build: make build script more ergonomic

* Moved cloning functionality into its own `cloneSrc` function
* Start writing compiled data into CWD instead of user home dir, in
  order to prevent mangling between projects
* Introduce `LEI_LUAU_SRC` variable to allow users to provide a path to
  an already checked out luau source dir; when not set, a temporary
  directory is created and removed after compilation
* Do not panic if cmake build dir already exists, just skip creating in
  that case
* Automatically set required C includes path for commands
* Added warning to commands if the `.lei` directory is not present in
  the gitignore

.gitignore

@@ -17,5 +17,8 @@
 # Project-local glide cache, RE: https://github.com/Masterminds/glide/issues/736
 .glide/
 
+# Build script compiled data
+.lei/
+
 # Dependency directories (remove the comment below to include it)
 # vendor/

build/build.go

@@ -19,25 +19,29 @@ func bail(err error) {
 	}
 }
 
-func buildVm(artifactPath string, cmakeFlags ...string) {
+func cloneSrc() string {
 	color.Blue.Println("> Cloning luau-lang/luau")
 
-	dir, homeDirErr := os.MkdirTemp("", "lei-build")
+	dir, tempDirErr := os.MkdirTemp("", "lei-build")
-	bail(homeDirErr)
+	bail(tempDirErr)
-
-	defer os.RemoveAll(dir)
 
 	// Clone down the Luau repo and checkout the required tag
 	Exec("git", "", "clone", "https://github.com/luau-lang/luau.git", dir)
 	Exec("git", dir, "checkout", LUAU_VERSION)
 
 	color.Green.Printf("> Cloned repo to%s\n\n", dir)
+	return dir
+}
 
+func buildVm(srcPath string, artifactPath string, includesDir string, cmakeFlags ...string) {
 	color.Blue.Println("> Compile libLuau.VM.a")
 
 	// Build the Luau VM using CMake
-	buildDir := path.Join(dir, "cmake")
+	buildDir := path.Join(srcPath, "cmake")
-	bail(os.Mkdir(buildDir, os.ModePerm))
+	buildDirErr := os.Mkdir(buildDir, os.ModePerm)
+	if buildDirErr != nil && !os.IsExist(buildDirErr) {
+		bail(buildDirErr)
+	}
 
 	defaultCmakeFlags := []string{"..", "-DCMAKE_BUILD_TYPE=RelWithDebInfo", "-DLUAU_EXTERN_C=ON", "-DCMAKE_POLICY_VERSION_MINIMUM=3.5"}
 	Exec("cmake", buildDir, append(defaultCmakeFlags, cmakeFlags...)...)
@@ -49,17 +53,37 @@ func buildVm(artifactPath string, cmakeFlags ...string) {
 	artifactFile, artifactErr := os.ReadFile(path.Join(buildDir, ARTIFACT_NAME))
 	bail(artifactErr)
 	bail(os.WriteFile(artifactPath, artifactFile, os.ModePerm))
+
+	// Copy the header files into the includes directory
+	headerDir := path.Join(srcPath, "VM", "include")
+	headerFiles, headerErr := os.ReadDir(headerDir)
+	bail(headerErr)
+	for _, file := range headerFiles {
+		src := path.Join(headerDir, file.Name())
+		dest := path.Join(includesDir, file.Name())
+
+		headerContents, headerReadErr := os.ReadFile(src)
+		bail(headerReadErr)
+
+		os.WriteFile(dest, headerContents, os.ModePerm)
+	}
 }
 
 func main() {
-	homeDir, homeDirErr := os.UserHomeDir()
+	workDir, workDirErr := os.Getwd()
-	bail(homeDirErr)
+	bail(workDirErr)
 
-	artifactDir := path.Join(homeDir, ".lei")
+	artifactDir := path.Join(workDir, ".lei")
 	artifactPath := path.Join(artifactDir, ARTIFACT_NAME)
 	lockfilePath := path.Join(artifactDir, ".lock")
+	includesDir := path.Join(artifactDir, "includes")
 
-	bail(os.MkdirAll(artifactDir, os.ModePerm))
+	bail(os.MkdirAll(includesDir, os.ModePerm)) // includesDir is the deepest dir, creates all
+
+	gitignore, gitignoreErr := os.ReadFile(".gitignore")
+	if gitignoreErr == nil && !strings.Contains(string(gitignore), ".lei") {
+		color.Yellow.Println("> WARN: The gitignore in the CWD does not include `.lei`, consider adding it")
+	}
 
 	// TODO: Args for clean build
 	args := os.Args[1:]
@@ -68,11 +92,13 @@ func main() {
 	cmakeFlags := []string{}
 	features := []string{}
 
+	// TODO: maybe use env vars for this config instead
 	for _, arg := range args {
 		if arg == "--enable-vector4" {
 			features = append(features, "LUAU_VECTOR4")
 			// FIXME: This flag apparently isn't recognized by cmake for some reason
 			cmakeFlags = append(cmakeFlags, "-DLUAU_VECTOR_SIZE=4")
+
 		} else {
 			goArgs = append(goArgs, arg)
 		}
@@ -84,11 +110,17 @@ func main() {
 	}
 
 	serFeatures := fmt.Sprintf("%v", features)
-	toCleanBuild := string(lockfileContents) != serFeatures
+	toCleanBuild := (string(lockfileContents) != serFeatures) || os.Getenv("LEI_CLEAN_BUILD") == "true"
 	if _, err := os.Stat(artifactPath); err == nil && !toCleanBuild {
 		fmt.Printf("[build] Using existing artifact at %s\n", artifactPath)
 	} else {
-		buildVm(artifactPath, cmakeFlags...)
+		srcPath, notUnset := os.LookupEnv("LEI_LUAU_SRC")
+		if !notUnset {
+			srcPath = cloneSrc()
+			defer os.RemoveAll(srcPath)
+		}
+
+		buildVm(srcPath, artifactPath, includesDir, cmakeFlags...)
 		bail(os.WriteFile(lockfilePath, []byte(serFeatures), os.ModePerm))
 	}
 
@@ -110,6 +142,7 @@ func main() {
 			"CGO_LDFLAGS",
 			fmt.Sprintf("-L %s -lLuau.VM -lm -lstdc++", artifactDir),
 		).
+		WithVar("CGO_CFLAGS", fmt.Sprintf("-I%s", includesDir)).
 		WithVar("CGO_ENABLED", "1").
 		PipeAll(Forward).
 		ToCommand()