Remove the "@expression" attribute now that it has a better spelling

Author: DougGregor

include/swift/AST/DiagnosticsParse.def

@@ -2043,6 +2043,8 @@ ERROR(macro_attribute_introduced_name_requires_argument,PointsToFirstBadToken,
       "introduced name kind %0 requires a single argument '(name)'", (Identifier))
 ERROR(macro_attribute_introduced_name_requires_no_argument,PointsToFirstBadToken,
       "introduced name kind %0 must not have an argument", (Identifier))
+WARNING(macro_expression_attribute_removed,PointsToFirstBadToken,
+      "@expression has been removed in favor of @freestanding(expression)", ())
 
 ERROR(unexpected_attribute_expansion,PointsToFirstBadToken,
       "unexpected token '%0' in expanded attribute list'",

lib/AST/Decl.cpp

@@ -9825,8 +9825,6 @@ SourceRange MacroDecl::getSourceRange() const {
 
 MacroRoles MacroDecl::getMacroRoles() const {
   MacroRoles contexts = None;
-  if (getAttrs().hasAttribute<ExpressionAttr>())
-    contexts |= MacroRole::Expression;
   for (auto attr : getAttrs().getAttributes<DeclarationAttr>())
     contexts |= attr->getMacroRole();
   for (auto attr : getAttrs().getAttributes<MacroRoleAttr>())

lib/Parse/ParseDecl.cpp

@@ -3779,6 +3779,17 @@ ParserStatus Parser::parseDeclAttribute(
     return makeParserSuccess();
   }
 
+  // Old spelling for @freestanding(expression).
+  if (DK == DAK_Count && Tok.getText() == "expression") {
+    SourceLoc attrLoc = consumeToken();
+    diagnose(attrLoc, diag::macro_expression_attribute_removed)
+      .fixItReplace(SourceRange(AtLoc, attrLoc), "@freestanding(expression)");
+    return makeParserResult(MacroRoleAttr::create(
+        Context, AtLoc, SourceRange(AtLoc, attrLoc),
+        MacroSyntax::Freestanding, MacroRole::Expression, { },
+        /*isImplicit*/ false));
+  }
+
   if (DK != DAK_Count && !DeclAttribute::shouldBeRejectedByParser(DK)) {
     parseNewDeclAttribute(Attributes, AtLoc, DK, isFromClangAttribute);
     return makeParserSuccess();

lib/Sema/TypeCheckAttr.cpp

@@ -160,7 +160,6 @@ class AttributeChecker : public AttributeVisitor<AttributeChecker> {
   IGNORED_ATTR(Preconcurrency)
   IGNORED_ATTR(BackDeploy)
   IGNORED_ATTR(Documentation)
-  IGNORED_ATTR(Expression)
   IGNORED_ATTR(Declaration)
   IGNORED_ATTR(MacroRole)
 #undef IGNORED_ATTR

lib/Sema/TypeCheckDeclOverride.cpp

@@ -1626,7 +1626,6 @@ namespace  {
 
     UNINTERESTING_ATTR(RuntimeMetadata)
 
-    UNINTERESTING_ATTR(Expression)
     UNINTERESTING_ATTR(Declaration)
     UNINTERESTING_ATTR(MacroRole)
 #undef UNINTERESTING_ATTR

test/Macros/macros_diagnostics.swift

@@ -1,8 +1,9 @@
 // RUN: %target-typecheck-verify-swift -enable-experimental-feature Macros -module-name MacrosTest
 
-@freestanding(expression) macro stringify<T>(_ value: T) -> (T, String) = #externalMacro(module: "MacroDefinition", type: "StringifyMacro")
+@expression macro stringify<T>(_ value: T) -> (T, String) = #externalMacro(module: "MacroDefinition", type: "StringifyMacro")
 // expected-note@-1 2{{'stringify' declared here}}
 // expected-warning@-2{{external macro implementation type}}
+// expected-warning@-3{{@expression has been removed in favor of @freestanding(expression)}}{{1-12=@freestanding(expression)}}
 @freestanding(expression) macro missingMacro1(_: Any) = MissingModule.MissingType // expected-note{{'missingMacro1' declared here}}
 // expected-warning@-1{{external macro definitions are now written using #externalMacro}}{{57-82=#externalMacro(module: "MissingModule", type: "MissingType")}}
 // expected-warning@-2{{external macro implementation type}}

utils/gyb_syntax_support/AttributeKinds.py

@@ -903,12 +903,6 @@ def __init__(self, name, swift_name=None):
                                   ABIBreakingToAdd, ABIBreakingToRemove,
                                   APIBreakingToAdd, APIBreakingToRemove,
                                   code=130),
-
-    SimpleDeclAttribute('expression', 'Expression',
-                        OnMacro,
-                        ABIStableToAdd, ABIStableToRemove, APIStableToAdd, APIBreakingToRemove,  # noqa: E501
-                        code=140),
-
     DeclAttribute('declaration', 'Declaration',
                   OnMacro, AllowMultipleAttributes,
                   ABIStableToAdd, ABIStableToRemove, APIStableToAdd, APIBreakingToRemove,  # noqa: E501