[ObjC] Implement @available in the Parser and AST

This patch adds a new AST node: ObjCAvailabilityCheckExpr, and teaches the
Parser and Sema to generate it. This node represents an availability check of
the form:

  @available(macos 10.10, *);

Which will eventually compile to a runtime check of the host's OS version. This
is the first patch of the feature I proposed here:
http://lists.llvm.org/pipermail/cfe-dev/2016-July/049851.html

Differential Revision: https://reviews.llvm.org/D22171

llvm-svn: 275654

1 files changed, 24 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 0c8a9136948..57159fb5971 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -15083,3 +15083,27 @@ Sema::ActOnObjCBoolLiteral(SourceLocation OpLoc, tok::TokenKind Kind) {
   return new (Context)
       ObjCBoolLiteralExpr(Kind == tok::kw___objc_yes, BoolT, OpLoc);
 }
+
+ExprResult Sema::ActOnObjCAvailabilityCheckExpr(
+    llvm::ArrayRef<AvailabilitySpec> AvailSpecs, SourceLocation AtLoc,
+    SourceLocation RParen) {
+
+  StringRef Platform = getASTContext().getTargetInfo().getPlatformName();
+
+  auto Spec = std::find_if(AvailSpecs.begin(), AvailSpecs.end(),
+                           [&](const AvailabilitySpec &Spec) {
+                             return Spec.getPlatform() == Platform;
+                           });
+
+  VersionTuple Version;
+  if (Spec != AvailSpecs.end())
+    Version = Spec->getVersion();
+  else
+    // This is the '*' case in @available. We should diagnose this; the
+    // programmer should explicitly account for this case if they target this
+    // platform.
+    Diag(AtLoc, diag::warn_available_using_star_case) << RParen << Platform;
+
+  return new (Context)
+      ObjCAvailabilityCheckExpr(Version, AtLoc, RParen, Context.BoolTy);
+}