Support: Pass wrapped Error's error code through FileError

[dexonsmith]

Summary

Change FileError to pass through the error code from the Error it wraps.
This allows APIs that return ECError to transition to FileError without
changing returned std::error_code.

This was extracted from https://reviews.llvm.org/D109345.

[dexonsmith]

Note: I have an example of using this at https://reviews.llvm.org/D113226.

[dblaikie]

looks good, thanks!

llvm/lib/Support/Error.cpp

 }
 
 std::error_code inconvertibleErrorCode() {
   return std::error_code(static_cast<int>(ErrorErrorCode::InconvertibleError),
                          *ErrorErrorCat);
 }
 
 std::error_code FileError::convertToErrorCode() const {
+  std::error_code NestedEC = Err->convertToErrorCode();
+  if (NestedEC == inconvertibleErrorCode())
     return std::error_code(static_cast<int>(ErrorErrorCode::FileError),
                            *ErrorErrorCat);
+  return NestedEC;
 }
 
 Error errorCodeToError(std::error_code EC) {
   if (!EC)
     return Error::success();
   return Error(std::make_unique<ECError>(ECError(EC)));
 }
 

llvm/unittests/Support/ErrorTest.cpp

#endif
   EXPECT_EQ(toString(std::move(FE5)), "'': CustomError {5}");
 
   Error FE6 = createFileError("unused", make_error<CustomError>(6));
   handleAllErrors(std::move(FE6), [](std::unique_ptr<FileError> F) {
     EXPECT_EQ(F->messageWithoutFileInfo(), "CustomError {6}");
   });
 }
 
+TEST(Error, FileErrorErrorCode) {
+  for (std::error_code EC : {
+           make_error_code(std::errc::not_supported),
+           make_error_code(std::errc::invalid_argument),
+           make_error_code(std::errc::no_such_file_or_directory),
+       }) {
+    EXPECT_EQ(EC, errorToErrorCode(
+                      createFileError("file.bin", EC)));
+    EXPECT_EQ(EC, errorToErrorCode(
+                      createFileError("file.bin", /*Line=*/5, EC)));
+    EXPECT_EQ(EC, errorToErrorCode(
+                      createFileError("file.bin", errorCodeToError(EC))));
+    EXPECT_EQ(EC, errorToErrorCode(
+                      createFileError("file.bin", /*Line=*/5, errorCodeToError(EC))));
+  }
+
+  // inconvertibleErrorCode() should be wrapped to avoid a fatal error.
+  EXPECT_EQ(
+      "A file error occurred.",
+      errorToErrorCode(createFileError("file.bin", inconvertibleErrorCode()))
+          .message());
+  EXPECT_EQ(
+      "A file error occurred.",
+      errorToErrorCode(createFileError("file.bin", /*Line=*/5, inconvertibleErrorCode()))
+          .message());
+}
+
 enum class test_error_code {
   unspecified = 1,
   error_1,
   error_2,
 };
 
 } // end anon namespace