Fix completion of HashMap::new

The `ty` function in code_model returned the type with placeholders for type
parameters. That's nice for printing, but not good for completion, because
placeholders won't unify with anything else: So the type we got for `HashMap`
was `HashMap<K, V, T>`, which doesn't unify with `HashMap<?, ?, RandomState>`,
so the `new` method wasn't shown.

Now we instead return `HashMap<{unknown}, {unknown}, {unknown}>`, which does
unify with the impl type. Maybe we should just expose this properly as variables
though, i.e. we'd return something like `exists<type, type, type> HashMap<?0,
?1, ?2>` (in Chalk notation). It'll make the API more complicated, but harder to
misuse. (And it would handle cases like `type TypeAlias<T> = HashMap<T, T>` more
correctly.)

2 files changed, 36 insertions, 2 deletions

diff --git a/crates/ra_ide/src/completion/complete_path.rs b/crates/ra_ide/src/completion/complete_path.rs
index 65b3bf6e6..3db17f15f 100644
--- a/crates/ra_ide/src/completion/complete_path.rs
+++ b/crates/ra_ide/src/completion/complete_path.rs
@@ -1005,4 +1005,36 @@ mod tests {
         "###
         );
     }
+
+    #[test]
+    fn completes_hashmap_new() {
+        assert_debug_snapshot!(
+            do_reference_completion(
+                r"
+                struct RandomState;
+                struct HashMap<K, V, S = RandomState> {}
+
+                impl<K, V> HashMap<K, V, RandomState> {
+                    pub fn new() -> HashMap<K, V, RandomState> { }
+                }
+                fn foo() {
+                    HashMap::<|>
+                }
+                "
+            ),
+            @r###"
+        [
+            CompletionItem {
+                label: "new()",
+                source_range: [292; 292),
+                delete: [292; 292),
+                insert: "new()$0",
+                kind: Function,
+                lookup: "new",
+                detail: "pub fn new() -> HashMap<K, V, RandomState>",
+            },
+        ]
+        "###
+        );
+    }
 }
diff --git a/crates/ra_ide/src/completion/presentation.rs b/crates/ra_ide/src/completion/presentation.rs
index a4e9aefe2..910844244 100644
--- a/crates/ra_ide/src/completion/presentation.rs
+++ b/crates/ra_ide/src/completion/presentation.rs
@@ -273,8 +273,10 @@ impl Completions {
     pub(crate) fn add_enum_variant(&mut self, ctx: &CompletionContext, variant: hir::EnumVariant) {
         let is_deprecated = is_deprecated(variant, ctx.db);
         let name = variant.name(ctx.db);
-        let detail_types =
-            variant.fields(ctx.db).into_iter().map(|field| (field.name(ctx.db), field.ty(ctx.db)));
+        let detail_types = variant
+            .fields(ctx.db)
+            .into_iter()
+            .map(|field| (field.name(ctx.db), field.signature_ty(ctx.db)));
         let detail = match variant.kind(ctx.db) {
             StructKind::Tuple | StructKind::Unit => {
                 join(detail_types.map(|(_, t)| t.display(ctx.db).to_string()))