Auto merge of #142878 - GuillaumeGomez:rollup-53dohob, r=GuillaumeGomez

Rollup of 10 pull requests

Successful merges:

 - rust-lang/rust#142458 (Merge unboxed trait object error suggestion into regular dyn incompat error)
 - rust-lang/rust#142593 (Add a warning to LateContext::get_def_path)
 - rust-lang/rust#142594 (Add DesugaringKind::FormatLiteral)
 - rust-lang/rust#142740 (Clean-up `FnCtxt::is_destruct_assignment_desugaring`)
 - rust-lang/rust#142780 (Port `#[must_use]` to new attribute parsing infrastructure)
 - rust-lang/rust#142798 (Don't fail to parse a struct if a semicolon is used to separate fields)
 - rust-lang/rust#142856 (Add a few inline directives in rustc_serialize.)
 - rust-lang/rust#142868 (remove few allow(dead_code))
 - rust-lang/rust#142874 (cranelift: fix target feature name typo: "fxsr")
 - rust-lang/rust#142877 (Document why tidy checks if `eslint` is installed via `npm`)

r? `@ghost`
`@rustbot` modify labels: rollup

2 files changed, 15 insertions, 3 deletions

diff --git a/compiler/rustc_lint/src/context.rs b/compiler/rustc_lint/src/context.rs
index 414f2a1846b..297b8ef7e76 100644
--- a/compiler/rustc_lint/src/context.rs
+++ b/compiler/rustc_lint/src/context.rs
@@ -711,6 +711,15 @@ impl<'tcx> LateContext<'tcx> {
 
     /// Gets the absolute path of `def_id` as a vector of `Symbol`.
     ///
+    /// Note that this is kinda expensive because it has to
+    /// travel the tree and pretty-print. Use sparingly.
+    ///
+    /// If you're trying to match for an item given by its path, use a
+    /// diagnostic item. If you're only interested in given sections, use more
+    /// specific functions, such as [`TyCtxt::crate_name`]
+    ///
+    /// FIXME: It would be great if this could be optimized.
+    ///
     /// # Examples
     ///
     /// ```rust,ignore (no context or def id available)
diff --git a/compiler/rustc_lint/src/unused.rs b/compiler/rustc_lint/src/unused.rs
index 1620f425794..a868c887493 100644
--- a/compiler/rustc_lint/src/unused.rs
+++ b/compiler/rustc_lint/src/unused.rs
@@ -2,6 +2,7 @@ use std::iter;
 
 use rustc_ast::util::{classify, parser};
 use rustc_ast::{self as ast, ExprKind, HasAttrs as _, StmtKind};
+use rustc_attr_data_structures::{AttributeKind, find_attr};
 use rustc_errors::{MultiSpan, pluralize};
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::DefId;
@@ -368,10 +369,12 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
         }
 
         fn is_def_must_use(cx: &LateContext<'_>, def_id: DefId, span: Span) -> Option<MustUsePath> {
-            if let Some(attr) = cx.tcx.get_attr(def_id, sym::must_use) {
+            if let Some(reason) = find_attr!(
+                cx.tcx.get_all_attrs(def_id),
+                AttributeKind::MustUse { reason, .. } => reason
+            ) {
                 // check for #[must_use = "..."]
-                let reason = attr.value_str();
-                Some(MustUsePath::Def(span, def_id, reason))
+                Some(MustUsePath::Def(span, def_id, *reason))
             } else {
                 None
             }