[Sema] Walk MacroExpansionDecls in BaseDiagnosticWalker

I missed this in my previous PR, but this is needed
to ensure we visit macro arguments for macro expansion
exprs that have substitute MacroExpansionDecls since
we prefer to visit the arguments on the decl once
the expression has been expanded.

Author: hamishknight

lib/Sema/MiscDiagnostics.h

@@ -135,7 +135,11 @@ namespace swift {
 
   class BaseDiagnosticWalker : public ASTWalker {
     PreWalkAction walkToDeclPre(Decl *D) override {
-      return Action::VisitNodeIf(isa<PatternBindingDecl>(D));
+      // We don't walk into any nested local decls, except PatternBindingDecls,
+      // which are type-checked along with the parent, and MacroExpansionDecl,
+      // which needs to be visited to visit the macro arguments.
+      return Action::VisitNodeIf(isa<PatternBindingDecl>(D) ||
+                                 isa<MacroExpansionDecl>(D));
     }
 
     MacroWalking getMacroWalkingBehavior() const override {

test/Macros/macro_misc_diags.swift

@@ -77,10 +77,16 @@ _ = #identity(deprecatedFunc())
 // CHECK-DIAG: @__swiftmacro_6Client0017Clientswift_yEEFcfMX[[@LINE-2]]{{.*}}identityfMf1_.swift:1:1: warning: 'deprecatedFunc()' is deprecated
 // CHECK-DIAG: Client.swift:[[@LINE-2]]:15: warning: 'deprecatedFunc()' is deprecated
 
-#makeBinding(deprecatedFunc())
-// CHECK-DIAG: Client.swift:[[@LINE-1]]:14: warning: 'deprecatedFunc()' is deprecated
-// CHECK-DIAG: @__swiftmacro_6Client0017Clientswift_yEEFcfMX[[@LINE-3]]{{.*}}makeBindingfMf_.swift:1:9: warning: 'deprecatedFunc()' is deprecated
-// CHECK-DIAG: @__swiftmacro_6Client0017Clientswift_yEEFcfMX[[@LINE-4]]{{.*}}makeBindingfMf_.swift:1:5: warning: initialization of immutable value 'x' was never used
+#makeBinding((deprecatedFunc(), Int, {
+  if let _ = takesClosure {} {}
+}()))
+// CHECK-DIAG: Client.swift:[[@LINE-2]]:27: warning: trailing closure in this context is confusable with the body of the statement
+// CHECK-DIAG: Client.swift:[[@LINE-4]]:33: error: expected member name or initializer call after type name
+// CHECK-DIAG: Client.swift:[[@LINE-5]]:15: warning: 'deprecatedFunc()' is deprecated
+// CHECK-DIAG: @__swiftmacro_6Client0017Clientswift_yEEFcfMX[[@LINE-7]]{{.*}}makeBindingfMf_.swift:2:27: warning: trailing closure in this context is confusable with the body of the statement; pass as a parenthesized argument to silence this warning
+// CHECK-DIAG: @__swiftmacro_6Client0017Clientswift_yEEFcfMX[[@LINE-8]]{{.*}}makeBindingfMf_.swift:1:28: error: expected member name or initializer call after type name
+// CHECK-DIAG: @__swiftmacro_6Client0017Clientswift_yEEFcfMX[[@LINE-9]]{{.*}}makeBindingfMf_.swift:1:10: warning: 'deprecatedFunc()' is deprecated
+// CHECK-DIAG: @__swiftmacro_6Client0017Clientswift_yEEFcfMX[[@LINE-10]]{{.*}}makeBindingfMf_.swift:1:5: warning: initialization of immutable value
 
 struct S1 {
   #makeBinding(deprecatedFunc())