Auto merge of #112400 - WaffleLapkin:vtable_stats, r=compiler-errors

Collect VTable stats & add `-Zprint-vtable-sizes`

This is a bit hacky/buggy, but I'm not entirely sure how to fix it, so I want to ask reviewers for help...

To try this, use either of those:
- `cargo clean && RUSTFLAGS="-Zprint-vtable-sizes" cargo +toolchain b`
- `cargo clean && cargo rustc +toolchain -Zprint-vtable-sizes`
- `rustc +toolchain -Zprint-vtable-sizes ./file.rs`

2 files changed, 72 insertions, 0 deletions

diff --git a/tests/ui/traits/object/print_vtable_sizes.rs b/tests/ui/traits/object/print_vtable_sizes.rs
new file mode 100644
index 00000000000..5656094990b
--- /dev/null
+++ b/tests/ui/traits/object/print_vtable_sizes.rs
@@ -0,0 +1,61 @@
+// check-pass
+// compile-flags: -Z print-vtable-sizes
+#![crate_type = "lib"]
+
+trait A<T: help::V>: AsRef<[T::V]> + AsMut<[T::V]> {}
+
+trait B<T>: AsRef<T> + AsRef<T> + AsRef<T> + AsRef<T> {}
+
+trait C {
+    fn x() {} // not object safe, shouldn't be reported
+}
+
+// This ideally should not have any upcasting cost,
+// but currently does due to a bug
+trait D: Send + Sync + help::MarkerWithSuper {}
+
+// This can't have no cost without reordering,
+// because `Super::f`.
+trait E: help::MarkerWithSuper + Send + Sync {}
+
+trait F {
+    fn a(&self);
+    fn b(&self);
+    fn c(&self);
+
+    fn d() -> Self
+    where
+        Self: Sized;
+}
+
+trait G: AsRef<u8> + AsRef<u16> + help::MarkerWithSuper {
+    fn a(&self);
+    fn b(&self);
+    fn c(&self);
+    fn d(&self);
+    fn e(&self);
+
+    fn f() -> Self
+    where
+        Self: Sized;
+}
+
+// Traits with the same name
+const _: () = {
+    trait S {}
+};
+const _: () = {
+    trait S {}
+};
+
+mod help {
+    pub trait V {
+        type V;
+    }
+
+    pub trait MarkerWithSuper: Super {}
+
+    pub trait Super {
+        fn f(&self);
+    }
+}
diff --git a/tests/ui/traits/object/print_vtable_sizes.stdout b/tests/ui/traits/object/print_vtable_sizes.stdout
new file mode 100644
index 00000000000..3ba650bc360
--- /dev/null
+++ b/tests/ui/traits/object/print_vtable_sizes.stdout
@@ -0,0 +1,11 @@
+print-vtable-sizes { "crate_name": "<UNKNOWN_CRATE>", "trait_name": "D", "entries": "7", "entries_ignoring_upcasting": "4", "entries_for_upcasting": "3", "upcasting_cost_percent": "75" }
+print-vtable-sizes { "crate_name": "<UNKNOWN_CRATE>", "trait_name": "E", "entries": "6", "entries_ignoring_upcasting": "4", "entries_for_upcasting": "2", "upcasting_cost_percent": "50" }
+print-vtable-sizes { "crate_name": "<UNKNOWN_CRATE>", "trait_name": "G", "entries": "14", "entries_ignoring_upcasting": "11", "entries_for_upcasting": "3", "upcasting_cost_percent": "27.27272727272727" }
+print-vtable-sizes { "crate_name": "<UNKNOWN_CRATE>", "trait_name": "A", "entries": "6", "entries_ignoring_upcasting": "5", "entries_for_upcasting": "1", "upcasting_cost_percent": "20" }
+print-vtable-sizes { "crate_name": "<UNKNOWN_CRATE>", "trait_name": "B", "entries": "4", "entries_ignoring_upcasting": "4", "entries_for_upcasting": "0", "upcasting_cost_percent": "0" }
+print-vtable-sizes { "crate_name": "<UNKNOWN_CRATE>", "trait_name": "F", "entries": "6", "entries_ignoring_upcasting": "6", "entries_for_upcasting": "0", "upcasting_cost_percent": "0" }
+print-vtable-sizes { "crate_name": "<UNKNOWN_CRATE>", "trait_name": "_::S", "entries": "3", "entries_ignoring_upcasting": "3", "entries_for_upcasting": "0", "upcasting_cost_percent": "0" }
+print-vtable-sizes { "crate_name": "<UNKNOWN_CRATE>", "trait_name": "_::S", "entries": "3", "entries_ignoring_upcasting": "3", "entries_for_upcasting": "0", "upcasting_cost_percent": "0" }
+print-vtable-sizes { "crate_name": "<UNKNOWN_CRATE>", "trait_name": "help::MarkerWithSuper", "entries": "4", "entries_ignoring_upcasting": "4", "entries_for_upcasting": "0", "upcasting_cost_percent": "0" }
+print-vtable-sizes { "crate_name": "<UNKNOWN_CRATE>", "trait_name": "help::Super", "entries": "4", "entries_ignoring_upcasting": "4", "entries_for_upcasting": "0", "upcasting_cost_percent": "0" }
+print-vtable-sizes { "crate_name": "<UNKNOWN_CRATE>", "trait_name": "help::V", "entries": "3", "entries_ignoring_upcasting": "3", "entries_for_upcasting": "0", "upcasting_cost_percent": "0" }