[Support] Fix return type deduction in RetryAfterSignal

The default value of the ResultT template argument (which was there only
to avoid spelling out the long std::result_of template multiple times)
was being overriden by function call template argument deduction. This
manifested itself as a compiler error when calling the function as
FILE *X = RetryAfterSignal(nullptr, fopen, ...)
because the function would try to assign the result of fopen to
nullptr_t, but a more insidious side effect was that
RetryAfterSignal(-1, read, ...) would return "int" instead of "ssize_t",
losing precision along the way.

I fix this by having the function take the argument in a way that
prevents argument deduction from kicking in and add a test that makes
sure the return type is correct.

llvm-svn: 306003

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/unittests/Support/ErrnoTest.cpp b/llvm/unittests/Support/ErrnoTest.cpp
index 72b52c01ee3..888c162822d 100644
--- a/llvm/unittests/Support/ErrnoTest.cpp
+++ b/llvm/unittests/Support/ErrnoTest.cpp
@@ -12,6 +12,8 @@
 
 using namespace llvm::sys;
 
+static int *ReturnPointer() { return new int(47); }
+
 TEST(ErrnoTest, RetryAfterSignal) {
   EXPECT_EQ(1, RetryAfterSignal(-1, [] { return 1; }));
 
@@ -30,4 +32,7 @@ TEST(ErrnoTest, RetryAfterSignal) {
   EXPECT_EQ(2u, calls);
 
   EXPECT_EQ(1, RetryAfterSignal(-1, [](int x) { return x; }, 1));
+
+  std::unique_ptr<int> P{RetryAfterSignal(nullptr, ReturnPointer)};
+  EXPECT_EQ(47, *P);
 }