perf: parallelize code generation (#330)

Parallelize code generation via magefile deps to mitigate longer build times.

Author: reubeno

magefiles/magesrc/magesrc.go

@@ -5,6 +5,7 @@ package magesrc
 
 import (
 	"errors"
+	"strings"
 
 	"github.com/magefile/mage/mg"
 	"github.com/magefile/mage/sh"
@@ -17,7 +18,9 @@ var ErrSrcCode = errors.New("source code generation failed")
 func Generate() error {
 	mageutil.MagePrintln(mageutil.MsgStart, "Running code generation...")
 
-	err := sh.Run(mg.GoCmd(), "generate", "./...")
+	// We run code generation for all packages in parallel, up to the number of CPU cores.
+	// This saves meaningful time now that we have many packages with code generation.
+	err := generateForAllPackagesInParallel()
 	if err != nil {
 		return mageutil.PrintAndReturnError("Code generation failed.", ErrSrcCode, err)
 	}
@@ -26,3 +29,42 @@ func Generate() error {
 
 	return nil
 }
+
+func generateForAllPackagesInParallel() error {
+	paths, err := listPackages()
+	if err != nil {
+		return err
+	}
+
+	generateDeps := []interface{}{}
+
+	// Build up a list of dependencies to run in parallel; we'll let [mg.Deps] take care of
+	// the parallel execution.
+	for _, path := range paths {
+		generateDeps = append(generateDeps, mg.F(generateForPackage, path))
+	}
+
+	mg.Deps(generateDeps...)
+
+	return nil
+}
+
+// listPackages lists all Go packages in the current module.
+func listPackages() ([]string, error) {
+	out, err := sh.Output(mg.GoCmd(), "list", "./...")
+	if err != nil {
+		return nil, mageutil.PrintAndReturnError("Failed to list Go packages.", ErrSrcCode, err)
+	}
+
+	return strings.Split(strings.TrimSpace(out), "\n"), nil
+}
+
+// generateForPackage runs code generation for a specific package.
+func generateForPackage(path string) error {
+	err := sh.Run(mg.GoCmd(), "generate", path)
+	if err != nil {
+		return mageutil.PrintAndReturnError("Code generation failed.", ErrSrcCode, err)
+	}
+
+	return nil
+}