Add instructions on how to install ELP from source

Summary:
* Port and expand the instructions from the CONTRIBUTING file
* Point the CONTRIBUTING file to the new instructions

Reviewed By: alanz

Differential Revision: D53916555

fbshipit-source-id: 3098892ee7fadadece4b54890b234b7db59d14ff

CONTRIBUTING.md

@@ -12,38 +12,7 @@ requests as described below.
 
 The gold standard is the current config in [ci.yml](.github/workflows/ci.yml).
 
-A summary of these is
-
-Check out [eqwalizer](https://github.com/WhatsApp/eqwalizer/) next to erlang-language-platform (this repo).
-
-Install [sbt](https://www.scala-sbt.org/), and java >= 11
-
-```sh
-cd $PATH_TO_REPO/eqwalizer/eqwalizer
-sbt assembly
-```
-
-It gives a path to the file
-
-```sh
-export ELP_EQWALIZER_PATH=<the path>
-```
-
-e.g. on a particular machine this would be
-
-```sh
-export ELP_EQWALIZER_PATH=/home/alanz/mysrc/github/WhatsApp/eqwalizer/eqwalizer/target/scala-2.13/eqwalizer.jar
-```
-
-Then use `cargo build` as usual from this repository.
-
-Note: if you set `ELP_EQWALIZER_PATH` in your shell profile, it will be used by rust_analyzer in your IDE too.
-
-An alternative way to build is
-
-```sh
-ELP_EQWALIZER_PATH=../../../eqwalizer/eqwalizer/target/scala-2.13/eqwalizer.jar cargo build
-```
+You can find detailed instructions on how to compile ELP from source [here](./website/docs/get-started/install.md).
 
 ## Pull Requests
 

website/docs/get-started/install.md

@@ -4,32 +4,40 @@ sidebar_position: 2
 
 # Install ELP
 
-The easiest way to install to ELP is [from binary](#from-binary). It is also possible to compile it [from source](#from-source).
+The easiest way to install to ELP is [from binary](#from-binary). It is also
+possible to compile it [from source](#from-source).
 
 ## From Binary
 
-Visit our [releases](https://github.com/WhatsApp/erlang-language-platform/releases) page and download the `elp` tarball for the latest releases.
+Visit our
+[releases](https://github.com/WhatsApp/erlang-language-platform/releases) page
+and download the `elp` tarball for the latest releases.
 
-Packages are available in the _Assets_ section below each release. Each tarball name has the format:
+Packages are available in the _Assets_ section below each release. Each tarball
+name has the format:
 
 ```
 elp-[OS]-[ARCH]-[c]-otp-[OTP_VERSION].tar.gz
 ```
 
-Pick the appropriate version according to your Operating System (OS), Architecture (ARCH) and Erlang/OTP version (OTP_VERSION). For example, for my Darwin MacBook Pro where I have installed Erlang/OTP 25, I will pick:
+Pick the appropriate version according to your Operating System (OS),
+Architecture (ARCH) and Erlang/OTP version (OTP_VERSION). For example, for my
+Darwin MacBook Pro where I have installed Erlang/OTP 25, I will pick:
 
 ```
 elp-macos-x86_64-apple-darwin-otp-25.3.tar.gz
 ```
 
 :::tip
 
-Unsure about your architecture? Try the `uname -a` command.
-Unsure about your Erlang/OTP version? Try `erl -eval 'erlang:display(erlang:system_info(otp_release)), halt().'  -noshell`
+Unsure about your architecture? Try the `uname -a` command. Unsure about your
+Erlang/OTP version? Try
+`erl -eval 'erlang:display(erlang:system_info(otp_release)), halt().' -noshell`
 
 :::
 
-Untar the package and place the `elp` binary in a place visible by your `PATH``. For example:
+Untar the package and place the `elp` binary in a place visible by your `PATH``.
+For example:
 
 ```
 cd ~/Downloads
@@ -38,8 +46,62 @@ mv elp ~/bin
 export PATH=$PATH:~/bin
 ```
 
-Follow [these steps](cli.md#verify-elp-is-correctly-installed) to verify ELP is correctly installed.
+Follow [these steps](cli.md#verify-elp-is-correctly-installed) to verify ELP is
+correctly installed.
 
 ## From Source
 
-TBD.
+### Prerequisites
+
+To be able to compile ELP from source, you need a copy of the
+[eqWAlizer](https://github.com/WhatsApp/eqwalizer) typechecker for Erlang.
+
+Clone the eqWAlizer repository:
+
+```
+git clone https://github.com/WhatsApp/eqwalizer.git
+```
+
+Enter the `eqwalizer` repository and build it. Notice the double `eqwalizer` in
+the `pushd` command.
+
+```
+pushd eqwalizer/eqwalizer
+sbt assembly
+popd
+```
+
+Get the path of the produced `eqwalizer.jar` file:
+
+```
+find . -name eqwalizer.jar | readlink -f
+```
+
+Point the `ELP_EQWALIZER_PATH` environment variable to the path returned above:
+
+```
+export ELP_EQWALIZER_PATH=/path/to/eqwalizer.jar
+```
+
+### Compile ELP
+
+Clone the ELP repository:
+
+```
+git clone https://github.com/WhatsApp/erlang-language-platform.git
+```
+
+Enter the ELP repo and compile it:
+
+```
+cd erlang-language-platform
+cargo build --release
+```
+
+The produced executable will be available in: `target/release/elp`, so ensure it is included in your `PATH`. E.g.:
+
+```
+mkdir -p ~/bin
+mv target/releases/elp ~/bin
+export PATH=$PATH:~/bin
+```