From: Lang Hames <lhames@gmail.com>
Date: Tue, 29 Aug 2017 23:29:09 +0000 (+0000)
Subject: [Error] Add an optional error message to cantFail.
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=cfcd4a35478076a79343337aacb97062e0e0dd18;p=llvm

[Error] Add an optional error message to cantFail.

cantFail is the moral equivalent of an assertion that the wrapped call must
return a success value. This patch allows clients to include an associated
error message (the same way they would for an assertion for llvm_unreachable).

If the error message is not specified it will default to: "Failure value
returned from cantFail wrapped call".



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@312066 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/include/llvm/Support/Error.h b/include/llvm/Support/Error.h
index 6aca32bf076..bb40dbee053 100644
--- a/include/llvm/Support/Error.h
+++ b/include/llvm/Support/Error.h
@@ -676,9 +676,12 @@ LLVM_ATTRIBUTE_NORETURN void report_fatal_error(Error Err,
 ///
 ///   cantFail(foo(false));
 ///   @endcode
-inline void cantFail(Error Err) {
-  if (Err)
-    llvm_unreachable("Failure value returned from cantFail wrapped call");
+inline void cantFail(Error Err, const char *Msg = nullptr) {
+  if (Err) {
+    if (!Msg)
+      Msg = "Failure value returned from cantFail wrapped call";
+    llvm_unreachable(Msg);
+  }
 }
 
 /// Report a fatal error if ValOrErr is a failure value, otherwise unwraps and
@@ -695,11 +698,14 @@ inline void cantFail(Error Err) {
 ///   int X = cantFail(foo(false));
 ///   @endcode
 template <typename T>
-T cantFail(Expected<T> ValOrErr) {
+T cantFail(Expected<T> ValOrErr, const char *Msg = nullptr) {
   if (ValOrErr)
     return std::move(*ValOrErr);
-  else
-    llvm_unreachable("Failure value returned from cantFail wrapped call");
+  else {
+    if (!Msg)
+      Msg = "Failure value returned from cantFail wrapped call";
+    llvm_unreachable(Msg);
+  }
 }
 
 /// Report a fatal error if ValOrErr is a failure value, otherwise unwraps and
@@ -716,11 +722,14 @@ T cantFail(Expected<T> ValOrErr) {
 ///   Bar &X = cantFail(foo(false));
 ///   @endcode
 template <typename T>
-T& cantFail(Expected<T&> ValOrErr) {
+T& cantFail(Expected<T&> ValOrErr, const char *Msg = nullptr) {
   if (ValOrErr)
     return *ValOrErr;
-  else
-    llvm_unreachable("Failure value returned from cantFail wrapped call");
+  else {
+    if (!Msg)
+      Msg = "Failure value returned from cantFail wrapped call";
+    llvm_unreachable(Msg);
+  }
 }
 
 /// Helper for testing applicability of, and applying, handlers for
@@ -775,7 +784,7 @@ public:
   }
 };
 
-/// Specialization for functions of the form 'Error (std::unique_ptr<ErrT>)'.
+/// Specialization for functions of the form 'void (std::unique_ptr<ErrT>)'.
 template <typename ErrT>
 class ErrorHandlerTraits<void (&)(std::unique_ptr<ErrT>)> {
 public:
@@ -813,7 +822,7 @@ class ErrorHandlerTraits<RetT (C::*)(const ErrT &) const>
     : public ErrorHandlerTraits<RetT (&)(ErrT &)> {};
 
 /// Specialization for member functions of the form
-/// 'RetT (std::unique_ptr<ErrT>) const'.
+/// 'RetT (std::unique_ptr<ErrT>)'.
 template <typename C, typename RetT, typename ErrT>
 class ErrorHandlerTraits<RetT (C::*)(std::unique_ptr<ErrT>)>
     : public ErrorHandlerTraits<RetT (&)(std::unique_ptr<ErrT>)> {};
diff --git a/unittests/Support/ErrorTest.cpp b/unittests/Support/ErrorTest.cpp
index db332ebff7a..6010122a9a0 100644
--- a/unittests/Support/ErrorTest.cpp
+++ b/unittests/Support/ErrorTest.cpp
@@ -486,8 +486,9 @@ TEST(Error, CantFailSuccess) {
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS && !defined(NDEBUG)
 TEST(Error, CantFailDeath) {
   EXPECT_DEATH(
-      cantFail(make_error<StringError>("foo", inconvertibleErrorCode())),
-      "Failure value returned from cantFail wrapped call")
+      cantFail(make_error<StringError>("foo", inconvertibleErrorCode()),
+               "Cantfail call failed"),
+      "Cantfail call failed")
     << "cantFail(Error) did not cause an abort for failure value";
 
   EXPECT_DEATH(