[Testing/Support]: Better matching of Error failure states

[labath]

Summary

The existing Failed() matcher only allowed asserting that the operation
failed, but it was not possible to verify any details of the returned
error.

This patch adds two new matchers, which make this possible:

• Failed<InfoT>() verifies that the operation failed with a single error of a given type.
• Failed<InfoT>(M) additionally check that the contained error info object is matched by the nested matcher M.

To make these work, I've changed the implementation of the ErrorHolder
class. Now, instead of just storing the string representation of the
Error, it fetches the ErrorInfo objects and stores then as a list of
shared pointers. This way, ErrorHolder remains copyable, while still
retaining the full information contained in the Error object.

In case the Error object contains two or more errors, the new matchers
will fail to match, instead of trying to match all (or any) of the
individual ErrorInfo objects. This seemed to be the most sensible
behavior for when one wants to match exact error details, but I could be
convinced otherwise...

include/llvm/Testing/Support/Error.h

 class ValueMatchesMono
     : public testing::MatcherInterface<const ExpectedHolder<T> &> {
 public:
   explicit ValueMatchesMono(const testing::Matcher<T> &Matcher)
       : Matcher(Matcher) {}
 
   bool MatchAndExplain(const ExpectedHolder<T> &Holder,
                        testing::MatchResultListener *listener) const override {
-    if (!Holder.Success)
+    if (!Holder.Success())
       return false;
 
     bool result = Matcher.MatchAndExplain(*Holder.Exp, listener);
 
     if (result)
       return result;
     *listener << "(";
     Matcher.DescribeNegationTo(listener->stream());
operator testing::Matcher<const ExpectedHolder<T> &>() const {
     return MakeMatcher(
         new ValueMatchesMono<T>(testing::SafeMatcherCast<T>(Matcher)));
   }
 
 private:
   M Matcher;
 };
 
+template <typename InfoT>
+class ErrorMatchesMono : public testing::MatcherInterface<const ErrorHolder &> {
+public:
+  explicit ErrorMatchesMono(Optional<testing::Matcher<InfoT>> Matcher)
+      : Matcher(std::move(Matcher)) {}
+
+  bool MatchAndExplain(const ErrorHolder &Holder,
+                       testing::MatchResultListener *listener) const override {
+    if (Holder.Success())
+      return false;
+
+    if (Holder.Infos.size() > 1) {
+      *listener << "multiple errors";
+      return false;
+    }
+
+    auto &Info = *Holder.Infos[0];
+    if (!Info.isA<InfoT>()) {
+      *listener << "Error was not of given type";
+      return false;
+    }
+
+    if (!Matcher)
+      return true;
+
+    return Matcher->MatchAndExplain(static_cast<InfoT &>(Info), listener);
+  }
+
+  void DescribeTo(std::ostream *OS) const override {
+    *OS << "failed with Error of given type";
+    if (Matcher) {
+      *OS << " and the error ";
+      Matcher->DescribeTo(OS);
+    }
+  }
+
+  void DescribeNegationTo(std::ostream *OS) const override {
+    *OS << "succeeded or did not fail with the error of given type";
+    if (Matcher) {
+      *OS << " or the error ";
+      Matcher->DescribeNegationTo(OS);
+    }
+  }
+
+private:
+  Optional<testing::Matcher<InfoT>> Matcher;
+};
 } // namespace detail
 
 #define EXPECT_THAT_ERROR(Err, Matcher)                                        \
   EXPECT_THAT(llvm::detail::TakeError(Err), Matcher)
 #define ASSERT_THAT_ERROR(Err, Matcher)                                        \
   ASSERT_THAT(llvm::detail::TakeError(Err), Matcher)
 
 #define EXPECT_THAT_EXPECTED(Err, Matcher)                                     \
   EXPECT_THAT(llvm::detail::TakeExpected(Err), Matcher)
 #define ASSERT_THAT_EXPECTED(Err, Matcher)                                     \
   ASSERT_THAT(llvm::detail::TakeExpected(Err), Matcher)
 
-MATCHER(Succeeded, "") { return arg.Success; }
-MATCHER(Failed, "") { return !arg.Success; }
+MATCHER(Succeeded, "") { return arg.Success(); }
+MATCHER(Failed, "") { return !arg.Success(); }
+
+template <typename InfoT>
+testing::Matcher<const detail::ErrorHolder &> Failed() {
+  return MakeMatcher(new detail::ErrorMatchesMono<InfoT>(None));
+}
+
+template <typename InfoT, typename M>
+testing::Matcher<const detail::ErrorHolder &> Failed(M Matcher) {
+  return MakeMatcher(new detail::ErrorMatchesMono<InfoT>(
+      testing::SafeMatcherCast<InfoT>(Matcher)));
+}
 
 template <typename M>
 detail::ValueMatchesPoly<M> HasValue(M Matcher) {
   return detail::ValueMatchesPoly<M>(Matcher);
 }
 
 } // namespace llvm
 
 #endif

include/llvm/Testing/Support/SupportHelpers.h

 
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Error.h"
 #include "gtest/gtest-printers.h"
 
 namespace llvm {
 namespace detail {
 struct ErrorHolder {
-  bool Success;
-  std::string Message;
+  std::vector<std::shared_ptr<ErrorInfoBase>> Infos;
+
+  bool Success() const { return Infos.empty(); }
 };
 
 template <typename T> struct ExpectedHolder : public ErrorHolder {
   ExpectedHolder(ErrorHolder Err, Expected<T> &Exp)
       : ErrorHolder(std::move(Err)), Exp(Exp) {}
 
   Expected<T> &Exp;
 };
 
 inline void PrintTo(const ErrorHolder &Err, std::ostream *Out) {
-  *Out << (Err.Success ? "succeeded" : "failed");
-  if (!Err.Success) {
-    *Out << "  (" << StringRef(Err.Message).trim().str() << ")";
+  raw_os_ostream OS(*Out);
+  OS << (Err.Success() ? "succeeded" : "failed");
+  if (!Err.Success()) {
+    const char *Delim = "  (";
+    for (const auto &Info : Err.Infos) {
+      OS << Delim;
+      Delim = "; ";
+      Info->log(OS);
+    }
+    OS << ")";
   }
 }
 
 template <typename T>
 void PrintTo(const ExpectedHolder<T> &Item, std::ostream *Out) {
-  if (Item.Success) {
+  if (Item.Success()) {
     *Out << "succeeded with value " << ::testing::PrintToString(*Item.Exp);
   } else {
     PrintTo(static_cast<const ErrorHolder &>(Item), Out);
   }
 }
 } // namespace detail
 } // namespace llvm
 
 #endif

lib/Testing/Support/Error.cpp

 //===- llvm/Testing/Support/Error.cpp -------------------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Testing/Support/Error.h"
 
 #include "llvm/ADT/StringRef.h"
 
 using namespace llvm;
 
 llvm::detail::ErrorHolder llvm::detail::TakeError(llvm::Error Err) {
-  bool Succeeded = !static_cast<bool>(Err);
-  std::string Message;
-  if (!Succeeded)
-    Message = toString(std::move(Err));
-  return {Succeeded, Message};
+  std::vector<std::shared_ptr<ErrorInfoBase>> Infos;
+  handleAllErrors(std::move(Err),
+                  [&Infos](std::unique_ptr<ErrorInfoBase> Info) {
+                    Infos.emplace_back(std::move(Info));
+                  });
+  return {std::move(Infos)};
 }

unittests/Support/ErrorTest.cpp

TEST(Error, ErrorMatchers) {
   EXPECT_NONFATAL_FAILURE(
       EXPECT_THAT_ERROR(make_error<CustomError>(0), Succeeded()),
       "Expected: succeeded\n  Actual: failed  (CustomError { 0})");
 
   EXPECT_THAT_ERROR(make_error<CustomError>(0), Failed());
   EXPECT_NONFATAL_FAILURE(EXPECT_THAT_ERROR(Error::success(), Failed()),
                           "Expected: failed\n  Actual: succeeded");
 
+  EXPECT_THAT_ERROR(make_error<CustomError>(0), Failed<CustomError>());
+  EXPECT_NONFATAL_FAILURE(
+      EXPECT_THAT_ERROR(Error::success(), Failed<CustomError>()),
+      "Expected: failed with Error of given type\n  Actual: succeeded");
+  EXPECT_NONFATAL_FAILURE(
+      EXPECT_THAT_ERROR(make_error<CustomError>(0), Failed<CustomSubError>()),
+      "Error was not of given type");
+  EXPECT_NONFATAL_FAILURE(
+      EXPECT_THAT_ERROR(
+          joinErrors(make_error<CustomError>(0), make_error<CustomError>(1)),
+          Failed<CustomError>()),
+      "multiple errors");
+
+  EXPECT_THAT_ERROR(
+      make_error<CustomError>(0),
+      Failed<CustomError>(testing::Property(&CustomError::getInfo, 0)));
+  EXPECT_NONFATAL_FAILURE(
+      EXPECT_THAT_ERROR(
+          make_error<CustomError>(0),
+          Failed<CustomError>(testing::Property(&CustomError::getInfo, 1))),
+      "Expected: failed with Error of given type and the error is an object "
+      "whose given property is equal to 1\n"
+      "  Actual: failed  (CustomError { 0})");
+
   EXPECT_THAT_EXPECTED(Expected<int>(0), Succeeded());
   EXPECT_NONFATAL_FAILURE(
       EXPECT_THAT_EXPECTED(Expected<int>(make_error<CustomError>(0)),
                            Succeeded()),
       "Expected: succeeded\n  Actual: failed  (CustomError { 0})");
 
   EXPECT_THAT_EXPECTED(Expected<int>(make_error<CustomError>(0)), Failed());
   EXPECT_NONFATAL_FAILURE(