style-guide: Remove material about tool configurability

The style guide discusses the default Rust style. Configurability of
Rust formatting tools are not the domain of the style guide.

src/doc/style-guide/src/README.md

@@ -40,7 +40,6 @@ options.
 * Each level of indentation must be four spaces (that is, all indentation
   outside of string literals and comments must be a multiple of four).
 * The maximum width for a line is 100 characters.
-* A tool may choose to make some of these configurable.
 
 #### Block indent
 
@@ -99,8 +98,6 @@ fn bar() {}
 fn baz() {}
 ```
 
-Formatting tools may wish to make the bounds on blank lines configurable.
-
 ### [Module-level items](items.md)
 ### [Statements](statements.md)
 ### [Expressions](expressions.md)
@@ -231,10 +228,6 @@ complexity of an item (for example, that all components must be simple names,
 not more complex sub-expressions). For more discussion on suitable heuristics,
 see [this issue](https://github.com/rust-lang-nursery/fmt-rfcs/issues/47).
 
-Tools should give the user an option to ignore such heuristics and always use
-the normal formatting.
-
-
 ## [Non-formatting conventions](advice.md)
 
 ## [Cargo.toml conventions](cargo.md)

src/doc/style-guide/src/expressions.md

@@ -814,8 +814,7 @@ let arr = [combinable(
 )];
 ```
 
-Such behaviour should extend recursively, however, tools may choose to limit the
-depth of nesting.
+Such behaviour should extend recursively.
 
 Only where the multi-line sub-expression is a closure with an explicit block,
 this combining behaviour may be used where there are other arguments, as long as
@@ -852,9 +851,6 @@ compound expression, then use parentheses around it, e.g., `..(x + 1)`,
 Hexadecimal literals may use upper- or lower-case letters, but they must not be
 mixed within the same literal. Projects should use the same case for all
 literals, but we do not make a recommendation for either lower- or upper-case.
-Tools should have an option to convert mixed case literals to upper-case, and
-may have an option to convert all literals to either lower- or upper-case.
-
 
 ## Patterns
 

src/doc/style-guide/src/items.md

@@ -15,9 +15,6 @@ alphabetically. When sorting, `self` and `super` must come before any other
 names. Module declarations should not be moved if they are annotated with
 `#[macro_use]`, since that may be semantics changing.
 
-Tools should make the above ordering optional.
-
-
 ### Function definitions
 
 In Rust, people often find functions by searching for `fn [function-name]`, so
@@ -372,33 +369,6 @@ where
         + Index<RangeToInclusive<Idx>, Output = Self::Output> + Index<RangeFull>
 ```
 
-#### Option - `where_single_line`
-
-`where_single_line` is `false` by default. If `true`, then a where clause with
-exactly one component may be formatted on a single line if the rest of the
-item's signature is also kept on one line. In this case, there is no need for a
-trailing comma and if followed by a block, no need for a newline before the
-block. E.g.,
-
-```rust
-// May be single-lined.
-fn foo<T>(args) -> ReturnType
-where T: Bound {
-    body
-}
-
-// Must be multi-lined.
-fn foo<T>(
-    args
-) -> ReturnType
-where
-    T: Bound,
-{
-    body
-}
-```
-
-
 ### Type aliases
 
 Type aliases should generally be kept on one line. If necessary to break the
@@ -458,7 +428,7 @@ use a::b::{foo, bar, baz};
 #### Large list imports
 
 Prefer to use multiple imports rather than a multi-line import. However, tools
-should not split imports by default (they may offer this as an option).
+should not split imports by default.
 
 If an import does require multiple lines (either because a list of single names
 does not fit within the max width, or because of the rules for nested imports

src/doc/style-guide/src/statements.md

@@ -120,9 +120,6 @@ following are true:
 let Some(1) = opt else { return };
 ```
 
-Formatters may allow users to configure the value of the threshold
-used to determine whether a let-else statement is *short*.
-
 Otherwise, the let-else statement requires some line breaks.
 
 If breaking a let-else statement across multiple lines, never break between the