[jira] [Created] (ARROW-17784) [C++] Opening a dataset where partitioning variable is in the dataset should error differently

["Nicola Crane (Jira)" <ji...@apache.org>]

Nicola Crane created ARROW-17784:
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             Summary: [C++] Opening a dataset where partitioning variable is in the dataset should error differently
                 Key: ARROW-17784
                 URL: https://issues.apache.org/jira/browse/ARROW-17784
             Project: Apache Arrow
          Issue Type: Bug
          Components: C++
            Reporter: Nicola Crane


The error message given when the name of the partition given matches a field in the dataset is a bit misleading - can we catch this earlier and give a different error message?


{code:r}
/library(dplyr)
library(arrow)

tf <- tempfile()
dir.create(tf)
write_dataset(mtcars, tf, partitioning = "cyl", hive_style = FALSE)
# The schema fed into `partitioning` should refer to `cyl` and not `wt`, but the error message doesn't refer to the duplication here
open_dataset(tf, partitioning = schema(wt = int64())) %>% collect()
#> Error in `open_dataset()`:
#> ! Invalid: Unable to merge: Field wt has incompatible types: double vs int64
#> /home/nic2/arrow/cpp/src/arrow/type.cc:1692  fields_[i]->MergeWith(field)
#> /home/nic2/arrow/cpp/src/arrow/type.cc:1755  AddField(field)
#> /home/nic2/arrow/cpp/src/arrow/type.cc:1826  builder.AddSchema(schema)
#> /home/nic2/arrow/cpp/src/arrow/dataset/discovery.cc:262  Inspect(options.inspect_options)
{code}




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