add SandboxBuilder image override

src/cmd/sandbox.rs

@@ -146,6 +146,7 @@ pub struct SandboxBuilder {
     user: Option<String>,
     cmd: Vec<String>,
     enable_networking: bool,
+    image: Option<String>,
 }
 
 impl SandboxBuilder {
@@ -160,6 +161,7 @@ impl SandboxBuilder {
             user: None,
             cmd: Vec::new(),
             enable_networking: true,
+            image: None,
         }
     }
 
@@ -203,6 +205,14 @@ impl SandboxBuilder {
         self
     }
 
+    /// Override the image used for this sandbox.
+    ///
+    /// By default rustwide will use the image configured with [`WorkspaceBuilder::sandbox_image`].
+    pub fn image(mut self, image: SandboxImage) -> Self {
+        self.image = Some(image.name);
+        self
+    }
+
     pub(super) fn env<S1: Into<String>, S2: Into<String>>(mut self, key: S1, value: S2) -> Self {
         self.env.push((key.into(), value.into()));
         self
@@ -274,7 +284,11 @@ impl SandboxBuilder {
             args.push("--isolation=process".into());
         }
 
-        args.push(workspace.sandbox_image().name.clone());
+        if let Some(image) = self.image {
+            args.push(image);
+        } else {
+            args.push(workspace.sandbox_image().name.clone());
+        }
 
         for arg in self.cmd {
             args.push(arg);

src/crates/mod.rs

@@ -73,7 +73,8 @@ impl Crate {
         }
     }
 
-    pub(crate) fn copy_source_to(&self, workspace: &Workspace, dest: &Path) -> Result<(), Error> {
+    /// Copy this crate's source to `dest`. If `dest` already exists, it will be replaced.
+    pub fn copy_source_to(&self, workspace: &Workspace, dest: &Path) -> Result<(), Error> {
         if dest.exists() {
             info!(
                 "crate source directory {} already exists, cleaning it up",