[Frontend] Turn symbols-missing-from-TBD validation on by default in debug builds on Apple platforms.

include/swift/AST/DiagnosticsFrontend.def

@@ -220,6 +220,10 @@ ERROR(symbol_in_ir_not_in_tbd,none,
       "symbol '%0' (%1) is in generated IR file, but not in TBD file",
       (StringRef, StringRef))
 
+ERROR(tbd_validation_failure,none,
+      "please file a radar or open a bug on bugs.swift.org with this code, and "
+      "add -Xfrontend -validate-tbd-against-ir=none to squash the errors", ())
+
 ERROR(redundant_prefix_compilation_flag,none,
       "invalid argument '-D%0'; did you provide a redundant '-D' in your build settings?", 
       (StringRef))    

include/swift/Frontend/FrontendOptions.h

@@ -240,13 +240,14 @@ class FrontendOptions {
 
   /// The different modes for validating TBD against the LLVM IR.
   enum class TBDValidationMode {
+    Default,        ///< Do the default validation for the current platform.
     None,           ///< Do no validation.
     MissingFromTBD, ///< Only check for symbols that are in IR but not TBD.
     All, ///< Check for symbols that are in IR but not TBD and TBD but not IR.
   };
 
   /// Compare the symbols in the IR against the TBD file we would generate.
-  TBDValidationMode ValidateTBDAgainstIR = TBDValidationMode::None;
+  TBDValidationMode ValidateTBDAgainstIR = TBDValidationMode::Default;
 
   /// The install_name to use in the TBD file.
   std::string TBDInstallName;

lib/FrontendTool/FrontendTool.cpp

@@ -1144,9 +1144,20 @@ static bool validateTBDIfNeeded(CompilerInvocation &Invocation,
     return false;
 
   const auto &frontendOpts = Invocation.getFrontendOptions();
-  const auto mode = frontendOpts.ValidateTBDAgainstIR;
+  auto mode = frontendOpts.ValidateTBDAgainstIR;
   // Ensure all cases are covered by using a switch here.
   switch (mode) {
+  case FrontendOptions::TBDValidationMode::Default:
+#ifndef NDEBUG
+    // When a debug compiler is targeting an apple platform, we do some
+    // validation by default.
+    if (Invocation.getLangOptions().Target.getVendor() == llvm::Triple::Apple) {
+      mode = FrontendOptions::TBDValidationMode::MissingFromTBD;
+      break;
+    }
+#endif
+    // Otherwise, the default is to do nothing.
+    LLVM_FALLTHROUGH;
   case FrontendOptions::TBDValidationMode::None:
     return false;
   case FrontendOptions::TBDValidationMode::All:

lib/FrontendTool/TBD.cpp

@@ -113,6 +113,10 @@ static bool validateSymbolSet(DiagnosticEngine &diags,
     }
   }
 
+  if (error) {
+    diags.diagnose(SourceLoc(), diag::tbd_validation_failure);
+  }
+
   return error;
 }
 

stdlib/public/SwiftOnoneSupport/CMakeLists.txt

@@ -2,6 +2,10 @@ add_swift_library(swiftSwiftOnoneSupport ${SWIFT_STDLIB_LIBRARY_BUILD_TYPES} IS_
   # This file should be listed the first.  Module name is inferred from the
   # filename.
   SwiftOnoneSupport.swift
-  SWIFT_COMPILE_FLAGS "-parse-stdlib" "-Xllvm" "-sil-inline-generics=false" "${SWIFT_RUNTIME_SWIFT_COMPILE_FLAGS}"
+  # We have to disable validation of TBD files, because this module is
+  # _explicitly_ special-cased to result in extra symbols generated by the
+  # optimizer, meaning TBDGen can't (and shouldn't: it has to run
+  # pre-optimization for performance) list them.
+  SWIFT_COMPILE_FLAGS "-parse-stdlib" "-Xllvm" "-sil-inline-generics=false" "-Xfrontend" "-validate-tbd-against-ir=none" "${SWIFT_RUNTIME_SWIFT_COMPILE_FLAGS}"
   LINK_FLAGS "${SWIFT_RUNTIME_SWIFT_LINK_FLAGS}"
   INSTALL_IN_COMPONENT stdlib)