Specify the expected type of patterns

src/expressions.rst

@@ -3624,10 +3624,25 @@ A :t:`closure parameter` is a :t:`construct` that yields a set of
 :t:`[binding]s` that bind matched input :t:`[value]s` to :t:`[name]s` at the
 site of a :t:`call expression` or a :t:`method call expression`.
 
+:dp:`fls_81KOEXwps2HS`
+The :t:`type` of a :t:`closure parameter` is determined as follows:
+
+* :dp:`fls_XWJ9SFggdVeH`
+  If the :t:`closure parameter` lacks a :s:`TypeSpecification`, the :t:`type` is inferred form the usage of the :t:`closure parameter`.
+
+* :dp:`fls_mPWkIxTJErqx`
+  Otherwise the :t:`type` is the specified :t:`type`.
+
+:dp:`fls_MeLJqy28J4jr`
+The :t:`type` of a :t:`closure parameter` is the :t:`type` of the :t:`closure parameter`.
+
 :dp:`fls_r6gWLoNR7JMR`
 The :t:`pattern` of a :t:`closure parameter` shall be an
 :t:`irrefutable pattern`.
 
+:dp:`fls_zsaTK9snhXs0`
+The :t:`expected type` of the :t:`pattern` of a :t:`closure parameter` is the :t:`type` of the :t:`closure parameter`.
+
 :dp:`fls_qPeOL6ZhXsgH`
 The :t:`[binding]s` of all :t:`[pattern]s` of all :t:`[closure parameter]s` of a :t:`closure expression` shall not shadow another.
 
@@ -3731,6 +3746,9 @@ its :t:`loop body` as long as its :t:`subject expression` yields a :t:`value`.
 The :t:`type` of a :t:`subject expression` shall implement the
 :std:`core::iter::IntoIterator` :t:`trait`.
 
+:dp:`fls_fo6Aa6Td6rMA`
+The :t:`expected type` of the :t:`pattern` is the :t:`associated type` :std:`core::iter::IntoIterator::Item` of the :t:`subject expression`'s :std:`core::iter::IntoIterator` implementation.
+
 :dp:`fls_bmTjhKdpfgCB`
 The :t:`type` of an :t:`for loop expression` is the :t:`unit type`.
 
@@ -3924,6 +3942,9 @@ A :t:`while let loop expression` is a :t:`loop expression` that continues to
 evaluate its :t:`loop body` as long as its :t:`subject let expression` yields
 a :t:`value` that can be matched against its :t:`pattern`.
 
+:dp:`fls_bC60ZSC9yUOI`
+The :t:`expected type` of the :t:`pattern` is the :t:`type` of the :t:`subject let expression`.
+
 :dp:`fls_gTfSLePwHTES`
 The :t:`type` of an :t:`while let loop expression` is the :t:`unit type`.
 
@@ -4409,6 +4430,9 @@ An :t:`if let expression` is an :t:`expression` that evaluates either a
 :t:`block expression` or an :t:`else expression` depending on whether its
 :t:`pattern` can be matched against its :t:`subject let expression`.
 
+:dp:`fls_okVOYzTT6fBK`
+The :t:`expected type` of the :t:`pattern` is the :t:`type` of the :t:`subject let expression`.
+
 :dp:`fls_4vyrufo4qdeg`
 The :t:`type` of an :t:`if let expression` is the :t:`type` of its
 :t:`block expression`.
@@ -4526,6 +4550,9 @@ A :t:`final match arm` is the last :t:`match arm` of a :t:`match expression`.
 A :t:`match arm matcher` is a :t:`construct` that consists of a :t:`pattern` and
 a :t:`match arm guard`.
 
+:dp:`fls_zJQ4LecT1HYd`
+The :t:`expected type` of the :t:`pattern` of the :t:`match arm matcher` is the :t:`type` of the :t:`subject expression`.
+
 :dp:`fls_8wjdichfxp0y`
 A :t:`match arm body` is the :t:`operand` of a :t:`match arm`.
 
@@ -4555,7 +4582,7 @@ The :t:`type` of a :t:`match expression` is the :t:`unified type` of the
 
 :dp:`fls_g6xyz0beps3o`
 A :t:`match arm` is selected when its :t:`pattern` matches the
-:t:`subject expression` and its :t:`match arm guard` (if any) evaluates to
+:t:`value` of the :t:`subject expression` and its :t:`match arm guard` (if any) evaluates to
 ``true``.
 
 :dp:`fls_8dba4o5qg8js`

src/functions.rst

@@ -75,17 +75,38 @@ A :t:`self parameter` is a :t:`function parameter` expressed by :t:`keyword`
 A :t:`function` shall not specify a :t:`self parameter` unless it is an
 :t:`associated function`.
 
-:dp:`fls_icdzs1mjh0n4`
-A :t:`function` shall not specify a :s:`FunctionParameterVariadicPart` unless
-it is an :t:`external function`.
+:dp:`fls_AAYJDCNMJgTq`
+The :t:`type` of a :t:`parameter` is determined as follows:
+
+* :dp:`fls_PGtp39f6gJwU`
+  If the :t:`parameter` is a :t:`self parameter` without a :s:`TypeSpecification`:
+
+  * :dp:`fls_yZ2yIXxmy2ri`
+    And the :t:`self parameter` has token ``&`` and :t:`keyword` ``mut``, then the :t:`type` is ``&mut Self``.
+
+  * :dp:`fls_35aSvBxBnIzm`
+    And the :t:`self parameter` has token ``&`` and lacks :t:`keyword` ``mut``, then the :t:`type` is ``&Self``.
+
+  * :dp:`fls_Ogziu8S01qPQ`
+    And the :t:`self parameter` lacks token ``&`` and :t:`keyword` ``mut``, then the :t:`type` is ``Self``.
+
+* :dp:`fls_xCSsxYUZUFed`
+  Otherwise the :t:`type` is the specified :t:`type`.
 
 :dp:`fls_lxzinvqveuqh`
 The :t:`pattern` of a :t:`function parameter` shall be an :t:`irrefutable
 pattern`.
 
+:dp:`fls_kcAbTPZXQ5Y8`
+The :t:`expected type` of the :t:`pattern` of a :t:`function parameter` is the :t:`type` of the :t:`function parameter`.
+
 :dp:`fls_PGDKWK7nPvgw`
 The :t:`[binding]s` of all :t:`[pattern]s` of all :t:`[function parameter]s` of a :t:`function` shall not shadow another.
 
+:dp:`fls_icdzs1mjh0n4`
+A :t:`function` shall not specify a :s:`FunctionParameterVariadicPart` unless
+it is an :t:`external function`.
+
 :dp:`fls_vljy4mm0zca2`
 A :t:`return type` is the :t:`type` of the result a :t:`function`, :t:`closure type` or :t:`function pointer type` returns.
 

src/patterns.rst

@@ -57,8 +57,7 @@ it is not the inner :t:`pattern` of a :t:`slice pattern` or the :t:`pattern` of
 a possibly nested :t:`identifier pattern` of a :t:`slice pattern`\ ``.``
 
 :dp:`fls_cma5t8waon0x`
-The :t:`expected type` of a :t:`pattern` is the :t:`type` of the :t:`value` the
-:t:`pattern` is being matched against.
+The :t:`expected type` of a :t:`pattern` is the :t:`type` the :t:`pattern` is being matched against.
 
 :dp:`fls_TUanRT7WU14E`
 It is a static error when :t:`[lexical element]s` match multiple alternations
@@ -1255,7 +1254,7 @@ follows:
 Pattern Matching
 ----------------
 
-.. rubric:: Dynamic Semantics
+.. rubric:: Legality Rules
 
 :dp:`fls_tlwr4u7bjhh5`
 :t:`Pattern matching` that involves a :t:`pattern` and a context :t:`value`

src/statements.rst

@@ -75,6 +75,18 @@ alternatively executes a :t:`block expression`.
 If a :t:`let statement` lacks a :t:`block expression`, then the :t:`pattern` of
 the :t:`let statement` shall be an :t:`irrefutable pattern`.
 
+:dp:`fls_iB25BeFys0j8`
+The :t:`expected type` of the :t:`pattern` of the :t:`let statement` is determined as follows:
+
+* :dp:`fls_zObyLdya4DYc`
+  If the :t:`let statement` lacks a :t:`type ascription` and a :t:`let initializer, then the :t:`expected type` is the :t:`inferred type`.
+
+* :dp:`fls_r38TXWKQPjxv`
+  If the :t:`let statement` lacks a :t:`type ascription`, then the :t:`expected type` is the :t:`type` of the :t:`let initializer`.
+
+* :dp:`fls_6QSdwF4pzjoe`
+  Otherwise the :t:`expected type` is the :t:`type` specified by the :t:`type ascription`.
+
 :dp:`fls_1prqh1trybwz`
 The :t:`type` of a :t:`binding` introduced by a :t:`let statement` is
 determined as follows:
@@ -195,4 +207,3 @@ The following expression statement is not an index expression.
 .. code-block:: rust
 
    [42];
-