[Version 10.0] Feature support for global using directives

standard/basic-concepts.md

@@ -774,7 +774,8 @@ The ***scope*** of a name is the region of program text within which it is possi
 
 - The scope of a namespace member declared by a *namespace_member_declaration* ([§14.6](namespaces.md#146-namespace-member-declarations)) with no enclosing *namespace_declaration* is the entire program text.
 - The scope of a namespace member declared by a *namespace_member_declaration* within a *namespace_declaration* whose fully qualified name is `N`, is the *namespace_body* of every *namespace_declaration* whose fully qualified name is `N` or starts with `N`, followed by a period.
-- The scope of a name defined by an *extern_alias_directive* ([§14.4](namespaces.md#144-extern-alias-directives)) extends over the *using_directive*s, *global_attributes*, *statement_list*s, and *namespace_member_declaration*s of its immediately containing *compilation_unit* or *namespace_body*. An *extern_alias_directive* does not contribute any new members to the underlying declaration space. In other words, an *extern_alias_directive* is not transitive, but, rather, affects only the *compilation_unit* or *namespace_body* in which it occurs.
+- The scope of a name defined by an *extern_alias_directive* ([§14.4](namespaces.md#144-extern-alias-directives)) extends over the *global_using_directive*s, *using_directive*s, *global_attributes*, *statement_list*s, and *namespace_member_declaration*s of its immediately containing *compilation_unit* or *namespace_body*. An *extern_alias_directive* does not contribute any new members to the underlying declaration space. In other words, an *extern_alias_directive* is not transitive, but, rather, affects only the *compilation_unit* or *namespace_body* in which it occurs.
+- The scope of a name defined or imported by a *global_using_directive* extends over the *global_attributes* and *namespace_member_declaration*s of all the *compilation_unit*s in the program.
 - The scope of a name defined or imported by a *using_directive* ([§14.5](namespaces.md#145-using-directives)) extends over the *global_attributes*, *statement_list*s, and *namespace_member_declaration*s of the *compilation_unit* or *namespace_body* in which the *using_directive* occurs. A *using_directive* may make zero or more namespace or type names available within a particular *compilation_unit* or *namespace_body*, but does not contribute any new members to the underlying declaration space. In other words, a *using_directive* is not transitive but rather affects only the *compilation_unit* or *namespace_body* in which it occurs.
 - The scope of a type parameter declared by a *type_parameter_list* on a *class_declaration* ([§15.2](classes.md#152-class-declarations)) is the *class_base*, *type_parameter_constraints_clause*s, and *class_body* (or *record_class_body*) of that *class_declaration*.
     > *Note*: Unlike members of a class, this scope does not extend to derived classes. *end note*
@@ -1098,15 +1099,15 @@ where:
     > *Note*: Non-type members (constants, fields, methods, properties, indexers, operators, instance constructors, finalizers, and static constructors) and type members with a different number of type parameters are ignored when determining the meaning of the *namespace_or_type_name*. *end note*
   - Otherwise, for each namespace `N`, starting with the namespace in which the *namespace_or_type_name* occurs, continuing with each enclosing namespace (if any), and ending with the global namespace, the following steps are evaluated until an entity is located:
     - If `x` is zero and `I` is the name of a namespace in `N`, then:
-      - If the location where the *namespace_or_type_name* occurs is enclosed by a namespace declaration for `N` and the namespace declaration contains an *extern_alias_directive* or *using_alias_directive* that associates the name `I` with a namespace or type, then the *namespace_or_type_name* is ambiguous and a compile-time error occurs.
+      - If the location where the *namespace_or_type_name* occurs is enclosed by a namespace declaration for `N` and the namespace declaration contains an *extern_alias_directive* or *using_alias_directive* that associates the name `I` with a namespace or type, or any namespace declaration for `N` in the program contains a *global_using_alias_directive* that associates the name `I` with a namespace or type, then the *namespace_or_type_name* is ambiguous and a compile-time error occurs.
       - Otherwise, `R₀` refers to the namespace named `I` in `N`.
     - Otherwise, if `N` contains an accessible type having name `I` and `x` type parameters, then:
-      - If `x` is zero and the location where the *namespace_or_type_name* occurs is enclosed by a namespace declaration for `N` and the namespace declaration contains an *extern_alias_directive* or *using_alias_directive* that associates the name `I` with a namespace or type, then the *namespace_or_type_name* is ambiguous and a compile-time error occurs.
+      - If `x` is zero and the location where the *namespace_or_type_name* occurs is enclosed by a namespace declaration for `N` and the namespace declaration contains an *extern_alias_directive* or *using_alias_directive* that associates the name `I` with a namespace or type, or any namespace declaration for `N` in the program contains a *global_using_alias_directive* that associates the name `I` with a namespace or type, then the *namespace_or_type_name* is ambiguous and a compile-time error occurs.
       - Otherwise, `R₀` refers to the type constructed with the given type arguments.
     - Otherwise, if the location where the *namespace_or_type_name* occurs is enclosed by a namespace declaration for `N`:
-      - If `x` is zero and the namespace declaration contains an *extern_alias_directive* or *using_alias_directive* that associates the name `I` with an imported namespace or type, then `R₀` refers to that namespace or type.
-      - Otherwise, if the namespaces imported by the *using_namespace_directive*s of the namespace declaration contain exactly one type having name `I` and `x` type parameters, then `R₀` refers to that type constructed with the given type arguments.
-      - Otherwise, if the namespaces imported by the *using_namespace_directive*s of the namespace declaration contain more than one type having name `I` and `x` type parameters, then the *namespace_or_type_name* is ambiguous and a compile-time error occurs.
+      - If `x` is zero and the namespace declaration contains an *extern_alias_directive* or *using_alias_directive* that associates the name `I` with an imported namespace or type, or any namespace declaration for `N` in the program contains a *global_using_alias_directive* that associates the name `I` with an imported namespace or type, then `R₀` refers to that namespace or type.
+      - Otherwise, if the namespaces imported by the *using_namespace_directive*s of the namespace declaration and the namespaces and type declarations imported by the *global_using_namespace_directive*s and *global_using_static_directive*s of any namespace declaration for `N` in the program contain exactly one type having name `I` and `x` type parameters, then `R₀` refers to that type constructed with the given type arguments.
+      - Otherwise, if the namespaces imported by the *using_namespace_directive*s of the namespace declaration and the namespaces and type declarations imported by the *global_using_namespace_directive*s and *global_using_static_directive*s of any namespace declaration for `N` in the program contain more than one type having name `I` and `x` type parameters, then the *namespace_or_type_name* is ambiguous and a compile-time error occurs.
   - Otherwise, the *namespace_or_type_name* is undefined and a compile-time error occurs.
 
 If `R₀` has been resolved successfully the trailing part of the *namespace_or_type_name* is resolved. The trailing grammar fragment consists of `k ≥ 0` repetitions, with each repetition further resolving the referenced namespace or type.

standard/expressions.md

@@ -1605,15 +1605,15 @@ A *simple_name* is either of the form `I` or of the form `I<A₁, ..., Aₑ>`,
   - Otherwise, if the declaration of `T` includes a primary constructor parameter `I`, the result is the primary constructor parameter `I`.
 - Otherwise, for each namespace `N`, starting with the namespace in which the *simple_name* occurs, continuing with each enclosing namespace (if any), and ending with the global namespace, the following steps are evaluated until an entity is located:
   - If `e` is zero and `I` is the name of a namespace in `N`, then:
-    - If the location where the *simple_name* occurs is enclosed by a namespace declaration for `N` and the namespace declaration contains an *extern_alias_directive* or *using_alias_directive* that associates the name `I` with a namespace or type, then the *simple_name* is ambiguous and a compile-time error occurs.
+    - If the location where the *simple_name* occurs is enclosed by a namespace declaration for `N` and the namespace declaration contains an *extern_alias_directive* or *using_alias_directive* that associates the name `I` with a namespace or type, or any namespace declaration for `N` in the program contains a *global_using_alias_directive* that associates the name `I` with a namespace or type, then the *simple_name* is ambiguous and a compile-time error occurs.
     - Otherwise, the *simple_name* refers to the namespace named `I` in `N`.
   - Otherwise, if `N` contains an accessible type having name `I` and `e` type parameters, then:
-    - If `e` is zero and the location where the *simple_name* occurs is enclosed by a namespace declaration for `N` and the namespace declaration contains an *extern_alias_directive* or *using_alias_directive* that associates the name `I` with a namespace or type, then the *simple_name* is ambiguous and a compile-time error occurs.
+    - If `e` is zero and the location where the *simple_name* occurs is enclosed by a namespace declaration for `N` and the namespace declaration contains an *extern_alias_directive* or *using_alias_directive* that associates the name `I` with a namespace or type, or any namespace declaration for `N` in the program contains a *global_using_alias_directive* that associates the name `I` with a namespace or type, then the *simple_name* is ambiguous and a compile-time error occurs.
     - Otherwise, the *namespace_or_type_name* refers to the type constructed with the given type arguments.
   - Otherwise, if the location where the *simple_name* occurs is enclosed by a namespace declaration for `N`:
-    - If `e` is zero and the namespace declaration contains an *extern_alias_directive* or *using_alias_directive* that associates the name `I` with an imported namespace or type, then the *simple_name* refers to that namespace or type.
-    - Otherwise, if the namespaces imported by the *using_namespace_directive*s of the namespace declaration contain exactly one type having name `I` and `e` type parameters, then the *simple_name* refers to that type constructed with the given type arguments.
-    - Otherwise, if the namespaces imported by the *using_namespace_directive*s of the namespace declaration contain more than one type having name `I` and `e` type parameters, then the *simple_name* is ambiguous and a compile-time error occurs.
+    - If `e` is zero and the namespace declaration contains an *extern_alias_directive* or *using_alias_directive* that associates the name `I` with an imported namespace or type, or any namespace declaration for `N` in the program contains a *global_using_alias_directive* that associates the name `I` with an imported namespace or type, then the *simple_name* refers to that namespace or type.
+    - Otherwise, if the namespaces imported by the *using_namespace_directive*s of the namespace declaration and the namespaces and type declarations imported by the *global_using_namespace_directive*s and *global_using_static_directive*s of any namespace declaration for `N` in the program contain exactly one type having name `I` and `e` type parameters, then the *simple_name* refers to that type constructed with the given type arguments.
+    - Otherwise, if the namespaces imported by the *using_namespace_directive*s of the namespace declaration and the namespaces and type declarations imported by the *global_using_namespace_directive*s and *global_using_static_directive*s of any namespace declaration for `N` in the program contain more than one type having name `I` and `e` type parameters, then the *simple_name* is ambiguous and a compile-time error occurs.  
   > *Note*: This entire step is exactly parallel to the corresponding step in the processing of a *namespace_or_type_name* ([§7.8](basic-concepts.md#78-namespace-and-type-names)). *end note*
 - Otherwise, if `e` is zero and `I` is the identifier `_`, the *simple_name* is a *simple discard*, which is a form of declaration expression ([§12.20](expressions.md#1220-declaration-expressions)).
 - Otherwise, the *simple_name* is undefined and a compile-time error occurs.
@@ -2093,7 +2093,7 @@ The search for `C` proceeds as follows:
 
 - Starting with the closest enclosing namespace declaration, continuing with each enclosing namespace declaration, and ending with the containing compilation unit, successive attempts are made to find a candidate set of extension methods:
   - If the given namespace or compilation unit directly contains non-generic type declarations `Cᵢ` with eligible extension methods `Mₑ`, then the set of those extension methods is the candidate set.
-  - If namespaces imported by using namespace directives in the given namespace or compilation unit directly contain non-generic type declarations `Cᵢ` with eligible extension methods `Mₑ`, then the set of those extension methods is the candidate set.
+  - If types `Cᵢ` imported by *using_static_directive*s and directly declared in namespaces imported by *using_namespace_directive*s in the given namespace or compilation unit, and, if the containing compilation unit is reached, imported by *global_using_static_directive*s and directly declared in namespaces imported by *global_using_namespace_directive*s in the program, directly contain eligible extension methods `Mₑ`, then the set of those extension methods is the candidate set.
 - If no candidate set is found in any enclosing namespace declaration or compilation unit, a compile-time error occurs.
 - Otherwise, overload resolution is applied to the candidate set as described in [§12.6.4](expressions.md#1264-overload-resolution). If no single best method is found, a compile-time error occurs.
 - `C` is the type within which the best method is declared as an extension method.