[Legacy parser] No freestanding macros in @abi

SwiftSyntaxParser is already doing this, and we already diagnosed it in Sema anyway, so we’re just moving that diagnostic earlier so the ASTGen testing mode is happy. Also adding compiler tests for it.

Macro-related tests are not included in this commit; they require matching swift-syntax changes which are being negotiated.

Author: beccadax

include/swift/AST/DiagnosticsParse.def

@@ -1568,6 +1568,11 @@ ERROR(attr_unsupported_on_target, none,
 ERROR(attr_name_unsupported_on_target, none,
       "attribute '%0' is unsupported on target '%1'", (StringRef, StringRef))
 
+// abi attribute
+ERROR(attr_abi_incompatible_kind,none,
+      "cannot use %0 in '@abi'",
+      (DescriptiveDeclKind))
+
 // availability
 ERROR(attr_availability_platform,none,
       "expected platform name or '*' for '%0' attribute", (StringRef))

lib/Parse/ParseDecl.cpp

@@ -3357,9 +3357,18 @@ ParserStatus Parser::parseNewDeclAttribute(DeclAttributes &Attributes,
     }
 
     if (abiDecl) {
-      Attributes.add(new (Context) ABIAttr(abiDecl,
-                                           AtLoc, { Loc, rParenLoc },
-                                           /*implicit=*/false));
+      auto attr = new (Context) ABIAttr(abiDecl, AtLoc, { Loc, rParenLoc },
+                                        /*implicit=*/false);
+
+      // Diagnose syntactically invalid abiDecl kind here to match behavior of
+      // Swift parser.
+      if (!attr->canAppearOnDecl(abiDecl) && !isa<PatternBindingDecl>(abiDecl)){
+        diagnose(abiDecl->getLoc(), diag::attr_abi_incompatible_kind,
+                 abiDecl->getDescriptiveKind());
+        attr->setInvalid();
+      }
+
+      Attributes.add(attr);
     }
 
     break;

test/attr/attr_abi.swift

@@ -1285,6 +1285,7 @@ struct CustomAttrPropertyWrapper {
 }
 
 // CustomAttr for attached macro -- see Macros/macro_expand_peers.swift
+// Freestanding macro in @abi -- see Macros/macro_expand.swift
 
 // CustomAttr for result builder -- banned in '@abi'
 // Has no ABI impact on either a parameter or a decl.