[GitHub] [arrow] westonpace commented on a change in pull request #10326: ARROW-12791: [R] Better error handling for DatasetFactory$Finish() when no format specified

[GitBox <gi...@apache.org>]

westonpace commented on a change in pull request #10326:
URL: https://github.com/apache/arrow/pull/10326#discussion_r634594017



##########
File path: r/R/dataset.R
##########
@@ -93,8 +93,19 @@ open_dataset <- function(sources,
     return(dataset___UnionDataset__create(sources, schema))
   }
   factory <- DatasetFactory$create(sources, partitioning = partitioning, ...)
-  # Default is _not_ to inspect/unify schemas
-  factory$Finish(schema, isTRUE(unify_schemas))
+  
+  tryCatch(
+    # Default is _not_ to inspect/unify schemas
+    factory$Finish(schema, isTRUE(unify_schemas)),
+    error = function (e) {
+      msg <- conditionMessage(e)
+      if(grep("Parquet magic bytes not found in footer", msg)){
+        stop("Looks like these are not parquet files, did you mean to specify a 'format'?", call. = FALSE)

Review comment:
       So as an exploratory question, "If this message is universally better than the C++ message should the C++ message be changed?  Why or why not?"




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