From 4606168dd508007fb1014b6ab12b27e320e07038 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Esteban=20K=C3=BCber?= <esteban@kuber.com.ar>
Date: Sat, 13 Jun 2020 11:12:29 -0700
Subject: [PATCH] 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.
---
 src/librustc_resolve/build_reduced_graph.rs        |  1 +
 src/librustc_resolve/late/diagnostics.rs           |  2 +-
 src/librustc_resolve/lib.rs                        | 14 ++++++++------
 .../ui/suggestions/type-not-found-in-adt-field.rs  |  5 +++++
 .../suggestions/type-not-found-in-adt-field.stderr |  9 +++++++++
 5 files changed, 24 insertions(+), 7 deletions(-)
 create mode 100644 src/test/ui/suggestions/type-not-found-in-adt-field.rs
 create mode 100644 src/test/ui/suggestions/type-not-found-in-adt-field.stderr

diff --git a/src/librustc_resolve/build_reduced_graph.rs b/src/librustc_resolve/build_reduced_graph.rs
index 2ae063660e38..8661af6d7a1d 100644
--- a/src/librustc_resolve/build_reduced_graph.rs
+++ b/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;
                         }
diff --git a/src/librustc_resolve/late/diagnostics.rs b/src/librustc_resolve/late/diagnostics.rs
index b1a1f8725a18..28ff89f66925 100644
--- a/src/librustc_resolve/late/diagnostics.rs
+++ b/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 (
diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index 6bd73877fab7..f7ec919fa04e 100644
--- a/src/librustc_resolve/lib.rs
+++ b/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 {
diff --git a/src/test/ui/suggestions/type-not-found-in-adt-field.rs b/src/test/ui/suggestions/type-not-found-in-adt-field.rs
new file mode 100644
index 000000000000..6bd42472f5a5
--- /dev/null
+++ b/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() {}
diff --git a/src/test/ui/suggestions/type-not-found-in-adt-field.stderr b/src/test/ui/suggestions/type-not-found-in-adt-field.stderr
new file mode 100644
index 000000000000..cfad8c689d03
--- /dev/null
+++ b/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`.