swift-api-digester: add a flag to disable OS related diagnostics

For frameworks not shipping with OSs, the users should specify this flag
to avoid diagnosing some changes, such as the missing of OS availability
attributes.

Author: nkcsgexi

tools/swift-api-digester/ModuleAnalyzerNodes.h

@@ -145,6 +145,7 @@ struct CheckerOptions {
   bool AbortOnModuleLoadFailure;
   bool PrintModule;
   bool SwiftOnly;
+  bool SkipOSCheck;
   StringRef LocationFilter;
 };
 

tools/swift-api-digester/swift-api-digester.cpp

@@ -127,6 +127,12 @@ SwiftOnly("swift-only",
           llvm::cl::init(false),
           llvm::cl::cat(Category));
 
+static llvm::cl::opt<bool>
+DisableOSChecks("disable-os-checks",
+                llvm::cl::desc("Skip OS related diagnostics"),
+                llvm::cl::init(false),
+                llvm::cl::cat(Category));
+
 static llvm::cl::opt<bool>
 PrintModule("print-module", llvm::cl::desc("Print module names in diagnostics"),
             llvm::cl::cat(Category));
@@ -1006,7 +1012,8 @@ class PrunePass : public MatchedNodeListener, public SDKTreeDiffPass {
           // Diagnose the missing of @available attributes.
           // Decls with @_alwaysEmitIntoClient aren't required to have an
           // @available attribute.
-          if (!D->getIntroducingVersion().hasOSAvailability() &&
+          if (!Ctx.getOpts().SkipOSCheck &&
+              !D->getIntroducingVersion().hasOSAvailability() &&
               !D->hasDeclAttribute(DeclAttrKind::DAK_AlwaysEmitIntoClient)) {
             D->emitDiag(diag::new_decl_without_intro);
           }
@@ -2377,6 +2384,7 @@ static CheckerOptions getCheckOpts() {
   Opts.LocationFilter = options::LocationFilter;
   Opts.PrintModule = options::PrintModule;
   Opts.SwiftOnly = options::SwiftOnly;
+  Opts.SkipOSCheck = options::DisableOSChecks;
   return Opts;
 }