update trait ref

Author: mark-i-m

src/appendix/code-index.md

@@ -24,7 +24,7 @@ Item            |  Kind    | Short description           | Chapter            |
 `StringReader` | struct | This is the lexer used during parsing. It consumes characters from the raw source code being compiled and produces a series of tokens for use by the rest of the parser | [The parser] |  [src/libsyntax/parse/lexer/mod.rs](https://doc.rust-lang.org/nightly/nightly-rustc/syntax/parse/lexer/struct.StringReader.html)
 `syntax::token_stream::TokenStream` | struct | An abstract sequence of tokens, organized into `TokenTree`s | [The parser], [Macro expansion] | [src/libsyntax/tokenstream.rs](https://doc.rust-lang.org/nightly/nightly-rustc/syntax/tokenstream/struct.TokenStream.html)
 `TraitDef` | struct | This struct contains a trait's definition with type information | [The `ty` modules] |  [src/librustc/ty/trait_def.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc/ty/trait_def/struct.TraitDef.html)
-`TraitRef` | struct | Information about a trait reference (e.g. `P0: Trait<P1...Pn>`) | [Trait Solving: Goals and Clauses], [Trait Solving: Lowering impls]  |  [src/librustc/ty/sty.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc/ty/struct.TraitRef.html)
+`TraitRef` | struct | The combination of a trait and its input types (e.g. `P0: Trait<P1...Pn>`) | [Trait Solving: Goals and Clauses], [Trait Solving: Lowering impls]  |  [src/librustc/ty/sty.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc/ty/struct.TraitRef.html)
 `Ty<'tcx>` | struct | This is the internal representation of a type used for type checking | [Type checking] | [src/librustc/ty/mod.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc/ty/type.Ty.html)
 `TyCtxt<'cx, 'tcx, 'tcx>` | type | The "typing context". This is the central data structure in the compiler. It is the context that you use to perform all manner of queries. | [The `ty` modules] | [src/librustc/ty/context.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc/ty/struct.TyCtxt.html)