From 8d75a8f699c921724b1e01ce932de77d08533957 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Tue, 18 Apr 2023 19:25:57 +0000
Subject: [PATCH] Test downstream errors from bad index expr

---
 tests/ui/typeck/bad-index-due-to-nested.rs    | 30 +++++---
 .../ui/typeck/bad-index-due-to-nested.stderr  | 75 ++++++++++++++-----
 2 files changed, 76 insertions(+), 29 deletions(-)

diff --git a/tests/ui/typeck/bad-index-due-to-nested.rs b/tests/ui/typeck/bad-index-due-to-nested.rs
index 8f3b97dc741..2564b530004 100644
--- a/tests/ui/typeck/bad-index-due-to-nested.rs
+++ b/tests/ui/typeck/bad-index-due-to-nested.rs
@@ -1,15 +1,27 @@
-use std::collections::HashMap;
+use std::hash::Hash;
+use std::marker::PhantomData;
+use std::ops::Index;
 
-pub struct Graph<V> {
-    node_index_map: HashMap<V, usize>,
-}
+struct HashMap<K, V>(PhantomData<(K, V)>);
 
-impl<V> Graph<V> {
-    pub fn node_index(&self, node: V) -> usize {
-        self.node_index_map[&node]
-        //~^ ERROR the trait bound `V: Eq` is not satisfied
-        //~| ERROR the trait bound `V: Hash` is not satisfied
+impl<K, V> Index<&K> for HashMap<K, V>
+where
+    K: Hash,
+    V: Copy,
+{
+    type Output = V;
+
+    fn index(&self, k: &K) -> &V {
+        todo!()
     }
 }
 
+fn index<'a, K, V>(map: &'a HashMap<K, V>, k: K) -> &'a V {
+    map[k]
+    //~^ ERROR the trait bound `K: Hash` is not satisfied
+    //~| ERROR the trait bound `V: Copy` is not satisfied
+    //~| ERROR mismatched types
+    //~| ERROR mismatched types
+}
+
 fn main() {}
diff --git a/tests/ui/typeck/bad-index-due-to-nested.stderr b/tests/ui/typeck/bad-index-due-to-nested.stderr
index fdacba79396..e03b06b336e 100644
--- a/tests/ui/typeck/bad-index-due-to-nested.stderr
+++ b/tests/ui/typeck/bad-index-due-to-nested.stderr
@@ -1,29 +1,64 @@
-error[E0277]: the trait bound `V: Eq` is not satisfied
-  --> $DIR/bad-index-due-to-nested.rs:9:9
+error[E0277]: the trait bound `K: Hash` is not satisfied
+  --> $DIR/bad-index-due-to-nested.rs:20:5
    |
-LL |         self.node_index_map[&node]
-   |         ^^^^^^^^^^^^^^^^^^^ the trait `Eq` is not implemented for `V`
+LL |     map[k]
+   |     ^^^ the trait `Hash` is not implemented for `K`
    |
-note: required by a bound in `<HashMap<K, V, S> as Index<&Q>>`
-  --> $SRC_DIR/std/src/collections/hash/map.rs:LL:COL
+note: required by a bound in `<HashMap<K, V> as Index<&K>>`
+  --> $DIR/bad-index-due-to-nested.rs:9:8
+   |
+LL |     K: Hash,
+   |        ^^^^ required by this bound in `<HashMap<K, V> as Index<&K>>`
+help: consider restricting type parameter `K`
+   |
+LL | fn index<'a, K: std::hash::Hash, V>(map: &'a HashMap<K, V>, k: K) -> &'a V {
+   |               +++++++++++++++++
+
+error[E0277]: the trait bound `V: Copy` is not satisfied
+  --> $DIR/bad-index-due-to-nested.rs:20:5
+   |
+LL |     map[k]
+   |     ^^^ the trait `Copy` is not implemented for `V`
+   |
+note: required by a bound in `<HashMap<K, V> as Index<&K>>`
+  --> $DIR/bad-index-due-to-nested.rs:10:8
+   |
+LL |     V: Copy,
+   |        ^^^^ required by this bound in `<HashMap<K, V> as Index<&K>>`
 help: consider restricting type parameter `V`
    |
-LL | impl<V: std::cmp::Eq> Graph<V> {
-   |       ++++++++++++++
+LL | fn index<'a, K, V: std::marker::Copy>(map: &'a HashMap<K, V>, k: K) -> &'a V {
+   |                  +++++++++++++++++++
 
-error[E0277]: the trait bound `V: Hash` is not satisfied
-  --> $DIR/bad-index-due-to-nested.rs:9:9
+error[E0308]: mismatched types
+  --> $DIR/bad-index-due-to-nested.rs:20:9
    |
-LL |         self.node_index_map[&node]
-   |         ^^^^^^^^^^^^^^^^^^^ the trait `Hash` is not implemented for `V`
+LL | fn index<'a, K, V>(map: &'a HashMap<K, V>, k: K) -> &'a V {
+   |              - this type parameter
+LL |     map[k]
+   |         ^
+   |         |
+   |         expected `&K`, found type parameter `K`
+   |         help: consider borrowing here: `&k`
    |
-note: required by a bound in `<HashMap<K, V, S> as Index<&Q>>`
-  --> $SRC_DIR/std/src/collections/hash/map.rs:LL:COL
-help: consider restricting type parameter `V`
-   |
-LL | impl<V: std::hash::Hash> Graph<V> {
-   |       +++++++++++++++++
+   = note:   expected reference `&K`
+           found type parameter `K`
 
-error: aborting due to 2 previous errors
+error[E0308]: mismatched types
+  --> $DIR/bad-index-due-to-nested.rs:20:5
+   |
+LL | fn index<'a, K, V>(map: &'a HashMap<K, V>, k: K) -> &'a V {
+   |                 - this type parameter               ----- expected `&'a V` because of return type
+LL |     map[k]
+   |     ^^^^^^
+   |     |
+   |     expected `&V`, found type parameter `V`
+   |     help: consider borrowing here: `&map[k]`
+   |
+   = note:   expected reference `&'a V`
+           found type parameter `V`
 
-For more information about this error, try `rustc --explain E0277`.
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0277, E0308.
+For more information about an error, try `rustc --explain E0277`.