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Rollup merge of #114394 - joshtriplett:style-guide-as, r=calebcartwright

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style-guide: Document formatting of `as` casts (mostly like a binary operator)

`as` casts currently get formatted like a binary operator, except that
the second line can stack several `as` casts rather than breaking them
each onto their own line. Document this.

As far as I can tell (cc `@calebcartwright` for verification), this is not a 2024 edition change, it just documents current behavior.
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Matthias Krüger 2023-09-21 00:11:35 +02:00 committed by GitHub
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src/doc/style-guide/src/expressions.md
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@ -328,6 +328,26 @@ foo_bar
Prefer line-breaking at an assignment operator (either `=` or `+=`, etc.) rather
than at other binary operators.
### Casts (`as`)
Format `as` casts like a binary operator. In particular, always include spaces
around `as`, and if line-breaking, break before the `as` (never after) and
block-indent the subsequent line. Format the type on the right-hand side using
the rules for types.
However, unlike with other binary operators, if chaining a series of `as` casts
that require line-breaking, and line-breaking before the first `as` suffices to
make the remainder fit on the next line, don't break before any subsequent
`as`; instead, leave the series of types all on the same line:
```rust
let cstr = very_long_expression()
as *const str as *const [u8] as *const std::os::raw::c_char;
```
If the subsequent line still requires line-breaking, break and block-indent
before each `as` as with other binary operators.
## Control flow
Do not include extraneous parentheses for `if` and `while` expressions.
@ -426,14 +446,6 @@ assert_eq!(
);
```
## Casts (`as`)
Put spaces before and after `as`:
```rust
let cstr = "Hi\0" as *const str as *const [u8] as *const std::os::raw::c_char;
```
## Chains of fields and method calls
A chain is a sequence of field accesses, method calls, and/or uses of the try