Add resilience boundary around top-level code

Previously, the availability checker has assumed that no code in a module is available on less than the minimum deployment target. In modules using library evolution, this is not actually true--certain function bodies can be inlined into modules with lower minimum deployment targets, where they can run against versions of the library that had lower minimum deployment targets. By failing to check for availability violations in these function bodies that relate to versions below the minimum deployment target, we can end up allowing inlinable code that doesn't compile with the correct runtime linkage or has other serious problems.

This commit lowers the root type refinement context's avialability to the value of the -target-min-inlining-version option (if provided) and then raises it again inside the bodies of functions whose implementations are not exposed to clients. This introduces some incorrect typechecking of declaration signatures, but we'll fix that in another commit.

Author: beccadax

lib/Sema/TypeCheckAvailability.cpp

@@ -569,12 +569,19 @@ class TypeRefinementContextBuilder : private ASTWalker {
     if (auto afd = dyn_cast<AbstractFunctionDecl>(D))
       return bodyIsResilienceBoundary(afd);
 
-    return false;
+    // The only other case we care about is top-level code.
+    return isa<TopLevelCodeDecl>(D);
   }
 
   TypeRefinementContext *buildBodyRefinementContext(Decl *D) {
-    auto afd = cast<AbstractFunctionDecl>(D);
-    SourceRange range = afd->getBodySourceRange();
+    SourceRange range;
+    if (auto tlcd = dyn_cast<TopLevelCodeDecl>(D)) {
+      range = tlcd->getSourceRange();
+    } else if (auto afd = dyn_cast<AbstractFunctionDecl>(D)) {
+      range = afd->getBodySourceRange();
+    } else {
+      llvm_unreachable("unknown decl");
+    }
 
     AvailabilityContext DeploymentTargetInfo =
         AvailabilityContext::forDeploymentTarget(Context);

test/attr/attr_inlinable_available.swift

@@ -466,3 +466,20 @@ internal struct InternalStruct { // expected-note 3 {{add @available attribute}}
   var fInternal: AfterDeploymentTarget // expected-error {{'AfterDeploymentTarget' is only available in}}
 }
 
+// Top-level code, if somehow present in a resilient module, is treated like
+// a non-inlinable function.
+defer {
+  _ = AtDeploymentTarget()
+  _ = AfterDeploymentTarget() // expected-error {{'AfterDeploymentTarget' is only available in}} expected-note {{add 'if #available'}}
+}
+_ = NoAvailable()
+_ = BeforeInliningTarget()
+_ = AtInliningTarget()
+_ = BetweenTargets()
+_ = AtDeploymentTarget()
+_ = AfterDeploymentTarget() // expected-error {{'AfterDeploymentTarget' is only available in}} expected-note {{add 'if #available'}}
+
+if #available(macOS 11, iOS 14, tvOS 14, watchOS 7, *) {
+  _ = AfterDeploymentTarget()
+}
+