Rollup merge of #94670 - xFrednet:rfc-2383-expect-impl-after-party, r=flip1995,wesleywiser

Improve `expect` impl and handle `#[expect(unfulfilled_lint_expectations)]` (RFC 2383)

This PR updates unstable `ExpectationIds` in stashed diagnostics and adds some asserts to ensure that the stored expectations are really empty in the end. Additionally, it handles the `#[expect(unfulfilled_lint_expectations)]` case.

According to the [Errors and lints docs](https://rustc-dev-guide.rust-lang.org/diagnostics.html#diagnostic-levels) the `error` level should only be used _"when the compiler detects a problem that makes it unable to compile the program"_. As this isn't the case with `#[expect(unfulfilled_lint_expectations)]` I decided to only create a warning. To avoid adding a new lint only for this case, I simply emit a `unfulfilled_lint_expectations` diagnostic with an additional note.

---

r? `@wesleywiser` I'm requesting a review from you since you reviewed the previous PR https://github.com/rust-lang/rust/pull/87835. You are welcome to reassign it if you're busy :upside_down_face:

rfc: [RFC-2383](https://rust-lang.github.io/rfcs/2383-lint-reasons.html)

tracking issue: https://github.com/rust-lang/rust/issues/85549

cc: `@flip1995` In case you're also interested in this :)

1 files changed, 24 insertions, 1 deletions

diff --git a/compiler/rustc_errors/src/diagnostic.rs b/compiler/rustc_errors/src/diagnostic.rs
index 39ebd57b4b2..5c36c3c55b5 100644
--- a/compiler/rustc_errors/src/diagnostic.rs
+++ b/compiler/rustc_errors/src/diagnostic.rs
@@ -5,7 +5,8 @@ use crate::Substitution;
 use crate::SubstitutionPart;
 use crate::SuggestionStyle;
 use crate::ToolMetadata;
-use rustc_lint_defs::Applicability;
+use rustc_data_structures::stable_map::FxHashMap;
+use rustc_lint_defs::{Applicability, LintExpectationId};
 use rustc_serialize::json::Json;
 use rustc_span::edition::LATEST_STABLE_EDITION;
 use rustc_span::{MultiSpan, Span, DUMMY_SP};
@@ -138,6 +139,28 @@ impl Diagnostic {
         }
     }
 
+    pub fn update_unstable_expectation_id(
+        &mut self,
+        unstable_to_stable: &FxHashMap<LintExpectationId, LintExpectationId>,
+    ) {
+        if let Level::Expect(expectation_id) = &mut self.level {
+            if expectation_id.is_stable() {
+                return;
+            }
+
+            // The unstable to stable map only maps the unstable `AttrId` to a stable `HirId` with an attribute index.
+            // The lint index inside the attribute is manually transferred here.
+            let lint_index = expectation_id.get_lint_index();
+            expectation_id.set_lint_index(None);
+            let mut stable_id = *unstable_to_stable
+                .get(&expectation_id)
+                .expect("each unstable `LintExpectationId` must have a matching stable id");
+
+            stable_id.set_lint_index(lint_index);
+            *expectation_id = stable_id;
+        }
+    }
+
     pub fn has_future_breakage(&self) -> bool {
         match self.code {
             Some(DiagnosticId::Lint { has_future_breakage, .. }) => has_future_breakage,