# Development Guide
This document details more advanced options for developing in this codebase. It is not quite necessary to follow it, but it is likely that you'll find something you'll need from here.
## Documentation
The compiler is documented in [docs](docs/index.md). This is essential reading.
## Recommended workflow
We recommend the following overall workflow when developing for this repository:
* Fork this repository
* Always work in your fork
* Always keep your fork up to date
Before updating your fork, run this command:
```shell
git remote add upstream https://github.com/dotnet/fsharp.git
```
This will make management of multiple forks and your own work easier over time.
## Updating your fork
We recommend the following commands to update your fork:
```shell
git checkout main
git clean -xdf
git fetch upstream
git rebase upstream/main
git push
```
Or more succinctly:
```shell
git checkout main && git clean -xdf && git fetch upstream && git rebase upstream/main && git push
```
This will update your fork with the latest from `dotnet/fsharp` on your machine and push those updates to your remote fork.
## Developing on Windows
Install the latest released [Visual Studio](https://visualstudio.microsoft.com/vs/preview/) preview, as that is what the `main` branch's tools are synced with. Select the following workloads:
* .NET desktop development (also check F# desktop support, as this will install some legacy templates)
* Visual Studio extension development
You will also need the latest .NET 7 SDK installed from [here](https://dotnet.microsoft.com/download/dotnet/7.0).
Building is simple:
```shell
build.cmd
```
Desktop tests can be run with:
```shell
build.cmd -test -c Release
```
After you build the first time you can open and use this solution in Visual Studio:
```shell
.\VisualFSharp.sln
```
If you don't have everything installed yet, you'll get prompted by Visual Studio to install a few more things. This is because we use a `.vsconfig` file that specifies all our dependencies.
If you are just developing the core compiler and library then building ``FSharp.sln`` will be enough.
We recommend installing the latest Visual Studio preview and using that if you are on Windows. However, if you prefer not to do that, you will need to install the following:
* [.NET Framework 4.7.2](https://dotnet.microsoft.com/download/dotnet-framework/net472)
* [.NET 7](https://dotnet.microsoft.com/download/dotnet/7.0)
You'll need to pass an additional flag to the build script:
```shell
build.cmd -noVisualStudio
```
You can open `FSharp.sln` in your editor of choice.
## Developing on Linux or macOS
For Linux/Mac:
```shell
./build.sh
```
Running tests:
```shell
./build.sh --test
```
You can then open `FSharp.sln` in your editor of choice.
## Testing from the command line
You can find all test options as separate flags. For example `build -testAll`:
```shell
-testAll Run all tests
-testAllButIntegration Run all but integration tests
-testCambridge Run Cambridge tests
-testCompiler Run FSharpCompiler unit tests
-testCompilerService Run FSharpCompilerService unit tests
-testDesktop Run tests against full .NET Framework
-testCoreClr Run tests against CoreCLR
-testFSharpCore Run FSharpCore unit tests
-testFSharpQA Run F# Cambridge tests
-testScripting Run Scripting tests
-testVs Run F# editor unit tests
```
Running any of the above will build the latest changes and run tests against them.
## Using your custom compiler to build other projects
Building the compiler using `build.cmd` or `build.sh` will output artifacts in `artifacts\bin`.
To use your custom build of `Fsc`, add the `DotnetFscCompilerPath` property to your project's `.fsproj` file, adjusted to point at your local build directory, build configuration, and target framework as appropriate:
```xml
D:\Git\fsharp\artifacts\bin\fsc\Debug\net7.0\fsc.dll
```
## Updating FSComp.fs, FSComp.resx and XLF
If your changes involve modifying the list of language keywords in any way, (e.g. when implementing a new keyword), the XLF localization files need to be synced with the corresponding resx files. This can be done automatically by running
```shell
dotnet build src\Compiler /t:UpdateXlf
```
If you are on a Mac, you can run this command from the root of the repository:
```shell
sh build.sh -c Release
```
Or if you are on Linux:
```shell
./build.sh -c Release
```
## Updating baselines in tests
Some tests use "baseline" (.bsl) files. There is sometimes a way to update these baselines en-masse in your local build,
useful when some change affects many baselines. For example, in the `fsharpqa` and `FSharp.Compiler.ComponentTests` tests the baselines
are updated using scripts or utilities that allow the following environment variable to be set:
Windows:
CMD:
```shell
set TEST_UPDATE_BSL=1
```
PowerShell:
```shell
$env:TEST_UPDATE_BSL=1
```
Linux/macOS:
```shell
export TEST_UPDATE_BSL=1
```
Next, run a build script build (debug or release, desktop or coreclr, depending which baselines you need to update), and test as described [above](#Testing-from-the-command-line). For example:
`./Build.cmd -c Release -testCoreClr` to update Release CoreCLR baselines.
or
`./Build.cmd -c Release -testDesktop` to update Release .NET Framework baselines.
> **Note**
> Please note, that by default, **Release** version of IL baseline tests will be running in CI, so when updating baseline (.bsl) files, make sure to add `-c Release` flag to the build command.
## Automated Source Code Formatting
Some of the code in this repository is formatted automatically by [Fantomas](https://github.com/fsprojects/fantomas). To format all files use:
```cmd
dotnet fantomas . -r
```
The formatting is checked automatically by CI:
```cmd
dotnet fantomas . -r --check
```
At the time of writing only a subset of signature files (`*.fsi`) are formatted. See the settings in `.fantomasignore` and `.editorconfig`.
## Developing the F# tools for Visual Studio
As you would expect, doing this requires both Windows and Visual Studio are installed.
See [Developing on Windows](#Developing-on-Windows) for instructions to install what is needed; it's the same prerequisites.
### Quickly see your changes locally
First, ensure that `VisualFSharpDebug` is the startup project.
Then, use the **f5** or **ctrl+f5** keyboard shortcuts to test your tooling changes. The former will debug a new instance of Visual Studio. The latter will launch a new instance of Visual Studio, but with your changes installed.
Alternatively, you can do this entirely via the command line if you prefer that:
```shell
devenv.exe /rootsuffix RoslynDev
```
### Deploy your changes into a current Visual Studio installation
If you'd like to "run with your changes", you can produce a VSIX and install it into your current Visual Studio instance.
For this, run the following using the VS Developer PowerShell from the repo root:
```shell
VSIXInstaller.exe /u:"VisualFSharp"
VSIXInstaller.exe artifacts\VSSetup\Release\VisualFSharpDebug.vsix
```
It's important to use `Release` if you want to see if your changes have had a noticeable performance impact.
### Troubleshooting a failed build of the tools
You may run into an issue with a somewhat difficult or cryptic error message, like:
> error VSSDK1077: Unable to locate the extensions directory. "ExternalSettingsManager::GetScopePaths failed to initialize PkgDefManager for C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\Common7\IDE\devenv.exe".
Or hard crash on launch ("Unknown Error").
To fix this, delete these folders:
* `%localappdata%\Microsoft\VisualStudio\_(some number here)RoslynDev`
* `%localappdata%\Microsoft\VisualStudio\_(some number here)`
Where `` corresponds to the latest Visual Studio version on your machine.
## Coding conventions
* Coding conventions vary from file to file
* Format using [the F# style guide](https://learn.microsoft.com/dotnet/fsharp/style-guide/)
* Avoid tick identifiers like `body'`. They are generally harder to read and can't be inspected in the debugger as things stand. Generally use R suffix instead, e.g. `bodyR`. The R can stand for "rewritten" or "result"
* Avoid abbreviations like `bodyty` that are all lowercase. They are really hard to read for newcomers. Use `bodyTy` instead.
* See the compiler docs for common abbreviations
* Don't use `List.iter` and `Array.iter` in the compiler, a `for ... do ...` loop is simpler to read and debug
## Performance and debugging
Use the `Debug` configuration to test your changes locally. It is the default. Do not use the `Release` configuration! Local development and testing of Visual Studio tooling is not designed for the `Release` configuration.
### Writing and running benchmarks
Existing compiler benchmarks can be found in `tests\benchmarks\`.
### Benchmarking and profiling the compiler
**NOTE:** When running benchmarks or profiling compiler, and comparing results with upstream version, make sure:
* Always build both versions of compiler/FCS from source and not use pre-built binaries from SDK (SDK binaries are crossgen'd, which can affect performance).
* To run `Release` build of compiler/FCS.
### Example benchmark setup using [BenchmarkDotNet](https://github.com/dotnet/BenchmarkDotNet)
1. Perform a clean build of the compiler and FCS from source (as described in this document, build can be done with `-noVisualStudio` in case if FCS/FSharp.Core is being benchmarked/profiled).
2. Create a benchmark project (in this example, the project will be created in `tests\benchmarks\FCSBenchmarks`).
```shell
cd tests\benchmarks\FCSBenchmarks
dotnet new console -o FcsBench --name FcsBench -lang F#
```
3. Add needed packages and project references.
```shell
cd FcsBench
dotnet add package BenchmarkDotNet
dotnet add reference ..\..\..\src\Compiler\FSharp.Compiler.Service.fsproj
```
4. Additionally, if you want to test changes to the FSharp.Core (note that the relative path can be different)
```shell
dotnet add reference ..\..\..\src\FSharp.Core\FSharp.Core.fsproj
```
> as well as the following property have to be added to `FcsBench.fsproj`:
```xml
true
```
5. Add a new benchmark for FCS/FSharp.Core by editing `Program.fs`.
```fsharp
open System.IO
open FSharp.Compiler.CodeAnalysis
open FSharp.Compiler.Diagnostics
open FSharp.Compiler.Text
open BenchmarkDotNet.Attributes
open BenchmarkDotNet.Running
[]
type CompilerService() =
let mutable checkerOpt = None
let mutable sourceOpt = None
let parsingOptions =
{
SourceFiles = [|"CheckExpressions.fs"|]
ConditionalDefines = []
DiagnosticOptions = FSharpDiagnosticOptions.Default
LangVersionText = "default"
IsInteractive = false
LightSyntax = None
CompilingFsLib = false
IsExe = false
}
[]
member _.Setup() =
match checkerOpt with
| None ->
checkerOpt <- Some(FSharpChecker.Create(projectCacheSize = 200))
| _ -> ()
match sourceOpt with
| None ->
sourceOpt <- Some <| SourceText.ofString(File.ReadAllText("""C:\Users\vlza\code\fsharp\src\Compiler\Checking\CheckExpressions.fs"""))
| _ -> ()
[]
member _.ParsingTypeCheckerFs() =
match checkerOpt, sourceOpt with
| None, _ -> failwith "no checker"
| _, None -> failwith "no source"
| Some(checker), Some(source) ->
let results = checker.ParseFile("CheckExpressions.fs", source, parsingOptions) |> Async.RunSynchronously
if results.ParseHadErrors then failwithf "parse had errors: %A" results.Diagnostics
[]
member _.ParsingTypeCheckerFsSetup() =
match checkerOpt with
| None -> failwith "no checker"
| Some(checker) ->
checker.InvalidateAll()
checker.ClearLanguageServiceRootCachesAndCollectAndFinalizeAllTransients()
checker.ParseFile("dummy.fs", SourceText.ofString "dummy", parsingOptions) |> Async.RunSynchronously |> ignore
[]
let main _ =
BenchmarkRunner.Run() |> ignore
0
```
> For more detailed information about available BenchmarkDotNet options, please refer to [BenchmarkDotNet Documentation](https://benchmarkdotnet.org/articles/overview.html).
6. Build and run the benchmark.
```shell
dotnet build -c Release
dotnet run -c Release
```
7. You can find results in `.\BenchmarkDotNet.Artifacts\results\` in the current benchmark project directory.
```shell
> ls .\BenchmarkDotNet.Artifacts\results\
Directory: C:\Users\vlza\code\fsharp\tests\benchmarks\FCSBenchmarks\FcsBench\BenchmarkDotNet.Artifacts\results
Mode LastWriteTime Length Name
---- ------------- ------ ----
-a--- 4/25/2022 1:42 PM 638 Program.CompilerService-report-github.md
-a--- 4/25/2022 1:42 PM 1050 Program.CompilerService-report.csv
-a--- 4/25/2022 1:42 PM 1169 Program.CompilerService-report.html
```
> *-report-github.md can be used to post benchmark results to GitHub issue/PR/discussion or RFC.
>
>*-report.csv can be used for comparison purposes.
**Example output:**
``` ini
BenchmarkDotNet=v0.13.1, OS=Windows 10.0.25102
Intel Core i7-8750H CPU 2.20GHz (Coffee Lake), 1 CPU, 12 logical and 6 physical cores
.NET SDK=6.0.200
[Host] : .NET 6.0.3 (6.0.322.12309), X64 RyuJIT DEBUG
Job-GDIBXX : .NET 6.0.3 (6.0.322.12309), X64 RyuJIT
InvocationCount=1 UnrollFactor=1
```
| Method | Mean | Error | StdDev | Median | Gen 0 | Gen 1 | Allocated |
|--------------------- |---------:|--------:|--------:|---------:|----------:|----------:|----------:|
| ParsingTypeCheckerFs | 199.4 ms | 3.84 ms | 9.78 ms | 195.5 ms | 4000.0000 | 1000.0000 | 28 MB |
8. Repeat for any number of changes you would like to test.
9. **Optionally:** benchmark code and results can be included as part of the PR for future reference.
## Additional resources
The primary technical guide to the core compiler code is [The F# Compiler Technical Guide](https://github.com/dotnet/fsharp/blob/main/docs/index.md). Please read and contribute to that guide.
See the "Debugging The Compiler" section of this [article](https://medium.com/@willie.tetlow/f-mentorship-week-1-36f51d3812d4) for some examples.
## Addendum: configuring a proxy server
If you are behind a proxy server, NuGet client tool must be configured to use it:
See the Nuget config file documention for use with a proxy server [https://learn.microsoft.com/nuget/reference/nuget-config-file](https://learn.microsoft.com/nuget/reference/nuget-config-file)