Add Debug impls for ArrowWriter and SerializedFileWriter

[alamb]

This is an alternate, more targeted version of #4276

Which issue does this PR close?

N/A

Rationale for this change

This caught me when working on https://github.com/influxdata/influxdb_iox/pull/7855

I had to manually derive a Debug impl for a structure because the ArrowWriter didn't

What changes are included in this PR?

1. Add Debug impls for ArrowWriter and SerializedFileWriter

Are there any user-facing changes?

More Debug!

[tustvold]

Thank you, left two minor comments

[tustvold]

I think buffered_batches is just self.buffer.len()?

[alamb]

fixed

[tustvold]

FWIW #[derive(Debug)] on TrackedWrite would allow similar here, without needing a manual impl. SerializedFileWriter doesn't contain any non-public types on it

[alamb]

I tried to do this with

diff --git a/parquet/src/file/writer.rs b/parquet/src/file/writer.rs
index 93e8319b0..3ab50fb4b 100644
--- a/parquet/src/file/writer.rs
+++ b/parquet/src/file/writer.rs
@@ -48,6 +48,7 @@ use crate::schema::types::{
 /// A wrapper around a [`Write`] that keeps track of the number
 /// of bytes that have been written. The given [`Write`] is wrapped
 /// with a [`BufWriter`] to optimize writing performance.
+#[derive(Debug)]
 pub struct TrackedWrite<W: Write> {
     inner: BufWriter<W>,
     bytes_written: usize,
@@ -134,6 +135,7 @@ pub type OnCloseRowGroup<'a> = Box<
 /// - Once finished writing row group, close row group writer by calling `close`
 /// - Write subsequent row groups, if necessary.
 /// - After all row groups have been written, close the file writer using `close` method.
+#[derive(Debug)]
 pub struct SerializedFileWriter<W: Write> {
     buf: TrackedWrite<W>,
     schema: TypePtr,
@@ -148,17 +150,6 @@ pub struct SerializedFileWriter<W: Write> {
     kv_metadatas: Vec<KeyValue>,
 }
 
-impl<W: Write> Debug for SerializedFileWriter<W> {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        // implement Debug so this can be used with #[derive(Debug)]
-        // in client code rather than actually listing all the fields
-        f.debug_struct("SerializedFileWriter")
-            .field("descr", &self.descr)
-            .field("row_group_index", &self.row_group_index)
-            .field("kv_metadatas", &self.kv_metadatas)
-            .finish_non_exhaustive()
-    }
-}
 
 impl<W: Write> SerializedFileWriter<W> {
     /// Creates new file writer.

However, the compiler is complains like this ( I think it is saying I need to restrict the bound on SerializedFileWriter which I would prefer not to do as it would be backwards incompatible)

    Checking parquet v40.0.0 (/Users/alamb/Software/arrow-rs/parquet)
error[E0277]: `W` doesn't implement `std::fmt::Debug`
   --> parquet/src/arrow/arrow_writer/mod.rs:108:30
    |
108 |             .field("writer", &self.writer)
    |                              ^^^^^^^^^^^^ `W` cannot be formatted using `{:?}` because it doesn't implement `std::fmt::Debug`
    |
note: required for `file::writer::SerializedFileWriter<W>` to implement `std::fmt::Debug`
   --> parquet/src/file/writer.rs:138:10
    |
138 | #[derive(Debug)]
    |          ^^^^^ unsatisfied trait bound introduced in this `derive` macro
    = note: required for the cast from `file::writer::SerializedFileWriter<W>` to the object type `dyn std::fmt::Debug`
    = note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)
help: consider further restricting this bound
    |
96  | impl<W: Write + std::fmt::Debug> Debug for ArrowWriter<W> {
    |               +++++++++++++++++

[tustvold]

Aah, yeah makes sense

[viirya]

Is it meaningful to have W in debug? No much info from it. Looks ArrowWriter doesn't have it.

[alamb]

removed

[tustvold]

Thank you for this