Add feature and stubs for Linux VM builders v2

Cargo.toml

@@ -42,3 +42,5 @@ shadow-rs = { version = "0.36", features = ["metadata"] }
 [features]
 # This feature should be enabled when building static executable
 openssl-vendored = ["openssl/vendored"]
+# Use new version of Linux VM builder (unstable)
+vm-builder-v2 = []

src/builders_v2/mod.rs

@@ -0,0 +1 @@
+//! Builders v2.

src/commands/build.rs

@@ -1,5 +1,3 @@
-use crate::builders::skopeo_builder::SkopeoSyslinuxBuilder;
-use crate::builders::{BuildOptions, ImageBuilder};
 use crate::OutputFormat;
 use clap::ValueHint;
 use std::path::PathBuf;
@@ -206,9 +204,18 @@ impl BuildArgs {
     }
 }
 
+#[cfg(not(feature = "vm-builder-v2"))]
 async fn build(build_args: &BuildArgs) -> Result<(), Box<dyn std::error::Error>> {
+    use crate::builders::skopeo_builder::SkopeoSyslinuxBuilder;
+    use crate::builders::{BuildOptions, ImageBuilder};
+
     let options = BuildOptions::from(build_args);
     let builder = SkopeoSyslinuxBuilder {};
     builder.build(&options)?;
     Ok(())
 }
+
+#[cfg(feature = "vm-builder-v2")]
+async fn build(_build_args: &BuildArgs) -> Result<(), Box<dyn std::error::Error>> {
+    todo!()
+}

src/main.rs

@@ -8,7 +8,10 @@ use std::fs::File;
 use std::io::{self, Write};
 use std::path::PathBuf;
 
+#[cfg(not(feature = "vm-builder-v2"))]
 mod builders;
+#[cfg(feature = "vm-builder-v2")]
+mod builders_v2;
 mod commands;
 mod utils;
 mod version;