1 files changed, 24 insertions, 0 deletions
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 521fc3f2cbc..ec062852789 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -9695,6 +9695,30 @@ void Sema::computeNRVO(Stmt *Body, FunctionScopeInfo *Scope) {
     const_cast<VarDecl*>(NRVOCandidate)->setNRVOVariable(true);
 }
 
+bool Sema::canDelayFunctionBody(const Declarator &D) {
+  // We can't delay parsing the body of a constexpr function template (yet).
+  if (D.getDeclSpec().isConstexprSpecified())
+    return false;
+
+  // We can't delay parsing the body of a function template with a deduced
+  // return type (yet).
+  if (D.getDeclSpec().containsPlaceholderType()) {
+    // If the placeholder introduces a non-deduced trailing return type,
+    // we can still delay parsing it.
+    if (D.getNumTypeObjects()) {
+      const auto &Outer = D.getTypeObject(D.getNumTypeObjects() - 1);
+      if (Outer.Kind == DeclaratorChunk::Function &&
+          Outer.Fun.hasTrailingReturnType()) {
+        QualType Ty = GetTypeFromParser(Outer.Fun.getTrailingReturnType());
+        return Ty.isNull() || !Ty->isUndeducedType();
+      }
+    }
+    return false;
+  }
+
+  return true;
+}
+
 bool Sema::canSkipFunctionBody(Decl *D) {
   // We cannot skip the body of a function (or function template) which is
   // constexpr, since we may need to evaluate its body in order to parse the