document Closure capture precision

src/changelog.rst

@@ -169,17 +169,49 @@ Language changes in Rust 1.95.0
 
 - `Make operational semantics of pattern matching independent of crate and module <https://github.com/rust-lang/rust/pull/150681>`_
 
-FLS fixes/improvements
-----------------------
+  Previous behavior was not documented,
+  and a new paragraph was added to include the new behavior: :p:`fls_7EXHdE2eOVek`.
 
-- Changed paragraph: :p:`fls_1941wid94hlg`
+FLS maintenance
+---------------
+
+- Replace the term "simple path prefix" with "common path prefix", to improve clarity.
+
+- Changed paragraphs:
+
+  - :p:`fls_33hfay24hx8u`
+  - :p:`fls_uqy5w9uc8gla`
+  - :p:`fls_1941wid94hlg`
+
+- New section: :ref:`fls_buRbhu22Gfdu`
 
 - New paragraphs:
 
   - :p:`fls_CSuxTkwR96j9`
   - :p:`fls_LV94x3HlpBWk`
-
-- Replace the term "simple path prefix" with "common path prefix", to improve clarity.
+  - :p:`fls_rdDT7jsaOMbs`
+  - :p:`fls_j9WyKVyOLFon`
+  - :p:`fls_TbfUxVf8PKPs`
+  - :p:`fls_4TESOxGpEY2h`
+  - :p:`fls_eNkZWskzznW6`
+  - :p:`fls_v8IFXHJnXhez`
+  - :p:`fls_gujpU7p5n9Zx`
+  - :p:`fls_t8tFLUg8O83Q`
+  - :p:`fls_RaONmCLH2KGM`
+  - :p:`fls_Vt9C9mKxHOwo`
+  - :p:`fls_Fs12dmznjsMf`
+  - :p:`fls_iLH8X2U4ADHb`
+  - :p:`fls_HMJUXHrvOmPl`
+  - :p:`fls_Gj1znNpthHY6`
+  - :p:`fls_IFyJvb6mlFU4`
+  - :p:`fls_7NEEJgKSpQQ8`
+  - :p:`fls_kYFd3p06pWWV`
+  - :p:`fls_fATMTNUOHsfb`
+  - :p:`fls_fITor3jpmgrl`
+  - :p:`fls_UfvoShNTxVD2`
+  - :p:`fls_wAMHIDvLG0LM`
+  - :p:`fls_YuQxJCjneaW5`
+  - :p:`fls_nrTZ4mn6IJCl`
 
 Language changes in Rust 1.94.0
 -------------------------------

src/expressions.rst

@@ -5332,7 +5332,7 @@ within the :t:`capturing expression`, as follows:
    precedence:
 
    #. :dp:`fls_33hfay24hx8u`
-      :t:`By immutable reference capture`.
+      :t:`By immutable reference capture` (lowest precedence).
 
    #. :dp:`fls_wmxsd0i2yemf`
       :t:`By unique immutable reference capture` mode, if the
@@ -5342,12 +5342,77 @@ within the :t:`capturing expression`, as follows:
       :t:`By mutable reference capture` mode.
 
    #. :dp:`fls_uqy5w9uc8gla`
-      :t:`By value capture`.
+      :t:`By value capture` (highest precedence).
 
 :dp:`fls_wvob7114tfat`
 A tool selects the first :t:`capture mode` that is compatible with the use of
 the :t:`capture target`.
 
+.. _fls_G64vdcIyB2Is:
+
+Capture precision
+~~~~~~~~~~~~~~~~~
+
+:dp:`fls_j9WyKVyOLFon`
+A :dt:`place projection` is an :t:`array` :t:`index expression`, an automatic :t:`dereference`, an explicit :t:`dereference`, a :t:`field access expression`, a :t:`pattern destructuring` applied to a :t:`variable`, or a :t:`slice` :t:`index expression`.
+
+:dp:`fls_rdDT7jsaOMbs`
+A :dt:`capture path` is a sequence starting with a :t:`capture target` from the :t:`capturing environment` followed by zero or more :t:`[place projection]s` from that :t:`capture target`.
+
+:dp:`fls_TbfUxVf8PKPs`
+A :t:`closure expression` :t:`[borrow]s` or :t:`moves <by move>` the :t:`capture path`, as follows:
+
+- :dp:`fls_4TESOxGpEY2h`
+  When a :t:`capture path` and an ancestor :t:`capture path` are both :t:`captured <capturing>`, the ancestor :t:`capture path` is :t:`captured` with the highest :t:`capture mode` among the two :t:`[capture path]s`, recursively, for all such pairs of :t:`[capture path]s`.
+
+- :dp:`fls_eNkZWskzznW6`
+  The :t:`capture path` is truncated at the rightmost :t:`dereference` in the :t:`capture path` if the :t:`dereference` is applied to a :t:`shared reference`.
+
+:dp:`fls_Vt9C9mKxHOwo`
+A :t:`place` is :t:`captured` by :t:`immutable borrow` if its :t:`discriminant` is read by :t:`pattern matching`.
+
+:dp:`fls_v8IFXHJnXhez`
+A :t:`place` is not :t:`captured` when an :t:`underscore pattern` is used to bind it.
+
+:dp:`fls_gujpU7p5n9Zx`
+A :t:`place` is not :t:`captured` by using a :t:`rest pattern` when :t:`destructuring <pattern destructuring>` :t:`[struct]s`, :t:`[tuple]s`, and :t:`[enum]s` with a single :t:`enum variant`.
+
+:dp:`fls_t8tFLUg8O83Q`
+A :t:`field` is not :t:`captured` by being matched against a :t:`rest pattern`.
+
+:dp:`fls_RaONmCLH2KGM`
+An :t:`array` or :t:`slice` is :t:`captured` whole.
+
+:dp:`fls_Fs12dmznjsMf`
+Matching against an :t:`enum variant` of an :t:`enum` with more than one :t:`enum variant` :t:`captures <capturing>` the :t:`place` by :t:`immutable borrow`.
+
+:dp:`fls_7EXHdE2eOVek`
+Matching against an :t:`enum variant` of an :t:`enum` with one :t:`enum variant` does not :t:`capture <capturing>` the :t:`place`, unless the :t:`enum` is subject to :t:`attribute` ``non_exhaustive``, in which case the :t:`place` is captured by :t:`immutable borrow`.
+
+:dp:`fls_iLH8X2U4ADHb`
+Matching against a :t:`range pattern` :t:`captures <capturing>` the :t:`place` by :t:`immutable borrow`.
+
+:dp:`fls_HMJUXHrvOmPl`
+Matching a :t:`slice` against a :t:`slice pattern`, other than one with only a single :t:`rest pattern`, :t:`captures <capturing>` the :t:`slice` by :t:`immutable borrow`.
+
+:dp:`fls_Gj1znNpthHY6`
+Matching an :t:`array` against a :t:`slice pattern` does not :t:`capture <capturing>` the :t:`place`.
+
+:dp:`fls_IFyJvb6mlFU4`
+A :t:`closure expression` subject to keyword ``move`` :t:`captures <capturing>` the prefix of a :t:`capture path` that runs up to, but not including, the first :t:`dereference` of a :t:`reference`.
+
+:dp:`fls_7NEEJgKSpQQ8`
+A :t:`closure expression` :t:`captures <capturing>` the prefix of a :t:`capture path` that runs up to, but not including, the first :t:`dereference` of a :t:`raw pointer`.
+
+:dp:`fls_kYFd3p06pWWV`
+A :t:`closure expression` :t:`captures <capturing>` the prefix of a :t:`capture path` of a :t:`union` that runs up to the :t:`union` itself.
+
+:dp:`fls_fATMTNUOHsfb`
+A :t:`closure expression` :t:`captures <capturing>` the prefix of the :t:`capture path` that runs up to, but not including, the first :t:`field access expression` into a :t:`struct` that uses the :t:`attribute` :c:`repr` with modifier ``packed``, in unaligned :t:`[field]s` in a :t:`struct`.
+
+:dp:`fls_fITor3jpmgrl`
+Taking the address of an unaligned :t:`field` :t:`captures <capturing>` the entire :t:`struct`.
+
 .. _fls_ZfIBiJMf8qE1:
 
 Arithmetic Overflow

src/patterns.rst

@@ -138,6 +138,23 @@ A :t:`refutable constant` is a :t:`constant` of a :t:`refutable type`.
 
    if let core::option::Option::Some(y) = value {
 
+.. _fls_buRbhu22Gfdu:
+
+Pattern Destructuring
+---------------------
+
+:dp:`fls_UfvoShNTxVD2`
+:dt:`Pattern destructuring` is where :t:`[value]s` of :t:`[enum]s`, :t:`[struct]s`, and :t:`[tuple]s` are broken into :t:`[enum variant]s`, :t:`[struct field]s`, and :t:`[tuple field]s`, respectively.
+
+:dp:`fls_YuQxJCjneaW5`
+In a pattern whose :t:`subject expression` is an :t:`enum type`, an :t:`underscore pattern` matches a single :t:`enum variant`, and a :t:`rest pattern` matches the remaining variants.
+
+:dp:`fls_wAMHIDvLG0LM`
+In a pattern whose :t:`subject expression` is a :t:`struct type`, an :t:`underscore pattern` matches a single :t:`struct field`, and a :t:`rest pattern` matches the remaining fields.
+
+:dp:`fls_nrTZ4mn6IJCl`
+In a pattern whose :t:`subject expression` is a :t:`tuple type`, an :t:`underscore pattern` matches a single :t:`tuple field`, and a :t:`rest pattern` matches the remaining fields.
+
 .. _fls_7bxv8lybxm18:
 
 Identifier Patterns