Fixes #924 Add context to dated information

Author: igaray

Diff for: src/SUMMARY.md

@@ -107,7 +107,6 @@
         - [Lowering to logic](./traits/lowering-to-logic.md)
         - [Goals and clauses](./traits/goals-and-clauses.md)
         - [Canonical queries](./traits/canonical-queries.md)
-        - [Lowering module in rustc](./traits/lowering-module.md)
 - [Type checking](./type-checking.md)
     - [Method Lookup](./method-lookup.md)
     - [Variance](./variance.md)

Diff for: src/about-this-guide.md

@@ -30,10 +30,18 @@ There are six parts to this guide:
 [p5]: ./part-5-intro.md
 [app]: ./appendix/background.md
 
-The Guide itself is of course open-source as well, and the sources can
-be found at the [GitHub repository]. If you find any mistakes in the
-guide, please file an issue about it, or even better, open a PR
-with a correction!
+### Constant change
+
+Keep in mind that `rustc` is a real production-quality product, being worked upon continuously by a sizeable set of contributors.
+As such, it has its fair share of codebase churn and technical debt.
+In addition, many of the ideas discussed throughout this guide are idealized designs that are not fully realized yet.
+All this makes keeping this guide completely up to date on everything very hard!
+
+The Guide itself is of course open-source as well, and the sources can be found at the [GitHub repository].
+If you find any mistakes in the guide, please file an issue about it, or even better, open a PR with a correction!
+
+> “‘All conditioned things are impermanent’ — when one sees this with wisdom, one turns away from suffering.” _The Dhammapada, verse 277_
+
 
 ## Other places to find information
 

Diff for: src/overview.md

@@ -15,7 +15,6 @@ So first, let's look at what the compiler does to your code. For now, we will
 avoid mentioning how the compiler implements these steps except as needed;
 we'll talk about that later.
 
-
 - The compile process begins when a user writes a Rust source program in text
   and invokes the `rustc` compiler on it. The work that the compiler needs to
   perform is defined by command-line options. For example, it is possible to
@@ -159,17 +158,6 @@ satisfy/optimize for. For example,
 So, as you read through the rest of the guide, keep these things in mind. They
 will often inform decisions that we make.
 
-### Constant change
-
-Keep in mind that `rustc` is a real production-quality product.
-As such, it has its fair share of codebase churn and technical debt. A lot of
-the designs discussed throughout this guide are idealized designs that are not
-fully realized yet. And things keep changing so that it is hard to keep this
-guide completely up to date on everything!
-
-The compiler definitely has rough edges, but because of its design it is able
-to keep up with the requirements above.
-
 ### Intermediate representations
 
 As with most compilers, `rustc` uses some intermediate representations (IRs) to

Diff for: src/parallel-rustc.md

@@ -1,9 +1,10 @@
 # Parallel Compilation
 
 Most of the compiler is not parallel. This represents an opportunity for
-improving compiler performance. Much effort has been put into parallelizing
-`rustc`, but it is still pretty early days for this work. There is a lot of
-design and correctness work that needs to be done.
+improving compiler performance.
+
+As of December 2020, work on explicitly parallelizing the compiler has stalled.
+There is a lot of design and correctness work that needs to be done.
 
 One can try out the current parallel compiler work by enabling it in the
 `config.toml`.

Diff for: src/the-parser.md

@@ -1,7 +1,7 @@
 # Lexing and Parsing
 
-> The parser and lexer are currently undergoing a lot of refactoring, so parts
-> of this chapter may be out of date.
+As of January 2021, the lexer and parser are undergoing refactoring to allow
+extracting them into libraries.
 
 The very first thing the compiler does is take the program (in Unicode
 characters) and turn it into something the compiler can work with more