Make new type param suggestion more targetted

Do not suggest new type param when encountering a missing type in an ADT
field with generic parameters.

Fix #72640.

Author: estebank

src/librustc_resolve/build_reduced_graph.rs

@@ -485,6 +485,7 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                             module_path.push(Segment {
                                 ident: Ident { name: kw::PathRoot, span: source.ident.span },
                                 id: Some(self.r.next_node_id()),
+                                has_args: false,
                             });
                             source.ident.name = crate_name;
                         }

src/librustc_resolve/late/diagnostics.rs

@@ -920,7 +920,7 @@ impl<'a> LateResolutionVisitor<'a, '_, '_> {
         path: &[Segment],
     ) -> Option<(Span, &'static str, String, Applicability)> {
         let ident = match path {
-            [segment] => segment.ident,
+            [segment] if !segment.has_args => segment.ident,
             _ => return None,
         };
         match (

src/librustc_resolve/lib.rs

@@ -225,13 +225,15 @@ enum VisResolutionError<'a> {
     ModuleOnly(Span),
 }
 
-// A minimal representation of a path segment. We use this in resolve because
-// we synthesize 'path segments' which don't have the rest of an AST or HIR
-// `PathSegment`.
+/// A minimal representation of a path segment. We use this in resolve because we synthesize 'path
+/// segments' which don't have the rest of an AST or HIR `PathSegment`.
 #[derive(Clone, Copy, Debug)]
 pub struct Segment {
     ident: Ident,
     id: Option<NodeId>,
+    /// Signals whether this `PathSegment` has generic arguments. Used to avoid providing
+    /// nonsensical suggestions.
+    has_args: bool,
 }
 
 impl Segment {
@@ -240,7 +242,7 @@ impl Segment {
     }
 
     fn from_ident(ident: Ident) -> Segment {
-        Segment { ident, id: None }
+        Segment { ident, id: None, has_args: false }
     }
 
     fn names_to_string(segments: &[Segment]) -> String {
@@ -250,7 +252,7 @@ impl Segment {
 
 impl<'a> From<&'a ast::PathSegment> for Segment {
     fn from(seg: &'a ast::PathSegment) -> Segment {
-        Segment { ident: seg.ident, id: Some(seg.id) }
+        Segment { ident: seg.ident, id: Some(seg.id), has_args: seg.args.is_some() }
     }
 }
 
@@ -2017,7 +2019,7 @@ impl<'a> Resolver<'a> {
             path, opt_ns, record_used, path_span, crate_lint,
         );
 
-        for (i, &Segment { ident, id }) in path.iter().enumerate() {
+        for (i, &Segment { ident, id, has_args: _ }) in path.iter().enumerate() {
             debug!("resolve_path ident {} {:?} {:?}", i, ident, id);
             let record_segment_res = |this: &mut Self, res| {
                 if record_used {

src/test/ui/suggestions/type-not-found-in-adt-field.rs

@@ -0,0 +1,5 @@
+struct S {
+    m: Vec<Hashmap<String, ()>>, //~ ERROR cannot find type `Hashmap` in this scope
+    //~^ NOTE not found in this scope
+}
+fn main() {}

src/test/ui/suggestions/type-not-found-in-adt-field.stderr

@@ -0,0 +1,9 @@
+error[E0412]: cannot find type `Hashmap` in this scope
+  --> $DIR/type-not-found-in-adt-field.rs:2:12
+   |
+LL |     m: Vec<Hashmap<String, ()>>,
+   |            ^^^^^^^ not found in this scope
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0412`.