[NOT USEFUL] Start working on rust-lang#74207

This doesn't do what we actually want, which is apply the smart
suggestions from
https://doc.rust-lang.org/nightly/nightly-rustc/rustc_resolve/late/struct.LateResolutionVisitor.html#method.smart_resolve_report_errors.

Author: jyn514

src/librustc_resolve/diagnostics.rs

@@ -31,7 +31,7 @@ use crate::{ParentScope, PathResult, ResolutionError, Resolver, Scope, ScopeSet,
 type Res = def::Res<ast::NodeId>;
 
 /// A vector of spans and replacements, a message and applicability.
-crate type Suggestion = (Vec<(Span, String)>, String, Applicability);
+pub type Suggestion = (Vec<(Span, String)>, String, Applicability);
 
 /// Potential candidate for an undeclared or out-of-scope label - contains the ident of a
 /// similarly named label and whether or not it is reachable.

src/librustc_resolve/lib.rs

@@ -60,7 +60,8 @@ use std::{cmp, fmt, iter, ptr};
 use tracing::debug;
 
 use diagnostics::{extend_span_to_previous_binding, find_span_of_binding_until_next_binding};
-use diagnostics::{ImportSuggestion, LabelSuggestion, Suggestion};
+use diagnostics::{ImportSuggestion, LabelSuggestion};
+pub use diagnostics::Suggestion;
 use imports::{Import, ImportKind, ImportResolver, NameResolution};
 use late::{HasGenericParams, PathSource, Rib, RibKind::*};
 use macros::{MacroRulesBinding, MacroRulesScope};
@@ -3041,16 +3042,16 @@ impl<'a> Resolver<'a> {
 
     /// Rustdoc uses this to resolve things in a recoverable way. `ResolutionError<'a>`
     /// isn't something that can be returned because it can't be made to live that long,
-    /// and also it's a private type. Fortunately rustdoc doesn't need to know the error,
-    /// just that an error occurred.
+    /// and also it's a private type. However, we can still return the suggestion in case
+    /// an item failed to resolve.
     // FIXME(Manishearth): intra-doc links won't get warned of epoch changes.
     pub fn resolve_str_path_error(
         &mut self,
         span: Span,
         path_str: &str,
         ns: Namespace,
         module_id: DefId,
-    ) -> Result<(ast::Path, Res), ()> {
+    ) -> Result<(ast::Path, Res), Option<Suggestion>> {
         let path = if path_str.starts_with("::") {
             ast::Path {
                 span,
@@ -3071,8 +3072,11 @@ impl<'a> Resolver<'a> {
         };
         let module = self.get_module(module_id);
         let parent_scope = &ParentScope::module(module);
-        let res = self.resolve_ast_path(&path, ns, parent_scope).map_err(|_| ())?;
-        Ok((path, res))
+        match self.resolve_ast_path(&path, ns, parent_scope) {
+            Ok(res) => Ok((path, res)),
+            Err((_, ResolutionError::FailedToResolve { suggestion, .. })) => Err(suggestion),
+            Err(_) => Err(None),
+        }
     }
 
     // Resolve a path passed from rustdoc or HIR lowering.

src/librustdoc/core.rs

@@ -432,7 +432,7 @@ pub fn run_core(options: RustdocOptions) -> (clean::Crate, RenderInfo, RenderOpt
                                 TypeNS,
                                 LocalDefId { local_def_index: CRATE_DEF_INDEX }.to_def_id(),
                             )
-                            .unwrap_or_else(|()| {
+                            .unwrap_or_else(|_| {
                                 panic!("Unable to resolve external crate {}", extern_name)
                             });
                     }