3 files changed, 71 insertions, 15 deletions
diff --git a/src/doc/style-guide/src/README.md b/src/doc/style-guide/src/README.md
index f4d759673..9a59d8055 100644
--- a/src/doc/style-guide/src/README.md
+++ b/src/doc/style-guide/src/README.md
@@ -32,6 +32,19 @@ This should not be interpreted as forbidding developers from following a
 non-default style, or forbidding tools from adding any particular configuration
 options.
 
+## Bugs
+
+If the style guide differs from rustfmt, that may represent a bug in rustfmt,
+or a bug in the style guide; either way, please report it to the style team or
+the rustfmt team or both, for investigation and fix.
+
+If implementing a new formatting tool based on the style guide and default Rust
+style, please test it on the corpus of existing Rust code, and avoid causing
+widespread breakage. The implementation and testing of such a tool may surface
+bugs in either the style guide or rustfmt, as well as bugs in the tool itself.
+
+We typically resolve bugs in a fashion that avoids widespread breakage.
+
 ## Formatting conventions
 
 ### Indentation and line width
diff --git a/src/doc/style-guide/src/expressions.md b/src/doc/style-guide/src/expressions.md
index 32c604f9f..12037b599 100644
--- a/src/doc/style-guide/src/expressions.md
+++ b/src/doc/style-guide/src/expressions.md
@@ -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.
@@ -400,7 +420,12 @@ constructs. For example, a macro use `foo!(a, b, c)` can be parsed like a
 function call (ignoring the `!`), so format it using the rules for function
 calls.
 
-### Special case macros
+The style guide defines specific formatting for particular macros in the
+language or standard library. The style guide does not define formatting for
+any third-party macros, even if similar to those in the language or standard
+library.
+
+### Format string macros
 
 For macros which take a format string, if all other arguments are *small*,
 format the arguments before the format string on a single line if they fit, and
@@ -421,14 +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
diff --git a/src/doc/style-guide/src/items.md b/src/doc/style-guide/src/items.md
index a6d941f6d..b215de6ad 100644
--- a/src/doc/style-guide/src/items.md
+++ b/src/doc/style-guide/src/items.md
@@ -367,26 +367,52 @@ where
 ## Type aliases
 
 Keep type aliases on one line when they fit. If necessary to break the line, do
-so after the `=`, and block-indent the right-hand side:
+so before the `=`, and block-indent the right-hand side:
 
 ```rust
 pub type Foo = Bar<T>;
 
 // If multi-line is required
-type VeryLongType<T, U: SomeBound> =
-    AnEvenLongerType<T, U, Foo<T>>;
+type VeryLongType<T, U: SomeBound>
+    = AnEvenLongerType<T, U, Foo<T>>;
 ```
 
-Where possible avoid `where` clauses and keep type constraints inline. Where
-that is not possible split the line before and after the `where` clause (and
-split the `where` clause as normal), e.g.,
+When there is a trailing `where` clause after the type, and no `where` clause
+present before the type, break before the `=` and indent. Then break before the
+`where` keyword and format the clauses normally, e.g.,
 
 ```rust
+// With only a trailing where clause
 type VeryLongType<T, U>
+    = AnEvenLongerType<T, U, Foo<T>>
+where
+    T: U::AnAssociatedType,
+    U: SomeBound;
+```
+
+When there is a `where` clause before the type, format it normally, and break
+after the last clause. Do not indent before the `=` to leave it visually
+distinct from the indented clauses that precede it. If there is additionally a
+`where` clause after the type, break before the `where` keyword and format the
+clauses normally.
+
+```rust
+// With only a preceding where clause.
+type WithPrecedingWC<T, U>
 where
     T: U::AnAssociatedType,
     U: SomeBound,
 = AnEvenLongerType<T, U, Foo<T>>;
+
+// Or with both a preceding and trailing where clause.
+type WithPrecedingWC<T, U>
+where
+    T: U::AnAssociatedType,
+    U: SomeBound,
+= AnEvenLongerType<T, U, Foo<T>>
+where
+    T: U::AnAssociatedType2,
+    U: SomeBound2;
 ```
 
 ## Associated types