define FileMap; fix #35

Author: mark-i-m

src/appendix/code-index.md

@@ -9,12 +9,13 @@ Item            |  Kind    | Short description           | Chapter            |
 `BodyId` | struct | One of four types of HIR node identifiers. | [Identifiers in the HIR] | [src/librustc/hir/mod.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc/hir/struct.BodyId.html)
 `CodeMap` | struct | The CodeMap maps the AST nodes to their source code | [The parser] | [src/libsyntax/codemap.rs](https://doc.rust-lang.org/nightly/nightly-rustc/syntax/codemap/struct.CodeMap.html)
 `CompileState` | struct | State that is passed to a callback at each compiler pass | [The Rustc Driver] | [src/librustc_driver/driver.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_driver/driver/struct.CompileState.html)
+`ast::Crate` | struct | Syntax-level representation of a parsed crate | [The parser] | [src/librustc/hir/mod.rs](https://doc.rust-lang.org/nightly/nightly-rustc/syntax/ast/struct.Crate.html)
+`hir::Crate` | struct | More abstract, compiler-friendly form of a crate's AST | [The Hir] | [src/librustc/hir/mod.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc/hir/struct.Crate.html)
 `DefId` | struct | One of four types of HIR node identifiers. | [Identifiers in the HIR] | [src/librustc/hir/def_id.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc/hir/def_id/struct.DefId.html)
 `DiagnosticBuilder` | struct | A struct for building up compiler diagnostics, such as errors or lints | [Emitting Diagnostics] | [src/librustc_errors/diagnostic_builder.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.DiagnosticBuilder.html)
 `DocContext` | struct | A state container used by rustdoc when crawling through a crate to gather its documentation | [Rustdoc] | [src/librustdoc/core.rs](https://github.com/rust-lang/rust/blob/master/src/librustdoc/core.rs)
-`ast::Crate` | struct | Syntax-level representation of a parsed crate | [The parser] | [src/librustc/hir/mod.rs](https://doc.rust-lang.org/nightly/nightly-rustc/syntax/ast/struct.Crate.html)
+`FileMap` | struct | A single source within a `CodeMap` (e.g. the source code within a single file). | [The parser] | [src/libsyntax_pos/lib.rs](https://doc.rust-lang.org/nightly/nightly-rustc/syntax/codemap/struct.FileMap.html)
 `HirId` | struct | One of four types of HIR node identifiers. | [Identifiers in the HIR] | [src/librustc/hir/mod.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc/hir/struct.HirId.html)
-`hir::Crate` | struct | More abstract, compiler-friendly form of a crate's AST | [The Hir] | [src/librustc/hir/mod.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc/hir/struct.Crate.html)
 `NodeId` | struct | One of four types of HIR node identifiers. Being phased out. | [Identifiers in the HIR] | [src/libsyntax/ast.rs](https://doc.rust-lang.org/nightly/nightly-rustc/syntax/ast/struct.NodeId.html)
 `ParamEnv` | struct | Information about generic parameters or `Self`, useful for working with associated or generic items | [Parameter Environment] | [src/librustc/ty/mod.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc/ty/struct.ParamEnv.html)
 `ParseSess` | struct | This struct contains information about a parsing session | [The parser] | [src/libsyntax/parse/mod.rs](https://doc.rust-lang.org/nightly/nightly-rustc/syntax/parse/struct.ParseSess.html)

src/the-parser.md

@@ -22,10 +22,10 @@ The `syntax` crate contains several main players,
 - and a [visit module] for walking the AST and inspecting or mutating the AST
   nodes.
 
-The main entrypoint to the parser is via the various `parse_*` functions
-in the [parser module]. They let you do things like turn a filemap into a
-token stream, create a parser from the token stream, and then execute the
-parser to get a `Crate` (the root AST node).
+The main entrypoint to the parser is via the various `parse_*` functions in the
+[parser module]. They let you do things like turn a [`FileMap`][filemap] (e.g.
+the source in a single file) into a token stream, create a parser from the
+token stream, and then execute the parser to get a `Crate` (the root AST node).
 
 To minimise the amount of copying that is done, both the `StringReader` and
 `Parser` have lifetimes which bind them to the parent `ParseSess`. This contains
@@ -40,3 +40,4 @@ all the information needed while parsing, as well as the `CodeMap` itself.
 [`Parser`]: https://doc.rust-lang.org/nightly/nightly-rustc/syntax/parse/parser/struct.Parser.html
 [`StringReader`]: https://doc.rust-lang.org/nightly/nightly-rustc/syntax/parse/lexer/struct.StringReader.html
 [visit module]: https://doc.rust-lang.org/nightly/nightly-rustc/syntax/visit/index.html
+[filemap]: https://doc.rust-lang.org/nightly/nightly-rustc/syntax/codemap/struct.FileMap.html