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* Docs: split contributor guide into multiple pages

* Fix links

* Update docs/source/contributor-guide/howtos.md

Co-authored-by: Jonah Gao <[email protected]>

---------

Co-authored-by: Jonah Gao <[email protected]>
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87 changes: 87 additions & 0 deletions docs/source/contributor-guide/getting_started.md
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<!---
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements. See the NOTICE file
distributed with this work for additional information
regarding copyright ownership. The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied. See the License for the
specific language governing permissions and limitations
under the License.
-->

# Getting Started

This section describes how you can get started at developing DataFusion.

## Windows setup

```shell
wget https://az792536.vo.msecnd.net/vms/VMBuild_20190311/VirtualBox/MSEdge/MSEdge.Win10.VirtualBox.zip
choco install -y git rustup.install visualcpp-build-tools
git-bash.exe
cargo build
```

## Protoc Installation

Compiling DataFusion from sources requires an installed version of the protobuf compiler, `protoc`.

On most platforms this can be installed from your system's package manager

```
# Ubuntu
$ sudo apt install -y protobuf-compiler
# Fedora
$ dnf install -y protobuf-devel
# Arch Linux
$ pacman -S protobuf
# macOS
$ brew install protobuf
```

You will want to verify the version installed is `3.12` or greater, which introduced support for explicit [field presence](https://github.com/protocolbuffers/protobuf/blob/v3.12.0/docs/field_presence.md). Older versions may fail to compile.

```shell
$ protoc --version
libprotoc 3.12.4
```

Alternatively a binary release can be downloaded from the [Release Page](https://github.com/protocolbuffers/protobuf/releases) or [built from source](https://github.com/protocolbuffers/protobuf/blob/main/src/README.md).

## Bootstrap environment

DataFusion is written in Rust and it uses a standard rust toolkit:

- `cargo build`
- `cargo fmt` to format the code
- `cargo test` to test
- etc.

Note that running `cargo test` requires significant memory resources, due to cargo running many tests in parallel by default. If you run into issues with slow tests or system lock ups, you can significantly reduce the memory required by instead running `cargo test -- --test-threads=1`. For more information see [this issue](https://github.com/apache/datafusion/issues/5347).

Testing setup:

- `rustup update stable` DataFusion uses the latest stable release of rust
- `git submodule init`
- `git submodule update`

Formatting instructions:

- [ci/scripts/rust_fmt.sh](../../../ci/scripts/rust_fmt.sh)
- [ci/scripts/rust_clippy.sh](../../../ci/scripts/rust_clippy.sh)
- [ci/scripts/rust_toml_fmt.sh](../../../ci/scripts/rust_toml_fmt.sh)

or run them all at once:

- [dev/rust_lint.sh](../../../dev/rust_lint.sh)
129 changes: 129 additions & 0 deletions docs/source/contributor-guide/howtos.md
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<!---
Licensed to the Apache Software Foundation (ASF) under one
or more contributor license agreements. See the NOTICE file
distributed with this work for additional information
regarding copyright ownership. The ASF licenses this file
to you under the Apache License, Version 2.0 (the
"License"); you may not use this file except in compliance
with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing,
software distributed under the License is distributed on an
"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
KIND, either express or implied. See the License for the
specific language governing permissions and limitations
under the License.
-->

# HOWTOs

## How to add a new scalar function

Below is a checklist of what you need to do to add a new scalar function to DataFusion:

- Add the actual implementation of the function to a new module file within:
- [here](https://github.com/apache/datafusion/tree/main/datafusion/functions-array) for array functions
- [here](https://github.com/apache/datafusion/tree/main/datafusion/functions/src/crypto) for crypto functions
- [here](https://github.com/apache/datafusion/tree/main/datafusion/functions/src/datetime) for datetime functions
- [here](https://github.com/apache/datafusion/tree/main/datafusion/functions/src/encoding) for encoding functions
- [here](https://github.com/apache/datafusion/tree/main/datafusion/functions/src/math) for math functions
- [here](https://github.com/apache/datafusion/tree/main/datafusion/functions/src/regex) for regex functions
- [here](https://github.com/apache/datafusion/tree/main/datafusion/functions/src/string) for string functions
- [here](https://github.com/apache/datafusion/tree/main/datafusion/functions/src/unicode) for unicode functions
- create a new module [here](https://github.com/apache/datafusion/tree/main/datafusion/functions/src/) for other functions.
- New function modules - for example a `vector` module, should use a [rust feature](https://doc.rust-lang.org/cargo/reference/features.html) (for example `vector_expressions`) to allow DataFusion
users to enable or disable the new module as desired.
- The implementation of the function is done via implementing `ScalarUDFImpl` trait for the function struct.
- See the [advanced_udf.rs] example for an example implementation
- Add tests for the new function
- To connect the implementation of the function add to the mod.rs file:
- a `mod xyz;` where xyz is the new module file
- a call to `make_udf_function!(..);`
- an item in `export_functions!(..);`
- In [sqllogictest/test_files], add new `sqllogictest` integration tests where the function is called through SQL against well known data and returns the expected result.
- Documentation for `sqllogictest` [here](https://github.com/apache/datafusion/blob/main/datafusion/sqllogictest/README.md)
- Add SQL reference documentation [here](https://github.com/apache/datafusion/blob/main/docs/source/user-guide/sql/scalar_functions.md)

[advanced_udf.rs]: https://github.com/apache/datafusion/blob/main/datafusion-examples/examples/advanced_udaf.rs
[sqllogictest/test_files]: https://github.com/apache/datafusion/tree/main/datafusion/sqllogictest/test_files

## How to add a new aggregate function

Below is a checklist of what you need to do to add a new aggregate function to DataFusion:

- Add the actual implementation of an `Accumulator` and `AggregateExpr`:
- In [datafusion/expr/src](../../../datafusion/expr/src/aggregate_function.rs), add:
- a new variant to `AggregateFunction`
- a new entry to `FromStr` with the name of the function as called by SQL
- a new line in `return_type` with the expected return type of the function, given an incoming type
- a new line in `signature` with the signature of the function (number and types of its arguments)
- a new line in `create_aggregate_expr` mapping the built-in to the implementation
- tests to the function.
- In [sqllogictest/test_files], add new `sqllogictest` integration tests where the function is called through SQL against well known data and returns the expected result.
- Documentation for `sqllogictest` [here](https://github.com/apache/datafusion/blob/main/datafusion/sqllogictest/README.md)
- Add SQL reference documentation [here](https://github.com/apache/datafusion/blob/main/docs/source/user-guide/sql/aggregate_functions.md)

## How to display plans graphically

The query plans represented by `LogicalPlan` nodes can be graphically
rendered using [Graphviz](https://www.graphviz.org/).

To do so, save the output of the `display_graphviz` function to a file.:

```rust
// Create plan somehow...
let mut output = File::create("/tmp/plan.dot")?;
write!(output, "{}", plan.display_graphviz());
```

Then, use the `dot` command line tool to render it into a file that
can be displayed. For example, the following command creates a
`/tmp/plan.pdf` file:

```bash
dot -Tpdf < /tmp/plan.dot > /tmp/plan.pdf
```

## How to format `.md` document

We are using `prettier` to format `.md` files.

You can either use `npm i -g prettier` to install it globally or use `npx` to run it as a standalone binary. Using `npx` required a working node environment. Upgrading to the latest prettier is recommended (by adding `--upgrade` to the `npm` command).

```bash
$ prettier --version
2.3.0
```

After you've confirmed your prettier version, you can format all the `.md` files:

```bash
prettier -w {datafusion,datafusion-cli,datafusion-examples,dev,docs}/**/*.md
```

## How to format `.toml` files

We use `taplo` to format `.toml` files.

For Rust developers, you can install it via:

```sh
cargo install taplo-cli --locked
```

> Refer to the [Installation section][doc] on other ways to install it.
>
> [doc]: https://taplo.tamasfe.dev/cli/installation/binary.html
```bash
$ taplo --version
taplo 0.9.0
```

After you've confirmed your `taplo` version, you can format all the `.toml` files:

```bash
taplo fmt
```
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