chore: implement incremental build for FableLibrary tasks

.github/workflows/build.yml

@@ -175,11 +175,11 @@ jobs:
 
       - name: Fable Tests - Python (linux)
         if: matrix.platform == 'ubuntu-latest'
-        run: ./build.sh test python --skip-fable-library
+        run: ./build.sh test python
 
       - name: Fable Tests - Python (Windows)
         if: matrix.platform == 'windows-latest'
-        run: .\build.bat test python --skip-fable-library
+        run: .\build.bat test python
 
   # Separate build job for Rust (will run in parallel)
   build-rust:
@@ -209,7 +209,7 @@ jobs:
         run: ./build.sh fable-library --rust
 
       - name: Fable Tests - Rust
-        run: ./build.sh test rust --skip-fable-library --${{ matrix.test }}
+        run: ./build.sh test rust --${{ matrix.test }}
 
   # Separate build job for Dart
   build-dart:

.gitignore

@@ -232,3 +232,5 @@ Cargo.lock
 
 # This file is copied as part of the Restore task
 tests/React/Components.Copied.fs
+
+.build-cache/

CLAUDE.md

@@ -19,7 +19,7 @@ The build system is implemented in F# at `src/Fable.Build/`. All commands go thr
 # Run tests (targets: javascript, typescript, python, dart, rust, beam, integration)
 ./build.sh test javascript
 ./build.sh test javascript --watch                # Watch mode (recompile on changes)
-./build.sh test javascript --skip-fable-library   # Skip fable-library rebuild (only if fable-library source is unchanged)
+./build.sh test javascript --force-fable-library  # Force fable-library rebuild (needed if you modified Fable compiler to fix the generation of `src/fable-library-*/**/*.fs` files)
 
 # Python-specific options
 ./build.sh test python --skip-fable-library-core  # Skip slow Rust extension + .pyi rebuild (Python only)
@@ -29,7 +29,7 @@ The build system is implemented in F# at `src/Fable.Build/`. All commands go thr
 ./build.sh quicktest javascript                   # Also: typescript, python, dart, rust, beam
 ```
 
-`--skip-fable-library` is safe when changes are only in `src/Fable.Transforms/` or other compiler code. If you modified runtime library source (e.g., `src/fable-library-py/`, `src/fable-library-ts/`), do not skip. If you already ran `./build.sh fable-library` separately, use `--skip-fable-library` when running tests right afterwards to avoid rebuilding.
+In most cases, you should not need to use `--force-fable-library`. Only use it if you modified compiler code that affects how F# files used in `src/fable-library-*/` are generated (e.g., changes to `FSharp2Fable.fs` that affect how F# AST is transformed into Fable AST for library files).
 
 Build output goes to `temp/`: transpiled runtime libraries in `temp/fable-library-<target>/` and test output in `temp/tests/<target>/` (e.g., `temp/fable-library-beam/` and `temp/tests/beam/`).
 

src/Fable.Build/Fable.Build.fsproj

@@ -6,8 +6,9 @@
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Utils.fs" />
-    <Compile Include="Utils/LastVersionFinder.fs" />
     <Compile Include="Workspace.fs" />
+    <Compile Include="Utils/LastVersionFinder.fs" />
+    <Compile Include="Utils/IncrementalBuild.fs" />
     <Compile Include="SimpleExec.Extensions.fs" />
     <Compile Include="FableLibrary/Core.fs" />
     <Compile Include="FableLibrary/Python.fs" />
@@ -46,6 +47,7 @@
     <PackageReference Include="EasyBuild.Tools" Version="6.0.0" />
     <PackageReference Include="Fake.IO.FileSystem" Version="6.1.4" />
     <PackageReference Include="FsToolkit.ErrorHandling" Version="5.2.0" />
+    <PackageReference Include="Microsoft.Extensions.FileSystemGlobbing" Version="10.0.5" />
     <PackageReference Include="SimpleExec" Version="13.0.0" />
     <PackageReference Include="Thoth.Json.Net" Version="12.0.0" />
     <PackageReference Include="Semver" Version="3.0.0" />

src/Fable.Build/FableLibrary/Beam.fs

@@ -9,7 +9,12 @@ type BuildFableLibraryBeam() =
             Path.Combine("src", "fable-library-beam"),
             Path.Combine("src", "fable-library-beam"),
             Path.Combine("temp", "fable-library-beam"),
-            Path.Combine("temp", "fable-library-beam")
+            Path.Combine("temp", "fable-library-beam"),
+            [
+                Path.Combine("src", "fable-library-beam", "**", "*.erl")
+                Path.Combine("src", "fable-library-beam", "**", "*.fs")
+                Path.Combine("src", "fable-library-ts", "**", "*.fs")
+            ]
         )
 
     override this.CopyStage() =

src/Fable.Build/FableLibrary/Core.fs

@@ -1,19 +1,26 @@
 namespace Build.FableLibrary
 
 open BlackFox.CommandLine
-open Fake.IO
 open System.IO
 open Build.Utils
-open Build.Utils
-open System.Diagnostics
 open SimpleExec
+open Microsoft.Extensions.FileSystemGlobbing
+open Microsoft.Extensions.FileSystemGlobbing.Abstractions
 
 /// <summary>
 /// Building fable-library is similar enough for all the targets
 /// that we can use this class to standardise the process.
 /// </summary>
 type BuildFableLibrary
-    (language: string, libraryDir: string, sourceDir: string, buildDir: string, outDir: string, ?fableLibArg: string)
+    (
+        language: string,
+        libraryDir: string,
+        sourceDir: string,
+        buildDir: string,
+        outDir: string,
+        inputPatterns: string list,
+        ?fableLibArg: string
+    )
     =
 
     // It seems like the different target have a different way of supporting
@@ -62,37 +69,50 @@ type BuildFableLibrary
 
             tryDelete 3
 
-    member this.Run(?skipIfExist: bool) =
+    member this.Run(?forceBuild: bool) =
         let toConsole (s: string) = System.Console.WriteLine(s)
 
-        let skipIfExist = defaultArg skipIfExist false
-
-        if skipIfExist && Directory.Exists outDir then
-            "Skipping Fable build stage" |> toConsole
-
-        else
-
-            "Cleaning build directory" |> toConsole
-
-            this.deleteDirectoryRobust buildDir
-
-            "Building Fable.Library" |> toConsole
-
-            let args =
-                CmdLine.appendRaw sourceDir
-                >> CmdLine.appendPrefix "--outDir" outDir
-                >> CmdLine.appendPrefix "--fableLib" fableLibArg
-                >> CmdLine.appendPrefix "--lang" language
-                >> CmdLine.appendPrefix "--exclude" "Fable.Core"
-                >> CmdLine.appendPrefix "--define" "FABLE_LIBRARY"
-                >> CmdLine.appendRaw "--noCache"
-                // Target implementation can require additional arguments
-                >> this.FableArgsBuilder
-
-            Command.Fable(args)
-
-            "Copy stage" |> toConsole
-            this.CopyStage()
-
-            "Post Fable build stage" |> toConsole
-            this.PostFableBuildStage()
+        let matcher = new Matcher()
+        matcher.AddIncludePatterns(inputPatterns)
+        // Ignore well-known build output folders from MSBuild
+        matcher.AddExcludePatterns([ "**/obj/**"; "**/bin/**" ])
+
+        let directoryInfo = DirectoryInfo(Path.Resolve())
+        let dirWrapper = DirectoryInfoWrapper(directoryInfo)
+
+        let inputFiles =
+            matcher.Execute(dirWrapper).Files
+            |> Seq.map (fun file -> Path.Combine(directoryInfo.FullName, file.Path))
+            |> Seq.toList
+
+        IncrementalBuild.run
+            $"fable-library-%s{this.Language}"
+            (defaultArg forceBuild false)
+            inputFiles
+            [ Path.Resolve(this.OutDir) ]
+            (fun () ->
+                "Cleaning build directory" |> toConsole
+
+                this.deleteDirectoryRobust buildDir
+
+                "Building Fable.Library" |> toConsole
+
+                let args =
+                    CmdLine.appendRaw sourceDir
+                    >> CmdLine.appendPrefix "--outDir" outDir
+                    >> CmdLine.appendPrefix "--fableLib" fableLibArg
+                    >> CmdLine.appendPrefix "--lang" language
+                    >> CmdLine.appendPrefix "--exclude" "Fable.Core"
+                    >> CmdLine.appendPrefix "--define" "FABLE_LIBRARY"
+                    >> CmdLine.appendRaw "--noCache"
+                    // Target implementation can require additional arguments
+                    >> this.FableArgsBuilder
+
+                Command.Fable(args)
+
+                "Copy stage" |> toConsole
+                this.CopyStage()
+
+                "Post Fable build stage" |> toConsole
+                this.PostFableBuildStage()
+            )

src/Fable.Build/FableLibrary/Dart.fs

@@ -11,6 +11,10 @@ type BuildFableLibraryDart() =
             Path.Combine("src", "fable-library-dart"),
             Path.Combine("temp", "fable-library-dart"),
             Path.Combine("temp", "fable-library-dart"),
+            [
+                Path.Combine("src", "fable-library-dart", "**", "*.dart")
+                Path.Combine("src", "fable-library-dart", "**", "*.fs")
+            ],
             Path.Combine(".", "temp", "fable-library-dart")
         )
 

src/Fable.Build/FableLibrary/Python.fs

@@ -4,19 +4,25 @@ open System.IO
 open Fake.IO
 open Build.Utils
 open SimpleExec
-open BlackFox.CommandLine
 
-type BuildFableLibraryPython(?skipCore: bool) =
+type BuildFableLibraryPython(?skipCore: bool, ?postFableBuildStage: unit -> unit) =
     inherit
         BuildFableLibrary(
             language = "python",
             libraryDir = Path.Combine("src", "fable-library-py"),
             sourceDir = Path.Combine("src", "fable-library-py", "fable_library"),
             buildDir = Path.Combine("temp", "fable-library-py"),
-            outDir = Path.Combine("temp", "fable-library-py", "fable_library")
+            outDir = Path.Combine("temp", "fable-library-py", "fable_library"),
+            inputPatterns =
+                [
+                    Path.Combine("src", "fable-library-py", "**", "*.py")
+                    Path.Combine("src", "fable-library-py", "**", "*.fs")
+                    Path.Combine("src", "fable-library-ts", "**", "*.fs")
+                ]
         )
 
     let skipCore = defaultArg skipCore false
+    let postFableBuildStage = defaultArg postFableBuildStage ignore
 
     override this.CopyStage() =
         // Copy all Python/F# files to the build directory
@@ -53,3 +59,6 @@ type BuildFableLibraryPython(?skipCore: bool) =
         Command.Run("uv", $"run ruff check --select I,F401 --fix {this.BuildDir}")
         // Run Ruff formatter on all generated files
         Command.Run("uv", $"run ruff format {this.BuildDir}")
+
+        // Run the post fable buil stage if provided (used for quicktest to install the library in editable mode)
+        postFableBuildStage ()

src/Fable.Build/FableLibrary/Rust.fs

@@ -12,7 +12,13 @@ type BuildFableLibraryRust() =
             Path.Combine("src", "fable-library-rust"),
             Path.Combine("src", "fable-library-rust", "src"),
             Path.Combine("temp", "fable-library-rust"),
-            Path.Combine("temp", "fable-library-rust", "src")
+            Path.Combine("temp", "fable-library-rust", "src"),
+            inputPatterns =
+                [
+                    Path.Combine("src", "fable-library-rust", "**", "*.rs")
+                    Path.Combine("src", "fable-library-rust", "**", "*.fs")
+                    Path.Combine("src", "fable-library-rust", "Cargo.toml")
+                ]
         )
 
     override this.PostFableBuildStage() =

src/Fable.Build/FableLibrary/TypeScript.fs

@@ -13,6 +13,10 @@ type BuildFableLibraryTypeScript() =
             Path.Combine("src", "fable-library-ts"),
             Path.Combine("temp", "fable-library-ts"),
             Path.Combine("temp", "fable-library-ts"),
+            [
+                Path.Combine("src", "fable-library-ts", "**", "*.ts")
+                Path.Combine("src", "fable-library-ts", "**", "*.fs")
+            ],
             Path.Combine(".", "temp", "fable-library-ts")
         )
 

src/Fable.Build/Main.fs

@@ -32,7 +32,7 @@ Available commands:
             beam                    Run for BEAM (Erlang)
 
         Options:
-            --skip-fable-library    Skip building fable-library if folder already exists
+            --force-fable-library   Force building fable-library
             --watch                 Watch for changes and re-run the tests
 
     test                            Run the main tests suite
@@ -49,7 +49,7 @@ Available commands:
 
         Options for all except integration and standalone:
             --watch                 Watch for changes and re-run the tests
-            --skip-fable-library    Skip building fable-library if folder already exists
+            --force-fable-library   Force building fable-library
             --no-dotnet             When in watch mode, do not run the .NET tests
 
         Options for JavaScript:
@@ -73,28 +73,28 @@ Available commands:
                                     on top of of Node.js
 
         Options:
-            --skip-fable-library    Skip building fable-library if folder already exists
+            --force-fable-library   Force building fable-library
             --no-minify             Don't minify the JavaScript output
             --watch                 Watch for changes and recompile
 
     worker-js                       Compile the worker for the standalone version of Fable
 
         Options:
-            --skip-fable-library    Skip building fable-library if folder already exists
+            --force-fable-library   Force building fable-library
             --no-minify             Don't minify the JavaScript output
 
     compiler-js                     Compile the Fable compiler to JavaScript
 
         Options:
-            --skip-fable-library    Skip building fable-library if folder already exists
+            --force-fable-library   Force building fable-library
             --no-minify             Don't minify the JavaScript output
 
     package                         Generate local package for Fable.Cli and Fable.Core
                                     allowing to use this local package for testing
                                     inside of other projects
 
         Options:
-            --skip-fable-library    Skip building fable-library if folder already exists
+            --force-fable-library   Force building fable-library
 
     publish                         Publish the different packages to NuGet and NPM
                                     based on the CHANGELOG.md files

src/Fable.Build/Package.fs

@@ -12,14 +12,14 @@ open EasyBuild.Tools.PackageJson
 let private packageDestination = Path.Resolve("temp", "packages")
 
 let handle (args: string list) =
-    let skipFableLibrary = args |> List.contains "--skip-fable-library"
+    let forceFableLibrary = args |> List.contains "--force-fable-library"
     // Build all the fable-libraries
-    BuildFableLibraryBeam().Run(skipFableLibrary)
-    BuildFableLibraryDart().Run(skipFableLibrary)
-    BuildFableLibraryJavaScript().Run(skipFableLibrary)
-    BuildFableLibraryPython().Run(skipFableLibrary)
-    BuildFableLibraryRust().Run(skipFableLibrary)
-    BuildFableLibraryTypeScript().Run(skipFableLibrary)
+    BuildFableLibraryBeam().Run(forceFableLibrary)
+    BuildFableLibraryDart().Run(forceFableLibrary)
+    BuildFableLibraryJavaScript().Run(forceFableLibrary)
+    BuildFableLibraryPython().Run(forceFableLibrary)
+    BuildFableLibraryRust().Run(forceFableLibrary)
+    BuildFableLibraryTypeScript().Run(forceFableLibrary)
 
     Directory.clean packageDestination
 

src/Fable.Build/Publish.fs

@@ -87,12 +87,14 @@ let private publishNpm (projectDir: string) =
 
 let handle (args: string list) =
     // Build all the fable-libraries
-    BuildFableLibraryBeam().Run()
-    BuildFableLibraryDart().Run()
-    BuildFableLibraryJavaScript().Run()
-    BuildFableLibraryPython().Run()
-    BuildFableLibraryRust().Run()
-    BuildFableLibraryTypeScript().Run()
+    // Force rebuld of fable-libraries to make sure they are generated with the latest
+    // version of the compiler
+    BuildFableLibraryBeam().Run(true)
+    BuildFableLibraryDart().Run(true)
+    BuildFableLibraryJavaScript().Run(true)
+    BuildFableLibraryPython().Run(true)
+    BuildFableLibraryRust().Run(true)
+    BuildFableLibraryTypeScript().Run(true)
 
     // Handle the NPM packages
 
@@ -132,8 +134,8 @@ let handle (args: string list) =
     // Trigger fable-compiler-js target to make sure everything is ready for publish
     // Note: fable-standalone is built as part of fable-compiler-js
     // so no need to build it separately
-    // Note 2: We already built fable-library, so we skip it here
-    CompilerJs.handle [ "--skip-fable-library" ]
+    // Note 2: We already built fable-library, it will be skipped thanks to incremental build
+    CompilerJs.handle []
 
     publishNpm ProjectDir.fable_standalone
     publishNpm ProjectDir.fable_compiler_js

src/Fable.Build/Quicktest/Core.fs

@@ -20,10 +20,10 @@ type QuicktestConfig =
     }
 
 let genericQuicktest (config: QuicktestConfig) (args: string list) =
-    let skipFableLibrary = args |> List.contains "--skip-fable-library"
+    let forceFableLibrary = args |> List.contains "--force-fable-library"
     let isWatch = args |> List.contains "--watch"
 
-    config.FableLibBuilder.Run(skipFableLibrary)
+    config.FableLibBuilder.Run(forceFableLibrary)
 
     let appendRunMode (cmdLine: CmdLine) =
         match config.RunMode with