Extend XCADDY_GO_BUILD_FLAGS usage (#102)

Commit 47f9ded is not sufficient alone to
ensure that all go modules are installed with write bit set because 'go mod'
or 'go get' might install modules as read-only, too.

If set, the environment variable is appended for the other go commands that
support build flags.

builder.go

@@ -30,7 +30,6 @@ import (
 
 	"github.com/Masterminds/semver/v3"
 	"github.com/caddyserver/xcaddy/internal/utils"
-	"github.com/google/shlex"
 )
 
 // Builder can produce a custom Caddy build with the
@@ -105,6 +104,10 @@ func (b Builder) Build(ctx context.Context, outputFile string) error {
 
 	// tidy the module to ensure go.mod and go.sum are consistent with the module prereq
 	tidyCmd := buildEnv.newCommand(utils.GetGo(), "mod", "tidy")
+	buildFlags := buildEnv.parseBuildFlags()
+	if len(buildFlags) > 0 {
+		tidyCmd.Args = append(tidyCmd.Args, buildFlags...)
+	}
 	if err := buildEnv.runCommand(ctx, tidyCmd, b.TimeoutGet); err != nil {
 		return err
 	}
@@ -117,13 +120,8 @@ func (b Builder) Build(ctx context.Context, outputFile string) error {
 		// support dlv
 		cmd.Args = append(cmd.Args, "-gcflags", "all=-N -l")
 	} else {
-		if b.BuildFlags != "" {
-			// override build flags from environment if given
-			flags, err := shlex.Split(b.BuildFlags)
-			if err != nil {
-				log.Fatalf("[FATAL] Splitting arguments failed: %s", b.BuildFlags)
-			}
-			cmd.Args = append(cmd.Args, flags...)
+		if len(buildFlags) > 0 {
+			cmd.Args = append(cmd.Args, buildFlags...)
 		} else {
 			cmd.Args = append(cmd.Args,
 				"-ldflags", "-w -s", // trim debug symbols

environment.go

@@ -28,6 +28,7 @@ import (
 	"time"
 
 	"github.com/caddyserver/xcaddy/internal/utils"
+	"github.com/google/shlex"
 )
 
 func (b Builder) newEnvironment(ctx context.Context) (*environment, error) {
@@ -266,15 +267,41 @@ func (env environment) execGoGet(ctx context.Context, modulePath, moduleVersion,
 	// breaks the command since it treats the empty string as a
 	// distinct argument, so we're using an if statement to avoid it.
 	var cmd *exec.Cmd
+	args := []string{"get", "-d", "-v"}
+	buildFlags := env.parseBuildFlags()
+	if len(buildFlags) > 0 {
+		args = append(args, buildFlags...)
+	}
 	if caddy != "" {
-		cmd = env.newCommand(utils.GetGo(), "get", "-d", "-v", mod, caddy)
+		args = append(args, mod, caddy)
 	} else {
-		cmd = env.newCommand(utils.GetGo(), "get", "-d", "-v", mod)
+		args = append(args, mod)
 	}
+	cmd = env.newCommand(utils.GetGo(), args...)
 
 	return env.runCommand(ctx, cmd, env.timeoutGoGet)
 }
 
+// parseBuildFlags splits buildFlags to array that can be appended to a go
+// command that supports build flags. If parsing fails or value is empty, empty
+// list will be returned.
+func (env environment) parseBuildFlags() []string {
+	var v []string
+
+	if env.buildFlags == "" {
+		return v
+	}
+
+	flags, err := shlex.Split(env.buildFlags)
+	if err != nil {
+		log.Printf("[ERROR] Splitting arguments failed: %s", env.buildFlags)
+		return v
+	}
+	v = append(v, flags...)
+
+	return v
+}
+
 type goModTemplateContext struct {
 	CaddyModule string
 	Plugins     []string