diagnostics: line wrapping/heading changes

Minor stylistic changes to some of the diagnostic documentation: adding
line wrapping to the Markdown source and changing the capitalization of
the headings to be consistent with other pages.

Signed-off-by: David Wood <david.wood@huawei.com>

Author: davidtwco

src/diagnostics/diagnostic-codes.md

@@ -1,4 +1,4 @@
-# Diagnostic Codes
+# Diagnostic codes
 We generally try to assign each error message a unique code like `E0123`. These
 codes are defined in the compiler in the `diagnostics.rs` files found in each
 crate, which basically consist of macros. The codes come in two varieties: those
@@ -60,7 +60,7 @@ To actually issue the error, you can use the `struct_span_err!` macro:
 struct_span_err!(self.tcx.sess, // some path to the session here
                  span, // whatever span in the source you want
                  E0592, // your new error code
-                 &format!("text of the error"))
+                 fluent::example::an_error_message)
     .emit() // actually issue the error
 ```
 
@@ -69,8 +69,8 @@ call `.emit()`:
 
 ```rust
 struct_span_err!(...)
-    .span_label(another_span, "something to label in the source")
-    .span_note(another_span, "some separate note, probably avoid these")
+    .span_label(another_span, fluent::example::example_label)
+    .span_note(another_span, fluent::example::separate_note)
     .emit_()
 ```
 

src/diagnostics/diagnostic-items.md

@@ -1,39 +1,38 @@
 # Diagnostic Items
-
-## Background
-
-While writing lints it's common to check for specific types, traits and functions. This raises
-the question on how to check for these. Types can be checked by their complete type path.
-However, this requires hard coding paths and can lead to misclassifications in some edge cases.
-To counteract this, rustc has introduced diagnostic items that are used to identify types via
+While writing lints it's common to check for specific types, traits and
+functions. This raises the question on how to check for these. Types can be
+checked by their complete type path. However, this requires hard coding paths
+and can lead to misclassifications in some edge cases. To counteract this,
+rustc has introduced diagnostic items that are used to identify types via
 [`Symbol`]s.
 
-## How To Find Diagnostic Items
-
-Diagnostic items are added to items inside `rustc`/`std`/`core` with the `rustc_diagnostic_item`
-attribute. The item for a specific type can be found by opening the source code in the
-documentation and looking for this attribute. Note that it's often added with the `cfg_attr`
-attribute to avoid compilation errors during tests. A definition often looks like this:
+## Finding diagnostic items
+Diagnostic items are added to items inside `rustc`/`std`/`core` with the
+`rustc_diagnostic_item` attribute. The item for a specific type can be found by
+opening the source code in the documentation and looking for this attribute.
+Note that it's often added with the `cfg_attr` attribute to avoid compilation
+errors during tests. A definition often looks like this:
 
 ```rs
 // This is the diagnostic item for this type   vvvvvvv
 #[cfg_attr(not(test), rustc_diagnostic_item = "Penguin")]
 struct Penguin;
 ```
 
-Diagnostic items are usually only added to traits, types and standalone functions. If the goal
-is to check for an associated type or method, please use the diagnostic item of the item and
-reference [*How To Use Diagnostic Items*](#how-to-use-diagnostic-items).
-
-## How To Add Diagnostic Items
+Diagnostic items are usually only added to traits, types and standalone
+functions. If the goal is to check for an associated type or method, please use
+the diagnostic item of the item and reference [*How To Use Diagnostic
+Items*](#how-to-use-diagnostic-items).
 
+## Adding diagnostic items
 A new diagnostic item can be added with these two steps:
 
-1. Find the target item inside the Rust repo. Now add the diagnostic item as a string via the 
-    `rustc_diagnostic_item` attribute. This can sometimes cause compilation errors while running
-    tests. These errors can be avoided by using the `cfg_attr` attribute with the `not(test)`
-    condition (it's fine adding then for all `rustc_diagnostic_item` attributes as a preventive
-    manner). At the end, it should look like this:
+1. Find the target item inside the Rust repo. Now add the diagnostic item as a
+   string via the `rustc_diagnostic_item` attribute. This can sometimes cause
+   compilation errors while running tests. These errors can be avoided by using
+   the `cfg_attr` attribute with the `not(test)` condition (it's fine adding
+   then for all `rustc_diagnostic_item` attributes as a preventive manner). At
+   the end, it should look like this:
 
     ```rs
     // This will be the new diagnostic item        vvv
@@ -44,41 +43,45 @@ A new diagnostic item can be added with these two steps:
     For the naming conventions of diagnostic items, please refer to
     [*Naming Conventions*](#naming-conventions).
 
-2. As of <!-- date: 2022-02 --> February 2022, diagnostic items in code are accessed via symbols in
-    [`rustc_span::symbol::sym`]. To add your newly created diagnostic item simply open the
-    module file and add the name (In this case `Cat`) at the correct point in the list.
-
-Now you can create a pull request with your changes. :tada: (Note that when using diagnostic
-items in other projects like Clippy, it might take some time until the repos get synchronized.)
-
-## Naming Conventions
-
-Diagnostic items don't have a set in stone naming convention yet. These are some guidelines that
-should be used for the future, but might differ from existing names:
-
-* Types, traits and enums are named using UpperCamelCase (Examples: `Iterator`, `HashMap`, ...)
-* For type names that are used multiple times like `Writer` it's good to choose a more precise
-  name, maybe by adding the module to it. (Example: `IoWriter`)
-* Associated items should not get their own diagnostic items, but instead be accessed indirectly
-  by the diagnostic item of the type they're originating from.
-* Freestanding functions like `std::mem::swap()` should be named using `snake_case` with one
-  important (export) module as a prefix (Example: `mem_swap`, `cmp_max`)
-* Modules should usually not have a diagnostic item attached to them. Diagnostic items were
-  added to avoid the usage of paths, using them on modules would therefore most likely to be
-  counterproductive.
-
-## How To Use Diagnostic Items
-
+2. As of <!-- date: 2022-02 --> February 2022, diagnostic items in code are
+   accessed via symbols in [`rustc_span::symbol::sym`]. To add your newly
+   created diagnostic item simply open the module file and add the name (In
+   this case `Cat`) at the correct point in the list.
+
+Now you can create a pull request with your changes. :tada: (Note that when
+using diagnostic items in other projects like Clippy, it might take some time
+until the repos get synchronized.)
+
+## Naming conventions
+Diagnostic items don't have a set in stone naming convention yet. These are
+some guidelines that should be used for the future, but might differ from
+existing names:
+
+* Types, traits and enums are named using UpperCamelCase (Examples: `Iterator`,
+* `HashMap`, ...)
+* For type names that are used multiple times like `Writer` it's good to choose
+  a more precise name, maybe by adding the module to it. (Example: `IoWriter`)
+* Associated items should not get their own diagnostic items, but instead be
+  accessed indirectly by the diagnostic item of the type they're originating
+  from.
+* Freestanding functions like `std::mem::swap()` should be named using
+  `snake_case` with one important (export) module as a prefix (Example:
+  `mem_swap`, `cmp_max`)
+* Modules should usually not have a diagnostic item attached to them.
+  Diagnostic items were added to avoid the usage of paths, using them on
+  modules would therefore most likely to be counterproductive.
+
+## Using diagnostic items
 In rustc, diagnostic items are looked up via [`Symbol`]s from inside the
-[`rustc_span::symbol::sym`] module. These can then be mapped to [`DefId`]s using
-[`TyCtxt::get_diagnostic_item()`] or checked if they match a [`DefId`] using
-[`TyCtxt::is_diagnostic_item()`]. When mapping from a diagnostic item to a [`DefId`] the method
-will return a `Option<DefId>`. This can be `None` if either the symbol isn't a diagnostic item
-or the type is not registered, for instance when compiling with `#[no_std]`. All following
-examples are based on [`DefId`]s and their usage.
-
-### Check For A Type 
-
+[`rustc_span::symbol::sym`] module. These can then be mapped to [`DefId`]s
+using [`TyCtxt::get_diagnostic_item()`] or checked if they match a [`DefId`]
+using [`TyCtxt::is_diagnostic_item()`]. When mapping from a diagnostic item to
+a [`DefId`] the method will return a `Option<DefId>`. This can be `None` if
+either the symbol isn't a diagnostic item or the type is not registered, for
+instance when compiling with `#[no_std]`. All following examples are based on
+[`DefId`]s and their usage.
+
+### Example: Checking for a type
 ```rust
 use rustc_span::symbol::sym;
 
@@ -92,8 +95,7 @@ fn example_1(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
 }
 ```
 
-### Check For A Trait Implementation
-
+### Example: Checking for a trait implementation
 ```rust
 /// This example checks if a given [`DefId`] from a method is part of a trait
 /// implementation defined by a diagnostic item.
@@ -110,24 +112,23 @@ fn is_diag_trait_item(
 ```
 
 ### Associated Types
-
-Associated types of diagnostic items can be accessed indirectly by first getting the [`DefId`]
-of the trait and then calling [`TyCtxt::associated_items()`]. This returns an [`AssocItems`]
-object which can be used for further checks. Checkout 
+Associated types of diagnostic items can be accessed indirectly by first
+getting the [`DefId`] of the trait and then calling
+[`TyCtxt::associated_items()`]. This returns an [`AssocItems`] object which can
+be used for further checks. Checkout
 [`clippy_utils::ty::get_iterator_item_ty()`] for an example usage of this.
 
-### Usage In Clippy
-
-Clippy tries to use diagnostic items where possible and has developed some wrapper and utility
-functions. Please also refer to its documentation when using diagnostic items in Clippy. (See
-[*Common tools for writing lints*][clippy-Common-tools-for-writing-lints].)
-
-## Related Issues
+### Usage in Clippy
+Clippy tries to use diagnostic items where possible and has developed some
+wrapper and utility functions. Please also refer to its documentation when
+using diagnostic items in Clippy. (See [*Common tools for writing
+lints*][clippy-Common-tools-for-writing-lints].)
 
-This lists some related issues. These are probably only interesting to people who really want to
-take a deep dive into the topic :)
+## Related issues
+This lists some related issues. These are probably only interesting to people
+who really want to take a deep dive into the topic :)
 
-* [rust#60966]: The Rust PR that introduced diagnostic items 
+* [rust#60966]: The Rust PR that introduced diagnostic items
 * [rust-clippy#5393]: Clippy's tracking issue for moving away from hard coded paths to
   diagnostic item
 

src/diagnostics/error-guaranteed.md

@@ -1,5 +1,4 @@
 # `ErrorGuaranteed`
-
 The previous sections have been about the error message that a user of the
 compiler sees. But emitting an error can also have a second important side
 effect within the compiler source code: it generates an
@@ -19,7 +18,6 @@ There are some important considerations about the usage of `ErrorGuaranteed`:
   Thus, you should not rely on
   `ErrorGuaranteed` when deciding whether to emit an error, or what kind of error
   to emit.
-
 * `ErrorGuaranteed` should not be used to indicate that a compilation _will
   emit_ an error in the future. It should be used to indicate that an error
   _has already been_ emitted -- that is, the [`emit()`][emit] function has
@@ -30,7 +28,6 @@ There are some important considerations about the usage of `ErrorGuaranteed`:
 Thankfully, in most cases, it should be statically impossible to abuse
 `ErrorGuaranteed`.
 
-
 [errorguar]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.ErrorGuaranteed.html
 [rerrors]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/index.html
 [dsp]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.Handler.html#method.delay_span_bug