Diagnose Availability for Parameterized Existential Types

CodaFi · CodaFi · commit 82099b171dbb · 2022-05-03T23:35:08.000-07:00
Usages of parameterized existential types that involve runtime type metadata to resolve must be gated on the appropriate OS version in which those features have landed. This means the following usage classes must appear gated:

- Checked casts (is, as?, as!)
- As arguments to generic types (Foo&lt;any P&lt;T&gt;&gt;)
- As type witnesses to protocol conformances
- In erasure expressions (and optional-to-any erasure expressions)
- In metatypes
- Tuples

What does this leave?

- Concrete usages
  - any P&lt;T&gt; as a parameter or result type
  - Any amount of optional types around existential types
  - Static casts (as)

It's worth calling out the fact that usages of parameterized existential types in tuples are banned but usages in struct members are not. This is due to the fact that Tuple identity and runtime layout is determined by a metadata query against each component type. Whereas for a struct, the opaque type layout does not depend upon the type metadata of the fields at runtime, and the identity of the struct is determined nominally rather than structurally.

Practically, this means that one can work around the lack of tuples by defining a struct with an equivalent type structure as fields:

struct AdHocEraser { var x: any P&lt;T&gt; }

rdar://92197245
diff --git a/include/swift/AST/DiagnosticsSema.def b/include/swift/AST/DiagnosticsSema.def
@@ -5589,6 +5589,11 @@ ERROR(availability_concurrency_only_version_newer, none,
       "concurrency is only available in %0 %1 or newer",
       (StringRef, llvm::VersionTuple))
 
+ERROR(availability_parameterized_protocol_only_version_newer, none,
+      "runtime support for parameterized protocol types is only available in "
+      "%0 %1 or newer",
+      (StringRef, llvm::VersionTuple))
+
 NOTE(availability_guard_with_version_check, none,
      "add 'if #available' version check", ())
 
diff --git a/lib/Sema/TypeCheckAvailability.cpp b/lib/Sema/TypeCheckAvailability.cpp
@@ -15,11 +15,12 @@
 //===----------------------------------------------------------------------===//
 
 #include "TypeCheckAvailability.h"
+#include "MiscDiagnostics.h"
 #include "TypeCheckConcurrency.h"
-#include "TypeChecker.h"
 #include "TypeCheckObjC.h"
-#include "MiscDiagnostics.h"
+#include "TypeChecker.h"
 #include "swift/AST/ASTWalker.h"
+#include "swift/AST/GenericEnvironment.h"
 #include "swift/AST/Initializer.h"
 #include "swift/AST/NameLookup.h"
 #include "swift/AST/Pattern.h"
@@ -2773,6 +2774,74 @@ bool isSubscriptReturningString(const ValueDecl *D, ASTContext &Context) {
   return resultTy->isString();
 }
 
+static bool diagnosePotentialParameterizedProtocolUnavailability(
+    SourceRange ReferenceRange, const DeclContext *ReferenceDC,
+    const UnavailabilityReason &Reason) {
+  ASTContext &Context = ReferenceDC->getASTContext();
+
+  auto RequiredRange = Reason.getRequiredOSVersionRange();
+  {
+    auto Err = Context.Diags.diagnose(
+        ReferenceRange.Start,
+        diag::availability_parameterized_protocol_only_version_newer,
+        prettyPlatformString(targetPlatform(Context.LangOpts)),
+        Reason.getRequiredOSVersionRange().getLowerEndpoint());
+
+    // Direct a fixit to the error if an existing guard is nearly-correct
+    if (fixAvailabilityByNarrowingNearbyVersionCheck(
+            ReferenceRange, ReferenceDC, RequiredRange, Context, Err))
+      return true;
+  }
+  fixAvailability(ReferenceRange, ReferenceDC, RequiredRange, Context);
+  return true;
+}
+
+bool swift::diagnoseParameterizedProtocolAvailability(
+    SourceRange ReferenceRange, const DeclContext *ReferenceDC) {
+  // Check the availability of parameterized existential runtime support.
+  ASTContext &ctx = ReferenceDC->getASTContext();
+  if (ctx.LangOpts.DisableAvailabilityChecking)
+    return false;
+
+  if (!shouldCheckAvailability(ReferenceDC->getAsDecl()))
+    return false;
+
+  auto runningOS = TypeChecker::overApproximateAvailabilityAtLocation(
+      ReferenceRange.Start, ReferenceDC);
+  auto availability = ctx.getParameterizedExistentialRuntimeAvailability();
+  if (!runningOS.isContainedIn(availability)) {
+    return diagnosePotentialParameterizedProtocolUnavailability(
+        ReferenceRange, ReferenceDC,
+        UnavailabilityReason::requiresVersionRange(
+            availability.getOSVersion()));
+  }
+  return false;
+}
+
+static void
+maybeDiagParameterizedExistentialErasure(ErasureExpr *EE,
+                                         const ExportContext &Where) {
+  if (auto *OE = dyn_cast<OpaqueValueExpr>(EE->getSubExpr())) {
+    auto *OAT = OE->getType()->getAs<OpenedArchetypeType>();
+    if (!OAT)
+      return;
+
+    auto opened = OAT->getGenericEnvironment()->getOpenedExistentialType();
+    if (!opened || !opened->hasParameterizedExistential())
+      return;
+
+    (void)diagnoseParameterizedProtocolAvailability(EE->getLoc(),
+                                                    Where.getDeclContext());
+  }
+
+  if (EE->getType() &&
+      EE->getType()->isAny() &&
+      EE->getSubExpr()->getType()->hasParameterizedExistential()) {
+    (void)diagnoseParameterizedProtocolAvailability(EE->getLoc(),
+                                                    Where.getDeclContext());
+  }
+}
+
 bool swift::diagnoseExplicitUnavailability(
     const ValueDecl *D,
     SourceRange R,
@@ -2989,6 +3058,17 @@ class ExprAvailabilityWalker : public ASTWalker {
       diagnoseDeclRefAvailability(Context.getRegexDecl(), Range);
       diagnoseDeclRefAvailability(RLE->getInitializer(), Range);
     }
+    if (auto *EE = dyn_cast<ErasureExpr>(E)) {
+      maybeDiagParameterizedExistentialErasure(EE, Where);
+    }
+    if (auto *CC = dyn_cast<ExplicitCastExpr>(E)) {
+      if (!isa<CoerceExpr>(CC) &&
+          CC->getCastType()->hasParameterizedExistential()) {
+        SourceLoc loc = CC->getCastTypeRepr() ? CC->getCastTypeRepr()->getLoc()
+                                              : E->getLoc();
+        diagnoseParameterizedProtocolAvailability(loc, Where.getDeclContext());
+      }
+    }
     if (auto KP = dyn_cast<KeyPathExpr>(E)) {
       maybeDiagKeyPath(KP);
     }
@@ -3749,7 +3829,12 @@ class ProblematicTypeFinder : public TypeDeclFinder {
 
     ModuleDecl *useModule = Where.getDeclContext()->getParentModule();
     auto subs = ty->getContextSubstitutionMap(useModule, ty->getDecl());
-    (void) diagnoseSubstitutionMapAvailability(Loc, subs, Where);
+    (void)diagnoseSubstitutionMapAvailability(
+        Loc, subs, Where,
+        /*depTy=*/Type(),
+        /*replacementTy=*/Type(),
+        /*useConformanceAvailabilityErrorsOption=*/false,
+        /*suppressParameterizationCheckForOptional=*/ty->isOptional());
     return Action::Continue;
   }
 
@@ -3781,6 +3866,19 @@ class ProblematicTypeFinder : public TypeDeclFinder {
       }
     }
 
+    if (auto *TT = T->getAs<TupleType>()) {
+      for (auto component : TT->getElementTypes()) {
+        // Let the walker find inner tuple types, we only want to diagnose
+        // non-compound components.
+        if (component->is<TupleType>())
+          continue;
+
+        if (component->hasParameterizedExistential())
+          (void)diagnoseParameterizedProtocolAvailability(
+              Loc, Where.getDeclContext());
+      }
+    }
+
     return TypeDeclFinder::walkToTypePost(T);
   }
 };
@@ -3895,14 +3993,27 @@ swift::diagnoseSubstitutionMapAvailability(SourceLoc loc,
                                            SubstitutionMap subs,
                                            const ExportContext &where,
                                            Type depTy, Type replacementTy,
-                                           bool useConformanceAvailabilityErrorsOption) {
+                                           bool useConformanceAvailabilityErrorsOption,
+                                           bool suppressParameterizationCheckForOptional) {
   bool hadAnyIssues = false;
   for (ProtocolConformanceRef conformance : subs.getConformances()) {
     if (diagnoseConformanceAvailability(loc, conformance, where,
                                         depTy, replacementTy,
                                         useConformanceAvailabilityErrorsOption))
       hadAnyIssues = true;
   }
+
+  // If we're looking at \c (any P)? (or any other depth of optional) then
+  // there's no availability problem.
+  if (suppressParameterizationCheckForOptional)
+    return hadAnyIssues;
+
+  for (auto replacement : subs.getReplacementTypes()) {
+    if (replacement->hasParameterizedExistential())
+      if (diagnoseParameterizedProtocolAvailability(loc,
+                                                    where.getDeclContext()))
+        hadAnyIssues = true;
+  }
   return hadAnyIssues;
 }
 
diff --git a/lib/Sema/TypeCheckAvailability.h b/lib/Sema/TypeCheckAvailability.h
@@ -224,13 +224,14 @@ diagnoseConformanceAvailability(SourceLoc loc,
                                 Type replacementTy=Type(),
                                 bool useConformanceAvailabilityErrorsOption = false);
 
-bool
-diagnoseSubstitutionMapAvailability(SourceLoc loc,
-                                    SubstitutionMap subs,
-                                    const ExportContext &context,
-                                    Type depTy=Type(),
-                                    Type replacementTy=Type(),
-                                    bool useConformanceAvailabilityErrorsOption = false);
+bool diagnoseSubstitutionMapAvailability(
+    SourceLoc loc,
+    SubstitutionMap subs, 
+    const ExportContext &context,
+    Type depTy = Type(),
+    Type replacementTy = Type(),
+    bool useConformanceAvailabilityErrorsOption = false,
+    bool suppressParameterizationCheckForOptional = false);
 
 /// Diagnose uses of unavailable declarations. Returns true if a diagnostic
 /// was emitted.
@@ -267,6 +268,11 @@ bool diagnoseExplicitUnavailability(
     const ExportContext &where,
     bool useConformanceAvailabilityErrorsOption = false);
 
+/// Diagnose uses of the runtime features of parameterized protools. Returns
+/// \c true if a diagnostic was emitted.
+bool diagnoseParameterizedProtocolAvailability(SourceRange loc,
+                                               const DeclContext *DC);
+
 /// Check if \p decl has a introduction version required by -require-explicit-availability
 void checkExplicitAvailability(Decl *decl);
 
diff --git a/lib/Sema/TypeCheckProtocol.cpp b/lib/Sema/TypeCheckProtocol.cpp
@@ -4919,6 +4919,17 @@ void ConformanceChecker::ensureRequirementsAreSatisfied() {
   if (where.isImplicit())
     return;
 
+  Conformance->forEachTypeWitness([&](const AssociatedTypeDecl *assoc,
+                                      Type type, TypeDecl *typeDecl) -> bool {
+    // Make sure any associated type witnesses don't make reference to a
+    // parameterized existential type, or we're going to have trouble at
+    // runtime.
+    if (type->hasParameterizedExistential())
+      (void)diagnoseParameterizedProtocolAvailability(typeDecl->getLoc(),
+                                                      where.getDeclContext());
+    return false;
+  });
+
   for (auto req : proto->getRequirementSignature().getRequirements()) {
     if (req.getKind() == RequirementKind::Conformance) {
       auto depTy = req.getFirstType();
