From 25d8c856681120581315edcdb48257c99af6b45c Mon Sep 17 00:00:00 2001
From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Fri, 10 May 2013 04:31:10 +0000
Subject: [PATCH] C++1y auto return type: when a function contains no 'return'
 statements at all, substitute 'void' into the return type rather than
 replacing it with 'void', so that we maintain the 'auto' type sugar.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@181584 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Sema/SemaDecl.cpp                      | 31 +++++++++++++---------
 lib/Sema/SemaStmt.cpp                      |  4 +--
 test/SemaCXX/cxx1y-deduced-return-type.cpp |  5 ++++
 3 files changed, 24 insertions(+), 16 deletions(-)

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index a50b5e7c7f..d14b10559d 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -8849,7 +8849,9 @@ 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
   // rest of the file.
-  return !FD->isConstexpr();
+  // We cannot skip the body of a function with an undeduced return type,
+  // because any callers of that function need to know the type.
+  return !FD->isConstexpr() && !FD->getResultType()->isUndeducedType();
 }
 
 Decl *Sema::ActOnSkippedFunctionBody(Decl *Decl) {
@@ -8879,18 +8881,21 @@ Decl *Sema::ActOnFinishFunctionBody(Decl *dcl, Stmt *Body,
   if (FD) {
     FD->setBody(Body);
 
-    if (getLangOpts().CPlusPlus1y && !FD->isInvalidDecl() &&
-        !FD->isDependentContext()) {
-      if (FD->getResultType()->isUndeducedType()) {
-        // If the function has a deduced result type but contains no 'return'
-        // statements, the result type as written must be exactly 'auto', and
-        // the deduced result type is 'void'.
-        if (!FD->getResultType()->getAs<AutoType>()) {
-          Diag(dcl->getLocation(), diag::err_auto_fn_no_return_but_not_auto)
-            << FD->getResultType();
-          FD->setInvalidDecl();
-        }
-        Context.adjustDeducedFunctionResultType(FD, Context.VoidTy);
+    if (getLangOpts().CPlusPlus1y && !FD->isInvalidDecl() && Body &&
+        !FD->isDependentContext() && FD->getResultType()->isUndeducedType()) {
+      // If the function has a deduced result type but contains no 'return'
+      // statements, the result type as written must be exactly 'auto', and
+      // the deduced result type is 'void'.
+      if (!FD->getResultType()->getAs<AutoType>()) {
+        Diag(dcl->getLocation(), diag::err_auto_fn_no_return_but_not_auto)
+          << FD->getResultType();
+        FD->setInvalidDecl();
+      } else {
+        // Substitute 'void' for the 'auto' in the type.
+        TypeLoc ResultType = FD->getTypeSourceInfo()->getTypeLoc().
+            IgnoreParens().castAs<FunctionProtoTypeLoc>().getResultLoc();
+        Context.adjustDeducedFunctionResultType(
+            FD, SubstAutoType(ResultType.getType(), Context.VoidTy));
       }
     }
 
diff --git a/lib/Sema/SemaStmt.cpp b/lib/Sema/SemaStmt.cpp
index 248665ac86..b5ff7a30a9 100644
--- a/lib/Sema/SemaStmt.cpp
+++ b/lib/Sema/SemaStmt.cpp
@@ -2553,9 +2553,7 @@ Sema::ActOnReturnStmt(SourceLocation ReturnLoc, Expr *RetValExp) {
   if (RetValExp && DiagnoseUnexpandedParameterPack(RetValExp))
     return StmtError();
 
-  // FIXME: Unify this and C++1y auto function handling. In particular, we
-  // should allow 'return { 1, 2, 3 };' in a lambda to deduce
-  // 'std::initializer_list<int>'.
+  // FIXME: Unify this and C++1y auto function handling.
   if (isa<CapturingScopeInfo>(getCurFunction()))
     return ActOnCapScopeReturnStmt(ReturnLoc, RetValExp);
 
diff --git a/test/SemaCXX/cxx1y-deduced-return-type.cpp b/test/SemaCXX/cxx1y-deduced-return-type.cpp
index f0146f88d6..eb6f6aaf9b 100644
--- a/test/SemaCXX/cxx1y-deduced-return-type.cpp
+++ b/test/SemaCXX/cxx1y-deduced-return-type.cpp
@@ -295,7 +295,12 @@ namespace NoReturn {
   auto f() {}
   void (*p)() = &f;
 
+  auto f(); // ok
+
   auto *g() {} // expected-error {{cannot deduce return type 'auto *' for function with no return statements}}
+
+  auto h() = delete; // expected-note {{explicitly deleted}}
+  auto x = h(); // expected-error {{call to deleted}}
 }
 
 namespace UseBeforeComplete {
-- 
2.40.0