specify lifetime extension of pin! and format_args! arguments

Author: dianne

src/destructors.md

@@ -442,11 +442,18 @@ are all extending expressions. The borrows in `&0 + &1` and `f(&mut 0)` are not.
 The operand of any extending borrow expression has its temporary scope
 extended.
 
+> [!NOTE]
+> [Invocations][macro invocation] of the built-in macros [`pin!`] and [`format_args!`] expand to borrow their arguments.
+> They are subject to lifetime extension as follows:
+> * The argument to an extending [`pin!`] macro invocation expression is extending and has an extended temporary scope.
+> * Apart from the format string, the arguments to an extending [`format_args!`] macro invocation expression are extending and have extended temporary scopes.
+
 #### Examples
 
 Here are some examples where expressions have extended temporary scopes:
 
 ```rust
+# use std::pin::pin;
 # fn temp() {}
 // The temporary that stores the result of `temp()` lives in the same scope
 // as x in these cases.
@@ -456,6 +463,8 @@ let x = &temp() as &dyn Send;
 # x;
 let x = (&*&temp(),);
 # x;
+let x = pin!(temp());
+# x;
 let x = { [Some(&temp()) ] };
 # x;
 let ref x = temp();
@@ -510,6 +519,7 @@ There is one additional case to be aware of: when a panic reaches a [non-unwindi
 [initialized]: glossary.md#initialized
 [interior mutability]: interior-mutability.md
 [lazy boolean expression]: expressions/operator-expr.md#lazy-boolean-operators
+[macro invocation]: macros.md#macro-invocation
 [non-unwinding ABI boundary]: items/functions.md#unwinding
 [panic]: panic.md
 [place context]: expressions.md#place-expressions-and-value-expressions
@@ -554,3 +564,6 @@ There is one additional case to be aware of: when a panic reaches a [non-unwindi
 [`match`]: expressions/match-expr.md
 [`while let`]: expressions/loop-expr.md#while-let-patterns
 [`while`]: expressions/loop-expr.md#predicate-loops
+
+[`pin!`]: std::pin::pin
+[`format_args!`]: core::format_args