Auto merge of #75534 - Aaron1011:feature/new-future-breakage, r=pnkfelix

Implement rustc side of report-future-incompat

cc https://github.com/rust-lang/rust/issues/71249

This is an alternative to `@pnkfelix's` initial implementation in https://github.com/pnkfelix/rust/commits/prototype-rustc-side-of-report-future-incompat (mainly because I started working before seeing that branch :smile: ).

My approach outputs the entire original `Diagnostic`, in a way that is compatible with incremental compilation. This is not yet integrated with compiletest, but can be used manually by passing `-Z emit-future-incompat-report` to `rustc`.

Several changes are made to support this feature:
* The `librustc_session/lint` module is moved to a new crate `librustc_lint_defs` (name bikesheddable). This allows accessing lint definitions from `librustc_errors`.
* The `Lint` struct is extended with an `Option<FutureBreakage>`. When present, it indicates that we should display a lint in the future-compat report. `FutureBreakage` contains additional information that we may want to display in the report (currently, a `date` field indicating when the crate will stop compiling).
* A new variant `rustc_error::Level::Allow` is added. This is used when constructing a diagnostic for a future-breakage lint that is marked as allowed (via `#[allow]` or `--cap-lints`). This allows us to capture any future-breakage diagnostics in one place, while still discarding them before they are passed to the `Emitter`.
* `DiagnosticId::Lint` is extended with a `has_future_breakage` field, indicating whether or not the `Lint` has future breakage information (and should therefore show up in the report).
* `Session` is given access to the `LintStore` via a new `SessionLintStore` trait (since `librustc_session` cannot directly reference `LintStore` without a cyclic dependency). We use this to turn a string `DiagnosticId::Lint` back into a `Lint`, to retrieve the `FutureBreakage` data.

Currently, `FutureBreakage.date` is always set to `None`. However, this could potentially be interpreted by Cargo in the future.

I've enabled the future-breakage report for the `ARRAY_INTO_ITER` lint, which can be used to test out this PR. The intent is to use the field to allow Cargo to determine the date of future breakage (as described in [RFC 2834](https://github.com/rust-lang/rfcs/blob/master/text/2834-cargo-report-future-incompat.md)) without needing to parse the diagnostic itself.

cc `@pnkfelix`

2 files changed, 5 insertions, 1 deletions

diff --git a/compiler/rustc_interface/src/passes.rs b/compiler/rustc_interface/src/passes.rs
index a1487aa0060..072194e332a 100644
--- a/compiler/rustc_interface/src/passes.rs
+++ b/compiler/rustc_interface/src/passes.rs
@@ -286,7 +286,10 @@ pub fn register_plugins<'a>(
         }
     });
 
-    Ok((krate, Lrc::new(lint_store)))
+    let lint_store = Lrc::new(lint_store);
+    sess.init_lint_store(lint_store.clone());
+
+    Ok((krate, lint_store))
 }
 
 fn pre_expansion_lint(sess: &Session, lint_store: &LintStore, krate: &ast::Crate) {
diff --git a/compiler/rustc_interface/src/tests.rs b/compiler/rustc_interface/src/tests.rs
index 235e049c3f5..9332554eede 100644
--- a/compiler/rustc_interface/src/tests.rs
+++ b/compiler/rustc_interface/src/tests.rs
@@ -477,6 +477,7 @@ fn test_debugging_options_tracking_hash() {
     untracked!(dump_mir_dir, String::from("abc"));
     untracked!(dump_mir_exclude_pass_number, true);
     untracked!(dump_mir_graphviz, true);
+    untracked!(emit_future_incompat_report, true);
     untracked!(emit_stack_sizes, true);
     untracked!(hir_stats, true);
     untracked!(identify_regions, true);