Move drop elaboration infrastructure.

`rustc_mir_dataflow/src/elaborate_drops.rs` contains some infrastructure
used by a few MIR passes: the `elaborate_drop` function, the
`DropElaborator` trait, etc.

`rustc_mir_transform/src/elaborate_drops.rs` (same file name, different
crate) contains the `ElaborateDrops` pass. It relies on a lot of the
infrastructure from `rustc_mir_dataflow/src/elaborate_drops.rs`.

It turns out that the drop infrastructure is only used in
`rustc_mir_transform`, so this commit moves it there. (The only
exception is the small `DropFlagState` type, which is moved to the
existing `rustc_mir_dataflow/src/drop_flag_effects.rs`.) The file is
renamed from `rustc_mir_dataflow/src/elaborate_drops.rs` to
`rustc_mir_transform/src/elaborate_drop.rs` (with no trailing `s`)
because (a) the `elaborate_drop` function is the most important export,
and (b) `rustc_mir_transform/src/elaborate_drops.rs` already exists.

All the infrastructure pieces that used to be `pub` are now
`pub(crate)`, because they are now only used within
`rustc_mir_transform`.

1 files changed, 1 insertions, 2 deletions

diff --git a/compiler/rustc_mir_dataflow/src/lib.rs b/compiler/rustc_mir_dataflow/src/lib.rs
index 0cc79b0c939..a8a56baa1ff 100644
--- a/compiler/rustc_mir_dataflow/src/lib.rs
+++ b/compiler/rustc_mir_dataflow/src/lib.rs
@@ -15,7 +15,7 @@ use rustc_middle::ty;
 // Please change the public `use` directives cautiously, as they might be used by external tools.
 // See issue #120130.
 pub use self::drop_flag_effects::{
-    drop_flag_effects_for_function_entry, drop_flag_effects_for_location,
+    DropFlagState, drop_flag_effects_for_function_entry, drop_flag_effects_for_location,
     move_path_children_matching, on_all_children_bits, on_lookup_result_bits,
 };
 pub use self::framework::{
@@ -26,7 +26,6 @@ use self::move_paths::MoveData;
 
 pub mod debuginfo;
 mod drop_flag_effects;
-pub mod elaborate_drops;
 mod errors;
 mod framework;
 pub mod impls;