'mypackage.subpkg'>
+        ---------------------------------------------
+        ```python
+        <module 'mypackage.subpkg'>
+        ```
+        ---------------------------------------------
+        info[hover]: Hovered content is
+         --> mypackage/__init__.py:2:7
+          |
+        2 | from .subpkg import subpkg
+          |       ^^^-^^
+          |       |  |
+          |       |  Cursor offset
+          |       source
+        3 |
+        4 | x = subpkg
+          |
+        ");
+    }
+
+    #[test]
+    fn hover_submodule_import_from_confusing_real_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg import sub<CURSOR>pkg
+
+                x = subpkg
+                "#,
+            )
+            .source(
+                "mypackage/subpkg/__init__.py",
+                r#"
+                subpkg: int = 10
+                "#,
+            )
+            .build();
+
+        // int is correct
+        assert_snapshot!(test.hover(), @r"
+        int
+        ---------------------------------------------
+        ```python
+        int
+        ```
+        ---------------------------------------------
+        info[hover]: Hovered content is
+         --> mypackage/__init__.py:2:21
+          |
+        2 | from .subpkg import subpkg
+          |                     ^^^-^^
+          |                     |  |
+          |                     |  Cursor offset
+          |                     source
+        3 |
+        4 | x = subpkg
+          |
+        ");
+    }
+
+    #[test]
+    fn hover_submodule_import_from_confusing_use() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg import subpkg
+
+                x = sub<CURSOR>pkg
+                "#,
+            )
+            .source(
+                "mypackage/subpkg/__init__.py",
+                r#"
+                subpkg: int = 10
+                "#,
+            )
+            .build();
+
+        // int is correct
+        assert_snapshot!(test.hover(), @r"
+        int
+        ---------------------------------------------
+        ```python
+        int
+        ```
+        ---------------------------------------------
+        info[hover]: Hovered content is
+         --> mypackage/__init__.py:4:5
+          |
+        2 | from .subpkg import subpkg
+        3 |
+        4 | x = subpkg
+          |     ^^^-^^
+          |     |  |
+          |     |  Cursor offset
+          |     source
+          |
+        ");
+    }
+
     impl CursorTest {
         fn hover(&self) -> String {
             use std::fmt::Write;

crates/ty_ide/src/rename.rs

@@ -1223,4 +1223,207 @@ result = func(10, y=20)
 
         assert_snapshot!(test.rename("z"), @"Cannot rename");
     }
+
+    #[test]
+    fn rename_submodule_import_from_use() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg.submod import val
+
+                x = sub<CURSOR>pkg
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // TODO(submodule-imports): we should refuse to rename this (it's the name of a module)
+        assert_snapshot!(test.rename("mypkg"), @r"
+        info[rename]: Rename symbol (found 1 locations)
+         --> mypackage/__init__.py:4:5
+          |
+        2 | from .subpkg.submod import val
+        3 |
+        4 | x = subpkg
+          |     ^^^^^^
+          |
+        ");
+    }
+
+    #[test]
+    fn rename_submodule_import_from_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .sub<CURSOR>pkg.submod import val
+
+                x = subpkg
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // Refusing to rename is correct
+        assert_snapshot!(test.rename("mypkg"), @"Cannot rename");
+    }
+
+    #[test]
+    fn rename_submodule_import_from_wrong_use() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg.submod import val
+
+                x = sub<CURSOR>mod
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // Refusing to rename is good/fine here, it's an undefined reference
+        assert_snapshot!(test.rename("mypkg"), @"Cannot rename");
+    }
+
+    #[test]
+    fn rename_submodule_import_from_wrong_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg.sub<CURSOR>mod import val
+
+                x = submod
+                "#,
+            )
+            .source("mypackage/subpkg/__init__.py", r#""#)
+            .source(
+                "mypackage/subpkg/submod.py",
+                r#"
+                val: int = 0
+                "#,
+            )
+            .build();
+
+        // Refusing to rename is good here, it's a module name
+        assert_snapshot!(test.rename("mypkg"), @"Cannot rename");
+    }
+
+    #[test]
+    fn rename_submodule_import_from_confusing_shadowed_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .sub<CURSOR>pkg import subpkg
+
+                x = subpkg
+                "#,
+            )
+            .source(
+                "mypackage/subpkg/__init__.py",
+                r#"
+                subpkg: int = 10
+                "#,
+            )
+            .build();
+
+        // Refusing to rename is good here, it's the name of a module
+        assert_snapshot!(test.rename("mypkg"), @"Cannot rename");
+    }
+
+    #[test]
+    fn rename_submodule_import_from_confusing_real_def() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg import sub<CURSOR>pkg
+
+                x = subpkg
+                "#,
+            )
+            .source(
+                "mypackage/subpkg/__init__.py",
+                r#"
+                subpkg: int = 10
+                "#,
+            )
+            .build();
+
+        // Renaming the integer is correct
+        assert_snapshot!(test.rename("mypkg"), @r"
+        info[rename]: Rename symbol (found 3 locations)
+         --> mypackage/__init__.py:2:21
+          |
+        2 | from .subpkg import subpkg
+          |                     ^^^^^^
+        3 |
+        4 | x = subpkg
+          |     ------
+          |
+         ::: mypackage/subpkg/__init__.py:2:1
+          |
+        2 | subpkg: int = 10
+          | ------
+          |
+        ");
+    }
+
+    #[test]
+    fn rename_submodule_import_from_confusing_use() {
+        let test = CursorTest::builder()
+            .source(
+                "mypackage/__init__.py",
+                r#"
+                from .subpkg import subpkg
+
+                x = sub<CURSOR>pkg
+                "#,
+            )
+            .source(
+                "mypackage/subpkg/__init__.py",
+                r#"
+                subpkg: int = 10
+                "#,
+            )
+            .build();
+
+        // TODO(submodule-imports): this is incorrect, we should rename the `subpkg` int
+        // and the RHS of the import statement (but *not* rename the LHS).
+        //
+        // However us being cautious here *would* be good as the rename will actually
+        // result in a `subpkg` variable still existing in this code, as the import's LHS
+        // `DefinitionKind::ImportFromSubmodule` would stop being overwritten by the RHS!
+        assert_snapshot!(test.rename("mypkg"), @r"
+        info[rename]: Rename symbol (found 1 locations)
+         --> mypackage/__init__.py:4:5
+          |
+        2 | from .subpkg import subpkg
+        3 |
+        4 | x = subpkg
+          |     ^^^^^^
+          |
+        ");
+    }
 }