# SynthTool (for client libraries)

![Diagram of relationship between Autosynth, Synthtool, and Github](../images/flow.png)

This tool helps to generate and layout cloud client libraries. Synthtool runs the [GAPIC (Generated API Client) Generator][GAPIC] via [Google API Artifact Manager (artman)][artman].

[GAPIC]: https://github.com/googleapis/gapic-generator
[artman]: https://github.com/googleapis/artman

## Prerequisites

1. **Linux**  This tool runs on Linux only.  No other platforms are supported.

2. **Python 3.6** Either install it from [python.org][python_downloads] or use
[pyenv][] to get 3.6.

3. **Bazel**  can be downloaded from [bazel.build](https://bazel.build/).

4. **Docker**  Some synth.py files require [Docker] to generate code.

5. Clone this repository and install this library with pip:

    ```
    cd synthtool
    python3 -m pip install -e .
    ```


[python_downloads]: https://www.python.org/downloads/
[pyenv]: https://github.com/pyenv/pyenv
[Docker]: https://docs.docker.com/v17.09/engine/installation/#desktop


## Basic usage
To start the process of generation, clone the destination repository.
```
git clone git@github.com:googleapis/python-tasks.git
cd python-tasks/
```

### Running `synthtool`
If a `synth.py` script is not present, create a new one.

You can create one from scratch or copy one from another library.
 - e.g. the `synth.py` for the Cloud Tasks API for [Python][python_tasks_synth_py],
[Java][java_tasks_synth_py], [Node.js][node_tasks_synth_py], [PHP][php_tasks_synth_py],
or [Ruby][ruby_tasks_synth_py].

Run `synthtool`:

```
python3 -m synthtool
```

After `synthtool` runs successfully:
 - Investigate the changes it made
 - Run the library tests
 - Commit and push the changes to a branch and open a Pull Request

Find examples below in different programming languages (Cloud Tasks API used as an example).

### Python
- Clone the destination repository:
  ```
  git clone git@github.com:googleapis/python-tasks.git
  cd python-tasks/
  ```
- Run `synthtool` to generate using the existing [`synth.py`][python_tasks_synth_py]
  file for the [Python Client for Cloud Tasks API][python_tasks_library]:
  ```
  python3 -m synthtool
  ```
- See the Python [Contributing Guide][python_contributing]
  or instructions to install dependencies, run tests, and submit a contribution.

[python_tasks_library]: https://github.com/googleapis/python-tasks
[python_tasks_synth_py]: https://github.com/googleapis/python-tasks/blob/master/synth.py
[python_contributing]: https://github.com/googleapis/python-tasks/blob/master/CONTRIBUTING.rst

### Java
- Clone the destination repository:
  ```
  git clone git@github.com:googleapis/java-tasks.git
  cd java-tasks/
  ```
- Run `synthtool` to generate using the existing [`synth.py`][java_tasks_synth_py]
  file for the [Google Cloud Java Client for Cloud Tasks][java_tasks_library]:
  ```
  python3 -m synthtool
  ```
- See the Java [Contributing Guide][java_contributing]
  or instructions to install dependencies, run tests, and submit a contribution.

[java_tasks_library]: https://github.com/googleapis/java-tasks
[java_tasks_synth_py]: https://github.com/googleapis/java-tasks/blob/master/synth.py
[java_contributing]: https://github.com/googleapis/java-tasks/blob/master/CONTRIBUTING.md

### Node.js
- Clone the destination repository:
  ```
  git clone git@github.com:googleapis/nodejs-tasks.git
  cd nodejs-tasks/
  ```
- Run `synthtool` to generate using the existing [`synth.py`][node_tasks_synth_py]
  file for the [Google Cloud Tasks Node.js Client][node_tasks_library]:
  ```
  python3 -m synthtool
  ```
- See the Node.js [Contributing Guide][node_tasks_contributing]
  or instructions to install dependencies, run tests, and submit a contribution.

[node_tasks_library]: https://github.com/googleapis/nodejs-tasks
[node_tasks_synth_py]: https://github.com/googleapis/nodejs-tasks/blob/master/synth.py
[node_tasks_contributing]: https://github.com/googleapis/nodejs-tasks/blob/master/CONTRIBUTING.md

### PHP
- Clone the destination repository:
  ```
  git clone git@github.com:googleapis/google-cloud-php.git
  cd google-cloud-php/
  ```
- Navigate to the destination directory:
  ```
  cd Tasks/
  ```
- Run `synthtool` to generate using the existing [`synth.py`][php_tasks_synth_py]
  file for the [Google Cloud Tasks client for PHP][php_tasks_library]:
  ```
  python3 -m synthtool
  ```
- See the PHP [Contributing Guide][php_contributing]
  or instructions to install dependencies, run tests, and submit a contribution.

[php_tasks_library]: https://github.com/googleapis/google-cloud-php/tree/master/Tasks
[php_tasks_synth_py]: https://github.com/googleapis/google-cloud-php/blob/master/Tasks/synth.py
[php_contributing]: https://github.com/googleapis/google-cloud-php/blob/master/CONTRIBUTING.md

### Ruby
- Clone the destination repository:
  ```
  git clone git@github.com:googleapis/google-cloud-ruby.git
  cd google-cloud-ruby/
  ```
- Navigate to the destination directory:
  ```
  cd google-cloud-tasks/
  ```
- Run `synthtool` to generate using the existing [`synth.py`][ruby_tasks_synth_py]
  file for the [Ruby Client for Cloud Tasks API][ruby_tasks_library]:
  ```
  python3 -m synthtool
  ```
- See the Ruby [Contributing Guide][ruby_contributing]
  or instructions to install dependencies, run tests, and submit a contribution.

[ruby_tasks_library]: https://github.com/googleapis/google-cloud-ruby/tree/master/google-cloud-tasks
[ruby_tasks_synth_py]: https://github.com/googleapis/google-cloud-ruby/blob/master/google-cloud-tasks/synth.py
[ruby_contributing]: https://github.com/googleapis/google-cloud-ruby/blob/master/.github/CONTRIBUTING.md

## Features

### Common transforms

Functions in synthtool make it easier to copy files, merge files, etc.
See the [pydocs](https://htmlpreview.github.io/?https://github.com/googleapis/synthtool/blob/master/synthtool/pydoc.html) for more details.

### Templating
SynthTool supports template files using [Jinja](http://jinja.pocoo.org/).

Templates are found in subdirectories of [`synthtool/gcp/templates/`](gcp/templates/)
for each language,
 - e.g. the template directories for [Python][python_templates],
[Node.js][node_templates], [PHP][php_templates], or [Ruby][ruby_templates].

[python_templates]: gcp/templates/python_library/
[node_templates]: gcp/templates/node_library/
[php_templates]: gcp/templates/php_library/
[ruby_templates]:  gcp/templates/ruby_library/

You can generate and copy templates using `gcp.CommonTemplates` in your `synth.py`:
```py
common_templates = gcp.CommonTemplates()

templates = common_templates.node_library()
s.copy(templates)
```

You can provide variables to templates as keyword arguments to the library generation method:

```py
common_templates = gcp.CommonTemplates()

templates = common_templates.node_library(version=5, show_version=True, previous_versions=[1,2,3,4])

s.copy(templates)
```

Template files can access any values provided, e.g.
 - `README.md.j2`
    ```py
    {% if show_version %}
    The version is {{ version }}

    {% if previous versions is defined %}
    Previous versions:
      {% for ver in previous_versions %}
      - {{ ver }}
      {% endfor %}
    {% endif %}
    {% endif %}
    ```

For more information on how to use Synthtool templating for Python Samples, view [/py_templating_instructions](./py_templating_instructions)

You can learn more about Jinga templating in the
[Template Designer Documentation](http://jinja.pocoo.org/docs/templates/).

### googleapis-private
SynthTool supports generation from googleapis/googleapis-private.

```py
gapic = gcp.GAPICGenerator()

library = gapic.node_library('speech', 'v1', private=True)
```
2FA is required to clone a private repo.

* **Using SSH:** Before running Synthtool, set the environment variable `AUTOSYNTH_USE_SSH` to `true`.

The repo is cloned using SSH.
* **Using HTTPS:** Generate a [GitHub Personal Access Token](https://github.com/settings/tokens) with scope `repo`.
Run `synthtool`.

When GitHub prompts for your GitHub password, provide the access token instead.

```
synthtool > Cloning googleapis-private.
Username for 'https://github.com': busunkim96
Password for 'https://busunkim96@github.com':
```

### Artman Version
SynthTool uses the latest version of the [Artman Docker image](https://hub.docker.com/r/googleapis/artman).
You can change this by setting the environment variable `SYNTHTOOL_ARTMAN_VERSION` to the desired version tag.

```
export SYNTHTOOL_ARTMAN_VERSION=0.16.2
```

### GAPIC Generator Python Version
SynthTool uses the latest version of [gcr.io/gapic-images/gapic-generator-python](https://gcr.io/gapic-images/gapic-generator-python). You can change this by
setting the environment variable `SYNTHTOOL_GAPIC_GENERATOR_PYTHON_VERSION` to the desired version tag.

```
export SYNTHTOOL_GAPIC_GENERATOR_PYTHON_VERSION=0.22.0
```

Alternatively you can set the generator version by passing it to `gapic.py_library`.

```python
import synthtool as s
import synthtool.gcp as gcp

gapic = gcp.GAPICMicrogenerator()

library = gapic.py_library(
    "bigquery/connection", "v1beta1", generator_version="0.22.0"
)
```

### Local Googleapis
SynthTool supports generation from a local copy of googleapis.
Specify the path to `googleapis` in the environment variable `SYNTHTOOL_GOOGLEAPIS`.

```
export SYNTHTOOL_GOOGLEAPIS=path/to/local/googleapis
```

### Local GAPIC Generator
SynthTool supports generation from a local copy of [gapic-generator](https://github.com/googleapis/gapic-generator).
Specify the path to `gapic-generator` in the environment variable `SYNTHTOOL_GENERATOR`.

```
export SYNTHTOOL_GENERATOR=path/to/local/gapic-generator
```

Don't forget to compile `gapic-generator` before running SynthTool.

```
cd path/to/local/gapic-generator
./gradlew fatJar
```

### Local Template Files
SynthTool supports specifying a local directory of templates. Specify the path to the root
template directory (not a SynthTool clone) in the environment variable `SYNTHTOOL_TEMPLATES`.

```
export SYNTHTOOL_TEMPLATES=path/to/local/templates
```

### Include .proto files
SynthTool supports copying .proto API definition files from googleapis.

```py
gapic = gcp.GAPICGenerator()

library = gapic.node_library('speech', 'v1', include_protos=True)
```

## Context-Aware Commits

Autosynth runs synthtool on your `synth.py` nightly or more frequently.
By default, it runs synthtool once, and if the generated code differs,
creates a PR with the differences.

Autosynth can also find which changes in upstream repositories triggered changes
in the generated code.  To enable this behavior (context-aware commits),
set one or both of the following flags in you synth.py file:

```py
AUTOSYNTH_MULTIPLE_COMMITS
AUTOSYNTH_MULTIPLE_PRS
```

### Example

Assume that since the library source code was last generated, A, B and X, Y 
were committed to googleapis and synthtool respectively, and they all triggered
changes in the generated library code.

| [googleapis](https://github.com/googleapis/googleapis) | [synthtool (templates)](gcp/templates) |
| :--------: | :-------------------: |
|  A         |  X                    |
|  B         |  Y                    |


Here's what autosynth generates for each flag setting.

```py
AUTOSYNTH_MULTIPLE_COMMITS = True
```

Autosynth creates one PR, with a single commit for each original commit:
| PR |
| - |
| A |
| B |
| X |
| Y |

***

```py
AUTOSYNTH_MULTIPLE_COMMITS = True
AUTOSYNTH_MULTIPLE_PRS = True
```

Autosynth creates two PRs, with a single commit for each original commit:
| PR1 |
| - |
| A |
| B |

| PR2 |
| - |
| X |
| Y |


***

```py
AUTOSYNTH_MULTIPLE_PRS = True
```

Autosynth creates two PRs, with a single commit combining all the 
original commits.

| PR1 |
| - |
| AB |

| PR2 |
| - |
| XY |


## Helpful tips
### Where does the generated code go?
SynthTool runs [Artman](https://hub.docker.com/r/googleapis/artman) which creates generated code that
can be found at `~/.cache/synthtool/googleapis<-private>/artman_genfiles`. This is useful for figuring out
what it is you need to copy for your specific library.

### Warning: Don't lint manually-written code in synth.py!

Ben had the misfortune to discover a corner case where autosynth deleted a file that Ben never intended or expected it to delete.

Here is what happened:

1. Autosynth cannot directly observe which files your synth.py generates, because synth.py could literally do anything, including launch the space shuttle.  So, Autosynth figures out which files were generated by examining all the file system reads and writes that happened while synth.py was executing.  Any file that is written to or copied to is deemed to have been generated by synth.py and recorded as a generatedFiles in synth.metadata.

2. NodeJS's synth.py ran the linter on manually-written sample files in the repo.  A new version of the linter was pulled in, which modified a manually-written sample file.  Autosynth observed the write and concluded that the manually-written file was a generated file, and listed it in generatedFiles in synth.metadata.  The next time Autosynth ran, the linter made no changes, and the manually-written sample file was not written to.  Autosynth concluded the manually-written sample file was no longer being generated, and deleted it.

#### Lesson Learned:
Make sure your synth.py does not touch any manually-written files in the repo.