[ty] Fix rare panic with highly cyclic TypeVar definitions (#21059)

Cargo.lock

@@ -3563,7 +3563,7 @@ checksum = "28d3b2b1366ec20994f1fd18c3c594f05c5dd4bc44d8bb0c1c632c8d6829481f"
 [[package]]
 name = "salsa"
 version = "0.24.0"
-source = "git+https://github.com/salsa-rs/salsa.git?rev=d38145c29574758de7ffbe8a13cd4584c3b09161#d38145c29574758de7ffbe8a13cd4584c3b09161"
+source = "git+https://github.com/salsa-rs/salsa.git?rev=25b3ef146cfa2615f4ec82760bd0c22b454d0a12#25b3ef146cfa2615f4ec82760bd0c22b454d0a12"
 dependencies = [
  "boxcar",
  "compact_str",
@@ -3587,12 +3587,12 @@ dependencies = [
 [[package]]
 name = "salsa-macro-rules"
 version = "0.24.0"
-source = "git+https://github.com/salsa-rs/salsa.git?rev=d38145c29574758de7ffbe8a13cd4584c3b09161#d38145c29574758de7ffbe8a13cd4584c3b09161"
+source = "git+https://github.com/salsa-rs/salsa.git?rev=25b3ef146cfa2615f4ec82760bd0c22b454d0a12#25b3ef146cfa2615f4ec82760bd0c22b454d0a12"
 
 [[package]]
 name = "salsa-macros"
 version = "0.24.0"
-source = "git+https://github.com/salsa-rs/salsa.git?rev=d38145c29574758de7ffbe8a13cd4584c3b09161#d38145c29574758de7ffbe8a13cd4584c3b09161"
+source = "git+https://github.com/salsa-rs/salsa.git?rev=25b3ef146cfa2615f4ec82760bd0c22b454d0a12#25b3ef146cfa2615f4ec82760bd0c22b454d0a12"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -4521,7 +4521,6 @@ name = "ty_test"
 version = "0.0.0"
 dependencies = [
  "anyhow",
- "bitflags 2.9.4",
  "camino",
  "colored 3.0.0",
  "insta",

Cargo.toml

@@ -146,7 +146,7 @@ regex-automata = { version = "0.4.9" }
 rustc-hash = { version = "2.0.0" }
 rustc-stable-hash = { version = "0.1.2" }
 # When updating salsa, make sure to also update the revision in `fuzz/Cargo.toml`
-salsa = { git = "https://github.com/salsa-rs/salsa.git", rev = "d38145c29574758de7ffbe8a13cd4584c3b09161", default-features = false, features = [
+salsa = { git = "https://github.com/salsa-rs/salsa.git", rev = "25b3ef146cfa2615f4ec82760bd0c22b454d0a12", default-features = false, features = [
     "compact_str",
     "macros",
     "salsa_unstable",

crates/ty_python_semantic/resources/mdtest/regression/1377_iteration_count_mismatch.md

@@ -0,0 +1,149 @@
+# Iteration count mismatch for highly cyclic type vars
+
+Regression test for <https://github.com/astral-sh/ty/issues/1377>.
+
+The code is an excerpt from <https://github.com/Gobot1234/steam.py> that is minimal enough to
+trigger the iteration count mismatch bug in Salsa.
+
+<!-- expect-panic: execute: too many cycle iterations -->
+
+```toml
+[environment]
+extra-paths= ["/packages"]
+```
+
+`main.py`:
+
+```py
+from __future__ import annotations
+
+from typing import TypeAlias
+
+from steam.message import Message
+
+TestAlias: TypeAlias = tuple[Message]
+```
+
+`/packages/steam/__init__.py`:
+
+```py
+
+```
+
+`/packages/steam/abc.py`:
+
+```py
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import TYPE_CHECKING, Generic, Protocol
+
+from typing_extensions import TypeVar
+
+if TYPE_CHECKING:
+    from .clan import Clan
+    from .group import Group
+
+UserT = TypeVar("UserT", covariant=True)
+MessageT = TypeVar("MessageT", bound="Message", default="Message", covariant=True)
+
+class Messageable(Protocol[MessageT]): ...
+
+ClanT = TypeVar("ClanT", bound="Clan | None", default="Clan | None", covariant=True)
+GroupT = TypeVar("GroupT", bound="Group | None", default="Group | None", covariant=True)
+
+class Channel(Messageable[MessageT], Generic[MessageT, ClanT, GroupT]): ...
+
+ChannelT = TypeVar("ChannelT", bound=Channel, default=Channel, covariant=True)
+
+class Message(Generic[UserT, ChannelT]): ...
+```
+
+`/packages/steam/chat.py`:
+
+```py
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, Generic, TypeAlias
+
+from typing_extensions import Self, TypeVar
+
+from .abc import Channel, ClanT, GroupT, Message
+
+if TYPE_CHECKING:
+    from .clan import Clan
+    from .message import ClanMessage, GroupMessage
+
+ChatT = TypeVar("ChatT", bound="Chat", default="Chat", covariant=True)
+MemberT = TypeVar("MemberT", covariant=True)
+
+AuthorT = TypeVar("AuthorT", covariant=True)
+
+class ChatMessage(Message[AuthorT, ChatT], Generic[AuthorT, MemberT, ChatT]): ...
+
+ChatMessageT = TypeVar("ChatMessageT", bound="GroupMessage | ClanMessage", default="GroupMessage | ClanMessage", covariant=True)
+
+class Chat(Channel[ChatMessageT, ClanT, GroupT]): ...
+
+ChatGroupTypeT = TypeVar("ChatGroupTypeT", covariant=True)
+
+class ChatGroup(Generic[MemberT, ChatT, ChatGroupTypeT]): ...
+```
+
+`/packages/steam/channel.py`:
+
+```py
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, Any
+
+from .chat import Chat
+
+if TYPE_CHECKING:
+    from .clan import Clan
+
+class ClanChannel(Chat["Clan", None]): ...
+```
+
+`/packages/steam/clan.py`:
+
+```py
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, TypeVar
+
+from typing_extensions import Self
+
+from .chat import ChatGroup
+
+class Clan(ChatGroup[str], str): ...
+```
+
+`/packages/steam/group.py`:
+
+```py
+from __future__ import annotations
+
+from .chat import ChatGroup
+
+class Group(ChatGroup[str]): ...
+```
+
+`/packages/steam/message.py`:
+
+```py
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from typing_extensions import TypeVar
+
+from .abc import BaseUser, Message
+from .chat import ChatMessage
+
+if TYPE_CHECKING:
+    from .channel import ClanChannel
+
+class GroupMessage(ChatMessage["str"]): ...
+class ClanMessage(ChatMessage["ClanChannel"]): ...
+```

crates/ty_test/Cargo.toml

@@ -23,12 +23,11 @@ ty_static = { workspace = true }
 ty_vendored = { workspace = true }
 
 anyhow = { workspace = true }
-bitflags = { workspace = true }
 camino = { workspace = true }
 colored = { workspace = true }
 insta = { workspace = true, features = ["filters"] }
 memchr = { workspace = true }
-path-slash ={ workspace = true }
+path-slash = { workspace = true }
 regex = { workspace = true }
 rustc-hash = { workspace = true }
 rustc-stable-hash = { workspace = true }

crates/ty_test/README.md

@@ -180,6 +180,20 @@ snapshotting.
 At present, there is no way to do inline snapshotting or to request more granular
 snapshotting of specific diagnostics.
 
+## Expected panics
+
+It is possible to write tests that expect the type checker to panic during checking. Ideally, we'd fix those panics
+but being able to add regression tests even before is useful.
+
+To mark a test as expecting a panic, add an HTML comment like this:
+
+```markdown
+<!-- expect-panic: assertion `left == right` failed: Can't merge cycle heads -->
+```
+
+The text after `expect-panic:` is a substring that must appear in the panic message. The message is optional;
+but it is recommended to avoid false positives.
+
 ## Multi-file tests
 
 Some tests require multiple files, with imports from one file into another. For this purpose,

crates/ty_test/src/lib.rs

@@ -8,7 +8,7 @@ use parser as test_parser;
 use ruff_db::Db as _;
 use ruff_db::diagnostic::{Diagnostic, DiagnosticId, DisplayDiagnosticConfig};
 use ruff_db::files::{File, FileRootKind, system_path_to_file};
-use ruff_db::panic::catch_unwind;
+use ruff_db::panic::{PanicError, catch_unwind};
 use ruff_db::parsed::parsed_module;
 use ruff_db::system::{DbWithWritableSystem as _, SystemPath, SystemPathBuf};
 use ruff_db::testing::{setup_logging, setup_logging_with_filter};
@@ -319,6 +319,7 @@ fn run_test(
     let mut snapshot_diagnostics = vec![];
 
     let mut any_pull_types_failures = false;
+    let mut panic_info = None;
 
     let mut failures: Failures = test_files
         .iter()
@@ -338,10 +339,17 @@ fn run_test(
                     .map(|error| Diagnostic::invalid_syntax(test_file.file, error, error)),
             );
 
-            let mdtest_result = attempt_test(db, check_types, test_file, "run mdtest", None);
+            let mdtest_result = attempt_test(db, check_types, test_file);
             let type_diagnostics = match mdtest_result {
                 Ok(diagnostics) => diagnostics,
-                Err(failures) => return Some(failures),
+                Err(failures) => {
+                    if test.should_expect_panic().is_ok() {
+                        panic_info = Some(failures.info);
+                        return None;
+                    }
+
+                    return Some(failures.into_file_failures(db, "run mdtest", None));
+                }
             };
 
             diagnostics.extend(type_diagnostics);
@@ -367,22 +375,20 @@ fn run_test(
                 }));
             }
 
-            let pull_types_result = attempt_test(
-                db,
-                pull_types,
-                test_file,
-                "\"pull types\"",
-                Some(
-                    "Note: either fix the panic or add the `<!-- pull-types:skip -->` \
-                    directive to this test",
-                ),
-            );
+            let pull_types_result = attempt_test(db, pull_types, test_file);
             match pull_types_result {
                 Ok(()) => {}
                 Err(failures) => {
                     any_pull_types_failures = true;
                     if !test.should_skip_pulling_types() {
-                        return Some(failures);
+                        return Some(failures.into_file_failures(
+                            db,
+                            "\"pull types\"",
+                            Some(
+                                "Note: either fix the panic or add the `<!-- pull-types:skip -->` \
+                    directive to this test",
+                            ),
+                        ));
                     }
                 }
             }
@@ -391,6 +397,39 @@ fn run_test(
         })
         .collect();
 
+    match panic_info {
+        Some(panic_info) => {
+            let expected_message = test
+                .should_expect_panic()
+                .expect("panic_info is only set when `should_expect_panic` is `Ok`");
+
+            let message = panic_info
+                .payload
+                .as_str()
+                .unwrap_or("Box<dyn Any>")
+                .to_string();
+
+            if let Some(expected_message) = expected_message {
+                assert!(
+                    message.contains(expected_message),
+                    "Test `{}` is expected to panic with `{expected_message}`, but panicked with `{message}` instead.",
+                    test.name()
+                );
+            }
+        }
+        None => {
+            if let Ok(message) = test.should_expect_panic() {
+                if let Some(message) = message {
+                    panic!(
+                        "Test `{}` is expected to panic with `{message}`, but it didn't.",
+                        test.name()
+                    );
+                }
+                panic!("Test `{}` is expected to panic but it didn't.", test.name());
+            }
+        }
+    }
+
     if test.should_skip_pulling_types() && !any_pull_types_failures {
         let mut by_line = matcher::FailuresByLine::default();
         by_line.push(
@@ -596,17 +635,32 @@ fn create_diagnostic_snapshot(
 ///
 /// If a panic occurs, a nicely formatted [`FileFailures`] is returned as an `Err()` variant.
 /// This will be formatted into a diagnostic message by `ty_test`.
-fn attempt_test<'db, T, F>(
+fn attempt_test<'db, 'a, T, F>(
     db: &'db Db,
     test_fn: F,
-    test_file: &TestFile,
-    action: &str,
-    clarification: Option<&str>,
-) -> Result<T, FileFailures>
+    test_file: &'a TestFile,
+) -> Result<T, AttemptTestError<'a>>
 where
     F: FnOnce(&'db dyn ty_python_semantic::Db, File) -> T + std::panic::UnwindSafe,
 {
-    catch_unwind(|| test_fn(db, test_file.file)).map_err(|info| {
+    catch_unwind(|| test_fn(db, test_file.file))
+        .map_err(|info| AttemptTestError { info, test_file })
+}
+
+struct AttemptTestError<'a> {
+    info: PanicError,
+    test_file: &'a TestFile,
+}
+
+impl AttemptTestError<'_> {
+    fn into_file_failures(
+        self,
+        db: &Db,
+        action: &str,
+        clarification: Option<&str>,
+    ) -> FileFailures {
+        let info = self.info;
+
         let mut by_line = matcher::FailuresByLine::default();
         let mut messages = vec![];
         match info.location {
@@ -652,8 +706,8 @@ where
         by_line.push(OneIndexed::from_zero_indexed(0), messages);
 
         FileFailures {
-            backtick_offsets: test_file.backtick_offsets.clone(),
+            backtick_offsets: self.test_file.backtick_offsets.clone(),
             by_line,
         }
-    })
+    }
 }

crates/ty_test/src/parser.rs

@@ -9,6 +9,7 @@ use anyhow::bail;
 use ruff_db::system::{SystemPath, SystemPathBuf};
 use rustc_hash::FxHashMap;
 
+use crate::config::MarkdownTestConfig;
 use ruff_index::{IndexVec, newtype_index};
 use ruff_python_ast::PySourceType;
 use ruff_python_trivia::Cursor;
@@ -16,8 +17,6 @@ use ruff_source_file::{LineIndex, LineRanges, OneIndexed};
 use ruff_text_size::{TextLen, TextRange, TextSize};
 use rustc_stable_hash::{FromStableHash, SipHasher128Hash, StableSipHasher128};
 
-use crate::config::MarkdownTestConfig;
-
 /// Parse the Markdown `source` as a test suite with given `title`.
 pub(crate) fn parse<'s>(title: &'s str, source: &'s str) -> anyhow::Result<MarkdownTestSuite<'s>> {
     let parser = Parser::new(title, source);
@@ -145,13 +144,17 @@ impl<'m, 's> MarkdownTest<'m, 's> {
     pub(super) fn should_snapshot_diagnostics(&self) -> bool {
         self.section
             .directives
-            .contains(MdtestDirectives::SNAPSHOT_DIAGNOSTICS)
+            .has_directive_set(MdtestDirective::SnapshotDiagnostics)
+    }
+
+    pub(super) fn should_expect_panic(&self) -> Result<Option<&str>, ()> {
+        self.section.directives.get(MdtestDirective::ExpectPanic)
     }
 
     pub(super) fn should_skip_pulling_types(&self) -> bool {
         self.section
             .directives
-            .contains(MdtestDirectives::PULL_TYPES_SKIP)
+            .has_directive_set(MdtestDirective::PullTypesSkip)
     }
 }
 
@@ -495,6 +498,7 @@ impl<'s> Parser<'s> {
     fn parse_impl(&mut self) -> anyhow::Result<()> {
         const SECTION_CONFIG_SNAPSHOT: &str = "snapshot-diagnostics";
         const SECTION_CONFIG_PULLTYPES: &str = "pull-types:skip";
+        const SECTION_CONFIG_EXPECT_PANIC: &str = "expect-panic";
         const HTML_COMMENT_ALLOWLIST: &[&str] = &["blacken-docs:on", "blacken-docs:off"];
         const CODE_BLOCK_END: &[u8] = b"```";
         const HTML_COMMENT_END: &[u8] = b"-->";
@@ -506,16 +510,47 @@ impl<'s> Parser<'s> {
                         memchr::memmem::find(self.cursor.as_bytes(), HTML_COMMENT_END)
                     {
                         let html_comment = self.cursor.as_str()[..position].trim();
-                        if html_comment == SECTION_CONFIG_SNAPSHOT {
-                            self.process_mdtest_directive(MdtestDirective::SnapshotDiagnostics)?;
-                        } else if html_comment == SECTION_CONFIG_PULLTYPES {
-                            self.process_mdtest_directive(MdtestDirective::PullTypesSkip)?;
-                        } else if !HTML_COMMENT_ALLOWLIST.contains(&html_comment) {
+                        let (directive, value) = match html_comment.split_once(':') {
+                            Some((directive, value)) => {
+                                (directive.trim(), Some(value.trim().to_string()))
+                            }
+                            None => (html_comment, None),
+                        };
+
+                        match directive {
+                            SECTION_CONFIG_SNAPSHOT => {
+                                anyhow::ensure!(
+                                    value.is_none(),
+                                    "The `{SECTION_CONFIG_SNAPSHOT}` directive does not take a value."
+                                );
+                                self.process_mdtest_directive(
+                                    MdtestDirective::SnapshotDiagnostics,
+                                    None,
+                                )?;
+                            }
+                            SECTION_CONFIG_PULLTYPES => {
+                                anyhow::ensure!(
+                                    value.is_none(),
+                                    "The `{SECTION_CONFIG_PULLTYPES}` directive does not take a value."
+                                );
+                                self.process_mdtest_directive(
+                                    MdtestDirective::PullTypesSkip,
+                                    None,
+                                )?;
+                            }
+                            SECTION_CONFIG_EXPECT_PANIC => {
+                                self.process_mdtest_directive(MdtestDirective::ExpectPanic, value)?;
+                            }
+                            _ => {
+                                if !HTML_COMMENT_ALLOWLIST.contains(&html_comment) {
                                     bail!(
                                         "Unknown HTML comment `{html_comment}` -- possibly a typo? \
                                 (Add to `HTML_COMMENT_ALLOWLIST` if this is a false positive)"
                                     );
                                 }
+                            }
+                        }
+
                         self.cursor.skip_bytes(position + HTML_COMMENT_END.len());
                     } else {
                         bail!("Unterminated HTML comment.");
@@ -646,7 +681,7 @@ impl<'s> Parser<'s> {
             level: header_level.try_into()?,
             parent_id: Some(parent),
             config: self.sections[parent].config.clone(),
-            directives: self.sections[parent].directives,
+            directives: self.sections[parent].directives.clone(),
         };
 
         if !self.current_section_files.is_empty() {
@@ -793,7 +828,11 @@ impl<'s> Parser<'s> {
         Ok(())
     }
 
-    fn process_mdtest_directive(&mut self, directive: MdtestDirective) -> anyhow::Result<()> {
+    fn process_mdtest_directive(
+        &mut self,
+        directive: MdtestDirective,
+        value: Option<String>,
+    ) -> anyhow::Result<()> {
         if self.current_section_has_config {
             bail!(
                 "Section config to enable {directive} must come before \
@@ -814,7 +853,7 @@ impl<'s> Parser<'s> {
                  at most once.",
             );
         }
-        current_section.directives.add_directive(directive);
+        current_section.directives.add_directive(directive, value);
 
         Ok(())
     }
@@ -833,12 +872,14 @@ impl<'s> Parser<'s> {
     }
 }
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 enum MdtestDirective {
     /// A directive to enable snapshotting diagnostics.
     SnapshotDiagnostics,
     /// A directive to skip pull types.
     PullTypesSkip,
+
+    ExpectPanic,
 }
 
 impl std::fmt::Display for MdtestDirective {
@@ -846,40 +887,31 @@ impl std::fmt::Display for MdtestDirective {
         match self {
             MdtestDirective::SnapshotDiagnostics => f.write_str("snapshotting diagnostics"),
             MdtestDirective::PullTypesSkip => f.write_str("skipping the pull-types visitor"),
+            MdtestDirective::ExpectPanic => f.write_str("expect test to panic"),
         }
     }
 }
 
-bitflags::bitflags! {
-    /// Directives that can be applied to a Markdown test section.
-    #[derive(Default, Debug, Clone, Copy, PartialEq, Eq)]
-    pub(crate) struct MdtestDirectives: u8 {
-        /// We should snapshot diagnostics for this section.
-        const SNAPSHOT_DIAGNOSTICS = 1 << 0;
-        /// We should skip pulling types for this section.
-        const PULL_TYPES_SKIP = 1 << 1;
-    }
+/// The directives applied to a Markdown test section.
+#[derive(Default, Debug, Clone, PartialEq, Eq)]
+pub(crate) struct MdtestDirectives {
+    directives: FxHashMap<MdtestDirective, Option<String>>,
 }
 
 impl MdtestDirectives {
-    const fn has_directive_set(self, directive: MdtestDirective) -> bool {
-        match directive {
-            MdtestDirective::SnapshotDiagnostics => {
-                self.contains(MdtestDirectives::SNAPSHOT_DIAGNOSTICS)
-            }
-            MdtestDirective::PullTypesSkip => self.contains(MdtestDirectives::PULL_TYPES_SKIP),
-        }
+    fn has_directive_set(&self, directive: MdtestDirective) -> bool {
+        self.directives.contains_key(&directive)
     }
 
-    fn add_directive(&mut self, directive: MdtestDirective) {
-        match directive {
-            MdtestDirective::SnapshotDiagnostics => {
-                self.insert(MdtestDirectives::SNAPSHOT_DIAGNOSTICS);
-            }
-            MdtestDirective::PullTypesSkip => {
-                self.insert(MdtestDirectives::PULL_TYPES_SKIP);
-            }
+    fn get(&self, directive: MdtestDirective) -> Result<Option<&str>, ()> {
+        self.directives
+            .get(&directive)
+            .map(|s| s.as_deref())
+            .ok_or(())
     }
+
+    fn add_directive(&mut self, directive: MdtestDirective, value: Option<String>) {
+        self.directives.insert(directive, value);
     }
 }
 

fuzz/Cargo.toml

@@ -30,7 +30,7 @@ ty_python_semantic = { path = "../crates/ty_python_semantic" }
 ty_vendored = { path = "../crates/ty_vendored" }
 
 libfuzzer-sys = { git = "https://github.com/rust-fuzz/libfuzzer", default-features = false }
-salsa = { git = "https://github.com/salsa-rs/salsa.git", rev = "d38145c29574758de7ffbe8a13cd4584c3b09161", default-features = false, features = [
+salsa = { git = "https://github.com/salsa-rs/salsa.git", rev = "25b3ef146cfa2615f4ec82760bd0c22b454d0a12", default-features = false, features = [
     "compact_str",
     "macros",
     "salsa_unstable",