fix(printer): record closure Ty in type table after instance traversal (#129)

### Summary
- In `TyCollector::visit_ty` (`src/printer.rs`), after successful
closure instance traversal, record closure `Ty` metadata in `types`.
- Update integration golden files
(`tests/integration/programs/*.smir.json.expected`) to match emitted
closure `FunType` metadata.
- Keep `Makefile` integration path as
`TESTDIR=tests/integration/programs` to keep closure fixture output
paths stable.

### Context
In the closure arm of `TyCollector::visit_ty`, the code resolved and
visited the closure instance but returned without inserting the closure
`Ty` into `types`. Other type families were inserted; closures were the
exception.

This made downstream closure type lookup incomplete (notably for kmir
proof paths that consume exported type metadata). Recording closure `Ty`
closes that gap.

Related split: static/vtable alloc fallback changes were moved out to
[stable-mir-json#131](#131)
so this PR stays focused on closure metadata.

Dependency context: this PR is depended on by
[mir-semantics#957](runtimeverification/mir-semantics#957).

Author: Stevengre

Makefile

@@ -15,7 +15,7 @@ rustup-clear-toolchain:
 	rustup override unset --nonexistent
 	rustup toolchain uninstall "${TOOLCHAIN_NAME}"
 
-TESTDIR=$(CURDIR)/tests/integration/programs
+TESTDIR=tests/integration/programs
 
 .PHONY: integration-test
 integration-test: TESTS     ?= $(shell find $(TESTDIR) -type f -name "*.rs")

src/printer/ty_visitor.rs

@@ -4,9 +4,9 @@
 //! type trees, recording each relevant type along with its `TyKind` and
 //! `LayoutShape`. These collected types are later transformed into
 //! [`TypeMetadata`](super::schema::TypeMetadata) entries in the final output.
-//! Note that some special kinds (closures, function definitions/pointers, and
-//! coroutine witnesses) are traversed only to gather the types they reference
-//! and are not themselves stored as entries in the type map.
+//! Note that some special kinds (function definitions/pointers and coroutine
+//! witnesses) are traversed only to gather the types they reference and are
+//! not themselves stored as entries in the type map.
 
 extern crate rustc_middle;
 extern crate rustc_smir;
@@ -63,7 +63,13 @@ impl Visitor for TyCollector<'_> {
                 self.resolved.insert(*ty);
                 let instance =
                     Instance::resolve_closure(def, args, stable_mir::ty::ClosureKind::Fn).unwrap();
-                self.visit_instance(instance)
+                let control = self.visit_instance(instance);
+                // Mirror other branches: record closure Ty only when traversal succeeds.
+                if matches!(control, ControlFlow::Continue(_)) {
+                    let maybe_layout_shape = ty.layout().ok().map(|layout| layout.shape());
+                    self.types.insert(*ty, (ty.kind(), maybe_layout_shape));
+                }
+                control
             }
             // Break on CoroutineWitnesses, because they aren't expected when getting the layout
             TyKind::RigidTy(RigidTy::CoroutineWitness(..)) => {

tests/integration/programs/assert_eq.smir.json.expected

@@ -5745,6 +5745,11 @@
           "pointee_type": "elided"
         }
       }
+    ],
+    [
+      {
+        "FunType": "{closure@std::rt::lang_start<()>::{closure#0}}"
+      }
     ]
   ]
 }

tests/integration/programs/binop.smir.json.expected

@@ -10113,6 +10113,11 @@
           "pointee_type": "elided"
         }
       }
+    ],
+    [
+      {
+        "FunType": "{closure@std::rt::lang_start<()>::{closure#0}}"
+      }
     ]
   ]
 }

tests/integration/programs/char-trivial.smir.json.expected

@@ -2174,6 +2174,11 @@
           "pointee_type": "elided"
         }
       }
+    ],
+    [
+      {
+        "FunType": "{closure@std::rt::lang_start<()>::{closure#0}}"
+      }
     ]
   ]
 }

tests/integration/programs/closure-args.smir.json.expected

@@ -2612,6 +2612,16 @@
           "pointee_type": "elided"
         }
       }
+    ],
+    [
+      {
+        "FunType": "{closure@std::rt::lang_start<()>::{closure#0}}"
+      }
+    ],
+    [
+      {
+        "FunType": "{closure@tests/integration/programs/closure-args.rs:2:15: 2:28}"
+      }
     ]
   ]
 }

tests/integration/programs/closure-no-args.smir.json.expected

@@ -2307,6 +2307,16 @@
           "pointee_type": "elided"
         }
       }
+    ],
+    [
+      {
+        "FunType": "{closure@std::rt::lang_start<()>::{closure#0}}"
+      }
+    ],
+    [
+      {
+        "FunType": "{closure@tests/integration/programs/closure-no-args.rs:2:15: 2:24}"
+      }
     ]
   ]
 }

tests/integration/programs/const-arithm-simple.smir.json.expected

@@ -2427,6 +2427,11 @@
           "pointee_type": "elided"
         }
       }
+    ],
+    [
+      {
+        "FunType": "{closure@std::rt::lang_start<()>::{closure#0}}"
+      }
     ]
   ]
 }

tests/integration/programs/div.smir.json.expected

@@ -2528,6 +2528,11 @@
           "pointee_type": "elided"
         }
       }
+    ],
+    [
+      {
+        "FunType": "{closure@std::rt::lang_start<()>::{closure#0}}"
+      }
     ]
   ]
 }

tests/integration/programs/double-ref-deref.smir.json.expected

@@ -2350,6 +2350,11 @@
           "pointee_type": "elided"
         }
       }
+    ],
+    [
+      {
+        "FunType": "{closure@std::rt::lang_start<()>::{closure#0}}"
+      }
     ]
   ]
 }