[Support] Make all Errors convertible to std::error_code.

This is a temporary crutch to enable code that currently uses std::error_code
to be incrementally moved over to Error. Requiring all Error instances be
convertible enables clients to call errorToErrorCode on any error (not just
ECErrors created by conversion *from* an error_code).

This patch also moves code for Error from ErrorHandling.cpp into a new
Error.cpp file.

llvm-svn: 264221

include/llvm/Support/Error.h

@@ -35,6 +35,12 @@ public:
   /// Print an error message to an output stream.
   virtual void log(raw_ostream &OS) const = 0;
 
+  /// Convert this error to a std::error_code.
+  ///
+  /// This is a temporary crutch to enable interaction with code still
+  /// using std::error_code. It will be removed in the future.
+  virtual std::error_code convertToErrorCode() const = 0;
+
   // Check whether this instance is a subclass of the class identified by
   // ClassID.
   virtual bool isA(const void *const ClassID) const {
@@ -309,6 +315,8 @@ public:
     }
   }
 
+  std::error_code convertToErrorCode() const override;
+
 private:
   ErrorList(std::unique_ptr<ErrorInfoBase> Payload1,
             std::unique_ptr<ErrorInfoBase> Payload2) {
@@ -717,7 +725,8 @@ class ECError : public ErrorInfo<ECError> {
 public:
   ECError() = default;
   ECError(std::error_code EC) : EC(EC) {}
-  std::error_code getErrorCode() const { return EC; }
+  void setErrorCode(std::error_code EC) { this->EC = EC; }
+  std::error_code convertToErrorCode() const override { return EC; }
   void log(raw_ostream &OS) const override { OS << EC.message(); }
 
 protected:
@@ -738,7 +747,9 @@ inline Error errorCodeToError(std::error_code EC) {
 inline std::error_code errorToErrorCode(Error Err) {
   std::error_code EC;
   handleAllErrors(std::move(Err),
-                  [&](const ECError &ECE) { EC = ECE.getErrorCode(); });
+                  [&](const ErrorInfoBase &EI) {
+                    EC = EI.convertToErrorCode();
+                  });
   return EC;
 }
 

lib/Support/CMakeLists.txt

@@ -48,6 +48,7 @@ add_llvm_library(LLVMSupport
   DeltaAlgorithm.cpp
   DAGDeltaAlgorithm.cpp
   Dwarf.cpp
+  Error.cpp
   ErrorHandling.cpp
   FileUtilities.cpp
   FileOutputBuffer.cpp

lib/Support/Error.cpp

@@ -0,0 +1,45 @@
+//===----- lib/Support/Error.cpp - Error and associated utilities ---------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/Error.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/ManagedStatic.h"
+
+using namespace llvm;
+
+namespace {
+
+  enum class ErrorErrorCode {
+    MultipleErrors
+  };
+
+  class ErrorErrorCategory : public std::error_category {
+  public:
+    const char *name() const LLVM_NOEXCEPT override { return "Error"; }
+
+    std::string message(int condition) const override {
+      switch (static_cast<ErrorErrorCode>(condition)) {
+      case ErrorErrorCode::MultipleErrors:
+        return "Multiple errors";
+      };
+      llvm_unreachable("Unhandled error code");
+    }
+  };
+
+};
+
+void ErrorInfoBase::anchor() {}
+char ErrorInfoBase::ID = 0;
+
+static ManagedStatic<ErrorErrorCategory> ErrorErrorCat;
+
+std::error_code ErrorList::convertToErrorCode() const {
+  return std::error_code(static_cast<int>(ErrorErrorCode::MultipleErrors),
+                         *ErrorErrorCat);
+}

lib/Support/ErrorHandling.cpp

@@ -139,9 +139,6 @@ void LLVMResetFatalErrorHandler() {
   remove_fatal_error_handler();
 }
 
-void ErrorInfoBase::anchor() {}
-char ErrorInfoBase::ID = 0;
-
 #ifdef LLVM_ON_WIN32
 
 #include <winerror.h>

unittests/Support/ErrorTest.cpp

@@ -9,6 +9,7 @@
 
 #include "llvm/Support/Error.h"
 #include "llvm/Support/Errc.h"
+#include "llvm/Support/ErrorHandling.h"
 #include "gtest/gtest.h"
 #include <memory>
 
@@ -30,6 +31,10 @@ public:
     OS << "CustomError { " << getInfo() << "}";
   }
 
+  std::error_code convertToErrorCode() const override {
+    llvm_unreachable("CustomError doesn't support ECError conversion");
+  }
+
 protected:
   // This error is subclassed below, but we can't use inheriting constructors
   // yet, so we can't propagate the constructors through ErrorInfo. Instead
@@ -57,6 +62,10 @@ public:
     OS << "CustomSubError { " << getInfo() << ", " << getExtraInfo() << "}";
   }
 
+  std::error_code convertToErrorCode() const override {
+    llvm_unreachable("CustomSubError doesn't support ECError conversion");
+  }
+
 protected:
   int ExtraInfo;
 };