Merge pull request #19127 from ChayimFriedman2/different-generic-args

feat: Refactor path lowering and serve a new path diagnostic

crates/hir-def/src/data.rs

@@ -250,6 +250,7 @@ bitflags::bitflags! {
         const RUSTC_HAS_INCOHERENT_INHERENT_IMPLS = 1 << 3;
         const SKIP_ARRAY_DURING_METHOD_DISPATCH = 1 << 4;
         const SKIP_BOXED_SLICE_DURING_METHOD_DISPATCH = 1 << 5;
+        const RUSTC_PAREN_SUGAR = 1 << 6;
     }
 }
 
@@ -294,6 +295,9 @@ impl TraitData {
         if attrs.by_key(&sym::rustc_has_incoherent_inherent_impls).exists() {
             flags |= TraitFlags::RUSTC_HAS_INCOHERENT_INHERENT_IMPLS;
         }
+        if attrs.by_key(&sym::rustc_paren_sugar).exists() {
+            flags |= TraitFlags::RUSTC_PAREN_SUGAR;
+        }
 
         let mut skip_array_during_method_dispatch =
             attrs.by_key(&sym::rustc_skip_array_during_method_dispatch).exists();

crates/hir-def/src/path.rs

@@ -173,10 +173,7 @@ impl Path {
                 segments: path.mod_path().segments(),
                 generic_args: Some(path.generic_args()),
             },
-            Path::LangItem(_, seg) => PathSegments {
-                segments: seg.as_ref().map_or(&[], |seg| std::slice::from_ref(seg)),
-                generic_args: None,
-            },
+            Path::LangItem(_, seg) => PathSegments { segments: seg.as_slice(), generic_args: None },
         }
     }
 
@@ -240,6 +237,11 @@ pub struct PathSegment<'a> {
     pub args_and_bindings: Option<&'a GenericArgs>,
 }
 
+impl PathSegment<'_> {
+    pub const MISSING: PathSegment<'static> =
+        PathSegment { name: &Name::missing(), args_and_bindings: None };
+}
+
 #[derive(Debug, Clone, Copy)]
 pub struct PathSegments<'a> {
     segments: &'a [Name],

crates/hir-def/src/resolver.rs

@@ -327,8 +327,9 @@ impl Resolver {
                     | LangItemTarget::ImplDef(_)
                     | LangItemTarget::Static(_) => return None,
                 };
+                // Remaining segments start from 0 because lang paths have no segments other than the remaining.
                 return Some((
-                    ResolveValueResult::Partial(type_ns, 1, None),
+                    ResolveValueResult::Partial(type_ns, 0, None),
                     ResolvePathResultPrefixInfo::default(),
                 ));
             }