1 files changed, 140 insertions, 3 deletions

diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 9dac93abbab..9cbfcd1503a 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -7132,6 +7132,69 @@ void Sema::EmitAvailabilityWarning(AvailabilityResult AR,
 
 namespace {
 
+/// Returns true if the given statement can be a body-like child of \p Parent.
+bool isBodyLikeChildStmt(const Stmt *S, const Stmt *Parent) {
+  switch (Parent->getStmtClass()) {
+  case Stmt::IfStmtClass:
+    return cast<IfStmt>(Parent)->getThen() == S ||
+           cast<IfStmt>(Parent)->getElse() == S;
+  case Stmt::WhileStmtClass:
+    return cast<WhileStmt>(Parent)->getBody() == S;
+  case Stmt::DoStmtClass:
+    return cast<DoStmt>(Parent)->getBody() == S;
+  case Stmt::ForStmtClass:
+    return cast<ForStmt>(Parent)->getBody() == S;
+  case Stmt::CXXForRangeStmtClass:
+    return cast<CXXForRangeStmt>(Parent)->getBody() == S;
+  case Stmt::ObjCForCollectionStmtClass:
+    return cast<ObjCForCollectionStmt>(Parent)->getBody() == S;
+  case Stmt::CaseStmtClass:
+  case Stmt::DefaultStmtClass:
+    return cast<SwitchCase>(Parent)->getSubStmt() == S;
+  default:
+    return false;
+  }
+}
+
+class StmtUSEFinder : public RecursiveASTVisitor<StmtUSEFinder> {
+  const Stmt *Target;
+
+public:
+  bool VisitStmt(Stmt *S) { return S != Target; }
+
+  /// Returns true if the given statement is present in the given declaration.
+  static bool isContained(const Stmt *Target, const Decl *D) {
+    StmtUSEFinder Visitor;
+    Visitor.Target = Target;
+    return !Visitor.TraverseDecl(const_cast<Decl *>(D));
+  }
+};
+
+/// Traverses the AST and finds the last statement that used a given
+/// declaration.
+class LastDeclUSEFinder : public RecursiveASTVisitor<LastDeclUSEFinder> {
+  const Decl *D;
+
+public:
+  bool VisitDeclRefExpr(DeclRefExpr *DRE) {
+    if (DRE->getDecl() == D)
+      return false;
+    return true;
+  }
+
+  static const Stmt *findLastStmtThatUsesDecl(const Decl *D,
+                                              const CompoundStmt *Scope) {
+    LastDeclUSEFinder Visitor;
+    Visitor.D = D;
+    for (auto I = Scope->body_rbegin(), E = Scope->body_rend(); I != E; ++I) {
+      const Stmt *S = *I;
+      if (!Visitor.TraverseStmt(const_cast<Stmt *>(S)))
+        return S;
+    }
+    return nullptr;
+  }
+};
+
 /// \brief This class implements -Wunguarded-availability.
 ///
 /// This is done with a traversal of the AST of a function that makes reference
@@ -7147,6 +7210,7 @@ class DiagnoseUnguardedAvailability
 
   /// Stack of potentially nested 'if (@available(...))'s.
   SmallVector<VersionTuple, 8> AvailabilityStack;
+  SmallVector<const Stmt *, 16> StmtStack;
 
   void DiagnoseDeclAvailability(NamedDecl *D, SourceRange Range);
 
@@ -7157,6 +7221,15 @@ public:
         SemaRef.Context.getTargetInfo().getPlatformMinVersion());
   }
 
+  bool TraverseStmt(Stmt *S) {
+    if (!S)
+      return true;
+    StmtStack.push_back(S);
+    bool Result = Base::TraverseStmt(S);
+    StmtStack.pop_back();
+    return Result;
+  }
+
   void IssueDiagnostics(Stmt *S) { TraverseStmt(S); }
 
   bool TraverseIfStmt(IfStmt *If);
@@ -7214,9 +7287,73 @@ void DiagnoseUnguardedAvailability::DiagnoseDeclAvailability(
     SemaRef.Diag(D->getLocation(), diag::note_availability_specified_here)
         << D << /* partial */ 3;
 
-    // FIXME: Replace this with a fixit diagnostic.
-    SemaRef.Diag(Range.getBegin(), diag::note_unguarded_available_silence)
-        << Range << D;
+    auto FixitDiag =
+        SemaRef.Diag(Range.getBegin(), diag::note_unguarded_available_silence)
+        << Range << D
+        << (SemaRef.getLangOpts().ObjC1 ? /*@available*/ 0
+                                        : /*__builtin_available*/ 1);
+
+    // Find the statement which should be enclosed in the if @available check.
+    if (StmtStack.empty())
+      return;
+    const Stmt *StmtOfUse = StmtStack.back();
+    const CompoundStmt *Scope = nullptr;
+    for (const Stmt *S : llvm::reverse(StmtStack)) {
+      if (const auto *CS = dyn_cast<CompoundStmt>(S)) {
+        Scope = CS;
+        break;
+      }
+      if (isBodyLikeChildStmt(StmtOfUse, S)) {
+        // The declaration won't be seen outside of the statement, so we don't
+        // have to wrap the uses of any declared variables in if (@available).
+        // Therefore we can avoid setting Scope here.
+        break;
+      }
+      StmtOfUse = S;
+    }
+    const Stmt *LastStmtOfUse = nullptr;
+    if (isa<DeclStmt>(StmtOfUse) && Scope) {
+      for (const Decl *D : cast<DeclStmt>(StmtOfUse)->decls()) {
+        if (StmtUSEFinder::isContained(StmtStack.back(), D)) {
+          LastStmtOfUse = LastDeclUSEFinder::findLastStmtThatUsesDecl(D, Scope);
+          break;
+        }
+      }
+    }
+
+    const SourceManager &SM = SemaRef.getSourceManager();
+    SourceLocation IfInsertionLoc =
+        SM.getExpansionLoc(StmtOfUse->getLocStart());
+    SourceLocation StmtEndLoc =
+        SM.getExpansionRange(
+              (LastStmtOfUse ? LastStmtOfUse : StmtOfUse)->getLocEnd())
+            .second;
+    if (SM.getFileID(IfInsertionLoc) != SM.getFileID(StmtEndLoc))
+      return;
+
+    StringRef Indentation = Lexer::getIndentationForLine(IfInsertionLoc, SM);
+    const char *ExtraIndentation = "    ";
+    std::string FixItString;
+    llvm::raw_string_ostream FixItOS(FixItString);
+    FixItOS << "if (" << (SemaRef.getLangOpts().ObjC1 ? "@available"
+                                                      : "__builtin_available")
+            << "(" << SemaRef.getASTContext().getTargetInfo().getPlatformName()
+            << " " << Introduced.getAsString() << ", *)) {\n"
+            << Indentation << ExtraIndentation;
+    FixitDiag << FixItHint::CreateInsertion(IfInsertionLoc, FixItOS.str());
+    SourceLocation ElseInsertionLoc = Lexer::findLocationAfterToken(
+        StmtEndLoc, tok::semi, SM, SemaRef.getLangOpts(),
+        /*SkipTrailingWhitespaceAndNewLine=*/false);
+    if (ElseInsertionLoc.isInvalid())
+      ElseInsertionLoc =
+          Lexer::getLocForEndOfToken(StmtEndLoc, 0, SM, SemaRef.getLangOpts());
+    FixItOS.str().clear();
+    FixItOS << "\n"
+            << Indentation << "} else {\n"
+            << Indentation << ExtraIndentation
+            << "// Fallback on earlier versions\n"
+            << Indentation << "}";
+    FixitDiag << FixItHint::CreateInsertion(ElseInsertionLoc, FixItOS.str());
   }
 }