Replace Display by a pretty printing trait for Ty

This allows removing the names from Adt and FnDef (and more later), as a first
step towards aligning more with chalk's Ty :)

crates/ra_ide_api/src/completion/presentation.rs

@@ -1,7 +1,7 @@
 //! This modules takes care of rendering various defenitions as completion items.
 use join_to_string::join;
 use test_utils::tested_by;
-use hir::{Docs, PerNs, Resolution};
+use hir::{Docs, PerNs, Resolution, HirDisplay};
 use ra_syntax::ast::NameOwner;
 
 use crate::completion::{
@@ -22,7 +22,7 @@ impl Completions {
             field.name(ctx.db).to_string(),
         )
         .kind(CompletionItemKind::Field)
-        .detail(field.ty(ctx.db).subst(substs).to_string())
+        .detail(field.ty(ctx.db).subst(substs).display(ctx.db).to_string())
         .set_documentation(field.docs(ctx.db))
         .add_to(self);
     }
@@ -30,7 +30,7 @@ impl Completions {
     pub(crate) fn add_pos_field(&mut self, ctx: &CompletionContext, field: usize, ty: &hir::Ty) {
         CompletionItem::new(CompletionKind::Reference, ctx.source_range(), field.to_string())
             .kind(CompletionItemKind::Field)
-            .detail(ty.to_string())
+            .detail(ty.display(ctx.db).to_string())
             .add_to(self);
     }
 
@@ -154,7 +154,10 @@ impl Completions {
             None => return,
         };
         let detail_types = variant.fields(ctx.db).into_iter().map(|field| field.ty(ctx.db));
-        let detail = join(detail_types).separator(", ").surround_with("(", ")").to_string();
+        let detail = join(detail_types.map(|t| t.display(ctx.db).to_string()))
+            .separator(", ")
+            .surround_with("(", ")")
+            .to_string();
 
         CompletionItem::new(CompletionKind::Reference, ctx.source_range(), name.to_string())
             .kind(CompletionItemKind::EnumVariant)

crates/ra_ide_api/src/hover.rs

@@ -3,6 +3,7 @@ use ra_syntax::{
     AstNode, SyntaxNode, TreeArc, ast::{self, NameOwner, VisibilityOwner, TypeAscriptionOwner},
     algo::{find_covering_node, find_node_at_offset, find_leaf_at_offset, visit::{visitor, Visitor}},
 };
+use hir::HirDisplay;
 
 use crate::{db::RootDatabase, RangeInfo, FilePosition, FileRange, NavigationTarget};
 
@@ -134,9 +135,9 @@ pub(crate) fn type_of(db: &RootDatabase, frange: FileRange) -> Option<String> {
     let infer = function.infer(db);
     let source_map = function.body_source_map(db);
     if let Some(expr) = ast::Expr::cast(node).and_then(|e| source_map.node_expr(e)) {
-        Some(infer[expr].to_string())
+        Some(infer[expr].display(db).to_string())
     } else if let Some(pat) = ast::Pat::cast(node).and_then(|p| source_map.node_pat(p)) {
-        Some(infer[pat].to_string())
+        Some(infer[pat].display(db).to_string())
     } else {
         None
     }