# What changes were proposed in this pull request?
In the PR, I propose to improve the error message from `from_json`/`from_csv` by combining errors from all schema parsers:
- DataType.fromJson (except CSV)
- CatalystSqlParser.parseDataType
- CatalystSqlParser.parseTableSchema
Before the changes, `from_json` does not show error messages from the first parser in the chain that could mislead users.
### Why are the changes needed?
Currently, `from_json` outputs the error message from the fallback schema parser which can confuse end-users. For example:
```scala
val invalidJsonSchema = """{"fields": [{"a":123}], "type": "struct"}"""
df.select(from_json($"json", invalidJsonSchema, Map.empty[String, String])).show()
```
The JSON schema has an issue in `{"a":123}` but the error message doesn't point it out:
```
mismatched input '{' expecting {'ADD', 'AFTER', ...}(line 1, pos 0)
== SQL ==
{"fields": [{"a":123}], "type": "struct"}
^^^
org.apache.spark.sql.catalyst.parser.ParseException:
mismatched input '{' expecting {'ADD', 'AFTER', ... }(line 1, pos 0)
== SQL ==
{"fields": [{"a":123}], "type": "struct"}
^^^
```
### Does this PR introduce _any_ user-facing change?
Yes, after the changes for the example above:
```
Cannot parse the schema in JSON format: Failed to convert the JSON string '{"a":123}' to a field.
Failed fallback parsing: Cannot parse the data type:
mismatched input '{' expecting {'ADD', 'AFTER', ...}(line 1, pos 0)
== SQL ==
{"fields": [{"a":123}], "type": "struct"}
^^^
Failed fallback parsing:
mismatched input '{' expecting {'ADD', 'AFTER', ...}(line 1, pos 0)
== SQL ==
{"fields": [{"a":123}], "type": "struct"}
^^^
```
### How was this patch tested?
- By existing tests suites like `JsonFunctionsSuite` and `JsonExpressionsSuite`.
- Add new test to `JsonFunctionsSuite`.
- Re-gen results for `json-functions.sql`.
Closes#30183 from MaxGekk/fromDDL-error-msg.
Authored-by: Max Gekk <max.gekk@gmail.com>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
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