Add support to syntax tree

lib/Parse/ParseDecl.cpp

@@ -595,8 +595,10 @@ bool Parser::parseSpecializeAttributeArguments(
       auto ParamLabel = Tok.getText();
       SyntaxParsingContext ArgumentContext(
           SyntaxContext, ParamLabel == "target"
-                             ? SyntaxKind::TargetFunctionEntry
+                             ? SyntaxKind::TargetFunctionEntry :
-                             : SyntaxKind::LabeledSpecializeEntry);
+                             (ParamLabel == "availability" ?
+                              SyntaxKind::AvailabilityEntry
+                              : SyntaxKind::LabeledSpecializeEntry));
       if (ParamLabel != "exported" && ParamLabel != "kind" &&
           ParamLabel != "target" && ParamLabel != "spi" &&
           ParamLabel != "spiModule" && ParamLabel != "availability") {

test/SILGen/availability_attribute.swift

@@ -34,3 +34,7 @@ public struct AvailableStruct {
         public func availableNestedMethod() {}
     }
 }
+
+@_specialize(exported: true, availability: macOS 11, iOS 13, *; where T == Int)
+//@_specialize(exported: true, where T == Int)
+public func testAvailability<T>(_ t: T) {}

utils/gyb_syntax_support/AttributeNodes.py

@@ -102,10 +102,25 @@ ATTRIBUTE_NODES = [
          element='Syntax', element_name='SpecializeAttribute',
          element_choices=[
              'LabeledSpecializeEntry',
+             'AvailabilityEntry',
              'TargetFunctionEntry',
              'GenericWhereClause',
          ]),
 
+    Node('AvailabilityEntry', kind='Syntax',
+         description='''
+         The availability argument for the _specialize attribute
+         ''',
+         children=[
+             Child('Label', kind='IdentifierToken',
+                   description='The label of the argument'),
+             Child('Colon', kind='ColonToken',
+                   description='The colon separating the label and the value'),
+             Child('AvailabilityList', kind='AvailabilitySpecList',
+                   collection_element_name='Availability'),
+             Child('Semicolon', kind='SemicolonToken'),
+         ]),
+
     # Representation of e.g. 'exported: true,'
     # labeled-specialize-entry -> identifier ':' token ','?
     Node('LabeledSpecializeEntry', kind='Syntax',

utils/gyb_syntax_support/NodeSerializationCodes.py

@@ -253,6 +253,7 @@ SYNTAX_NODE_SERIALIZATION_CODES = {
     'TargetFunctionEntry': 248,
     'PostfixIfConfigExpr': 250,
     'UnavailabilityCondition': 251,
+    'AvailabilityEntry' : 252,
 }