[wildcard-variables] Add more explicit details on functions and records. (#3802)

* [wildcard-variables] Add more explicit details on functions and records.

* Rewrite record type positional fields and add newline.

* Named fields of record types are unchanged.

Author: kallentu

working/wildcards/feature-specification.md

@@ -4,7 +4,9 @@ Author: Bob Nystrom
 
 Status: In-progress
 
-Version 1.2
+Version 1.3
+
+## Motivation
 
 Pattern matching brings a new way to declare variables. Inside patterns, any
 variable whose name is `_` is considered a "wildcard". It behaves like a
@@ -74,6 +76,8 @@ library privacy comes into play.
 
 ## Proposal
 
+### Local declarations
+
 A *local declaration* is any of:
 
 *   Function parameters. This includes top-level functions, local functions,
@@ -85,6 +89,10 @@ A *local declaration* is any of:
     Foo(_, this._, super._, void _(), {_}) {}
 
     list.where((_) => true);
+
+    void f(void g(_, _)) {}
+
+    typedef T = void Function(String _, String _);
     ```
 
 *   Local variable declaration statement variables.
@@ -127,8 +135,35 @@ means you can have multiple local declarations named `_` in the same namespace
 without a collision error. The initializer, if there is one, is still executed,
 but the value is not accessible.
 
-Other declarations: top-level variables, top-level function names, type names,
-member names, etc. are unchanged. They can be named `_` as they are today.
+### Record type positional fields
+
+```dart
+typedef R = (String _, String _);
+(int _, int _) record;
+```
+
+It is currently an error for a record field name to begin with `_`
+(including just a bare `_`). We relax that error to only apply to record
+fields whose name begins with `_` followed by at least one other character
+(even if those later character(s) are `_`).
+
+Named fields of record types are unchanged. It is still a compile-time error for a named field name to start with `_`.
+
+### Local function declarations
+
+```dart
+void f() {
+  _() {} // Error.
+  _(); // Error.
+}
+```
+
+It's an error to declare a local function declaration named `_`.
+
+### Other declarations
+
+Top-level variables, top-level function names, type names, member names,
+etc. are unchanged. They can be named `_` as they are today.
 
 We do not change how identifier *expressions* behave. Members can be named `_`
 and you can access them from inside the class where the member is declared
@@ -403,6 +438,11 @@ This lint is included in the core lint set which means that the scale of the bre
 
 ## Changelog
 
+### 1.3
+
+- Add section on local function declarations. Discussion: [language/#3790](https://github.com/dart-lang/language/issues/3790)
+- Add section on record type positionals and more examples with function types. Discussion: [language/#3791](https://github.com/dart-lang/language/issues/3791)
+
 ### 1.2
 
 - Add information about the [`no_wildcard_variable_uses`](https://dart.dev/tools/linter-rules/no_wildcard_variable_uses) lint.