docs:Update rustc-dev-guide-book

    Rename `StringReader` to `Lexer` and update links.

    The `StringReader` struct link is invalid since
    pr:Merge `TokenTreesReader` into `StringReader`.

src/doc/rustc-dev-guide/src/appendix/code-index.md

@@ -24,7 +24,7 @@ Item            |  Kind    | Short description           | Chapter            |
 `SourceFile` | struct | Part of the `SourceMap`. Maps AST nodes to their source code for a single source file. Was previously called FileMap | [The parser] | [compiler/rustc_span/src/lib.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_span/struct.SourceFile.html)
 `SourceMap` | struct | Maps AST nodes to their source code. It is composed of `SourceFile`s. Was previously called CodeMap | [The parser] | [compiler/rustc_span/src/source_map.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_span/source_map/struct.SourceMap.html)
 `Span` | struct  | A location in the user's source code, used for error reporting primarily | [Emitting Diagnostics] | [compiler/rustc_span/src/span_encoding.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_span/struct.Span.html)
-`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] |  [compiler/rustc_parse/src/lexer/mod.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/lexer/struct.StringReader.html)
+`Lexer` | 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] |  [compiler/rustc_parse/src/lexer/mod.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/lexer/struct.Lexer.html)
 `rustc_ast::token_stream::TokenStream` | struct | An abstract sequence of tokens, organized into `TokenTree`s | [The parser], [Macro expansion] | [compiler/rustc_ast/src/tokenstream.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_ast/tokenstream/struct.TokenStream.html)
 `TraitDef` | struct | This struct contains a trait's definition with type information | [The `ty` modules] |  [compiler/rustc_middle/src/ty/trait_def.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/trait_def/struct.TraitDef.html)
 `TraitRef` | struct | The combination of a trait and its input types (e.g. `P0: Trait<P1...Pn>`) | [Trait Solving: Goals and Clauses]  |  [compiler/rustc_middle/src/ty/sty.rs](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/type.TraitRef.html)

src/doc/rustc-dev-guide/src/guides/editions.md

@@ -91,7 +91,7 @@ stability.
 ## Edition parsing
 
 For the most part, the lexer is edition-agnostic.
-Within [`StringReader`], tokens can be modified based on edition-specific behavior.
+Within [`Lexer`], tokens can be modified based on edition-specific behavior.
 For example, C-String literals like `c"foo"` are split into multiple tokens in editions before 2021.
 This is also where things like reserved prefixes are handled for the 2021 edition.
 
@@ -114,7 +114,7 @@ For example, the deprecated `start...end` pattern syntax emits the
 [`ellipsis_inclusive_range_patterns`] lint on editions before 2021, and in 2021 is an hard error via
 the `emit_err` method.
 
-[`StringReader`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/lexer/struct.StringReader.html
+[`Lexer`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/lexer/struct.Lexer.html
 [`ParseSess::edition`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_session/parse/struct.ParseSess.html#structfield.edition
 [`ellipsis_inclusive_range_patterns`]: https://doc.rust-lang.org/nightly/rustc/lints/listing/warn-by-default.html#ellipsis-inclusive-range-patterns
 

src/doc/rustc-dev-guide/src/overview.md

@@ -38,7 +38,7 @@ Unicode character encoding.
 
 The token stream passes through a higher-level lexer located in
 [`rustc_parse`] to prepare for the next stage of the compile process. The
-[`StringReader`] `struct` is used at this stage to perform a set of validations
+[`Lexer`] `struct` is used at this stage to perform a set of validations
 and turn strings into interned symbols (_interning_ is discussed later).
 [String interning] is a way of storing only one immutable
 copy of each distinct string value.
@@ -153,7 +153,7 @@ the final binary.
 [`rustc_parse::parser::Parser`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/parser/struct.Parser.html
 [`rustc_parse`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/index.html
 [`simplify_try`]: https://github.com/rust-lang/rust/pull/66282
-[`StringReader`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/lexer/struct.StringReader.html
+[`Lexer`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/lexer/struct.Lexer.html
 [`Ty<'tcx>`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.Ty.html
 [borrow checking]: borrow_check.md
 [codegen]: backend/codegen.md
@@ -342,7 +342,7 @@ Compiler performance is a problem that we would like to improve on
 (and are always working on). One aspect of that is parallelizing
 `rustc` itself.
 
-Currently, there is only one part of rustc that is parallel by default: 
+Currently, there is only one part of rustc that is parallel by default:
 [code generation](./parallel-rustc.md#Codegen).
 
 However, the rest of the compiler is still not yet parallel. There have been

src/doc/rustc-dev-guide/src/the-parser.md

@@ -13,7 +13,7 @@ This happens in two stages: Lexing and Parsing.
 
   2. _Parsing_ takes streams of tokens and turns them into a structured form
   which is easier for the compiler to work with, usually called an [*Abstract
-  Syntax Tree* (AST)][ast] . 
+  Syntax Tree* (AST)][ast] .
 
 ## The AST
 
@@ -52,7 +52,7 @@ the token stream, and then execute the parser to get a [`Crate`] (the root AST
 node).
 
 To minimize the amount of copying that is done,
-both [`StringReader`] and [`Parser`] have lifetimes which bind them to the parent [`ParseSess`].
+both [`Lexer`] and [`Parser`] have lifetimes which bind them to the parent [`ParseSess`].
 This contains all the information needed while parsing, as well as the [`SourceMap`] itself.
 
 Note that while parsing, we may encounter macro definitions or invocations.
@@ -67,7 +67,7 @@ Code for lexical analysis is split between two crates:
   constituting tokens. Although it is popular to implement lexers as generated
   finite state machines, the lexer in [`rustc_lexer`] is hand-written.
 
-- [`StringReader`] integrates [`rustc_lexer`] with data structures specific to
+- [`Lexer`] integrates [`rustc_lexer`] with data structures specific to
   `rustc`. Specifically, it adds `Span` information to tokens returned by
   [`rustc_lexer`] and interns identifiers.
 
@@ -76,7 +76,7 @@ Code for lexical analysis is split between two crates:
 [`ParseSess`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_session/parse/struct.ParseSess.html
 [`rustc_lexer`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_lexer/index.html
 [`SourceMap`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_span/source_map/struct.SourceMap.html
-[`StringReader`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/lexer/struct.StringReader.html
+[`Lexer`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/lexer/struct.Lexer.html
 [ast module]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_ast/ast/index.html
 [ast]: ./ast-validation.md
 [parser]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_parse/parser/index.html