Auto merge of rust-lang#101620 - cjgillot:compute_lint_levels_by_def, r=oli-obk

Compute lint levels by definition

Lint levels are currently computed once for the whole crate. Any code that wants to emit a lint depends on this single `lint_levels(())` query. This query contains the `Span` for each attribute that participates in the lint level tree, so any code that wants to emit a lint basically depends on the spans in all files in the crate.

Contrary to hard errors, we do not clear the incremental session on lints, so this implicit world dependency pessimizes incremental reuse. (And is furthermore invisible for allowed lints.)

This PR completes rust-lang#99634 (thanks for the initial work `@fee1-dead)` and includes it in the dependency graph.

The design is based on 2 queries:
1. `lint_levels_on(HirId) -> FxHashMap<LintId, LevelAndSource>` which accesses the attributes at the given `HirId` and processes them into lint levels.  The `TyCtxt` is responsible for probing the HIR tree to find the user-visible level.
2. `lint_expectations(())` which lists all the `#[expect]` attributes in the crate.

This PR also introduces the ability to reconstruct a `HirId` from a `DepNode` by encoding the local part of the `DefPathHash` and the `ItemLocalId` in the two `u64` of the fingerprint.  This allows for the dep-graph to directly recompute `lint_levels_on` directly, without having to force the calling query.

Closes rust-lang#95094.
Supersedes rust-lang#99634.

Author: bors

compiler/rustc_errors/src/diagnostic.rs

@@ -338,9 +338,10 @@ impl Diagnostic {
             // 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
+            let mut stable_id = unstable_to_stable
                 .get(&expectation_id)
-                .expect("each unstable `LintExpectationId` must have a matching stable id");
+                .expect("each unstable `LintExpectationId` must have a matching stable id")
+                .normalize();
 
             stable_id.set_lint_index(lint_index);
             *expectation_id = stable_id;

compiler/rustc_errors/src/lib.rs

@@ -1167,7 +1167,7 @@ impl HandlerInner {
 
         if let Some(expectation_id) = diagnostic.level.get_expectation_id() {
             self.suppressed_expected_diag = true;
-            self.fulfilled_expectations.insert(expectation_id);
+            self.fulfilled_expectations.insert(expectation_id.normalize());
         }
 
         if matches!(diagnostic.level, Warning(_))

compiler/rustc_lint/src/context.rs

@@ -560,7 +560,7 @@ pub struct LateContext<'tcx> {
 
 /// Context for lint checking of the AST, after expansion, before lowering to HIR.
 pub struct EarlyContext<'a> {
-    pub builder: LintLevelsBuilder<'a>,
+    pub builder: LintLevelsBuilder<'a, crate::levels::TopDown>,
     pub buffered: LintBuffer,
 }
 

compiler/rustc_lint/src/early.rs

@@ -59,6 +59,7 @@ impl<'a, T: EarlyLintPass> EarlyContextAndPass<'a, T> {
         F: FnOnce(&mut Self),
     {
         let is_crate_node = id == ast::CRATE_NODE_ID;
+        debug!(?id);
         let push = self.context.builder.push(attrs, is_crate_node, None);
 
         self.check_id(id);

compiler/rustc_lint/src/expect.rs

@@ -16,8 +16,10 @@ fn check_expectations(tcx: TyCtxt<'_>, tool_filter: Option<Symbol>) {
         return;
     }
 
+    let lint_expectations = tcx.lint_expectations(());
     let fulfilled_expectations = tcx.sess.diagnostic().steal_fulfilled_expectation_ids();
-    let lint_expectations = &tcx.lint_levels(()).lint_expectations;
+
+    tracing::debug!(?lint_expectations, ?fulfilled_expectations);
 
     for (id, expectation) in lint_expectations {
         // This check will always be true, since `lint_expectations` only